EuCARD-BOO-2011-002

European Coordination for Accelerator Research and Development

PUBLICATION

European infrastructures for R&D and testof superconducting radio-frequency

cavities and cryo-modules

Weingarten, W (CERN)

29 September 2011

The research leading to these results has received funding from the European Commissionunder the FP7 Research Infrastructures project EuCARD, grant agreement no. 227579.

This work is part of EuCARD Work Package 4: AccNet: Accelerator Science Networks.

The electronic version of this EuCARD Publication is available via the EuCARD web site<http://cern.ch/eucard> or on the CERN Document Server at the following URL :

<http://cdsweb.cern.ch/record/1386310

EuCARD-BOO-2011-002

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European Infrastructures for R&D and Test of Superconducting Radio‐Frequency Cavities and Cryo‐modules

Wolfgang Weingarten/CERN

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Contents

I. Introduction and scope ............................................................................................................2

II. SRF for accelerator application, past and present ....................................................................3

A. A brief historical review ............................................................................................................3

B. The present status ....................................................................................................................6

III. About the need for a SRF test infrastructure ...........................................................................7

A. International cooperation ‐ examples ......................................................................................9

B. Present funding schemes ........................................................................................................10

1. CERN consortia ...........................................................................................................10

2. European Union consortia (FP7 program) ................................................................10

3. National Consortia and Bilateral Funding Schemes ..................................................11

4. International schemes ...............................................................................................11

IV. Important future research topics and priorities ....................................................................12

A. Accelerating gradient...............................................................................................................12

B. RF losses ‐ Q‐value ..................................................................................................................15

C. Reproducibility of performance ..............................................................................................20

1. Quench and field emission .........................................................................................20

2. Diagnostics .................................................................................................................22

3. Measures to improve reproducibility ........................................................................22

a) Thermal conductivity ....................................................................................22

b) Thin film cavities ...........................................................................................22

D. Proposal for future R&D work ................................................................................................23

1. Niobium .....................................................................................................................24

2. Alternate materials ....................................................................................................26

V. Capacity and availability needs related to emerging European projects ................................27

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A. Logistical needs .......................................................................................................................28

B. Needs for R&D initiatives ........................................................................................................29

VI. Conclusions .............................................................................................................................30

VII. Glossary ..................................................................................................................................32

Acknowledgments ...............................................................................................................................34

ANNEX

SRF related specific equipment available in European Accelerator Laboratories ...............................35

Table 1: General purpose manufacture/workshop tools ........................................................35

Table 2: Specific manufacture/assembly facilities and inspection/testing tools ....................36

Table 3: Surface treatment/coating/final cleaning .................................................................38

Table 4: Warm test places ‐ high power coupler ....................................................................40

Table 5: Cold test places ‐ low power .....................................................................................41

Table 6: Cold test places ‐ high power ....................................................................................43

Table 7: Sample characterisation and other test/inspection equipment ...............................45

Specific SRF related equipment available elsewhere ..........................................................................48

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I. Introduction and scope

The need for a European facility to build and test superconducting RF accelerating structures and cryo‐modules (SRF test facility) was extensively discussed during the preparation of EuCARD1,2. It comprised a distributed network of equipment across Europe to be assessed and, if needed, completed by hardware. It also addressed the quest for a deeper basic understanding, a better control and optimisation of the manufacture of superconducting RF structures with the aim of a substantial improvement of the accelerating gradient, a reduction of its spread and a cost minimisation. However, consequent to EU budget restrictions, the proposal was not maintained. Instead, a more detailed analysis was requested by a sub‐task inside the EuCARD Network3 AccNet ‐ RFTech4.

The main objective of this “SRF sub‐task” consists of intensifying a collaborative effort between European accelerator labs. The aim focused on planning and later identifying for European accelerator users a multi‐purpose state‐of‐the‐art network of equipment for R&D and testing of SRF cavities and cryo‐modules. The duration of this sub‐task was agreed to be two years, after which the results were to be presented to the funding agencies. This shall be achieved by this report.

This report is inevitably biased by the author’s opinion and preconceptions although a balanced assessment was aimed at. It summarizes the discussions held with individuals and during specific workshops or conferences organized in 2009 ‐ 2011 under the auspices of RFTech5 and other EuCARD annual meetings6. It shall answer the following questions:

1. Is there a need for a SRF test infrastructure, distributed across, and managed by, European accelerator labs?

2. What research topics are important for the future of SRF technology and what priorities should be attributed to them?

1 https://eucard.web.cern.ch/EuCARD/index.html 2 http://esgard‐omia.web.cern.ch/ESGARD‐OMIA/Programme.html 3 https://eucard.web.cern.ch/EuCARD/activities/networks/WP4/ 4 http://accnet.web.cern.ch/accnet/RFTech/ 5 http://accnet.web.cern.ch/accnet/Activity_Reports/2009/RFTech_SRF_videoconference.pdf https://indico.desy.de/conferenceDisplay.py?confId=2831 http://lpsc.in2p3.fr/Indico/conferenceDisplay.py?confId=530 http://indico.cern.ch/conferenceDisplay.py?confId=118190 6 https://indico.cern.ch/internalPage.py?pageId=7&confId=115634 http://indico.cern.ch/conferenceDisplay.py?confId=118190

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3. Is the capacity and available equipment sufficient to cope with the demands of emerging European projects?

II. SRF for accelerator application, past and present

A. A brief historical review

When defining a program, “road map”, or strategy for the future, it is good advice to look into the past. A short summary of milestones in the development of RF Superconductivity (SRF) for accelerator applications shall serve as a guideline for future initiatives, to be proposed in this report.

RF studies on superconducting materials had already been performed many years before the BCS theory laid the ground for understanding superconductivity, which happened in 1957. Only one year later this theory was extended from DC to RF. Investigations on superconducting cavities were mainly conducted inside an academic environment to test the new theories.

The reputation of SRF in the accelerator community was dubious in the late 1960s. This was mainly because the accelerating gradients obtained were relatively small (several MV/m) and, even worse, the physical limitations were not identified. However, the high energy physics community needed more efficient and power saving accelerating systems compared to what was available at that time. The reason was that important discoveries were made at SLAC on the substructure of the proton, by hitting it with electron beams accelerated in a conventional way in pulsed mode driven copper structures. These discoveries, later decorated with the Nobel Prize, opened up the quest for higher energies and luminosities in order to resolve even more subtle structures inside the proton. Electron positron colliders entered the high energy physics field that were operated in continuous wave mode. It happened that at the same time, at the end of the 1960s, encouraging performances of small size sc cavities were obtained in several research labs by applying new techniques, such as electro‐polishing (EP) and UHV firing. The excellent results inspired sufficient confidence in the potential of SRF technology, because higher accelerating gradients than in conventional copper accelerating structures now became accessible, and ‐ even better ‐ in continuous wave mode. This hope made coincidence experiments possible with sufficient statistics.

