Technical Design Report

for the Design, Construction, Commissioning and Operation of MATS

(within the NUSTAR Collaboration)

Precision Measurements of Very Short-Lived Nuclei using an

Advanced Trapping System for Highly-Charged Ions

Johannes Gutenberg-Universität Mainz December 15, 2005

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LOI Identification Nº 8 [ * obtained from the FAIR project team] FAIR- PAC: make cross

where applicable APPA [ ]

NUSTAR [ X ] QCD [ ] Date: 15.12.2005 Technical Design Report for the Design, Construction, Commissioning

and Operation of MATS Abstract:

The mass and its inherent connection with the nuclear binding energy is a fundamental property of a nuclide, a unique “fingerprint”. Thus, precise mass values are important for a variety of applications, ranging from nuclear-structure studies like the investigation of shell closures and the onset of deformation, test of nuclear mass models and mass formulas, to tests of the weak interaction and of the Standard Model. The required relative accuracy ranges from 10-5 to below 10-8 for radionuclides, which most often have half-lives well below 1 s. Substantial progress in Penning trap mass spectrometry has made this method a prime choice for precision measurements on rare isotopes. The technique has the potential to provide high accuracy and sensitivity even for very short-lived nuclides. Furthermore, ion traps can be used and offer advantages for precision decay studies.

With MATS (Precision Measurements of very short-lived nuclei using an Advanced Trapping System for highly-charged ions) at FAIR we aim for applying two techniques to very short-lived radionuclides: High-accuracy mass measurements and in-trap conversion electron and alpha spectroscopy. The experimental setup of MATS is a unique combination of an electron beam ion trap for charge breeding, ion traps for beam preparation, and a high precision Penning trap system for mass measurements and decay studies.

For the mass measurements, MATS offers both a high accuracy and a high sensitivity. A relative mass uncertainty of 10-9 can be reached by employing highly-charged ions and a non-destructive Fourier-Transform-Ion-Cyclotron-Resonance (FT-ICR) detection technique on single stored ions. This accuracy limit is important for fundamental interaction tests, but also allows to study the fine structure of the nuclear mass surface with unprecedented accuracy, whenever required. The use of the FT-ICR technique provides true single ion sensitivity. This is essential to access isotopes that are produced with minimum rates and that very often are the most interesting ones. Instead of pushing for highest accuracy, the high charge state of the ions can also be used to reduce the storage time of the ions, hence making measurements on even shorter-lived isotopes possible.

Decay studies in ion traps will become possible with MATS. Novel spectroscopic tools for in-trap high-resolution conversion-electron and charged-particle spectroscopy from carrier-free sources will be developed, aiming e.g. at the measurements of quadrupole moments and E0 strengths. With the possibility of both high-accuracy mass measurements of shortest-lived isotopes and decay studies, its high sensitivity and accuracy potential MATS is ideally suited to for the study of very exotic nuclides that are only produced at the FAIR facility. Spokesperson, email, telephone number: Dr. Klaus Blaum Institute of Physics University of Mainz blaumk@uni-mainz.dePhone: +49-6131-39-22883 Fax: +49-6131-39-25179

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Members of the MATS Collaboration

BELGIUM

Paul-Henri Heenen B-1050 Bruxelles, Belgium, PNTPM, CP229, Universite Libre de Bruxelles

CANADA

Laura Blomley, Jens Dilling, Vladimir Ryjkov, Mathew Smith CA-BC V6T 2A3 Vancouver, Canada, TRIUMF

FRANCE

Georges Audi, Cyril Bachelet, David Lunney, Céline Guénaut F-91405 Orsay/Paris, France, CSNSM-IN2P3,CNRS

FINLAND

Juha Äystö, Ari Jokinen, Iain Moore F-Jyväskylä, Finland, Department of Physics, P.O. Box 35, FIN-40014 University of Jyväskylä

GERMANY

Martin Breitenfeld, Alexander Herlert, Gerrit Marx, Lutz Schweikhard, Falk Ziegler D-17487 Greifswald, Germany, Institute of Physics, Ernst-Moritz-Arndt University

Paul-Gerhard Reinhard D-91054 Erlangen, Germany, Institute of Theoretical Physics II, Friedrich-Alexander University Erlangen-Nürnberg

Dietrich Beck, Michael Block, Hans Geissel, Sophie Heinz, Frank Herfurth, Oliver Kester, Yuri A. Litvinov, Yuri N. Novikov, Wolfgang Quint, Christoph Scheidenberger, Martin Winkler, Chabouh Yazidjian D-64291 Darmstadt, Germany, GSI

Klaus Blaum, Immanuel Bloch, Michael Dworschak, Rafael Ferrer, Sebastian George, Alban Kellerbauer, Jens Ketelaer, Susanne Kreim, Dennis Neidherr, Wilfried Nörtershäuser, Birgit Schabinger, Stefan Stahl, Christine Weber D-55099 Mainz, Germany, Institute of Physics, Johannes Gutenberg University

Timo Dickel, Martin Petrick, Wolfgang R. Plaß D-35390 Gießen, Germany, II. Institute of Physics, Justus-Liebig University

Dietrich Habs, Veli Kolhinen, Michael Sewtz, Jerzy Szerypo, Peter G. Thirolf D-85748 Garching, Germany, Department of Physics, Ludwig-Maximilians University München

Joachim Ullrich, José R. Crespo López-Urrutia D-69117 Heidelberg, Germany, MPI Kernphysik

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INDIA

Parnika Das, Amlan Ray Kolkata, Bidhanagar, India, Variable Energy Cyclotron Centre, 1/AF SWEDEN

Tomas Fritioff, Reinhold Schuch, Nagy Szilard S-10691 Stockholm, Sweden, SCFAB, Stockholm University

USA

Dieter Schneider US-CA 94550-9234 Livermore, USA, Lawrence Livermore National Laboratory

Michael Bender, Georg Bollen, Milan Matos, Stefan Schwarz US-MI 48824-1321 East Lansing, USA, Michigan State University, NSCL

In total: 8 Countries; 15 Institutes; 63 Members Spokesperson: Klaus Blaum blaumk@uni-mainz.de +49-6131-39-22883 Deputy: Frank Herfurth f.herfurth@gsi.de +49-6159-71-1360 José R. Crespo crespojr@mpi-hd.mpg.de +49-6221-516-521 Contact @ GSI Frank Herfurth f.herfurth@gsi.de +49-6159-71-1360

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Figure of the proposed experimental setup:

4,5

m10,5 m

MPS

2,0

4,3

m4,

4 m

Test- ionsource

PreparationPenning trap

MeasurementPenning trap

EBIT

EBIT

m/q selection

Top View Ground Floor

Side View

Roof crane (2 ton)

HV Cage

HV Cage

HV Cage

Ground Floor

First Floor

HV Cage

Test- ionsource

PreparationPenning trap

Figure 1: Proposed high-accuracy Penning trap mass spectrometer and in-trap conversion electron

spectroscopy setup. For charge breeding an electron beam ion trap (EBIT) will be used.

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Table of Contents

A Introduction and Overview……… ........................................................................................ 7 B Systems ................................................................................................................................... 14 1 Subsystems.............................................................................................................................. 14 1.1 Ion beam cooler and buncher .................................................................................................. 14 1.2 Charge Breeding electron beam ion trap (EBIT) .................................................................... 16 1.3 q/A Selection........................................................................................................................... 19 1.4 Preparation Penning trap ......................................................................................................... 21 1.5 Measurement Penning trap...................................................................................................... 23 1.6 Instrumentation for mass spectrometry................................................................................... 25 1.7 In-trap spectroscopy detectors................................................................................................. 27 2 Trigger, DACQ, Controls, On-line/Off-line Computing ........................................................ 29 3 Beam/Target Requirements..................................................................................................... 29 4 Physics Performance ............................................................................................................... 29 C Implementation and Installation ......................................................................................... 30 1 Cave and Annex Facilities, Civil Engineering, Cranes, Elevators, Air Conditioning

(Temperature and Humidity Stability requirements), Cooling, Gases.................................... 30 2 Detector –Machine Interface................................................................................................... 33 3 Assembly and installation ....................................................................................................... 33 D Commissioning ...................................................................................................................... 35 E Operation ............................................................................................................................... 35 F Safety ...................................................................................................................................... 36 G Organization and Responsibilities, Planning...................................................................... 37 H Relation to other Projects ..................................................................................................... 48 I Other issues............................................................................................................................ 48 J References and Acknowledgements..................................................................................... 49

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Table of Figures

1 Proposed MATS setup .............................................................................................................. 4 2 Experimental test of ft-value corrections of superallowed β−decays ....................................... 9 3 Two-neutron separation energies in the vicinity of Z = 82 ..................................................... 10 4 Nuclear chart with the relative mass uncertainties of all known nuclides .............................. 13 5 Penning trap facilities worldwide............................................................................................ 14 6 Electrode layout of the LEBIT-buncher.................................................................................. 15 7 Schematic figure of the MR-TOF separator............................................................................ 17 8 Schematic diagram of the “ion circus”.................................................................................... 18 9 Scheme of the Heidelberg EBIT design.................................................................................. 19 10 Charge breeding of Sn at 1.1 keV beam energy...................................................................... 20 11 Charge breeding of Sn at 6.4 keV beam energy...................................................................... 20 12 Sketch of the magnetic multi-passage spectrometer ............................................................... 22 13 Proposed high-accuracy measurement Penning trap............................................................... 26 14 Ion detector setup for mass spectrometry................................................................................ 28 15 Ion yields measured with a MCP detector .............................................................................. 28 16 In-trap electron conversion spectroscopy arrangement........................................................... 30 17 Achievable mass uncertainty................................................................................................... 34 18 Floor plan of the MATS setup ................................................................................................ 35

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A Introduction and Overview: Physics cases and required precision:

The mass is a fundamental property of a nuclide, a unique “fingerprint”. High-accuracy mass values give us access to the nuclear binding energies that represent the sum of all the nucleonic interactions [Lunn2003]. Thus, accurate mass values contribute to a variety of fundamental studies including tests of the Standard Model and the weak interaction (see Table 1) [Blau2005]. Accuracy required for the mass depends on the physics being investigated and ranges from δm/m = 10-5 to better than 10-8 for radionuclides which often have half-lives considerably less than a second [Boll2001, Herf2003]. High-accuracy mass values allow identification problems between ground state and isomeric states to be solved and to resolve fine-structure effects on the mass surface. Five physics cases shall be discussed here in more detail. In addition the application and advantage of in-trap conversion electron and alpha spectroscopy will be discussed.

Table 1: Fields of application and the generally required relative uncertainty on the measured mass δm/m to probe the associated physics.

Field Mass uncertainty Chemistry: identification of molecules 10-5 – 10-6 Nuclear physics: shells, sub-shells, pairing 10-6 Nuclear fine structure: deformation, halos 10-7 – 10-8 Astrophysics: r-process, rp-process, waiting points 10-7 Nuclear models and mass formulas: IMME 10-7 – 10-8 Weak interaction studies: CVC hypothesis, CKM unitarity 10-8

(a) Isomer resolution:

An important issue in direct mass measurements is to resolve isomeric and ground states since nearly one third of the nuclides in the nuclear chart have long-lived isomeric states with – in many cases – unknown excitation energies. For this, a very high resolving power of 106 and higher is needed [Schw2001]. Furthermore, it is possible to determine the sequence of isomeric states using high-resolution mass spectrometry or to prepare an isomerically pure beam, as recently demonstrated in the case of 68Cu [Blau2004] and 70Cu [VanR2004]. An empirical formula for the resolving power is given by [Boll2001]: R = m / ∆m = νc / ∆νc (FWHM) ≈ 1.25·νc·TRF.

A resolving power of R ≈ 106 is reached in a Penning trap with B = 7 T for singly charged A = 100 ions with an excitation time of TRF ≈ 1 s (for sufficiently long half-lives). Even higher resolving powers can be reached by further increasing the RF-excitation time. In the case of short-lived nuclides, the resolving power will be limited by the half-life, but can be considerably improved with increased charge states since νc scales with q. To resolve e.g. the discrepancies between theoretical predictions and experimental data for the ground and first isomeric state in 131Sn [Foge1999], a resolving power of 107 is required. (b) Test of the conserved vector current hypothesis and the unitarity of the CKM matrix:

The Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix V parameterises the weak charged current interactions of quarks. The Standard Model does not predict the content of the CKM matrix, and the values of individual matrix elements are determined from weak decays of the relevant quarks.

