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Lecture #3
Atomic Physics with Stored andCooled Ions
Klaus BlaumGesellschaft für Schwerionenforschung, GSI, Darmstadt
and CERN, Physics Department, Geneva, Switzerland
Summer School, Lanzhou, China, 9 – 17 August 2004
3. Lecture: Production of radioactive nuclei
and highly-charged ions 1. Production techniques for radioactive ion beams (RIB)2. The heavy ion accelerator facility GSI3. The on-line isotope separator ISOLDE at CERN4. Production of highly-charged ions (HCI)
- at GSI- with an Electron Beam Ion Trap (EBIT)
Ion traps, heavy ion cooler rings andlaser traps at accelerators
Stockholm • • Aarhus
• Tokyo
• CERN • GSI Heidelberg
Argonne• • Berkeley
• Jyväskylä
• Stony Brook • Vancouver
•MSU k • Lanzhou
plans at GANIL, KVI Groningen, Leuven, Penning trap for neutron lifetime at ILL, Grenobleoff-line experiments at Los Alamos
Radioactive ion beam production: principle
ε = f ( )Transmission, element, half-life, ionization, ...
0.1 / day - > 1012 / s
ion beam preparation, separation, acceleration/deceleration, ...
PrinciplePrimary beam Secondary beamnuclear
reactionI0 IRIB
Reaction rateCross sections 1 pb – > 10 b Beam flux 1011 – 1015 /cm2 /sTarget thickness 0.1 – 100 g/cm2
R = σreaction · φprimary · Ntarget
RIB intensity
IRIB = ε · R
Proton-induced reactions (e.g. ISOLDE, ISAC)
protons
pn
+ Spallation
+ + Fragmentation
+ + Fission
201Fr
11Li X
143Cs Y
238U1 GeV
Heavy-ion-induced reactions (e.g. GSI)
Fragmentation
Coulomb dissociation
Fusion
ISOL versus fragmentation
FragmentationISOL
accelerator1 GeV protons,Light ions
1 GeV/u heavy ions
productiontargetthick thin
ion source
100 keV 1 GeV/u
electromagneticseparationhigh intensities for
long-lived isotopeslimitation at T1/2 < 10 ms
high beam qualityno refaractory elements
low intensities
limitation only at T1/2 < 1µs
low beam qualityall elements
postaccelerator
decellerator
some MeV At rest
ISOL and fragmentation facilities are complementary
Concept for in-flight separation
Primary beam heavy ions
Target thin
Separation gas-filledseparators
B<q>=Z1/3 v/vBohr
velocityFilters
E x B
fragment separators
BBρ = mv /qEρ = mv2/q
Experiment
B: magnetic field E: electric sector fieldρ: deflection radius m: massv: velocity q: charge stateZ: atomic number
Concept for ISOL
ions p, d, n Primary beam
Target thin thick
Catcher
Ion Source
Extraction +Separation
solidgas
various
Manipulation and cooling of RIB and HCI
good beam qualityhigh intensity
MS
MS
Target
ionsource
heavy ions, <2GeV/u
protons, 1 GeV
beam coolinglow emittance, energy spread
accumulation and bunchingsignal-to-noise ratio, beam transfer, beam energy variation
beam purificationclean ion beams
Improvements via:
Demands:
The heavy ion accelerator GSI
Mission:Construction and operation
of accelerators; research with heavy ions
Personnel:ca. 700 employees
(250 scientists and engineers)