At that time universities with high energy physics research interests joined in the efforts of understanding SRF. The number of research institutes participating in SRF developments increased significantly. The academic interest became so high that the “Workshop on RF Superconductivity” was founded (1980). It is still alive today and is organized now as the SRF

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Conference with biannual periodicity. New materials were studied for SRF accelerator application (Nb3Sn) in the 1970s. New powerful diagnostics methods were developed and industrialized, very often in fruitful collaborations between universities and accelerator centres. Also by trial and error, but very soon by rigorous research work, various limitations of SRF cavity performance were identified and cured, one after the other.

These early successes opened up an enthusiastic effort for continuously increasing applications for accelerator projects. In parallel, progress in computer codes both to solve either the relatively complicated theoretical expressions for RF superconductivity and to solve the electromagnetic fields inside cavities allowed careful and judicious design work. In the mid 1970s proposals were made to build very high energy electron‐positron colliders, with SRF accelerating systems as a serious option (LEP and the electron ring of HERA). It took another 20 years of R&D and industrialisation efforts before such a large electron positron collider such as LEP became a reality and still a few years more before LEP reached its maximum energy (209 GeV) by means of the upgrade with sc cavities.

The actual situation is as such: Starting from relatively small scale applications and pilot installations for nuclear physics (e‐linacs, sc microtron) and heavy ion physics, sc cavities of steadily increasing varieties are now operated successfully in many research areas. They stretch from nuclear physics and particle physics, to light sources for material sciences. The sc cavities are used in accelerators, such as electron linacs, equipped sometimes with re‐circulating arcs to increase efficiency. These accelerating systems for electrons are upgraded to FELs, e+e‐ storage rings and sometimes transformed into B‐factories and light sources. Proton‐proton storage rings equipped with a sc accelerating system explore the energy frontier such as the LHC. Proton linacs with a sc acceleration system serve for multi‐purpose applications, such as neutron sources, accelerating heavy ions and radioactive beams, etc. Superconducting cavities are also applied for steering or shaping the particle bunches (crab and 3rd harmonics cavities).

The history of SRF may be divided into two periods. During the first one, roughly between 1965 and 1985, universities played an important role in scientific innovations that happened in the R&D phase of SRF for accelerator application. During the second period, as of 1985 up until now, the pursuit of large scale accelerator technology and engineering was mostly done in research centres. The large scale series of components was mainly manufactured in close collaboration between industry and research centres.

The participation of universities was crucial in the first phase for guaranteeing a successful start. Innovations were often initiated at universities. They required limited resources and met academic standards. The role of universities faded, because the innovations gradually moved from existence proofs of excellently performing cavities, new materials, diagnostic tools or new treatments and techniques, towards prototyping as well as reliability and series

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production issues. In short, R&D for sc accelerators switched from research to technology and engineering. This shift required larger resources that could no longer be burdened to universities and required extensive engineering know‐how.

A key issue was the early implication of industry during this second phase. Industry responded positively towards niobium material improvement, pre‐series production of cryo‐modules, and rationalisation of the production chain to achieve cost effectiveness. Industry accomplished remarkably well the transfer of know‐how acquired at research centres. These achievements culminated in the successful pilot tests and continuous operation of SRF cavities in accelerators, owing to the close collaboration between research centres and companies.

The increasing use and acquisition of operational experience obtained in the accelerator centres with niobium sc cavities led to research and development to fully exploit the niobium technology with even larger accelerator projects in focus. The efforts were successful and paid off in a steady improvement of performance of niobium cavities up to close to the theoretical limits, at least in individual cavities (Fig. 1). It should be kept in mind, nonetheless, that it took about 40 years until the theoretical performance limit for niobium cavities was demonstrated.

Figure 1: Progress of field gradient with single cell cavities7.

7 A. Yamamoto, Superconducting RF cavity development for the International Linear Collider, ASC 2008.

The arrow indicates the approximate position of the theoretical ceiling in accelerating gradient

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Superconductors other than niobium were also studied during the first phase of research and development but did not cope with the requirements for low loss cavities for accelerators at a reasonable gradient. Copper cavities coated with a thin niobium layer on the inside were an exception. They could occupy a “niche”, for reasons of economy and stability against quenches, after a vigorous research programme had been successfully concluded. This “niche” concerned collider rings such as LEP, mainly for cost reasons, and involved a huge number of sc cavities. It also concerned the much smaller RF system of the LHC, mainly for reliability and beam stability issues. The reason is that collider rings have their cost optimum at moderate accelerating gradients, about 10 MV/m, because the RF system is periodically re‐used by the circulating beams and not only once as in a sc linac. This number depends of course on the individual accelerator and its design parameters such as the manufacturing costs per meter of structure, cryogenic cooling needs and RF power requirements. Niobium coated cavities are also applied, for various reasons, in heavy ion accelerators and are foreseen for upgrade, such as HIE Isolde at CERN.

B. The present status

The present status of SRF for accelerator application can be described as follows:

On the one hand, spectacular technological progress was achieved. Technical work is actively pushed, even worldwide, in a collaborative effort. Large SRF test infrastructures and synergies between laboratories were created. Many sources of financing render this effort possible. The biggest contribution evidently concerns approved projects, such as XFEL and ESS. Other sources such as the EU Framework Programs contribute significantly to the pursuit of other studies and smaller projects. Industry is well integrated in the SRF activity and deserves credit for improvement of the niobium sheets many years ago as well as for providing the lion’s share of SRF components for existing and recent projects. Consequently, large projects such as XFEL are being constructed by an international effort. The preparation for more far reaching projects such as ILC is continuously and successfully progressing as well. Other ongoing R&D activities are pursued, in particular linked to

• proton drivers (ADS, SPL study @ CERN, ESS) to construct pilot cryo‐modules,

• heavy ion accelerators (e.g. HIE ISOLDE with improved niobium coating methods) to reduce costs by simplifying the design and to avoid quench limitation,

• LHC upgrade (e.g. with crab cavities) to increase luminosity,

• Energy Recovery Linacs (ERL) to save electrical grid power at very large beam power,

as well as many others.

These studies or projects are concentrated around accelerator research centres but with less technical and theoretical impact from research work done at universities, as it was in the past. However, links to universities are not neglected, recruitment being an example.

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University alumni with a Bachelor degree as well as technical and doctoral students receive supplementary qualifications in the research centres themselves, financed by them, national funding agencies or the EU.