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The CKM matrix is required to be unitarity. Today the only possible direct and accurate test of unitarity involves the top row of V, namely |Vud|2 + |Vus|2 + |Vub|2 = 1− ∆ . In the Standard Model with a unitary CKM matrix, ∆ is zero. Presently, the unitarity test fails by up to >2.7σ and the origin of ∆ is unclear. A deviation from unitarity has been found with nuclear β-decay [Town2003] and neutron-β-decay data [Abel2002]. Due to its large size, a determination of Vud is most important. In the CKM matrix, as assessed by the Particle Data Group [Eide2004], the unitarity constraint has pushed Vud about two to three standard deviations higher than given by the experiments. Updates of Vus with revised radiative corrections [Byte2003, Bijn2003] are in agreement with the current PDG value Vus [Eide2004] and even indicate a decrease of the central value by up to 1%. However, a recent report from E865 at BNL results in a larger Vus value [Sher2003]. With this value alone, one finds no significant deviation from CKM unitarity. On the other hand, the discrepancy between this BNL value and the value from K0

e3 is on the 3σ level. New measurements from NA48 confirm the discrepancy [Lai2004], whereas measurements from KTEV [Alex2004] find no deviation. Thus further investigations are needed.

A violation of unitarity in the first row of the CKM matrix is a challenge to the three generation Standard Model. The CKM data available so far do not preclude there being more than three generations; CKM matrix entries deduced from unitarity might be altered when the CKM matrix is expanded to accommodate more generations [Marc1996, Hagi2002]. A deviation ∆ has been related to concepts beyond the Standard Model, such as couplings to exotic fermions [Lang1988, Maal1990], to the existence of an additional Z boson [Lang1992, Marc1987], to supersymmetry or to the existence of right-handed currents in the weak interaction [Deut1977]. A non-unitarity of the CKM matrix in models with an extended quark sector gives rise to an induced neutron electric dipole moment that can be within reach of the next generation of experiments [Liao2001].

The most precise value for the Vud element can be extracted from the vector coupling constant GV derived from the mean Ft value of superallowed nuclear β-decay, in conjunction with the Fermi coupling constant from µ-decay Gµ: Vud

2 = GV2 / Gµ

2. Together with particle physics data from K and B meson decay, this can be used to test CKM unitarity. The experimental Ft value is expressed as:

Ft ≡ ft (1 + δR)(1 – δC) = K / (2|Vud|2 Gµ2 (1 + ∆R)) ,

where δR is the nucleus-dependent radiative correction, δC the isospin-symmetry-breaking correction, and ∆R the nucleus-independent radiative correction. Experimentally, Ft is accessible via the following measured quantities: the decay energy Q, the half-life T1/2, and the branching ratio R. The Q value enters to the fifth power into the calculation of the statistical rate function f and thus the masses of the mother and the daughter nuclei are needed with a precision of about 1x10-8 in order to reach a relative uncertainty of 0.1% on Ft. One should note, that the uncertainty in the derivation of Vud is dominated by theoretical uncertainties in the calculated corrections. Therefore parts of current nuclear experiments are focused on testing and refining those correction terms that depend on nuclear structure [Kell2004]. This is illustrated in Fig. 2, where the measured ft-values are compared to calculated ft-values derived from the mean Ft-value dividing by the theoretical corrections (taken from the recent compilation of superallowed 0+ → 0+ nuclear β-decays by J.C. Hardy and I.S. Towner [Hard2004]). The width of the colored fields shows the theoretical uncertainties.

The best-known nine cases 10C, 14O, 26mAl, 34Cl, 38mK, 42Sc, 46V, 50Mn, and 54Co show that several nuclei require improved measurements (of Q-values, half-lives or branching ratios) to reach the situation that the uncertainties are dominated by calculations. New measurements of the masses of the radioactive nuclei 46V and its daughter 46Ti have been performed recently with the Canadian Penning Trap mass spectrometer to an accuracy of 1x10-8 yielding a more accurate Ft-value for this superallowed transition [Sava2005]. The new Ft-value disagrees with the previous value and is significantly above the average. Two further series of 0+ nuclei present themselves: For the even-Z, Tz = -1 decays 22Mg [Mukh2004] and 34Ar [Herf2001a] and a number of new studies such as 18Ne, 26Si, 30S, 38Ca (measurement performed at LEBIT), and 42Ti are under way. Also for the odd-Z,

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Figure 2: Experimental ft-value plotted as a function of the charge on the daughter nucleus, Z. The bands

represent the theoretical quantity Ft/[(1+δR)(1-δC)]. The two groups distinguish those β emitters whose parent nuclei have isospin Tz = -1 (dark shading) from those with Tz = 0 (lighter shading) [Hard2004].

Tz = 0 systems, in addition to 74Rb [Kell2004] new candidates like 62Ga (measurement performed at JYFLTRAP), 66As, and 70Br will be tested. With these new cases, where larger theoretical variations from nuclide to nuclide are predicted, the quality of theoretical predictions for the corrections can be judged. If the calculations agree with experiment, they will confirm the reliability for the original nice transitions where the corrections are considerably smaller. (c) Proton-neutron interactions and the new masses:

The mass M(N,Z) of a nucleus with N neutrons and Z protons and its inherent connection with the binding energy B(N,Z) = {NMn + ZMp – M(N,Z)}c2 (where Mn is the mass of the neutron and Mp that of the proton) must be regarded as one of the most fundamental characteristics of a nucleus. The steady growth in the number of nuclides whose masses have been measured over the years and in the obtained precision and accuracy have contributed significantly to our understanding of nuclear structure since the nuclear masses or binding energies represent the sum of all the nucleonic interactions. Since the binding energy depends on the detailed composition of protons and neutrons, the mass of each of the more than 3000 nuclides as observed to date [Audi2003] is highly specific and represents a key property of a nuclear system. Viewing this ensemble of mass data over the nuclear chart, one can examine the hills and valleys that form the mass surface and make hypotheses about the effects of certain nuclear configurations. To unveil these effects, mass measurements with an accuracy of δm/m < 10-6 are required (see Table 1).

Differences of masses give separation energies (the energy needed to separate some nucleons from the nucleus), providing clues to shell structure and phase transitions. The most striking way in which shell structure manifests itself in mass systematics is through double differences of masses, i.e. the two-neutron separation energy

S2n(N,Z) = B(N,Z) – B(N-2,Z) in the case of the neutron shells, and the two-proton separation energy

S2p(N,Z) = B(N,Z) – B(N,Z-2)

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in the case of proton shells. Here, specific classes of interactions can be isolated. The single-nucleon separation energy is a less clear-cut indication because of the pairing effect [Lunn2003]. Mass measurements with relative mass precision of about 1x10-7 in long isotopic and isotonic chains allow to study the fine structure of the mass surface and clarify discontinuities in order to extract nuclear structure information from binding energies. As an example for such a systematic survey Fig. 3 shows the two-neutron separation energies in the vicinity of Z = 82 derived from the Atomic-Mass Evaluation AME1995 (top) and a more recent compilation including ISOLTRAP data (bottom) [Schw2001].

Figure 3: Two-neutron separation energies in the vicinity of Z = 82 as a function of neutron number. Shown

are S2n values derived from the Atomic-Mass Evaluation AME1995 (top) and a more recent compilation including ISOLTRAP data (bottom) [Schw2001].

The general trend is that S2n decreases as neutrons are added and deviations from this behavior

point to manifestations of microscopic nuclear structure effects. For example, at N = 126 there is a sharp decrease of S2n which indicates a neutron shell closure. Also very particular effects show up as one approaches the neutron mid-shell region near N = 104. A possible explanation might be the presence of shape coexistence configurations in this particular mass region, which has been discussed in much detail in [Heyd1983, Wood1992], and a mixing between the intruding configuration and the ground-state, causing local deviations from a smooth linear trend. This is

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particularly striking in the Hg and Pt nuclei and illustrates most impressively how masses give a first glimpse of nuclear structure.

Another highly interesting class of interaction is that of the last proton(s) with the last neutron(s) and is called δVpn [Zhan1989, VanI1995, Caki2005]. For example δVpn values show striking singularities for nuclei with N = Z, reflecting the T = 0 interaction. For even-even nuclei, δVpn is defined [Zhan1989, Bren1990] by

δVpn(Z,N) = ¼ [{B(Z,N) – B(Z,N-2)} – {B(Z-2,N) – B(Z-2,N-2)}] .

A given δVpn(Z,N) value for even-even nuclei refers to the interaction of the (Z-1) and Zth protons with the (N-1) and Nth neutrons.

In a recent study by R.B. Cakirli et al. [Caki2005], known masses from the new Atomic-Mass Evaluation AME2003 [Audi2003] were used to extract δVpn values to highlight the variations of the p-n interaction and to interpret the very characteristic behavior. δVpn values can help to explain and describe shell structure and orbit occupations near the Fermi surface, for example in the 208Pb region. Since the magnitude of variations in δVpn are in the order of 150-250 keV in a given region, the uncertainties in the δVpn values must be less than 30-50 keV to draw a clear conclusion. Since four masses enter in the δVpn(Z,N) equation, it becomes immediately obvious that meaningful trends can only be distinguished if the errors on each individual mass value are in the order of 10-20 keV corresponding to δm ≈ 5x10-8 for masses above A = 200. Presently only Penning trap mass spectrometers can reach this accuracy and only a very small number of mass values with this accuracy exist in the heavy mass region. The analysis by R.B. Cakirli et al. [Caki2005] shows the clear need of new high-accuracy mass measurements far from stability for nuclear structure studies.

(d) Nuclear masses far from stability to test new mass models:

The nucleus is a self-organized, many-body quantum system that interacts through the strong, weak and electromagnetic forces. Due to the lack of an exact description of the strong interaction and the complexity of the many-body nucleonic system, the binding energy can not be described by ab-initio theories. Instead, one has to rely on mass predictions by models (with the aim of a quantitative prediction of the total binding energy of a nucleus) and formulas (with the aim of a numerical calculation of masses on a physical basis) [Lunn2003]. The latter are based on a set of free parameters (up to several hundreds), which have to be constrained by local [Jäne1988] or empirical [Tach1988] comparison to experimental data. In particular, data far from the valley of β-stability represent well-suited test cases for the predictive power of models.

In the last few years there has been significant progress in the construction of purely microscopic mass models on the basis of self-consistent mean-field models. Large-scale fits of Skyrme-type interactions to all available masses became feasible [Gori2003]. When including phenomenological correction terms for correlation effects, these Skyrme mass fits compete with the best available microscopic-macroscopic models. More recent theoretical developments now allow the large-scale microscopic calculation of correlation energies, either in the framework of a symmetry-restored Generator Coordinate Method [Bend2004], or a microscopic Bohr-Hamiltonian [Flei2004]. Further development of the models is necessary to include all important correlation effects simultaneously, but the present results are most encouraging as they improve the masses around shell closures. For a more reliable extrapolation of masses, not only the models, but also the effective interactions used and the protocols for the adjustment of their coupling constants have to be improved. To that aim, it is highly desirable to have more data on neutron-rich nuclei beyond the neutron shell closures that separate the stable nuclei from the drip line. Their structure is mainly determined by the single-particle states above the shell closures, which are not completely constrained by the data on more stable nuclei.

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(e) In-trap conversion electron and alpha spectroscopy:

Presently high-resolution electron spectroscopy is limited by the thickness of radioactive sources due to scattering in the source material. Since ions localized in a Penning trap represent an ideal carrier-free source, where energy loss or scattering do not influence the line shape, we also plan to equip MATS with novel, highly efficient experimental techniques for in-trap conversion electron and α spectroscopy [Weis2002]. Moreover, by use of the preparation trap isobarically pure sources can be obtained. In addition in-trap α spectroscopy will be studied. Typically the α decay of a heavy even-even nucleus leads within 10-20% to the first excited 2+ state of the daughter nucleus [Sobi2001]. The populating α decay causes the emission of low-energy 'shake-off' electrons which allow the determination of the decay position [Gras1975]. After a lifetime (typically few hundred picoseconds) the 2+ state itself decays via L conversion, again producing several shake-off electrons. During the lifetime of the 2+ state the recoil nucleus typically moves by about 50-100 µm. Thus the origin of the shake-off electrons at the position of the conversion decay will be displaced by this distance with respect to the position of the initial α decay. In order to adapt this distance to the position resolution achievable in the electron detector, the magnetic field of the Penning trap on the axis behind the magnet can be adiabatically expanded, e.g. from 7 T at the trap center to 7×10-3 T in about 1 m distance. Thus the position of the two electron components can be detected in distance of about 1.5-3 mm, sufficient for the position resolution of a segmented electron detector.