Instruments:Accelerators
UNILAC/SIS/ESR;large spectrometersand detector systems
Altogether over 1000 users, 400 from abroad
(100 internal users)Budget:65 Mio €
Operation: 52 Mio €Investments: 13 Mio €
http://www.gsi.de
Research programm at GSI
Atomic Physics
15%
Plasma Physics
5%
AstrophysicsCosmology
Nuclear Physics
50%
AcceleratorDevelopment
10%
Materials Research
5%
Biophysics &Tumortherapy
15%
New Technologies
New Materials
Clinical Application
Joint effort of GSI & university groups and international collaboration
Ion (stopping and) collection devices at GSI
Existing Collection Devices
SISESR
+ STOPPINGSHIPTRAP
Planned DevicesHITRAP
FRS gas cell
The ISOLDE facility at CERN
Control room
HV-Platform
RILIS laser hut
Robots
Radioactive laboratory
1.4 GeV protonsfrom PS-Booster
HRS-Target
GPS-Target
COLLAPS
ISOLTRAP
http://isolde.web.cern.ch/isolde
E. Kugler, Hyp. Int. 129, 23-42 (2000).
ISOLDE Target
Protons
8 V500 A
9 V1000 A
E. Kugler, Hyp. Int. 129, 23-42 (2000).
Ionization techniques:• Surface ionization• Plasma ionization• Resonant laser ionization
before after http://isolde.web.cern.ch/isolde
Resonance Ionization Laser Ion Source (RILIS)
1. Surface Ionization Ion Source:No isobaric selectivity, limited applicability
2. Plasma Ion Source (ECR-Source):No isobaric selectivity
3. Resonance Ionization Laser Ion Source (RILIS):High isobaric selectivity by resonant laser ionizationLimitation by surface ionized isobars
U. Köster, V. Fedoseyev et al.,
Spectrochim Acta 58B, 1047 (2003)
Accessibility of elements by RILIS
1H 2He
3Li 4Be 5B 6C 7N 8O 9F 10Ne
11Na 12Mg 13Al 14SI 15P 16S 17Cl 18Ar
19K 20Ca 21Sc 22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 31Ga 32Ge 33As 34Se 35Br 36Kr
37Rb 38Sr 39Y 40Zr 41Nb 42Mo 43Tc 44Ru 45Rh 46Pd 47Ag 48Cd 49In 50Sn 51Sb 52Te 53I 54Xe
55Cs 56Ba 57La 72Hf 73Ta 74W 75Re 76Os 77Ir 78Pt 79Au 80Hg 81Tl 82Pb 83Bi 84Po 85At 86Rn
87Fr 88Ra 89Ac 104Rf 105Ha 106 107 108 109 110 111 112 113
58Ce 95Pr 60Nd 61Pm 62Sm 63Eu 64Gd 65Tb 66Dy 67Ho 68Er 69Tm 70Yb 71Lu
90Th 91Pa 92U 93Np 94Pu 95Am 96Cm 97Bk 98Fc 99Es 100Fm 101Md 102No 103Lr
Elements studied with dye – laser RIS Dye - laser RIS possible
Ti:Sa laser RIS demonstrated Ti:Sa laser RIS possible
U. Köster, V. Fedoseyev et al.,
Spectrochim Acta 58B, 1047 (2003)
K. W. et al, Proceedings RnB 6, ANL,USA
Nucl. Instr. Meth. in Phys. Res., in press
At ISOLDE in total >70 elements, >600 isotopes available!
Physics at ISOLDE
Nuclear Physics49%
Nuclear Decay Spectroscopy and Reactions
Structure of NucleiExotic Decay Modes
Atomic Physics18%
Laser Spectroscopy and Direct Mass Measurements
Radii, Moments, Nuclear Binding Energies
Nuclear Astrophysics
14%Dedicated Nuclear
Decay/Reaction StudiesElement Synthesis,
Solar Processes
f ( N, Z )
Fundamental Physics
Direct Mass Measurements, Dedicated Decay Studies – WI
CKM unitarity tests, search for β-ν correlations, right-handed
currents
Applied Physics19%
Implanted Radioactive Probes, Tailored Isotopes for Diagnosis
and Therapy
Condensed matter physics and Life sciences
Ion stopping and collection devices at ISOLDE
Existing DevicesREXTRAP
WITCH Penning trapsISOLTRAP RFQ buncher
ISOLTRAP cooler trap
Planned DevicesISOLDE HRS cooler
MISTRAL cooler
Production of highly-charged ions at GSI
HCI production in an EBIT
axial potential
radial potential
topdrift tube
centerdrift tube
bottondrift tube
electron beam
trapped ions
LN
LHe
SC magnetcoils
electron gun
collector
drift tubes
window
EBIT II
The electron beam ion trap (EBIT) was developed at theLawrence Livermore National Laboratory (LLNL) in the late1980s by R. Marrs and M. Levine
2
The ionization process
Sequential electron impact ionization in an electron beam ion trap
As the ion charge state goes up:• growing ionization potential:
10 eV → 130000 eV• diminishing cross section:
10-16 cm2 → 10-24 cm2
130 keV
31 keV12 keV
n=1
n=2 n=3
electron beam with energy Ek
continuum
Competing processes: recombination
charge exchange with restgas neutral atomsN
n n
n
nn
n n
n
nn
Ne9+
solution: vacuum 10-13 Torr
(1000 atoms/cm3)
capture of free electrons
n n
n
nn
γ radiative recombination (RR)
solution: raising electron beam energy
Be--beam
60 µ
m
40 mm
trap potential Ut ≈ 100 V(Ut × ion charge) ≈ 5000 eV
6000 A/cm2
ne ≈ 1013 e-/cm3
longitudinally:electrodes
Principles of an EBIT (electron beam ion trap)
the trap:
axially:electron beam space charge
Evaporative cooling
• collisions with beam electrons heat up ion ensemble• light, less tightly trapped ions (e.g. Ne10+ ) evaporate removingthermal energy: a single Ne10+ takes away 2 keV (1 second additional life for a heavy ion)
• heavy, highly charged ions (e.g. Ba53+ ) remain trapped indefinitely
Ion temperatures from 1000 eV to 10 eV
Doppler width ∆λ/λ ≈ 1/20.000 (Ba53+)
High resolution spectroscopy