On the other hand, progress is often slow, due to the pressure of projects and their future users, and sometimes owing to trial and error. The theoretical understanding of the underlying physics does not always keep track with the technological progress. Problems of reproducibility of performance remain and require even stronger quality control at all stages of the manufacturing process. Decisions on any new high energy sc accelerator are on halt as long as results from the LHC experiments are lacking. Large world‐wide project proposals rely on the niobium technology. For good reasons the most reliable technology was therefore chosen. In particular, the technology of bulk niobium made large progress over the last 20 years. At present the niobium technology is the only choice for an accelerator project to be finished within specification, cost and time. Whether to choose niobium as a thin film or in bulk form depends on the specific application, e.g. the required accelerating gradient. There is hope that superconductors other than niobium offer more potential for future SRF projects. But no vigorous and financially well outfitted R&D program is in sight that goes beyond the niobium technology.

Therefore, the risk of stalemate of the SRF technology is real. To avoid the sc technology from being stalled, new R&D efforts are required to keep track and guide the technological advance, as was done in the past. Another unwelcome constraint is the increase of material cost for niobium, the only technical material in use for SRF. The cost of niobium increased considerably as it did for any other raw material. It nearly doubled within four years (520 €/kg in 2010).

In what follows, the three questions as mentioned in chapter II shall be addressed in the light of the long lead times required to go beyond the present technology based on niobium alone. This approach shall demonstrate that there is no fundamental reason to assume that the SRF technology is at its technological and theoretical limit.

III. About the need for a SRF test infrastructure

A. International cooperation - examples

The SRF community is relatively small and its members are well known among each other. If needed, mutual arrangements were and are taken individually between labs, even at a trans‐national or trans‐continental level, with focus on a specific project of common interest. The approach chosen is typical for “bottom‐up”. Examples are numerous and shall not be listed here, except for a few:

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• A Karlsruhe manufactured prototype sc cavity intended for electron positron storage rings such as PETRA and LEP was tested in the PETRA collider; the first beam test of a CERN manufactured sc cavity was arranged in collaboration with DESY and performed at PETRA as well.

• The SNS cavities were designed, manufactured and tested at JLAB.

• A 200 MHz mono‐cell copper cavity designated for a muon collider was manufactured and coated with a thin niobium film at CERN and tested in a wide vertical cryostat at Cornell, the only one available with the required size.

• The Beijing BEBC‐II storage ring was equipped with cryo‐modules from KEK.

• The ESS has taken collaboration arrangements for prototyping with many European accelerator labs having expertise in SRF.

There are many other collaborative efforts. The community is organized world‐wide, exchanges information efficiently, and practices fruitful collaborations, whenever it is needed. Periodic conferences/collaborations play a prominent role and complement each other, such as the biannual SRF conference8 and the International TESLA Technology Collaboration TTC9. Recently the international workshop on “Thin Films and new ideas on RF superconductivity” 10 joined these gatherings. TTC inherited its naming from an effort that started with a workshop in 1990 at Cornell University on TeV Electron Superconducting Linear Accelerator (TESLA) technology11. Meanwhile it covers many more technological fields in SRF than the naming indicates. Proton and heavy ion accelerators were included recently, because the technologies are similar to “TESLA technology” based accelerators. In summary, the international cooperation in SRF is extremely vigorous and fruitful.

B. Present funding schemes

The SRF community is well integrated in supra‐national integrative attempts which are also providing resources.

There are cross links to other institutes and funding schemes such as the following.

1. CERN consortia

• SPL study: CEA, CNRS, BNL, German Universities, ESS …

8 http://conferences.fnal.gov/srf2011/ 9 http://agenda.infn.it/conferenceDisplay.py?confId=3087 10 http://www.surfacetreatments.it/thinfilms/ 11 http://tesla‐new.desy.de/

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2. European Union consortia (FP7 program)

• CARE12 (JRA, precursor of EuCARD, mainly Work Package SRF)

• EuCARD1 (JRA, mainly Work Package 10, Superconducting RF technology for proton accelerators and electron linear accelerators)

• SLHC‐PP13

• ILC‐HiGrade14

• TIARA15

• CRISP (currently approved by EU and being launched)

• HL‐LHC (all under the auspices of ESGARD)

3. National Consortia and Bilateral Funding Schemes

• Special contribution of France to CERN

• Physics at the Terascale Initiative (D)16

• BMBF (D) Initiative (22 Oct 2008): TEMF Darmstadt, University Rostock, TUD, BUW …17 and more recent ones

4. International schemes

• The U.S. LHC Accelerator Research Program (LARP) consisting of four US laboratories, BNL, FNAL, LBNL, and SLAC, who collaborate with CERN on the Large Hadron Collider18

In conclusion, there exists de facto a distributed network of infrastructures for R&D and test of sc cavities and cryo‐modules, which is alive. So the need for a new network is certainly not a top priority. However the specific equipment available in the various accelerator centres is rapidly changing. Therefore a compact and rather detailed list of equipment is helpful to gain an updated overview and to asses whether the available equipment matches the projects and R&D work to come well. Therefore, in various discussions, the wish was uttered to list that equipment required for SRF, and, if needed, to propose completion of specific items. The available equipment related to SRF is therefore summarized in the Annex.

12 http://esgard.lal.in2p3.fr/Project/Activities/Current/ 13 http://info‐slhc‐pp.web.cern.ch/info‐SLHC‐PP/ 14 http://www.ilc‐higrade.eu/ 15 http://www.eu‐tiara.eu/ The main objective of TIARA (Test Infrastructure and Accelerator Research Area) is the integration of national and international accelerator R&D infrastructures into a single distributed European accelerator R&D facility. 16 http://www.terascale.de/ 17 http://www.bmbf.de/foerderungen/13099.php 18 http://www.uslarp.org/#

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IV. Important future research topics and priorities

A. Accelerating gradient

All SRF applications for accelerator projects are based on the metal niobium19. There is a good reason for that: niobium has the largest critical temperature Tc among all elements, is relatively ductile and commercially available in large quantities and different shapes.

However, niobium technology touches its predicted theoretical limits. Recent pulsed RF tests on a niobium cavity allowed raising of the accelerating gradient without being impeded by a quench (Fig. 2, top). This test confirmed a long‐standing conjecture, namely that the surface magnetic field determines the ultimate limit of the accelerating gradient. Its maximum is given by the superheating critical field Bsh, proportional to the thermodynamic critical field Bc and close to it by a factor depending on the purity of the niobium. This limitation is confirmed by recent tests on niobium samples with a specially designed device (quadrupole resonator): for niobium Bc = at 190 mT, and Bsh = 230 mT (Fig. 2, bottom). This device also allows evaluating the RF losses of sc samples.