Measuring the position of both electron components results in a lifetime measurement of the 2+ state with the recoil-distance method, allowing for a determination of the quadrupole deformation. In addition 0+ states can be populated in the α decay, whose lifetimes can be determined with the same experimental technique via shake-off and conversion electrons (in situations where the 0+ state is the first excited state). This would yield access to a measurement of the E(0) strength ρ2(E0). This method is suitable for all α-decaying isotopes e.g. produced at the Super-FRS via fragmentation of a 238U beam.

Position-sensitive α-recoil coincidence spectroscopy as well as position-sensitive electron spectroscopy allow for diagnostics of the size and shape of the ion cloud in the trap, while the conversion electron lines provide an unambiguous Z identification. Due to the rotational character of the converted transitions, from the measured energy of the K and L lines the rotational energy and thus the spin can be extracted. Therefore this experimental technique enables for an improved assignment of level schemes especially in odd nuclei compared to the so far used methods of α-spectroscopy. Performance and applicability of MATS

MATS is a novel and unique setup using an advanced trapping system and highly-charged ions for high-accuracy mass measurements and trap assisted spectroscopy. The proposed project aims for a relative mass precision of better than 10-8 even for nuclides with half-lives of only 10 ms. Assuming an overall efficiency of about 1-5% (depending on the speed of extraction for the low-energy branch gas catcher, the charge-breeding and trapping time) nuclides with yields of only a few 10/s are accessible. With the advantage of using highly-charged ions resolving powers of above 107 will be easily obtained, enough to resolve low lying isomers with excitation energies of a few 10 keV. Since the measurement technique can be applied to any nuclide of interest with proper yield and half-life, irrespective of the chemical behavior of the ion under investigation, all above discussed physics cases and mass candidates can be addressed with the novel high-accuracy Penning trap mass spectrometer MATS at the future facility FAIR.

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Why install MATS at the FAIR facility? Based on the latest Atomic-Mass Evaluation AME2003 [Audi2003] 2228 atomic masses out of

3180 known nuclides are measured or estimated from nuclear trends (see Fig. 4). 1158 masses are known with a relative mass uncertainty of δm/m ≤ 10-7, 181 masses with δm/m ≤ 10-8, and surprisingly only 24 nuclides with δm/m ≤ 10-9 where the heaviest one is 134Cs. Motivated by the physics cases addressed above many more masses, especially in the medium heavy and heavy mass region above A = 180 are needed with a precision of better than 5x10-8 (i.e. δm < 10 keV for A = 200). These physics questions can be ideally addressed by the MATS project.

10-9

10-8

10-7

10-6

10-5

10-4

mm

Ar

Ne

Se

Sn

NdPm

SmEu

DyHo

Yb

HgTlPb

BiPo

FrRa

CsBa

Ce

Sr

BrKrRb

N=8

Z=8

N=20

Z=20

N=28

N=28

Z=28

N=82

Z=82

N=126

N=152

N=152

CrMn

NiCu

Ga

N=20

NaMg

K

Pr

AgC1

C2

C3C4

C5

C6

C7

C8

C9

C10 C11 C12

C12

C13

C14

C15

C16

C17

C18

C19 C20

C21

C20

C22

C11

C4

Figure 4: Nuclear chart with the relative mass uncertainties δm/m of all known nuclides shown in a color

code (see scale bottom right of the nuclear chart, stable nuclides are marked in black) [Blau2005b]. Masses of gray-shaded nuclides are estimated from systematic trends [Audi2003]. The isobaric lines of the carbon clusters C1 to C22 demonstrate the advantage of using a “carbon cluster mass grid” for calibration purposes [Blau2002].

In precision measurements it is of crucial interest to have a clean and intense sample available

for the measurement, both can be achieved at FAIR even for nuclides that are not at all available elsewhere. The main regions where MATS will have unique possibilities due to its installation at the FAIR facility are very neutron rich nuclei and nuclides of elements that are not produced at ISOL facilities, e.g. it is expected that the neutron drip-line will be reached up to Z = 25. For very neutron-rich nuclides MATS will profit especially from the yields that are considerably higher than everywhere else in the world, but also from the very clean beam delivered by the SuperFRS. These clean conditions in combination with high yields and no persistent element selectivity will also ease considerably, in some cases permit for the first time, precision measurements for proton rich nuclides as for instance superallowed beta emitters. From the second generation facilities RIA is expected to be competitive but it will be in operation later than FAIR. The planned mass measurement program at the Munich FRM-II reactor also aims for very neutron rich nuclei but will not become operational within the next 5-7 years and will have due to the production mechanism only access to a limited number of radionuclides. In this respect FAIR seems to be the appropriate place for the installation of MATS.

Finally, MATS has the possibility to provide clean or even isomerically pure bunched beams which will be of high interest and advantage for other experiments proposed at FAIR, as e.g. LaSpec, a Laser Spectroscopy setup for the study of nuclear properties.

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Mass measurement program for radionuclides worldwide (“competition”): Trapping radioactive ions is becoming a routine technique in nuclear physics. The combination

of a radiofrequency Paul trap for beam preparation and a Penning trap for high-precision experiments like mass spectrometry and nuclear decay spectroscopy already plays a prominent role at almost all existing radioactive beam facilities, as shown in Fig. 5. The application of such devices is also planned in all future laboratories providing radioactive beams. New developments, like trapping devices in a cryogenic, ultra-clean environment, higher magnetic fields (e.g. in the LEBIT project at MSU [Schw2003b]), as well as the employment of laser ionization for beam purification [Blau2003,Wend2004] and charge breeders to produce highly-charged ions (e.g. in the TITAN project at TRIUMF/Vancouver [Dill2003]), show a bright future and provide a healthy competition for ion traps in nuclear physics research [Klug2003, Klug2004]. All projects are unique and have their particular strength. MATS at FAIR will be the first installation to combine cryogenic trapping systems and the use of high charge states for radioactive species with beam yields that in many cases exceed those available elsewhere, a prerequisite for becoming a front player in the field. MATS is therefore expected to be superior to many existing facilities concerning the achievable precision and the number of exotic radionuclides accessible.

Many of the above addressed physics motivations for high-accuracy mass spectrometry are also valid for the second mass measurement project within NUSTAR, named ILIMA. It aims for mass measurements with relative uncertainties of below 10-7 in storage rings using the Schottky Mass Spectrometry (SMS) method. Due to the long cooling times for SMS, access to very short-lived nuclei with a half-life below 1 s is not possible with this method. Instead, the Isochronous Mass Spectrometry (IMS) method can be used at ILIMA, a time-of-flight technique that allows to explore the lifetime region well below one millisecond. For mass measurements at ILIMA absolute calibrants from other sources, such as MATS, are important. While ILIMA can map a mass surface over a large area MATS is interested in specific nuclides where a high-precision is required. There are interesting candidates (a list of special cases and unresolved mass problems for the AME2003 can be found in [Waps2003], pp 169) where it is important to attack them from two different sides: by the storage ring and by the trap community. The experiments will be performed in a both cooperative and at the same time competitive spirit between ILIMA and MATS.

Figure 5: Storage rings and Penning trap facilities for high-accuracy mass measurements on stable, long-

lived and short-lived nuclides which are in operation, under construction or planned. The names of the experiments are taken from original publications [Blau2005].

16

B Systems

With MATS (Precision Measurements of very short-lived nuclei using an Advanced Trapping System for highly-charged ions) at FAIR we aim for applying two different techniques to very short-lived radionuclides: High-accuracy mass measurements and in-trap conversion electron and alpha spectroscopy. The experimental setup of MATS is a unique combination of an electron beam ion trap for charge breeding, ion traps for beam preparation, and a high-accuracy Penning trap system for mass measurements and decay studies. Each subsystem is a versatile tool itself and allows different high-accuracy experiments resulting in a broad physics output. All subsystems will be discussed individually in the following. 1. Subsystems

1.1 Ion beam cooler and buncher (linear radiofrequency ion trap) and separator for isobars

Ion beam preparation is critical for trapping rare exotic nuclides. Although gas cells thermalize reaction products with great efficiency and rapidity, they do so with significant diffusion which causes large emittances in the absence of confining forces. Providing the correct time structure for subsequent trapping is also imperative for preserving high efficiency. Segmented radiofrequency quadrupole (RFQ) cooler bunchers, providing transversal and longitudinal confinement in the presence of collisions between radioactive ions and light buffer gas atoms, have proven their efficiency and adaptability, now becoming standard elements for trapping systems. The first stage of MATS will be a second-generation cooler/buncher such as that used with the LEBIT facility [Schw2003], consisting of an open, cylindrical electrode geometry for the transverse RF field and tapered insertion electrodes for the longitudinal field (see Fig. 6). The system will be operated at cryogenic temperature which offers a potential gain of two orders of magnitude over a room temperature system.

Figure 6: Electrode layout of the LEBIT-buncher [Schw2003].

The RFQ is the connection between MATS and the gas catcher of the low energy branch of the

Super-FRS. It is required to match the beam emittance of the radioactive ions to the quite small acceptance of the EBIT electron beam, to guarantee high injection efficiency. Since it is yet not decided whether there will be an RFQ or a novel laser ion source trap (LIST) for bunched, low emittance beam release [Blau2003, Wend2004] along with the gas catcher, we decided to include such a device in our setup. In addition, the RFQ is ideally suited to provide bunched, low emittance

17

beams to other experiments, as e.g. to LaSpec. For collinear laser spectroscopy experiments this will result in a tremendous reduction in background as well as in line width as already demonstrated at IGISOL [Niem2002, Camp2002].

a) Simulations i) The detector

Not needed. ii) The beam

Beam transport will be simulated by using one of the two self-written programs by the collaborators S. Schwarz and W. Plaß. Detailed simulations studies have already been performed for the existing RFQs at ISOLTRAP [Herf2001b, Kell2001], JYFLTRAP [Niem2001], SHIPTRAP, and LEBIT [Schw2003].

b) Radiation hardness Due to the rather low beam intensities for the most interesting nuclei, radiation hardness is not

an issue.

c) Design The design will be based on the existing RFQs at ISOLTRAP [Herf2001b, Kell2001],

JYFLTRAP [Niem2001], SHIPTRAP, and LEBIT [Schw2003]. To adapt the system to the new requirements about half a year is needed.

d) Construction The construction phase including first test measurements is expected to take about two years.

e) Acceptance Tests Before installation of the RFQ cooler, off-line tests will assure that the required performance is

reached. Since the cooler is being built within the MATS collaboration, no formal acceptance tests as such are specified.

f) Calibration Calibration with respect to voltage and RF frequency will be done with ions from a stable off-

line ion source.

g) Request for test beams At the first stage no test with radioactive ions is needed. For the final commissioning a

radioactive test beam is required.

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In addition to the RFQ another separator for isobars might be needed which is presently under investigation: Separator for Isobars

While the SuperFRS will provide well separated beams to the LEB facility, it is to be expected that, in addition to the nuclides of interest, a large amount of contaminant ions may be released from the ion catcher. Molecular isobars could pose the most serious problem, since they cannot be suppressed sufficiently in standard RF quadrupoles. Instead, a multi-turn time-of-flight (MR-TOF) mass separator can be used, which would provide pre-separated ion bunches to the EBIT or the Penning traps and allow them to run at highest resolution.

In such an MR-TOF separator, ion bunches are formed in an RF trap and injected into an analyzer consisting of two electrostatic ion reflectors, in which the ions travel back and forth for a selectable duration, while they are separated in time according to their mass-to-charge ratio. Injection into and ejection from the analyzer is achieved by pulsing of the reflector electrodes. After ejection from the analyzer, a specific mass-to-charge ratio can be selected in a pulsed electric ion gate. In addition, a dynamic energy buncher is foreseen to reduce the longitudinal energy spread behind the ion gate. Such a device could have a mass resolving power of 104 to 105 and cycle times of down to 1 ms even for singly charged ions. In addition to acting as mass separator, it could also serve as mass spectrometer for mass measurements and diagnostics, if the ion gate is replaced by a microchannel-plate detector.

Reflector 1 Reflector 2

RF Trap Ion Gate

Reflector 1 Reflector 2

RF Trap Ion Gate

Figure 7: Schematic figure of the MR-TOF separator As an alternative to isobar separation by time-of-flight, an "ion circus" could be used. Such a device is formed from a classic (linear) radiofrequency quadrupole mass filter by bending it into a continuous circle. The total time spent by ions in the confining field can therefore be considerably increased by allowing them to make several orbits. This situation allows ion cooling to be effected with a reduced gas pressure load and a new possibility is also created: gradually increasing the mass resolving power of the device as the ions are cooled. Thus, the transmission losses that usually accompany high resolving power are reduced (or eliminated). The device is conceived such that ions may be injected and extracted by correctly-timed pulses at any quadrant of the ring, from whence comes the idea of the traffic “circus” (see figure)

19

Figure 8: Schematic diagram of the “ion circus”. The inset shows a non-segmented version of such a device used to make crystalline beams, the details of which are from [Schä2001]. a) Simulations Simulations are performed using the simulation programs SIMION and ITSIM. Of particular importance is the ion-optical design of the analyzer, since it determines the quality of the time separation. Additional work will be required to design the pulsed ion gate and the energy buncher, and to simulate the emittance of the device. b) Radiation hardness Radiation hardness is not an issue due to the low beam intensities. c) Design In Giessen, a small test-version of a MR-TOF has been designed and built as mass spectrometer, and the characterization of its performance is underway. The analyzer has an overall length of 40 cm and is operated with an acceleration voltage of 1.5 kV. So far peak widths have been measured, which correspond to a mass resolution of about 30000. This compares reasonably well with the calculated maximum mass resolving power of 70000. The design of the separator will be based on this test version, however an overall length of 1.5 m is foreseen to further improve the performance of the device. The ion circus concept is yet unproven but a funding application (to France’s new Agence National de Recherche) has been approved for three years so that simulations and prototype studies will start in early 2006. d) Construction Construction including first tests will take about one year. e) Acceptance tests Acceptance tests will be performed using beams with stable isotopes. f) Calibration Calibration will occur with stable isotopes delivered by an off-line ion-source. g) Request for test beams Not required.

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1.2 Charge breeding electron beam ion trap (EBIT)

The primary task of the electron beam ion trap (shown in Fig. 9) to create high charge states in a very short time, leads to the use of a high-intensity electron beam [Cres2001,Cres2004]. The use of non-immersed, compressed electron beams of 5A has been demonstrated already. Two new EBITs based on the successful Heidelberg EBIT design are assembled for tests at the MPI-K in Heidelberg. They implement electron guns capable of such high emission currents. In addition to the charge breeding task, the EBIT should be equipped with a high-resolution X-ray spectrometer to carry out spectroscopic measurements sensitive to nuclear size effects [Beie1998].

pump

pump

pump

manipulator

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collector

compensator

insulators

trap

Figure 9: Scheme of the Heidelberg design on which the proposed charge breeding EBIT will be based. The charge breeding EBIT proposed here follows the Heidelberg EBIT design closely, which

will also be used at the TITAN spectrometer [Sikl2005]. A cryogen-free superconducting magnet (6T) will be used for the compression of the electron beam to typical current densities between 1000 and 10000 A/cm2. The beam energy can be adjusted, in order to optimize the required charge state within a given breeding time. The Heidelberg EBIT can provide a maximum electron beam current of 535 mA, a beam diameter in the confinement region of about 70 µm, which corresponds roughly to a current density of 14000 A/cm2. With the higher beam current of the breeder EBIT the beam diameter will be larger, which results in a higher acceptance for injected ion beams. At the maximum electron beam energy of 50 kV, the EBIT can in principle produce bare ions up to Xe54+, and He-like ions across the periodic table. In order to increase the breeding efficiency, shell closures can be used to collect most of the ions in one charge state, by appropriate adjustment of the electron beam energy [Cres2004]. Figure 10 and figure 11 show the breeding for Sn-ions for moderate beam energies for Ni- and Ne-like configurations at different breeding times. High efficiencies already for short breeding times (<50ms) can be reached. Ions such as Sn40+ can be produced in breeding times in the order of 20 milliseconds at highest current densities.

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Figure 10: Charge breeding of Sn at 1.1 keV beam energy, 700 A/cm2 current density and 10-9 mbar residual

gas pressure. After 20 ms, nearly 80% of the ions are in the state Sn22+ (Ni-like closed-shell configuration).

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Figure 11: Charge breeding of Sn at 6.4 keV beam energy, 700 A/cm2 current density and 10-9 mbar residual

gas pressure. After 500 ms, nearly 40% of the ions are in the state Sn39+ and 40% in the state Sn40+ (Na-like and Ne-like configuration).

The EBIT can produce test beams of highly charged ions of stable isotopes independently of the

accelerator facility, and deliver them to the Penning trap. For this purpose external ion sources like a MEVVA (metal vapor vacuum arc) source or a surface ionization source can be used to inject low-charge ions into the EBIT. The Heidelberg EBIT also makes use of a laser ablation ion source to load the trap with ions from solid elements [Miro2003]. In this way, independent measurements, calibrations, and tests of the preparation and precision trap can fully exploit its capabilities during off-line times.

22

a) Simulations i) The detector

The charge state evolution is followed by means of a solid state energy dispersive X-ray detector. High-purity intrinsic Ge detectors have proven to be very well suited for this application. The re-combination lines (radiative/dielectronic) allow the determination of the charge state of the trapped ions in real-time. A high-resolution X-ray crystal spectrometer attached to the EBIT will provide additional information about the charge state, as well as to obtain atomic and nuclear size data.

An optical diagnostic port can be used for visible and laser spectroscopy diagnostics. The spectroscopic instrumentation developed at the MPI-K enables isotopic shifts in the visible and X-ray ranges to be resolved, and thus to obtain information about nuclear size effects, spin, and other relevant data. ii) The beam

Beam transport, injection, and extraction have been simulated using SIMION and TRICOMP, two software packages capable of calculating the electrostatic and magnetic fields and ion trajectories. TRICOMP also takes space-charge effects consistently into consideration. Meanwhile, practical tests at the Heidelberg EBIT facility will help to find optimized conditions. The acceptance of the EBIT electron beam for injected ions which is critical for the efficiency of the breeding process will be investigated via ion tracking simulations. Thus the required matching of the beam emittance via the RFQ cooler can be determined.

b) Radiation hardness Due to the rather low beam intensities for the most interesting nuclei, radiation hardness is not

an issue. The small amounts of short-lived radioactive isotopes introduced into the trap after the RFQ quadrupole are not expected to constitute a problem neither from the point of view of the radiation background level, nor from the radiation safety. Nonetheless, provisions for easy disassembly of the drift tubes and other exposed elements of the ion optics in order to facilitate a regular decontamination schedule will be taken into the design.

c) Design The design will be based on the existing EBITs that are operated at the MPI-K in Heidelberg.

Six months should be sufficient for the design changes to adapt the current EBIT design to the special needs at GSI (1 PhD).

d) Construction The workshops at the MPI-K in Heidelberg have already built two EBITs and as the MATS

EBIT will be similar, the construction phase including first test measurements and transfer to the final MATS setup is expected to take about two years.

e) Acceptance Tests Before installation of the EBIS, off-line tests at MPI-K in Heidelberg will assure that the

required performance is reached. For the commercial EBIT magnet a standard acceptance test by the company will be performed. Since the full charge breeder setup is being built within the MATS collaboration, no formal acceptance tests as such are specified.

f) Calibration No calibration needed.

g) Request for test beams After initial operation tests with stable isotopes, realistic external beams with non-radioactive

ions at somewhat higher intensities would be desirable to facilitate and optimize the fine tuning of the device, before weak radioactive beams are needed.

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1.3 q/A selection Since the creation of highly-charged ions in an EBIT is a statistical process a distribution of

different charge states for the ion of interest and, in addition, impurity ions is delivered. Therefore, a q/A-separation stage has to be installed to select the desired charge to mass ratio for injection into the Penning trap system. Due to floor space restrictions in the current LEB hall the trap system is located on the second floor while the EBIS is situated on the ground floor. Hence also a bender to inject ions from the EBIT into the Penning trap is required. In the current design the two functions are separated. An electrostatic bender is foreseen for bending the ions to the second floor while a magnetic multi-passage spectrometer (MPS), as shown in Fig. 12, could be utilized as q/A separator [Laka1992].

Figure 12: Left: Sketch of the magnetic multi-passage spectrometer for q/A selection. 4,5,6 and 7 are the

electrostatic lenses. Right: L are the lenses, K are additional steerer and correction elements [Laka1992].

A MPS consists of an electro-magnet with circular pole shoes and four ports where electrostatic lenses which can be operated as mirrors are installed. For instance an ion beam injected from the left experiences a 90 degree deflection in the magnetic field directing it into the mirror lens where it can be reflected back to the center of the magnet. Then it experiences another 90 degree bend and can either be ejected to the right or reflected one more time to direct the beam finally towards the upper port. Depending on the operation parameters of the electrostatic lens/mirror system an ion beam can be transported in three different directions. Since the resolution between different q/A values for a given B field strength depends on the length of the pathway in the field, or more precisely the area covered by the beam in the dipole field, a higher resolution is possible by multi passage operation. In the multi passage operation mode where the ion beam is making more than one passage through the magnet it has been shown that transport efficiencies on the order of 60% are possible. Therefore in the ground floor the MPS offers a flexible and efficient solution combining the different requirements of q/A selection and beam distribution system. The incoming beam from the LEB ion catcher can be either injected into the EBIT for charge breeding or bend to a detector for diagnosis. After charge breeding in the EBIT the selected charge state can be transferred to the traps via the electrostatic bender. In order to match the bending magnetic field to the charge state of the ions, either the ion beam energy or the magnetic field has to be varied between injection into the EBIT and extraction from the EBIT. A typical time scale for those field changes is the breeding time, which varies from 10-200 ms. Therefore the MPS magnet needs a laminated yoke, which allows pulsing in the timescale given above. The matching of the beam energy of highly charged ions from the EBIT can be done by changing the EBIT platform potential.

24

The MPS can be baked in order to reach a rest gas pressure below 10-9 mbar with turbo pumps at each port. The device requires about 1.6x1.6 m2 floor space, cooling water and 8 kW power. The weight is on the order of 800 kg. For the alignment of the MP spectrometer (and the other components) standard adjustment units should be available.

a) Simulations i) The detector

Not needed. ii) The beam

Beam transport will be simulated using SIMION and TRICOMP, two software packages capable of calculating the electrostatic and magnetic fields and ion trajectories. The ions from the EBIT will have an energy distribution, which requires an achromatic transport through the MPS. Electrostatic correction of the magnet energy dispersion, which is required for the achromatic transport needs to be calculated.

b) Radiation hardness Due to the rather low beam intensities for the most interesting nuclei, radiation hardness is not

an issue.

c) Design The design will be based on the existing MPS at the IAP of the Frankfurt University. The

existing device is available at GSI for test measurements in the design phase.

d) Construction The construction phase is expected to take less than one a year. Another PhD year is needed to

specify the system in respect to efficiency and resolving power.

e) Acceptance Tests Before installation of the magnetic multi-passage spectrometer, off-line tests will assure that the

required performance is reached. Main part of these performance tests are the transport of ions with a given energy spread. The correction elements for an achromatic transport will be tested therefore. Since the unit is being built within the MATS collaboration, no formal acceptance tests as such are specified.

f) Calibration The magnetic field strength of the MPS can be calibrated with a standard NMR probe. Further

calibration will be done with ions from a stable off-line ion source or with highly-charged stable noble gas ions from the EBIT.

g) Request for test beams Not required.