In real accelerating cavities the maximum magnetic field obtained touches the theoretical limit as well. Depending on the shape of the cavity this ultimate maximum magnetic field Bsh corresponds to about 56 MV/m accelerating gradient in non shape‐optimized elliptical cavities. Measurements on single cell cavities result in values close to that number.

19 except some early developments of lead plated copper cavities of relatively complicated shape, envisaged for heavy ion accelerators, and recently as cathode material for SRF electron guns because of its improved quantum efficiency

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Figure 2: Maximum surface magnetic field under RF exposure vs temperature for niobium cavity (top) and niobium sample (bottom) exceeding the thermodynamical critical field (Bc = 190 mT) by

about 20 %20, 21.

20 N. R. A. Valles and M. U. Liepe, Temperature dependence of the superheating field in niobium, http://arxiv.org/abs/1002.3182v1 21 Courtesy T. Junginger/CERN

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Figure 3: Q‐factor vs. accelerating gradient for a shape‐optimized mono‐cell niobium cavity (insert) from KEK ‐ Cornell collaboration22

Fig. 3 depicts the Q‐factor vs. accelerating gradient for a shape‐optimized mono‐cell niobium cavity which obtained 59 MV/m maximum gradient, 125 MV/m peak surface electric field and 206.5 mT peak surface magnetic field. The gradient was limited by a quench.

Two approaches may offer a solution to overcome this limitation in gradient. The first consists of choosing another material. As the superheating critical field Bsh is proportional to the thermodynamic critical field Bc, any metal with a larger Bc than niobium would be adequate, e.g. Nb3Sn of NbN (Table 1).

22 R.L. Geng , G.V. Eremeev, H. Padamsee, V.D. Shemelin, High gradient studies for ILC with single‐cell re‐entrant shape and elliptical shape cavities made of fine‐grain and large‐grain niobium, Proceedings of PAC07, Albuquerque, New Mexico, USA, p. 2337.

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Table 1: Possible materials for SRF application

Material Tc [K] Bc [T] Bc1 [T] Bc2 [T]Pb 7.2 0.08 n/a n/a Nb 9.2 0.2 0.17 0.4

Nb3Sn 18 0.54 0.05 30 NbN 16.2 0.23 0.02 15 MgB2 40 0.43 0.03 3.5 YBCO 93 1.4 0.01 100

The second approach proposed is based on one or several thin sc film ‐ insulator sandwiches on top of a bulk niobium substrate. The underlying idea consists in increasing the critical magnetic field of the uppermost layers by making them sufficiently thin and to rely on the exponential decay of the magnetic field with depth. The rational ground is the well known fact that the critical magnetic field of thin films is larger than for bulk because the shielding surface currents in the film are not yet fully developed; hence these currents cost less energy to develop than for bulk and can therefore exceed the maximum bulk surface currents. As they are proportional to the magnetic field, the bulk critical magnetic field is exceeded considerably, and by more the thinner the film is. The magnetic field inside the sandwich structure is becoming smaller and smaller going from one sandwich to the next deeper one. It must be guaranteed as a necessary condition that the remaining magnetic field at the interface to the bulk niobium substrate is below the superheating critical field there. The surface magnetic field at the uppermost surface can therefore be much larger than the superheating critical magnetic field of the bulk23.

This conjecture is certainly worth being tested. A first approach would consist in preparing a sandwiched sample for RF evaluation in a suitable host cavity (e.g. quadrupole resonator or TE011 cavity). Sample tests are convenient, or even mandatory, to fully characterize the superconducting properties on identical surfaces, both for RF and DC, before preparing real accelerating structures.

B. RF losses - Q-value

Large and costly projects such as a linear colliders with TeV beam energy require very large accelerating gradients. The simple reason is that the investment costs scale approximately with the length of the device, which, for constant beam energy, goes down inversely proportionally with the accelerating gradient. Large accelerating gradients are not for free and they are reflected in the operation costs. Increasing the accelerating gradient must be accompanied by a substantial reduction of the RF dissipation, which goes up with the square

23 A. Gurevich, Enhancement of RF breakdown of superconductors by multilayer coating, Appl. Phys. Lett. 88 (2006) 012511.

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of the gradient. An accelerating gradient of twice the design gradient for a linear collider application such as the ILC, under preservation of the overall RF dissipation and beam energy (i.e. cutting in half its length), would require doubling the Q‐value. An accelerating gradient of, say 100 MV/m, for a linear collider application such as the ILC, under preservation of the overall RF dissipation and its total length, would require a targeted Q‐value of 8·1010. The SRF technology would allow for such a number, because, on theoretical grounds, the maximum accelerating gradient (or magnetic surface field) is correlated with the critical temperature and consequently with a small RF dissipation (large Q‐value) (Fig. 4). The reason is that the critical temperature is proportional to the energy gap, and, from the BCS theory, the RF losses decrease exponentially with the energy gap.

Fig. 4: Critical magnetic field versus critical temperature of selected elemental superconductors24

Also for relatively moderate beam energies, a large Q‐value is mandatory in order to avoid causing problems by a cavity that might have degraded and not having sufficient reserve available in cooling power.

Indeed, such large Q‐values can be achieved in bulk niobium cavities. Q‐values exceeding 1011 were obtained in individual cavities up to accelerating gradients of more than 25 MV/m (Fig. 5).

24 http://hyperphysics.phy‐astr.gsu.edu/hbase/solids/scbc.html#c2

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Figure 5: Q‐value vs. acc. gradient; Q > 2·1011 corresponds to a residual resistance < 0.5 nΩ25

For the same reasons, other materials with a critical temperature Tc larger than that of niobium would offer even more potential, because they should allow for even smaller RF losses. This explains the attractiveness of classical high‐Tc superconductors, such as NbN and Nb3Sn.

Remarkably, for thin films of these classical high Tc, and also for niobium thin films, similar or even larger Q‐values than for bulk niobium were obtained. These include thin niobium film on copper substrate cavities and thin Nb3Sn or NbTiN film on niobium substrate cavities (Figs. 6 ‐ 8). However, the large Q‐values of these thin film cavities could not be preserved up to large accelerating gradients. They show a more pronounced decrease of the Q‐value with the accelerating gradient than bulk niobium cavities (Q‐slope). But it should be kept in mind that since these early efforts (late 1980s) the efforts invested into niobium cavities exceeded by far those for thin film cavities. This fact is another illustration why the most reliable technology was preferred to that with the largest potential.

25 H. Safa, High field behaviour of superconducting cavities, 10th Workshop RF Superconductivity, Tsukuba (Japan) 2001.

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Figure 6: Q(Ea) curves of the very first 352 MHz LEP niobium thin film cavities, manufacture in the late 1980s (curves 1 and 2) (left); Q(Ea) curves for a 500 MHz single‐cell NbTiN thin film cavity; upper

curve, measurements taken at 2.6 K, lower curve, measurmeents taken at 4.2 K (right)26.