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1.4 Preparation Penning trap

The preparation Penning trap will be used to provide the precision Penning trap and others with a cooled beam of highly-charged ions. Since highly-charged ions cannot be cooled by buffer gas collisions we have to implement other cooling techniques. The most promising techniques are electron cooling and sympathetic laser cooling. However, a new cooling scheme based on protons will be tested at the TITAN ion trap facility at TRIUMF/Canada [Ryjk2005]. The necessary research has to focus on the applicability and limits of electron cooling. This will be done to a large fraction within the HITRAP project [Beie2003, Herf2005]. The main effort will be at the University of Mainz where the existing trap setups will be used to test new detection methods and to investigate the operation of a large cylindrical trap operated at 4K. For a schematic drawing of a Penning trap setup see subproject 1.5 (Precision Penning trap).

The preparation trap will be installed in a superconducting magnetic solenoid of about 7T. In order to reach the necessary vacuum conditions to store highly-charged ions for an extended period of time, the trap needs to be kept at liquid helium temperature of 4K. Here a static cryogenic vacuum (XHV, < 10-15 mbar) will be reached by cryopumping. This allows also for improved in-trap detection via image currents for the diagnosis of the cooling process. To keep the trap at this low temperature it will be either coupled to the cooling reservoir of the superconducting coils of the magnet or a cryogen-free cold head will be used. Similar systems are already successfully used within the ATHENA [Amor2004] and ASACUSA [Yama2002] experiments at CERN for the handling and manipulation of positrons and antiprotons in order to create antihydrogen. For the second case of a cold head an EBIT ion source has been built recently by the Heidelberg collaborator. This cryogen-free system seems to be the most promising technique in terms of handling and maintenance. The HITRAP cooler trap will be based on this technique too [Herf2005] and it will serve as an important test case for such a trap.

a) Simulations Simulations are decisive for a detailed understanding of the mechanism of electron cooling.

Simulations for the determination of cross sections and cooling times have already been done within the HITRAP project at GSI [Bern2004]. They demonstrate the possibility to cool bare uranium in an electron bath in a Penning trap within a few seconds without significant recombination losses. Further investigations are in progress and performed by G. Zwicknagel at the University of Erlangen and within the HITRAP group at GSI.

i) The detector Detection is needed to diagnose the status and success of the cooling process as well as to

optimize it. For this, both, Multi-Channel-Plates based detector systems that are retractable are used as well as nondestructive image current detection. These types of detection are well understood and do not need additional simulations.

ii) The beam The beam handling will be simulated using mainly single particle trajectory tracking codes as for

instance SIMION. This code includes magnetic and electrostatic fields calculated from electrode geometry by solving the Poisson equation. This has the advantage that there are no approximations needed concerning fringe fields or field distribution.

b) Radiation hardness Due to the rather low beam intensities for the most interesting nuclei, radiation hardness is not

an issue.

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c) Design The design will be based on existing trap set-ups that have been supervised at the University of

Mainz. It is estimated that the design of the trap and its support elements will take about one man-year.

d) Construction The workshops at the University of Mainz have already built several traps for various projects

within Europe and concentrates the necessary experience to complete a complex trap setup in due time. The electroplating of the individual trap components can be done using existing GSI infrastructure. The completion phase is expected to take about two years with in total about two PostDoc man years and four PhD man years.

e) Acceptance Tests A standard acceptance test will be required of the magnet manufacturer. After installation of the

trap system, off line tests will assure that the required performance is reached. Since the traps are being built within the MATS collaboration, no formal acceptance tests as such are specified.

f) Calibration The only calibration needed is in order to know the magnetic field strength of the trap magnet.

This will be done first using a standard NMR probe by the manufacturer. With the operation of the internal test ion source, this will be done determining the cyclotron resonance frequency of stored ions.

g) Request for test beams In order to get the preparation trap operational an external test beam is not required. Stable ions

created by the charge breeder itself and singly charged ions from a test ion source will be used to make the necessary tests.

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1.5 Measurement Penning trap

The technique of mass measurements in a Penning trap (see Fig. 13) is well established for both, stable and short-lived nuclei (for the physics of a stored ion in a Penning trap see [Brow1986], for the application of traps to mass spectrometry see e.g. [Boll2004, Klug2003, Lunn2003]). This will minimize the actual research and development effort. However, the combination of high-accuracy mass measurements with in-trap decay spectroscopy is a new and novel approach and will require a new trap design. The trap needs to provide an excellent harmonic trapping potential while being a very open structure for the escape of the decay products. To define the limits and to investigate the influence of a novel electrode structure on the magnetic and electric fields extensive simulations need to be performed. These simulations include ion optics and trapped-ion dynamics studies as well as detection studies. In addition to the trap design, further R&D effort will be on the development of sensitive electronics and detectors for in-trap spectroscopy.

The most stringent requirement in the design of the measurement trap is the capability to perform high-accuracy mass measurements. Since this requires a minimized uncertainty in the frequency determination, the magnetic field needs to be as high (B ≥ 7 T), homogeneous (≤ ±0.1 ppm measured over a 10 mm diameter spherical volume), and stable (δB/δt×1/B ≤ 10-9 / h) as possible. At the same time, the planned in-trap decay experiments require sufficient space inside the bore, so that the bore diameter needs to be about 160 mm or larger (see Fig. 13 and 15).

During mass measurements the calibration of the magnetic field magnitude will be performed by the determination of the cyclotron frequency of stable ions with well-known masses. To this end, an off-line reference ion source will be installed which provides preferably also highly-charged ions. Here, carbon cluster ions provide the reference mass of choice [Blau2002] since the unified atomic mass unit is defined as 1/12 of the mass of 12C. Mass measurements on well-known masses allow the accuracy limit for the proposed setup to be studied [Kell2003].

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Figure 13: Proposed high-accuracy measurement Penning trap for mass spectrometry and in-trap

spectroscopy at the MATS project. The trap system is installed in a 7 T superconducting magnet. For mass spectrometry either a destructive time-of-flight cyclotron resonance or a non-destructive Fourier transform ion cyclotron resonance detection will be used. For in-trap spectroscopy an electron conversion detector setup will be installed.

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a) Simulations Simulations are necessary to study the excitation of the ion motion inside the hyperbolic high-accuracy Penning trap. Detailed simulation studies of the ion motion have already been performed at ISOLTRAP, a Penning trap mass spectrometer for short-lived radionuclides at ISOLDE/CERN.

i) The detector Destructive (time-of-flight ion cyclotron resonance, TOF-ICR) as well as non-destructive

detection techniques (Fourier-transform ion cyclotron resonance, FT-ICR) will be used to measure the cyclotron frequency of the stored ions. Both techniques are well known and novel detectors are presently under construction at the Universities of Mainz and Greifswald. Detailed simulations are not needed. See also subprojects 1.6 and 1.7 (detectors).

ii) The beam Beam simulation is mandatory to reach the envisaged accuracy. Mainly single particle trajectory

tracking codes will be used, as e.g. SIMION. This program calculates magnetic and electrostatic fields from a given electrode geometry by solving the Laplace / Poisson equation via a finite differential method. Ion trajectories within a given field geometry are calculated by using a Runge-Kutta (4th order) iteration technique. The injection, ejection, and storage in a Penning trap is well understood, however, there will be extensive calculations on these subjects to optimize the electrode shapes and setup. In addition self-written programs (by W. Plaß and S. Schwarz) will be used to calculate ion trajectories within the traps. To calculate field inhomogeneities induced e.g. by the trap material itself a code (SUSZI) by S. Schwarz is available.

b) Radiation hardness Since experiments are performed with single trapped ions, radiation hardness is not an issue.

c) Design The design will be made in close collaboration with different groups from e.g. Jyväskylä,

Munich, GSI and Mainz, since they have extensive experience in designing trap and detector setups. It is expected, that the design will take about two man-years.

d) Construction Due to its complexity the setup will be built in two stages. The first stage includes the trap in

order to be able to investigate all issues that are connected to a novel trap design operated at 4K. About three PhD man years and four PhD man years are required. This stage will already allow high-accuracy mass measurements. In a second stage the detectors for decay spectroscopy will be complemented.

e) Acceptance Tests A standard acceptance test will be required of the magnet manufacturer. After installation of the

trap system, off line tests will assure that the required performance is reached. Since the traps are being built within the MATS collaboration, no formal acceptance tests as such are specified.

f) Calibration The only calibration needed for the trap setup is in order to know the magnetic field strength of

the trap magnet. This will be done first using a standard NMR probe by the manufacturer. With the operation of the internal test ion source, this will be done determining the cyclotron resonance frequency of stored ions with well-known mass. The detectors around the trap will be calibrated first offline with standard calibration sources. The final calibration will be done on line with nuclides close to the nucleus to be measured. See also the section on detectors.

g) Request for test beams To get the measurement trap operational no external test beam is needed. Stable ions from the

charge breeder or singly charged ions from a test ion source will be used to make the necessary tests.

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1.6 Instrumentation for mass spectrometry (TOF and FT-ICR detectors)

For mass spectrometry two detection techniques will be implemented: the destructive detection with microchannel plate (MCP) detectors (see Fig. 14 left) or Channeltrons (see Fig. 14 right) and the non-destructive detection with the Fourier-Transform Ion-Cyclotron-Resonance (FT-ICR) method [Mars1998]. Both techniques are well established with respect to detection efficiency, design and construction.

Figure 14: For the destructive detection technique either a microchannel plate detector (left) or a Channeltron (right) will be used. The linear feedthrough enables to switch between the two detector types.

For mass determination the ions are ejected from the preparation or the precision Penning trap

towards a MCP detector for time-of-flight (TOF) ion cyclotron resonance mass spectrometry [Köni1995]. With a linear feedthrough each MCP array can be retracted and the beam line is thus open to a conversion electrode detector with a Channeltron for ion detection. The setup with a conversion electrode, where ions are accelerated to, allows a detection efficiency of about 100%, a factor of 2.5 higher than with standard MCP detectors (see Fig. 15). In addition, there is free access to the beam line and if the conversion electrode is turned off, the ions can be transported further to subsequent devices, e.g. to a tape station. It follows that in the case of the precision Penning trap even isomerically pure beams will become available for other experiments [Blau2004].

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Figure 15: Ion yields measured with a MCP detector (full symbols) and a conversion-dynode Channeltron

detector (open symbols) under the same experimental conditions. The observed gain factor is 2.5.

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For FT-ICR two systems are projected. In case of the preparation Penning trap a broad-band FT-ICR detection will be implemented. This allows the monitoring of the cooling process of the ions in the trap and a simple detection and mass analysis. In the precision Penning trap a narrow-band FT-ICR detection will be used. The cryogenic environment and the optimized, low-noise electronics enable the detection of single ions and thus a non-destructive detection and mass analysis of the stored ions [Webe2004, Webe2005]. The R&D will mostly concentrate on the development of this sensitive detection technique. It is closely related to the development of the precision Penning trap.

In addition to the usage for mass spectrometry, other MCP detectors will be installed in the beam line for beam diagnostics and tuning. The design and construction of these detectors is related to the ones used for mass determination which allows a shorter development time. a) Simulations

i) The detector The MCP/Channeltron detectors as well as the FT-ICR technique are well known and need no

further simulation. The only exception is the optimization of the detection efficiency, which should be, e.g., in the case of the conversion electrode detector with a Channeltron close to 100%.

ii) The beam The ion trajectories into the strong magnetic field of the superconducting magnet to operate the

trap and along the drift section between trap and detector need to be simulated to quantify the transport efficiency, e.g., through exit diaphragms etc.. Many simulation studies in this respect have already been performed at other existing trap experiments as e.g. ISOLTRAP, SHIPTRAP, JYFLTRAP, and LEBIT. The simulation program SIMION is well suited for this purpose.

b) Radiation hardness For most nuclei of interest the beam intensity will be rather low, therefore radiation hardness

will not be a matter of concern.

c) Design The design of the MCP/Channeltron detectors and the FT-ICR detection will be made in close

collaboration with the Greifswald, Mainz, and GSI groups, since they have extensive experience in the design of MCP detectors and FT-ICR setups. The design of the standard MCP/Channeltron detector and the broad-band FT-ICR detection is expected to take about one man year. The single ion detection with the narrow-band FT-ICR system is correlated to the design of the measurement (precision) Penning trap and will be a further development of a similar system presently under construction at the Institute of Physics at the University of Mainz.

d) Construction A similar MCP/Channeltron detector has been constructed at the workshop at the University of

Greifswald and other MCP detectors have been built at the University of Mainz. The FT-ICR detection technique is presently studied at the University of Greifswald and thus the construction of all detectors is expected to take one year. The narrow-band FT-ICR detection system is more delicate with respect to the electronics development. Special low-noise electronic parts need to be installed and tested in advance.

e) Acceptance Tests A standard acceptance test will be performed. After installation of the trap system, off line tests

will assure that the required performance is reached. Since the detectors are being built within the MATS collaboration, no formal acceptance tests as such are specified.