An essential by‐product is that these “classical” high Tc superconductors would also allow operation at 4.2 K instead of 2 K for sufficiently large RF frequencies; say beyond about 700 MHz (Fig. 8).

Figure 7: Q‐value vs. accelerating gradient curve of a typical high performance niobium cavity showing indicators of field dependent surface resistance (intermediate Q‐slope and Q‐drop)27.

26 C. Benvenuti, D. Bloess, E. Chiaveri, N. Hilleret, M. Minestrini and W. Weingarten, Proc. 4th Workshop RF Superconductivity 1989, KEK, Tsukuba (Japan), p. 869. 27 L. Lilje et al., Nucl. Instr. Meth. A 524 (2004) 1.

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The physical reason for the Q‐slope is presently under investigation in several laboratories. Several models were proposed to explain this observation, but a breakthrough in understanding is still pending. A most probable explanation is flux entry into the surface, preferentially at oxides or other non‐stoichiometric areas (nucleation centres) and its growth inside the superficial oxide layer under the action of the RF magnetic field.

Figure 8: Electric peak field dependence of Q‐value of a single‐cell 1.5 GHz cavity as measured before (Nb) and after Nb3Sn coating at 2 and 4.2 K. The electrical peak field of 27 MV/m corresponds to an

accelerating gradient of 12 MV/m28.

Fig. 9 presents a phase diagram for Nb3Sn, the material that was tested for accelerator application with the results as shown in Fig. 8. Only one individual phase is the correct one for SRF application. To prepare the correct one and suppress all other unwanted phases is a challenging task and might explain the results obtained so far as being inferior to bulk niobium at large accelerating gradients.

28 G. Müller, P. Kneisel, D. Mansen, H. Piel, J. Pouryamout, and R.W. Röth , Proc. of the 5th EPAC, London, p. 2085 (1996).

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Figure 9: Phase diagram of Nb and Sn showing many phases apart from the useful phase for SRF (Nb3Sn)29.

C. Reproducibility of performance

In spite of the remarkable successes in the performance of bulk niobium cavities in terms of accelerating gradient and Q‐value, as described before, issues such as the reproducibility of that performance in real accelerator cavities with many cells and in assembled cryo‐modules with many cavities remain challenging. The term “reproducibility” is understood as the variation of performance after application of an identical cavity treatment protocol. The scatter of performance proves that apart from the deterministic performance factors, such as temperature, frequency, magnetic field etc., there are others of stochastic nature, not strictly under control of the experimenter.

1. Quench and field emission

Reproducibility is at stake for several reasons. Whereas the average gradient doubled from about 15 MV/m to about 30 MV/m within the last decade, the relative scatter of the gradient remained about the same. The breakdown mechanism also remained unchanged.

29 A. Godeke, A review of the properties of Nb3Sn and their variation with A15 composition, morphology and strain state, Supercond. Sci. Technol. 19 (2006) R68–R80.

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The niobium cavities are in nearly all cases limited by a quench or by field emission. One flawed site on the surface is sufficient to limit the gradient of the cavity.

A quench is usually provoked by excessive local heat dissipation at a normal conducting defect under the action of a large magnetic surface field. As soon as the temperature in its vicinity comes close to the critical temperature Tc (at the magnetic surface field Bc) a temperature run‐away forces the circumjacent niobium normal conducting. The consequence is a periodic or single‐event instability, depending on the RF power available, leading to large RF dissipation.

Field emission is caused by a large electric surface field. The detrimental action of the mechanism of field emission consists in drawing energy out of the electromagnetic field of the cavity and loading it as kinetic energy to the cavity wall. In addition, equally bad, field emission aggravates exponentially with the accelerating gradient.

Field emission occurs at high gradients, however far below the theoretical predictions for ideal surfaces. Hence the process of field emission is more complex than treated in theory. Diagnostics on sc cavities accompanied by computer simulations and DC sample tests with a field emission microscope identified the field emitters as “dust” particles of various compositions. Since clean working practice was adopted from the vast experience accumulated in the semiconductor industry, the failure of sc cavities rate by field emission has considerably decreased.

Both effects are a nuisance for a reliable cavity operation, but one must keep in mind that they do not pose a fundamental limit. The ultimate limit in gradient was achieved in individual cavities without a quench, and a surface electric field as large as 1 GV/m was obtained locally on small niobium samples without field emission30.

Another reason affecting the reproducibility is the size of the superconducting surface. As even one single emitter or defect may degrade the performance of the cavity, it is clear the more cells a cavity has or the lower the frequency is the higher is the probability of a limitation of the gradient by either a field emitter or a defect.

As an illustration, about four decades R&D efforts passed until obtaining the theoretical limit of the niobium SRF technology in individual cavities ‐ more time will pass before we can obtain reproducible results in real accelerating structures.

30 A. Dangwal et al., Proceedings of SRF2007, Peking Univ., Beijing, China.

22

2. Diagnostics

The location of the quench or of a field emitting site can in principle be identified by suitable diagnostics. In most cases either a rotating arm or a fixed frame of thermometers is used. The signals they provide are visualised by a two dimensional loss distribution plot (temperature map). The thermometers allow detection of the additional heat flow on the cavity outside surface that originates on the inside from the quench locations or the impinging electrons. If inspected from the inside a defect is often found as a culprit on a weld. Quench locations show up as a circular heat sources, field emission electrons leave a linear trace, from which the emission site may be identified by computer simulations. Other diagnostics such as X‐ray sensors complement the diagnostics tools. Evidently suitable diagnostics is mandatory for manufacture control and fault analysis.

3. Measures to improve reproducibility

a) Thermal conductivity

High thermal conductivity niobium helps in stabilizing the temperature around the defect thus pushing the quench field up for the same type of defect. A more favoured heat removal allows smaller temperatures in the vicinity of the defect and hence larger magnetic fields or accelerating gradients. The transition from the superconducting phase to the normal conducting phase near Tc (B) is thus impeded. But even for niobium with high thermal conductivity a limitation of the gradient by a quench cannot be safely avoided.

b) Thin film cavities

Instead of pushing the thermal conductivity of niobium even further up an alternative does exist for instance, coating a thin niobium film inside a copper cavity making use of its intrinsic large thermal conductivity. All cavities for the LHC and the vast majority of cavities for LEP were produced by this technique. Among other advantages offered by this technique, field limitations by a quench were practically absent. Other advantages are a larger Q‐value at small gradients compared to bulk niobium cavities. However the decrease of the Q‐value with the gradient is more pronounced (Fig. 10). Irrespective of its potential for the future the technique of thin niobium film coating on copper is presently fully adequate for low and intermediate gradients as required in circular and heavy ion linear accelerators, as described before.