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f) Calibration In case of the MCP/Channeltron detector no calibration is needed, only the measurement of the

detection efficiency has to be performed. In case of the FT-ICR detection test measurements are required to calibrate the obtained frequency spectrum with respect to the applied trapping potential and the magnetic field.

g) Request for test beams Not required. The detectors and the FT-ICR system can be tested off-line.

1.7 In-trap spectroscopy detectors

In-trap conversion electron spectroscopy offers the unique possibility to study internal conversion electrons from carrier-free sources, thus avoiding energy loss and scattering effects that deteriorate the line shape and thus the energy resolution. The electrons will be transported along the strong magnetic field of the Penning trap to a detector positioned at the ejection side end of the trap. A sketch of an in-trap electron conversion spectroscopy setup is shown in Fig. 16.

Figure 16: Representative sketch of an in-trap electron conversion spectroscopy arrangement. In addition to

the conversion electron detector (CE), the figure illustrates an optional arrangement for in-trap detection of charged-particles (CP), gamma-rays and beta-particles. Such a complete setup would require a large diameter bore, about 160 mm or more to be practical. In this proposal we concentrate on the electron conversion detection and charged particle in the spirit given in the original Letter of Intent.

a) Simulations

Simulations are especially needed for the design of the segmented electron detector and for the optimization of the conversion-electron transport from the measurement trap to the detector.

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i) The detector A central idea for the in-trap spectroscopy studies is to localize the decay position within the trap

by guiding the electrons along a suitable magnetic field to the detector on the trap ejection axis. Therefore the granularity and the positioning of the annular segmented electron detector needs careful design, guided by tracking simulations using codes like e.g. SIMION.

ii) The beam Since the in-trap spectroscopy setup will be placed within the trap magnet, the same beam

simulation requirements as for the trap setup apply here as well.

b) Radiation hardness For most nuclei of interest the beam intensity will be rather low, therefore radiation hardness

will not be a matter of concern.

c) Design An annular, (Peltier-) cooled, segmented Si(Li) electron detector will be best suited. Such

detectors cannot be bought from the shelf but rather need development time at the manufacturer. For the optional charged-particle (α) spectroscopy detector a compact design for feeding the multiple signals from the highly-segmented detector to the electronics has to be found.

d) Construction The design and machining of the mechanical parts needed for the integration of the spectroscopy

detectors into the trap setup will be performed by the workshop of the LMU in Garching. The construction and test phase requires one PostDoc man year and about two PhD man years.

e) Acceptance Tests Upon delivery of the electron detector, laboratory acceptance tests will have to be performed

using standard electron calibration sources. Since the final detector arrangement are being setup within the MATS collaboration, no formal acceptance tests as such are specified.

f) Calibration The detectors around the trap will be calibrated first offline with standard electron calibration

sources. The final calibration will be done on line with nuclides close to the nucleus to be measured.

g) Request for test beams Since the characterization of the detector setup can be performed with standard test sources, no

request for test beams is needed.

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2. Synchronization, DACQ, Controls, On-line/Off-line Computing

For our purpose the beam into the stopper cell is already quasi-continuous. As a consequence, there is no need to synchronize MATS with the timing scheme of the accelerator. However, an interface between the accelerator, gas cell, and our control system is needed in order to make the important information concerning beam performance etc. available. The beam coming from the gas cell is continuous too. However, the RFQ will provide bunches below 1 µs length and all components of MATS behind the gas cell require synchronization with a precision of about 50 ns.

The data acquisition and controls will be very similar to systems used in presently operated trap systems and detector setups. The data rates are low and the main technical challenge is in the real-time handling of a large number of different parameters. With today’s technology the control and data acquisition requirements for MATS can be satisfied with standard PCs and standard interfaces like GPIB, ProfiBus and cards connected to the PCI slots as well as Ethernet. For synchronizing the different sub-systems, a PCI based digital pattern generator will be used.

Recently a new LabVIEW-based control system [Beck2004] has been implemented at the ISOLTRAP (ISOLDE/CERN, Switzerland), SHIPTRAP (GSI Darmstadt, Germany), and LEBIT (NSCL-MSU, USA) facilities by using the Control System (CS) framework which has been developed by EE/GSI during the last two years [Beck2003]. CS is an object-oriented, multi-threaded, event-driven framework with Supervisory Control and Data Acquisition (SCADA) functionality. It allows one to implement distributed systems by adding experiment specific add-ons. The sub-components buncher, cooler and measurement trap are similar to the ones that are used by the other experiments listed above. Solutions for their control exist within CS. Thus, CS is ideally suited for the MATS purposes and can be adapted and extended to our requirements. The detector part is described in the detector subproject.

In total, about four control PCs and two GUI PCs are required on-line for control, data acquisition and on-line analysis. The amount of acquired data is in the order of a few kBytes/s and the data can be stored on local hard disks. Only in the case of trap-assisted spectroscopy experiments a larger data rate of several MBytes/s occurs and the data will be stored either on tapes or large hard disks. The off-line data processing and analysis will require one PC.

The following is required as infrastructure from FAIR. • About 30 Ethernet ports for computers and Ethernet based devices. The network

should be protected via a firewall from normal network traffic inside FAIR. Services like name servers as well as access to the Ethernet outside FAIR are of course needed.

• The configuration data base of the experiment control system should be stored and backed up centrally. An access to centrally maintained Oracle database is desirable.

• The control PCs will use the actual Windows OS. Those should be maintained by the IT division of FAIR. However, administrator rights are required to develop and maintain MATS software.

3. Beam/Target Requirements a. Beam specifications:

Synchronization of the experiment is based on the timing of trapping. Thus there are no special requests for the primary beam except those set by an injection to the trap.

b. Running Scenario:

A typical mass measurement will take between a few hours and a few days for one nuclide depending on the requested precision and the available intensity. Since we aim to measure a limited number of nuclei which are carefully selected candidates in their physics importance, it will be sufficient to have about 5-6 data taking periods per year each lasting about four days to

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two weeks. This also reduces the man power effort in place, i.e. at FAIR. During these beam time periods, MATS would be the primary user at the low energy branch, however, there will be the possibility to share the beam with other users that need the beam for short time periods of few hours.

4. Physics Performance

The RFQ will be designed to provide bunched beams with a longitudinal emittance of about 10 eV µs and a transversal emittance of ~10 π mm mrad at 2.5 keV energy, ideally suited for injection into an EBIT. The cooling time within the buncher is 1 to a few ms and the overall efficiency can be as high as 50%.

The proposed EBIT can hold more than 109 charges for an electron-beam charge-compensation of 10%. The most dominant charge states (>30%) for some typical ions, charge bred for 20 ms in an EBIT with the parameters given above, are listed in Tab. 2.

Table 2: Peak charge-state after 20 ms breeding time.

Element Charge-state Element Charge-state 8O 7+ 20Ca 12+

11Na 9+ 36Kr 16+ 12Mg 9+ 37Rb 18+ 18Ar 11+ 51Sb 19+ 19K 11+ 54Xe 21+

The multi-passage spectrometer can be operated in single- or multi-passage mode, depending

on the required resolving power. In the multi-passage operation mode where the ion beam is making more than one passage through the magnet a transport efficiency of 60% is possible. The resolving power needs to be determined.

Special performances are required for the superconducting magnet of the precision trap in respect to the magnetic field magnitude (B ≥ 7 T), homogeneity (≤ ±0.1 ppm measured over a 10 mm diameter spherical volume), and stability (δB/δt×1/B ≤ 10-9 / h). For the superconducting magnet of the preparation trap and the EBIT standard devices can be used. Limitations in the precision of mass determinations are temperature and pressure fluctuations in the helium and nitrogen reservoir of the superconducting magnets. They cause changes in the magnetic susceptibility of the materials surrounding the precision Penning traps and thus in the magnetic field homogeneity. The effect of temperature and pressure fluctuations should be minimized by the implementation of a temperature (∆T < 0.1 K) and pressure (∆p < 0.2 mbar) stabilization system. The transport, capture, and ejection efficiency of a trap are close to 100%.

The resolving power achieved in a Penning trap is approximately equal to the product of the cyclotron frequency and the excitation duration Tex and the accuracy scales with the resolving power. The relative statistical mass uncertainty is then given by

δm/m ≈ m / (Tex q B N1/2) (SI units) where N is the number of detected ions. In order to obtain a high accuracy, i.e. a low mass uncertainty, high cyclotron frequencies through strong magnetic fields or high charge states, and long observation times are desirable. For radioactive ions far from stability the observation time is limited by the half-life while the number of detected ions is depending on the production yield and the available beam time. Since highly-charged ions have higher cyclotron frequencies the resolving power and the accuracy are increased; or vice versa, a high-accuracy mass measurement can be performed in a much shorter time as compared to the case of singly-charged ions, which gives access to very short-lived nuclides. Figure 17 shows the advantage of using

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highly-charged ions with respect to the accuracy in the case of an ion with mass 100 in a 7 T strong magnetic field.

The Channeltron detectors used for mass spectrometry experiments have overall efficiencies of 100%, MCP detectors in the order of 30-40%, depending on the kinetic energy of the ion.

0.01 0.1 1

1E-10

1E-9

1E-8

1E-7

1E-6

1000030001000

300

100A40+

δm / m

Tex / s

100A+

N = 100

1000030001000

300N = 100

Figure 17: The achievable mass uncertainty for a nuclide with mass A = 100 u as a function of the excitation

time in the Penning trap (B = 7 T) for two sets of charge states and different numbers of detected ions. The upper set of curves belong to singly charged ions, the lower set of curves to ions in the charge state 40+. The grey shaded area corresponds to an excitation time Tex of 50-200 ms.

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C Implementation and Installation 1. Cave and Annex Facilities, Civil Engineering, Cranes, Elevators, Air Conditioning

(Temperature and Humidity Stability requirements), Cooling, Gases a. access, floor plan:

Figure 18: Floor plan of the MATS setup. The required temporary storage and maintenance area of about 3m × 4m is not included in this floor plan. The floor plan with dimensions is given in the schematic drawing of Fig. 18 (see also overall setup Fig. 1). Overall an area of minimum 10m × 5m × 9m is required. This area does not include space required for a staircase to access the second floor and for temporary storage and maintenance (about 3m × 4m). For the installation of the superconducting magnets, the EBIT and the cryogenic trap setup (see Fig. 1) a roof crane (1-2 t) with a hook height of 9 m is needed. On the ground floor access with a lifting cart is needed for the transport of heavy parts or devices. Room temperature stabilization to one degree would be preferable. The option of an air

PumpBeam-

line

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Beam-lineBeamline

Rack 7Magnet

PumpPump

Table control PCsChair

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conditioned container serving as counting house should be considered. Alignment possibility for the beamline, the installation of the superconducting magnets and of the Si(Li) detector onto the trap ejection axis has to be provided.

b. electronic racks: RFQ: One rack needed for electronics. q/m separation: One rack needed for electronics and magnet power supply. EBIT: Two racks needed for the experiment control. One additional rack on a high-voltage cage (60 kV) is also needed. Penning traps: Five electronic racks (one for vacuum controllers, one for frequency generators, one for magnet supplies, and two for electronics) are needed. Detector: About one rack for detector and trigger electronics. in total: 11 standard full size 19” racks

c. cooling of detectors ( heat produced = heat removed!): RFQ: 2 kW of 16°C cooling water for turbopumps. q/A separation: 8 kW of 16oC cooling water for the magnet and the power supply. EBIT: 15 kW of 16°C cooling water for cryocoolers needed, 4 kW for turbopumps and magnets. Penning traps: 15 kW of 16°C cooling water for cryocoolers needed, 6 kW for turpopumps Detectors: Si(Li) detector will be Peltier cooled. TOF and FT-ICR detectors do not require cooling. Beamline: Already included in the numbers given above. In total: 50 kW of 16°C cooling water (these numbers are preliminary estimates since they depend on the final construction and components)

d. ventilation: No special ventilation is needed.

e. electrical power supplies: RFQ: 15 kW for high-voltage power supplies, pumps (including beamline) etc. q/A separation: 10 kW magnet power supply EBIT: 25 kW cryocooler power supply, trap power supplies, and pumps Penning traps and detectors: 20 kW for cryocoolers, 15 kW for remaining components including detectors. Beamline: Already included in the numbers given above. In total: 85 kW (these numbers are preliminary estimates since they depend on the final construction and components) General comment: A galvanically decoupled power grid for measurement electronics and a central grounding point has to be provided.

f. gas systems: Only small quantities of high purity gases needed for the RFQ, the EBIT, and for the trap system (the later only in the case of using singly charged ions and performing buffer-gas cooling). General comment: Pressurized air is needed for the MCP detectors and vacuum valves along the beam line.

g. cryo systems: RFQ: The RFQ will be operated either at LN2 or LHe temperature. EBIT: One to two cryocoolers will be operated at the EBIT Penning Traps: The superconducting magnets need LN2 and LHe cooling. Thus, a permanent liquid nitrogen line and a helium recovery line should be installed. The cryogenic trap systems will be installed in a cryogenic free cold head cryostat.