23

Figure 10: Q vs. accelerating gradient for 1500 MHz mono‐cell copper cavities at 1.7 K sputter coated with a thin niobium film under argon31 and krypton32 atmosphere (left and right, resp.).

D. Proposal for future R&D work Niobium bulk cavities are in a favoured position of being pushed still further in performance, because the approved and emerging projects are based on that technology. Therefore R&D resources will be available to further develop their performance. However, the long lead times needed to further develop a relatively complicated and multi‐discipline technology such as SRF, top priority should be attributed to materials beyond bulk niobium. Evidently every endeavour must be made to thoroughly understand the performance limitations including the Q‐slope. It is doubtful that a deeper understanding can be achieved without active participation in the experimental work of experts in superconductivity with a solid theoretical background. It is not sufficient to delegate the analysis merely to theorists without involving them in the experimental work. A reliable assessment of new SRF surfaces is eventually only possible by submitting them to RF exposure. Therefore all attempts to develop or improve host cavities for sample tests beyond what exists should have priority. Close collaborations with surface analysis laboratories are evidently needed to correlate the RF results on sample with those on DC.

For these reasons the proposal presented here will not cover the ongoing R&D work in relation with the approved or planned projects. This work is well underway and endowed with the resources needed. It follows the conventional paths, which comprise large RRR niobium as a starting material, shaping and welding, smoothing the welds by mechanical abrasion (tumbling), chemical or electrochemical removal of surface damage layers, heat treatment, rinsing with ultraclean water, mild baking, assembling under dust‐free conditions, etc. Thanks to continuous improvement of preparation techniques, with close

31P. Bosland, A. Aspart, E. Jacques, M. Ribeaudeau, IEEE Trans. Appl. Supercond. 9 (1999) 896. 32 V. Arbet‐Engels, C. Benvenuti, S. Calatroni, P. Darriulat, M. A. Peck, A.‐M. Valente, C. A. Van’t Hof, Nucl. Instr. Meth. A 463 (2001) 1.

24

application of lessons from the wafer preparation, the niobium technology matured up until achieving the theoretical limits, as described before. The manufacture steps need, of course, further improvements in quality assurance in order to keep the performance at a constant high level. Further efforts in theoretical understanding are followed as well, as for example the Q‐slope.

What will be proposed in what follows goes beyond this conventional path. The seeds for a strategy to eliminate the performance flaws of sc cavities as of today and to push further development are rather obvious from what was described before. Promising cures are the following.

1. Niobium

• RF Losses by field emission increase exponentially with the gradient, therefore overloading the cooling capacity of the refrigerator, and may lead to a quench and reduce the reproducibility of performance. The cure is conventional and followed up routinely. The procedures for processing and assembling the cavities and cryo‐modules are continuously improved by applying ultrapure clean conditions. The semiconductor industry has developed adequate techniques that are copied if needed. An example applicable for SRF can be the total absence of human intervention during the wafer processing, the human body being the principle source of dust. This possibility should be assessed for SRF purposes.

• Welding defects often cause a quench and also affect the reproducibility. The cure consists in completely avoiding welds that feature a high probability of defects. High thermal conductivity substrates are used to stabilize prevailing defects. Studies on thin niobium films on copper as a high thermal conductivity substrate deserve continuation; a possible shaping technique to produce seamless cavities without welds consists in spinning or hydro‐forming. One may both manufacture a copper cavity and coat it inside with a niobium film (Fig. 11) or one may produce a niobium cavity from a thin tube and cold‐ spray copper on the outside for mechanical stabilisation of the cavity shape33.

33 N. Valverde and S. Atieh, Novel fabrication techniques for SRF cavities, note CERN‐EN 8 March 2011

25

Figure 11: Hydro‐formed mono‐and multi‐cell copper cavities at 2.1 and 1.5 GHz34.

• The Q‐slope at intermediate gradients35 indicates that the RF losses increase more rapidly than predicted by theory and are largely insensitive to the treatment applied. Two possible cures are promising, always under the hypothesis of the Q‐slope being created by the entry of magnetic flux at low Bc nucleation centres:

(i) coat the niobium surface with a protective superconducting layer other than niobium to cover the nucleation centres for flux entry; this layer must be sufficiently thin to exclude that it may limit the accelerating gradient;

(ii) modify the morphology of the niobium oxides by vacuum firing the cavity; it should be remembered that the first breakthroughs in the niobium SRF technology were obtained by electro‐polishing and UHV firing.

These proposals should be accompanied by making extensive use of surface analysis methods (e.g. TEM). The contacts to material science institutions must be strengthened in order to obtain their expertise knowledge. Analyzing not only the impurity depth profile, as was done by now, but also the impurity lateral profile (plan view) in high resolution would be needed;

34 C. Hauviller, Fully hydroformed RF cavities, Proc. 1989 Part. Acc. Conf. Chicago, Ill. (USA). 35 The Q‐slope at high gradient (Q‐drop) can be cured by moderate baking of the cavity (120 – 140 °C)

26

• The accelerating gradient is not sufficient for future linear colliders for particle physics. A very promising cure is already actively followed in several SRF labs and should be boosted more. It consists in coating on top of the niobium substrate a sandwiched film of one or more bi‐layers of isolator and superconductor sufficiently thin that it can prevail in a magnetic field larger than the superheating field of niobium. This layer shall sufficiently reduce the magnetic field amplitude at the isolator‐niobium substrate interface. Samples possessing such an isolator niobium sandwich shall be validated under RF inside a host cavity (e. g.TE011 cavity or quadrupole resonator36) before applying this technique to a RF cavity.

2. Alternate materials

In view of the long lead time until technical maturity is achieved several alternatives to bulk or thin film niobium should be investigated as soon as possible.

• There is a continuous quest for lower RF losses compared to niobium. Alternatively, but closely linked to that, the operation of accelerating structures at 4.5 K instead in super‐fluid helium at 2K would be possible. Candidates to get around this issue are materials with a larger Tc than niobium, such as the “classical” high Tc superconductors, NbN and Nb3Sn.

• The limitation in accelerating gradient inherent to niobium shall be extended. As a cure is offered by the conjecture confirmed meanwhile that the ultimate limitation is proportional to the superheating magnetic field, being on its part proportional to the thermodynamic critical field Bth, Therefore materials with a larger Bth than niobium are promising, such as “classical” high Tc superconductors NbN or Nb3Sn.

These alternate materials have already been proven to possess Q‐values larger than niobium, however only at low gradient; the reason is probably their relatively complicated phase diagram; a wise beginning of a R&D program would consist in preparing samples and evaluating their performance under RF exposure again in a host cavity, before applying the optimized coating procedure to a full RF cavity or accelerating structure. Substrates to be studied are niobium or copper. Coating can be done by thermal diffusion of tin into niobium in a dedicated furnace or by co‐deposition of niobium and tin. The equipment needed consists of a vacuum furnace providing a temperature of about 1100 °C and co‐deposition

36 A quadrupole resonator is operational at CERN

27

equipment. The study can then extend to “multi‐layers” of a thin film of, say, niobium, Nb3Sn or NbN37.

These technical actions should be accompanied by a continuous funding and strong links with non‐accelerator institutes including universities for guidance in theory and application of surface analysis methods other than practiced by now.

V. Capacity and availability needs related to emerging European projects

Any missing equipment or initiatives, in the European context, shall be identified by comparing the needs of technical equipment with the available one, related to both R&D and emerging or approved projects. What future R&D work will require was described in the previous chapters. What emerging or approved projects will need in the forthcoming years is summarized in Table 2.

Table 2 shows that the different projects are pushing against different technical frontiers. Inspecting it shows that there are large variations in the specifications (number of cavities, beam current, accelerating gradient, etc.). These variations obviously define the need and scope of R&D work required for the future projects.

A large number of cavities will raise the question whether the available test facilities are sufficient in capacity and technical capability or need to be upgraded. This frontier concerns logistics, quality assurance, reproducibility of performance and cost. A large beam current will touch the frontier of the maximum total beam power and the individual power to be allotted per cavity by the power coupler. A large accelerating gradient accompanied by reasonably moderate RF losses, will require crossing the fundamental and technological limits of the SRF niobium technology.

These three frontiers ask for different approaches for a solution.

The cost and RF power coupler frontiers are not fundamental, but more of political and technological nature. The total beam power, instead of dumping it and facing the implications of safety and environment, may be reused by energy recovery schemes (ERL). The RF power to be imparted per cavity can for instance be reduced by limiting the number of cells or increasing the number of power couplers. These issues are nevertheless considered as outside the scope of this report, because they are already covered and

37 A. Gurevich, Enhancement of RF breakdown field of superconductors by multilayer coating, Appl. Phys. Letts. 88, 012511 (2006).

28

treated by the R&D work related to the up‐to‐date SRF projects. As they do not affect the future of the SRF field, they will not be discussed in more detail in what follows.

Table 2: Emerging/approved SRF projects related to ESFRI38

Field of research

Project (approved or

emerging)

First operation for users

Accelerated particles

Accelerating gradient [MV/m]

Current [mA]

Frequency [MHz]

Number of sc

cavities ESS: The

European Spallation

Source

2019 protons 15 50 352/704 234

European XFEL 2015 electrons 24 5 1300 909 Materials Sciences

FEL (ALICE, BERLinPro S‐

DALINAC, FLASH, ELBE)

2006‐2015 electrons ~5 – 251) ~1001) 1300 ~101)

HIE‐ISOLDE 2016 heavy ions 62) ≤ 10‐7 1) 101 32

FAIR/UNILAC 2014 heavy ions 52) 1 217 9

SPIRAL2 2012/13 deuterons/heavy

ions 6.52) 5 88 26

SPL (neutrino physics)

2015 protons 25 n/a 704 43)

HL‐LHC4) ~2020 protons 20‐255) 580 400 16

Astronomy, Astrophysics,

Nuclear and Particle

Physics

ILC 2012 (TDR) electrons 31.5 9 1300 266)

ADS MYRRHA 2023 protons ~5‐107) 2.5 ‐ 4 352/704 155 1) order of magnitude 2) per world region as defined in Global Design Effort (GDE)

3) for SPL study 4) crab cavities for luminosity upgrade

5) equivalent acc. gradient with 1 MV/m equivalent to 4 mT 6) the maximum magnetic surface in mT corresponds to about ten times this number 7) the maximum magnetic surface in mT corresponds to about five to ten times this number

A. Logistical needs

Being guided by the ESFRI Road map39, Table 2 summarizes the SRF related projects in Europe, either emerging, approved, or under construction. Based on the total number of cavities to be acquired the XFEL project is certainly the most ambitious one. The projects with smaller number of cavities are ESS, MYRRHA, HIE‐Isolde, and preparation for the ILC and SPIRAL2, in decreasing order. It is difficult to predict possible collisions as far as testing places are concerned. But there could be a coincidence, mainly as of 2012, for cavity reception and cryo‐module qualification tests for SLHC, ESS, ILC and HIE‐Isolde.

38 http://ec.europa.eu/research/infrastructures/index_en.cfm?pg=esfri 39 http://ec.europa.eu/research/infrastructures/pdf/esfri_report_20090123.pdf

29

B. Needs for R&D initiatives

Clean assembly and ultrapure water installations are in widespread use and operational. The technology has been adopted from the semiconductor industry, and staff in the SRF laboratories are aware of the need to permanently monitor and upgrade the existing equipment. Samples prepared with the aim to reduce field emission can be investigated in the scanning field emission microscope of Wuppertal University.

Hydro‐forming seamless niobium cavities is done at DESY, spinning at Legnaro, and hydro‐forming of seamless copper cavities has been done at CERN in the past and could be revitalized.

The Q‐slope is being studied theoretically, however only marginally with an active participation of theoreticians in superconductivity. Connections between them and experimentalists should be intensified, as is the case in the US. Sample testing equipment under RF exposure is available at CERN (quadrupole resonator with variable frequency range from 400 to 1200 MHz) and at IPN Orsay (TE011 cavity at 3.9 and 5.1 GHz). A dedicated furnace allowing the firing of niobium cavities up to 1800 °C under preservation of UHV conditions is available at Darmstadt University40. General purpose furnaces of different capacities and useful volumes are available at CERN. General purpose surface analysis tools are fairly common41; more sophisticated equipment is also available in European accelerator or other labs42. The collaboration with non accelerator labs could nevertheless be intensified.

Classical high‐Tc superconductors are at present not being investigated in Europe. The US started a campaign to reproduce the results on Nb3Sn coating on bulk niobium43. The main missing equipment is a furnace that should go up in temperature to at least 1250 °C. It would allow continuation of the past studies of coating with Nb3Sn on bulk niobium by a diffusion process. The excellent results already obtained raise hope for rapid improvement.

Multi‐layers are studied at Argonne Laboratory (US) and at CEA Saclay. This activity is certainly worth being endowed with sufficient resources and extended.