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2. Detector –Machine Interface

a. Vacuum: RFQ: The RFQ vacuum (without external gas load for buffer-gas cooling) should be at the level of 10-7 to 10-8 mbar. q/A separation: Since the MPS has to transport the highly-charged ions a vacuum of 10-9 to 10-10

mbar is required. EBIT: The EBIT vacuum at the level of 10-9 to 10-10 mbar in the collector and electron gun chambers, and below 10-13 in the trap region will be connected to the beam pipe vacuum with low-conductance apertures to keep the pressure differences as needed. Penning traps and detectors: Since the measurements will be performed with highly-charged ions special care on the vacuum is required. In the cryogenic trap system a vacuum of better than 10-12 mbar will be reached.

b. Beam pipe: A 100 mm diameter beam pipe is typically used for the beam transport, although much smaller diameters can be sufficient. To obtain the required excellent vacuum, backing of the beam pipe is planned.

c. Target, in-beam monitors, in-beam detectors: To monitor the beam injected into the EBIT, a position sensitive detector, a channeltron and a Faraday cup has to be implemented. The same diagnostic setup is required to control the ion beam ejected from the EBIT. Multichannel plate detectors will be used to optimize and control beam transport between each trap device. See also subproject 1.6.

d. Timing: Standard timing systems as presently already in use will be installed.

e. Radiation environment: A radiation environment should be avoided to minimize background on the detector.

f. Radiation shielding: The radiation produced by the EBIT at the intended energies is sufficiently shielded by the stainless steel vacuum chambers. Some critical parts are also shielded by 4mm lead sheet, as a precaution, as well as to reduce the background level of the diagnostic instrumentation. Levels well below 1 µSv/hour at 10 cm from the chambers and are typical for high-energy operation. For the Penning traps no extra radiation shielding is needed. Experiments are performed with one or few ions.

3. Assembly and installation

a. Size and weight of detector parts, space requirements: Almost all parts will be assembled and tested of line at the different involved institutes. The final installation in the cave will be done after all parts are tested and specified. The space needed for handling is indicated in the schematic drawing of Fig. 17. Permanent access is needed. The minimum overall space requirement is 10m x 5m x 9m. The multi-passage spectrometer has a wait of 800 kg which can only be installed with a lift or a roof crane. The EBIT as well as the two superconducting magnets (including instruments) have each a weight of about 0.5-1 T. For the final installation in the cave access by a roof crane is needed.

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b. Services and their connections: The superconducting magnets (EBIT and traps) as well as the RFQ ion beam cooler and buncher needs regular services, including twice a week filling of LN2 and about once a month filling of LHe for the magnets. A permanent LN2 line and a LHe recovery line will be requested. For the beam line valves and MCP detectors a permanent pressurized air line is needed. Detector needs only simple feed-throughs to provide signal transfer, cooling, etc..

c. Installation procedure: The experimental setup will be prepared and tested at different places, including the MPI-K in Heidelberg, the University of Mainz, the University of Greifswald, the University of Jyväskylä, and the Maier-Leibnitz-Laboratory in Garching. The EBIT setup (assembly weight of less than 1 t) can be rolled easily into its dedicated location at GSI as a whole. The electronic and trap setup is expected to be the major time factor at the MATS facility. The in-trap spectroscopy detector setup will be tested first at the home institute before transport to GSI. Laboratory space on-site has to be foreseen for final tests prior to installation at the beam line. Vacuum equipment and test electronics/data acqisition will be needed in this lab. The lab has to be approved for the use of radioactive calibration sources. Sufficient space (about 3m × 4m) will be needed for eventual repair works, maintenance, and temporary storage.

D Commissioning a) magnetic field measurements:

Magnetic field measurements of the superconducting magnets of the EBIT and the Penning traps will be first done offline at the institutes involved. For the final installation at FAIR a mapping of the magnetic fields in the near and far environment of MATS has to be performed to check the eventual influence of the strong (but shielded) magnetic field to the beamline and to other experiments. For the mapping a NMR probe will be used. Note: External magnetic field sources and magnetic field fluctuations in the environment have to be avoided. The stray field of the EBIT and the Penning trap magnets will be minimized by shielding.

b) alignment: The alignment of the setup is very crucial since the injection of the highly-charged ions into the strong magnetic field is extremely critical. Help by an expert is needed for the alignment of the setup at its final position in the cave. Standard optical geodesic instrumentation should be available. The alignment of detectors can be done along with alignment of traps onto the beam axis.

c) test runs: Since all tests can be performed with an off-line ion source or with highly-charged ions from the EBIT only a very limited amount of shifts for test runs will be requested.

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E Operation a) of each of the sub-projects

With respect to the Super-FRS, all MATS experiments will operate at fixed conditions for periods of several hours up to several days. Experimental concerns are limited to the manipulation of low energy ionic ensembles from the gas stopper and to the production, transport and detection of the highly-charged ions. Both aspects are decoupled from the operation of the production facility and will be performed by members of the MATS collaboration. For the stability of the system (vacuum, voltage, magnetic fields, etc.) it is required to have all individual components of MATS most of the time under full operation, even without a running radioactive beam experiment. The superconducting magnets will be cooled down without any interruption and need therefore permanent maintenance, i.e. filling of LN2 and LHe.

b) auxiliaries During the on-line operation of MATS stable conditions in respect to room temperature, magnetic stray fields etc. are mandatory to perform high-precision experiments. In addition crane movements and ramping of magnets in the near environment have to be avoided during operation since they cause magnetic field fluctuations in the trapping region and thus frequency shifts and systematic errors.

c) power, gas, cryo, etc: electrical power supplies: RFQ: 15 kW for high-voltage power supplies, pumps (including beamline) etc. q/A separation: 10 kW magnet power supply EBIT: 25 kW cryocooler power supply, trap power supplies, and pumps Penning traps and detectors: 20 kW for cryocoolers, 15 kW for remaining components including detectors. Beamline: Already included in the numbers given above. In total: 85 kW (these numbers are preliminary estimates since they depend on the final construction and components) General comment: A galvanically decoupled power grid for measurement electronics and a central grounding point has to be provided. cryo-systems: RFQ: The RFQ will be operated either at LN2 or LHe temperature. EBIT: One to two cryocoolers will be operated at the EBIT Penning Traps: The superconducting magnets need LN2 and LHe cooling. Thus, a permanent liquid nitrogen line and a helium recovery line should be installed. The cryogenic trap systems will be installed in a cryogenic free cold head cryostat. The superconducting magnets need about 300 litres of LN2 per week and 120 litres of LHe per month. gas systems: Only small quantities of high purity gases needed for the RFQ, the EBIT, and for the trap system (the later only in the case of using singly charged ions and performing buffer-gas cooling). General comment: Pressurized air is needed for the MCP detectors and vacuum valves along the beam line.

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F Safety a. General safety considerations:

The electrical safety of the setup will be assured at both sites by the responsible teams.

b. Radiation Environment: The EBIT device is setup within a radiation control area. All other components of MATS are freely accessible since the experiments will be performed with one or a few radioactive ions per second.

c. Safety systems: The high magnetic fields of the EBIT and the Penning traps are to be indicated with signs at the laboratory entrances. The high voltage of the RFQ and the EBIT will be indicated as well. Only authorized people are allowed to enter the experimental area.

G Organization and Responsibilities, Planning a. WBS- work package break down structure:

According to the defined milestones in section G.e (see below) the following working packages are identified for each subproject. Each of them can be pursued by a PhD student supervised by a PostDoc. RFQ:

Simulation studies and definition of the dimensions Design of the cryogenic RFQ ion beam cooler and buncher based on the system at

LEBIT/MSU Ordering, machining, and assembling of the vacuum components and RFQ structure Commissioning tests of vacuum and voltage. Determination of the performance (cooling time, emittance, and efficiency) with stable

ions from the off-line ion source Implementation into the MATS setup and acceptance tests with ions from the low energy

branch gas cell EBIT:

Definition of the required EBIT specification for charge breeding of short-lived radionuclides Order/Delivery of the magnet and vacuum parts. Design and machining of the customized parts (trap structure, electron gun etc.) Assembling of the EBIT and first commissioning tests of vacuum and voltage Ion production and charge breeding tests. Measurements of charge state distribution, breeding

time, breeding efficiency etc. with stable ions Installation at MATS and connection to the RFQ, MPS, and Penning trap system. Commissioning tests with stable ions Measurements with radioactive ions from the RFQ and determination of the physics

performance q/A selection:

Beam dynamics simulations. Design of the MPS: Specification of the magnet, the electrostatic lenses and the required

vacuum chambers. Order/Delivery of the magnet and vacuum parts. Machining of the customized parts. Installation at MATS and connection to the EBIT and Penning trap system. Commissioning tests with ions from the EBIT and other off-line ion sources.

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Preparation and precision Penning trap: (the design, development, machining and tests are similar and all take place at similar times, so only one list is provided for both systems)

Definition of the specification of the superconducting magnets, especially with respect to the required homogeneity of the magnetic field and the dimension of each magnet bore

Simulations and design of the Penning traps with respect to, e.g., the dimensions and materials (influence on homogeneity) and especially the FT-ICR detection systems

Design of an off-line ion source for later tests of the Penning trap systems Design of the cryogenic system for the precision Penning trap, especially with respect to

the ion detection with the narrow band FT-ICR detection system Simulations of the beam transport from the external ion source to the preparation trap,

then to the precision trap, and finally to the MCP/Channeltron detector Design of the injection/ejection into/from the Penning traps in close collaboration to

the simulations of the beam transport Construction of the Penning traps (1.5 years) Ordering and delivery of the superconducting magnets including the installation at the

final positions (1.5 years) Development and commissioning of the control system (1.5 years) Machining and installation of the beam line between and inside the superconducting

magnets (1.5 years) Installation of the detectors for mass spectrometry and spectroscopy and first off-line tests Installation of the Penning traps and first off-line tests Check of the accuracy of the spectroscopy detectors, first off-line mass measurements

with a check of the accuracy of the measured reference masses Instrumentation (detectors) for mass spectrometry:

Design of the MCP/Channeltron detector combination with corresponding simulation and optimization of electrodes and ion optics.

Construction of MCP/Channeltron detectors with following off-line tests of the ion detection efficiency and connection to the computerized control system.

Ordering and testing of a broad band FT-ICR system. Some tests can be performed at existing Penning trap experiments of collaborators.

Design of a narrow band FT-ICR system in close connection to the design of the precision Penning trap. This includes especially the design of low-noise detection electronics for cryogenic temperatures

Ordering and off-line testing of narrow band FT-ICR system and corresponding electronics Installation of the MCP/Channeltron detectors, the broad band FT-ICR system and the

narrow band FT-ICR system at MATS and first off-line tests (each system will be prepared by one PhD student)

Commissioning tests and off-line mass measurements of ions from off-line ion source In-trap conversion electron spectroscopy detectors:

Design of the segmented Si(Li) detector layout with corresponding simulation studies Design and manufacturing of the support structure Ordering and off-line testing of the detectors including specification measurements Implementation into the Penning trap setup and commissioning measurements with

radioactive ions

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b. Structure of experiment management: The whole project is embedded in the NUSTAR activities at the FAIR facility. This means that the NUSTAR management structures will be available and used for interproject contacts and collaboration. MATS has representatives in all working groups within NUSTAR that are relevant to the trap setup.

MATS has a spokesperson (K. Blaum) and two deputy spokespersons (J. Crespo, F. Herfurth). F. Herfurth is at the same time GSI contact person. The subproject leaders are taking the responsibility for different parts of MATS. The subprojects and their members are the following (marked in bold are the main responsibles or subproject leaders):

EBIT: José Crespo, Tomas Fritioff, Oliver Kester, D. Schneider, Joachim Ullrich q/A selection: Tomas Fritioff, M. Block, Sophie Heinz, Oliver Kester Traps (RFQ and Penning trap): F. Herfurth, Alban Kellerbauer, Stefan Kopecky, David

Lunney, Gerrit Marx, Jurek Szerypo, Christine Weber Instrumentation for mass spectrometry: Klaus Blaum, Alexander Herlert, Christine Weber,

Sophie Heinz, Chabouh Yazidjian Detectors for decay spectroscopy: Frank Herfurth, Ari Jokinen, Iain Moore, Peter Thirolf Control System: Dietrich Beck, Klaus Blaum, José Crespo, Frank Herfurth, Szilard Nagy Physics case: Juha Äystö, Klaus Blaum, José Crespo, Hans Geissel, Frank Herfurth,

David Lunney, Yuri Novikov, Christoph Scheidenberger, Lutz Schweikhard, Peter Thirolf

c. Responsibilities and Obligations:

Contribution UPS UGW UEN GSI UMZ UG UJ LLNL LMU HD ULB MSU SU TRIUMF VECCTheory X X X

Simulation Studies X X X X XAtomic-Mass Evaluation X X

Control System X XBeamlines X X X

Beamline Detectors XVacuum System X

RFQ Buncher + Switchyard X X XEBIT X X X

Q/A Separation X X X XOff-Line Ion Source X X XPreparation Trap X X X

Measurement Trap X X X X XElectronics X X

TOF Detector X X XFT-ICR Detector X X

In-Trap EC Detector X X

Institutes

X

Abbreviations: UPS – Université de Paris Sud (CSN - CSNSM/IN2P3-Orsay); UGW – University of Greifswald; UEN – University of Erlangen-Nürnberg; GSI – Gesellschaft für Schwerionenforschung Darmstadt; UMZ – University of Mainz; UG – University of Gießen; UJ – University of Jyväskylä; LLNL – Lawrence Livermore National Laboratory; LMU – Ludwig Maximilians University Munich; HD – Max Planck Institute for Nuclear Physics, Heidelberg; ULB – Universite Libre des Bruxelles; MSU – Michigan State University, East Lansing; SU – Stockholm University; TRIUMF – Tri-Universities Facility, Vancouver; VECC - Variable Energy Cyclotron Centre, Kolkata

Orsay (UPS) intends to contribute to the beamline, the control system, and to design and

construct the off-line ion source as well as contributions to the buncher and Penning trap systems. Support (0.5 evaluator year) for the data analysis and atomic-mass evaluation is available. Furthermore Workshop access is guaranteed.

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The University of Greifswald (UGW) is strongly interested in the mass spectrometry detection techniques and intents to apply for the required money to design and construct the time-of-flight cyclotron resonance detector as well as the Fourier transform ion cyclotron resonance detector. One PhD student and one PostDoc will mainly work on this project. One workshop person is permanently available.

One PhD student from the University of Erlangen-Nürnberg (UEN) and from the Universite Libre des Bruxelles (ULB) will mainly work on the nuclear structure theory and on ion-ion interaction calculations. Theory support is also promised from Michigan State University (MSU).

GSI Darmstadt will provide a LabView-based control system which can be implemented by using the Control System (CS) framework which has been developed by DVEE/GSI during the last two years. In addition manpower support is promised for the Penning trap design.

The institute of physics of the University of Mainz intents to apply for money for one of the superconducting Penning trap magnets including electronics. In addition one PostDoc and two PhD students will work on the trap design and construction. Workshop access for the full construction period is guaranteed. The Nuclear Chemistry Department is strongly interested in laser spectroscopic studies on trapped singly and highly-charged ions. Combined efforts to adapt the RFQ buncher as well as the trap setups (EBIT and Penning traps) is mandatory.

Gießen (UG) provides support for ion simulations studies, mandatory for the design of the RFQ and Penning traps.

LMU Munich (LMU) is willing to contribute to the development of the in-trap spectroscopy technique, especially aiming at in-trap conversion electrons. At appropriate time funding will be requested for equipment and personnel.

JYFL (UJ) is willing to contribute in a similar manner to that explained above for LMU, i.e. participating in the development of related techniques. However, it is worth noticing that the JYFL contribution is mainly of in-kind support, not direct investment to GSI. For example, an existing in-trap project at JYFL and availability of a large bore (diameter 160) superconducting solenoid (7 T) provides a good basis for research, development and testing of new techniques both off-line and on-line.

Lawrence Livermore National Laboratory provides knowledge for the design and construction of the EBIT.

The Max-Planck Institute for Nuclear Physics in Heidelberg (HD) is strongly interested in the experimental possibilities described in the current proposal, and in particular in using the radioactive isotopes for precision spectroscopic measurements. Therefore the MPI-K is committed to obtain and contribute the funding necessary for the charge breeding EBIT setup, and to support it during the construction with the personnel needed at the MPI-K site. Experiments and operation of the EBIT at the MATS facility will also be supported by our staff. Workshop access during the construction phase is guaranteed.

Members from the Michigan State (MSU) provide simulation programs to calculate magnetic field distributions and ion trajectories within a Penning trap as well as a RFQ ion beam cooler and buncher. MSU is also willing to contribute to the Penning trap design and construction work.

The SMILETRAP group from the University of Stockholm (SU) has outstanding experience in charge breeding with an EBIS and high-accuracy Penning trap mass spectrometry. They support the design and construction of the EBIT and the Penning traps.

Members from VECC, Kolkata, will perform simulation studies of the trap setup.

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d. Cost and Manpower Estimates

see APPENDIX A

e. Schedule with Milestones: RFQ cooler and buncher: The schedule for the assembling and testing of the RFQ cooler and buncher is given below. For the design, construction and off-line testing about 3 years are needed. The final implementation into the MATS setup and further checks and off-line mass measurements need another 1 year.

1 2 3 4 Year Milestone 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

Simulations studies (ion injection and ejection)

RFQ construction + order Assembly of the RFQ parts

Control system Vacuum + voltage tests

Tests with an off-line ion source, system specification

implementation of the RFQ at MATS

Acceptance tests with ions from the LEB gas cell

EBIT: The EBIT design will be based on an existing device, so not much development time is needed. A PostDoc should supervise the project at the beginning. The construction, setup, and test of the device can be done by a PhD student. The time schedule and milestones are given below.

1 2 3 4 Year Milestone 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

Define EBIT final specifications Order / Delivery EBIT magnet

Ion optics simulation Mechanical design changes

Machining of parts Assembly drift tubes

Assembly electron gun, collector Overall assembly, vacuum test

High voltage and control system Ion production test

Ion injection and extraction tests Transfer to GSI and installation

at MATS

Tests with ions from an off-line ion source

Tests with (radioactive) ions from the LEB

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q/A separation: The schedule for the assembling and testing of the q/m-selection with the MPS is given below. For the design, construction and off-line testing about 2 years are needed. The final implementation into the MATS setup and further checks and off-line mass measurements need another 1 year.

1 2 3 4 Year Milestone 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

Design calculations MPS, Beam dynamics

MPS construction + order Assembly of the MPS parts

Control System Vacuum tests

Tests with singly charged ions implementation of

MPS at MATS

Tests with highly charged Ions from breeder

Penning traps: The schedule for the assembling and testing of the preparation and measurement Penning trap setup plus detectors, the most crucial part of the experiment, is given below. Depending on the progress the installation of the in-trap decay spectroscopy detectors will be done after the first off-line mass-spectrometry test measurements. For the installation of the setup at its final position about one year is needed.

1 2 3 4 Year Milestone 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

Define SuMa specifications Order/Delivery SuMa

SuMa installation Trap simulation and design

Trap machining Trap completion

Detector / ion source Design injection/ejection

Control system Beam transport simulation/calc.

Beam line machining Beam line installation

Detector installation and tests Trap installation and tests

Accuracy check Off-line mass measurements

Instrumentation for mass spectrometry (TOF and FTICR detectors): The schedule for the assembling and testing of the detectors for mass spectrometry is given below. For the design, construction and off-line testing about two years are needed. For the final implementation into the MATS setup and further checks and off-line mass measurements another 2 years are needed.

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1 2 3 4 Year Milestone 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

Design MCP/Channeltron detectors

MCP/Channeltron detector construction and off-line tests

ordering and testing broad band FT-ICR system

design narrow band FTICR system

ordering and testing narrow band FT-ICR

Control System implementation of

MCP/Channeltron detectors

impementation of broad band FT-ICR

implementation of narrow band FT-ICR

System checks and off-line mass measurements

In-trap conversion electron spectroscopy detectors: The time schedule including milestones are given below. This subproject could be fulfilled within 2-3 years.

1 2 3 4 Year Milestone 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

Define segmented Si(Li) layout Order/Delivery Si(Li)

Design/Manufacture support structures

Setup of laboratory test bench Control System

Off- and Online laboratory tests Setup of detector/electronics at

trap

Commissioning measurements f. Organization: see organization of NUSTAR and section G.b of this technical proposal

H Relation to other Projects

In the Technical Proposals of “SPARC” and “HITRAP” it is also proposed to measure masses of highly-charged ions but with the goal to determine atomic-electron binding energies, and to perform QED tests exploiting an expected mass precision of 10-10

and better. However, the measurements performed are complementary since they are not aiming for short-lived nuclei. These measurements are limited due to the used cooling and production techniques to nuclei with half-lives above 10s.

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The other mass measurement project within NUSTAR is ILIMA. It aims for mass measurements with relative uncertainties of below 10-7 in storage rings using the Schottky Mass Spectrometry (SMS) method. Due to the long cooling times for SMS, access to very short-lived nuclei with a half-life below 1 s is not possible with this method. Instead, the Isochronous Mass Spectrometry (IMS) method can be used at ILIMA, a time-of-flight technique that allows to explore the lifetime region well below one millisecond. For mass measurements at ILIMA absolute calibrants from other sources, such as MATS, are important.

The in trap spectroscopy aspect is closely linked to DESPEC. R&D on detectors, electronics and data acquisition partly overlaps. One should also reserve a possibility to transfer complete or partial detection setups to the end of the trap facility, where they can be applied in dedicated experiments requiring isomerically purified beams. The possibility to provide clean or even isomerically pure bunched beams is of high interest also for other experiments as e.g. LaSpec (Laser Spectroscopy for the study of nuclear properties). Concerning high-accuracy mass spectrometry we expect some eventual common effort related to the SPIRAL2 project. I Other issues

Although ILIMA and MATS both aim for high-accuracy mass measurement of short-lived nuclides, both collaborations are of the opinion that due the vastly different technical approaches and mass measurement techniques involved, a combined proposal is not advantageous. However, there is a close collaboration between MATS and ILIMA concerning the physics case. Yuri Novikov (the ILIMA spokesperson) has joined the MATS collaboration in order to ensure the closest possible interaction. With the same intentions Klaus Blaum (the MATS spokesperson) joins the working group on the physics case for ILIMA.

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The members of the MATS collaboration thank Prof. Dr. Peter Butler (CERN/ISOLDE, Switzerland) and Prof. Dr. Rick Casten (Yale University, USA) for valuable comments to this technical design report. The MATS spokesperson (Klaus Blaum) is supported by the Helmholtz Association of National Research Centres (HGF) under Contract No. VH-NG-037.

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