Expertise and instruments would be available in specialized research centres, such as the Ernst‐Ruska Centre for Microscopy and Spectroscopy with Electrons at Jülich (Germany), to give an example

40 The furnace needs to be partially refurbished 41 E. g. SEM, Auger depth profiling, SIMS, Magnetisation, RRR and Tc measurements of superconductors, Eddy current surface scanning, ... 42 E. g. TEM, ERD, NRA, PIXE, RBS, Squid surface scanning, ... 43 Cornell University

30

VI. Conclusions

(i) The SRF community is relatively small and well known among each other and well integrated in supra‐national integrative attempts. De facto, a distributed network of infrastructures for R&D and test of sc cavities and cryo‐modules has been established in a bottom up approach in Europe and beyond. Therefore a need for a SRF test infrastructure, distributed across, and managed by, European accelerator labs, does not exist.

(ii) Important issues defining the research topics for the future of SRF technology are the accelerating gradient, the RF losses and the reproducibility of performance. As an increase of the accelerating gradient requires a simultaneous reduction of the RF losses, both topics have similar priority. The gradient limitation is in most cases caused by a surface defect or by field emission. Clean surface preparation and cavity assembling is absolutely mandatory to avoid field emission. Seamless cavities or thin niobium films on copper cavities may offer quench‐free performance. There is a gap in performance between small mono‐cell and large accelerating cavities, results on the latter being less reproducible. To assess the priority of solving the reproducibility issue depends primarily on scale of the specific project.

The niobium technology is approaching the predicted theoretical limit in accelerating gradient, the superheating critical magnetic field Bsh. To overcome this barrier, both materials with a larger Bc than niobium should be studied and the merits of thin superconductor ‐ insulator sandwiches should be continued to be explored. The most promising candidate for SRF application in the future is the classical high Tc superconductor Nb3Sn, because of its stoichiometry and therewith the appropriate phase is well known and it has the largest Bc among the sufficiently understood superconductors44. Complementary to, and equally important for, an increasing accelerating gradient is a larger Q‐value, in order to limit the cryogenic power and operating costs. This potential in principle is also in reach with Nb3Sn.

All surfaces that were used so far for SRF application suffer, though to a different degree, by an increase of the RF dissipation with the accelerating gradient more than expected (Q‐slope). As this observation is quite universal and lacks a physical explanation it should therefore be studied with priority and understood.

44 MgB2 and YBCO are not considered as such

31

Sample tests under RF and DC are important because they allow an independent assessment of, and a correlation between, RF and DC properties of sc materials. Host cavities are available in a few labs but their number should be increased.

Mutual interaction of universities and research centres laid the ground for technological and scientific innovations; their implementation was successfully driven by collaborative efforts between research centres and industry. The links between accelerator labs and non‐accelerator institutes and universities should be reinforced.

(iii) The available equipment in European accelerator labs is considerable and close to complete. It is adapted to the TESLA niobium technology and consequently satisfies the needs of XFEL. The largest concentrations of equipment are located around the laboratories such as DESY, CEA Saclay/IPN‐Orsay‐Supratech and CERN.

However, the revived interest and the upcoming projects for proton drivers (ESS, Myrrha, neutrino facories) demand a thorough re‐assessment of the available test infrastructures.

Equipment to produce thin niobium films on copper is traditionally housed at CERN, but also at INFN Legnaro. Research work is going on in the frame of the EuCARD initiative.

Any other research initiatives beyond these materials do not practically exist.

In view of the very long adolescence and in order to tap the full potential of the SRF technology, new materials and approaches should be pursued now. Encouraging results were already obtained in the past, such as for niobium film on copper and classical high Tc superconductors. If the same resources were applied for these materials as for niobium bulk material, progress is attainable.

32

VII. Glossary AccNet Accelerator Science Network

ADS Accelerator Driven Systems (neutron sources for nuclear waste transmutation or triggering subcritical fission reactors)

ALICE Accelerators and Lasers In Combined Experiments BCS surface resistance

Surface resistance that depends exponentially on the ration of energy gap and temperature

BCS theory Bardeen Cooper Schrieffer theory of superconductivity BEBC Beijing based electron positron collider

BERLinPro Berlin Energy Recovery Linac Project Beta Ratio of particle to light speed

B‐factory High luminosity electron positron storage producing abundantly B‐mesons CARE Coordinated Accelerator Research in Europe CERN Centre Européen pour la recherche nucléaire at Geneva (Switzerland)

Cooper pair Interacting electrons with opposite spin that carry the super‐current Crab cavity RF cavity for bunch rotation to make them collide head‐on

CRISP Cluster of Research Infrastructures for Synergies in Physics Critical magnetic

field Bc Magnetic field below which the metal is superconducting (at zero

temperature) Critical temperature

Tc Temperature below which the metal is superconducting (at zero magnetic

field) Cryo‐module String of sc cavities inside a dedicated cryostat equipped with all ancillary

elements required for accelerating a beam of particles EB welding Electron beam welding

ELBE Electron Linac for beams with high Brilliance and low Emittance at HZDR Dresden (Germany)

EP Electro‐Polishing ERD Elastic Recoil Detection ERL Electron Recovery Linac

ESFRI European Strategy Forum on Research Infrastructures ESGARD European Steering Group on Accelerator R&D

ESS European Spallation Source (for neutrons) EuCard European Coordinated Accelerator Research and Development

FEL Free electron laser Field emission Extraction of electrons off the surface by the action of the electric field

FP Framework program (Research Initiative of the European Union) HPR High Pressure Rinsing ILC International linear collider IOT Inductive Output Tube (RF power source)

IPN‐Supratech SRF technology platform for future accelerators shared between CEA‐Saclay and CNRS Institute de Physique Nucléaire at Université of Paris XI, Orsay

(France) ISOLDE Source of low‐energy beams of radioactive isotopes obtained from on‐line

isotope mass separator JRA Joint Research Activity

33

KEK Japanese centre for high energy physics at Tsukuba LARP US LHC Accelerator Research Program LeHC Large electron Hadron Collider LEP Large electron positron project at CERN, Geneva (Switzerland)

Linac Linear accelerator; “recirculating linacs” cf. under “recyclotron” Microtron Linear electron accelerator with D‐shaped magnets for beam recirculation

NRA Nuclear Reaction Analysis PETRA Positron electron tandem ring accelerator at DESY, Hamburg (Germany) PIXE Proton Induced X‐ray Emission

Quench Sudden breakdown of stored energy in a cavity and its local dissipation by the action of the magnetic field

RBS Rutherford Backscattering Spectroscopy Recyclotron Linear accelerator with distributed magnet system for beam recirculation

Residual surface resistance

Contribution to the surface resistance at small magnetic field in addition to the BCS surface resistance

RFTech Radio‐Frequency Technology networking activity SC Superconducting

S‐DALINAC Superconducting recyclotron housed at the Institute for Nuclear Physics at the University of Darmstadt (Germany)

SEM Scanning Electron Microscopy (with X‐ray analysis) SIMS Secondary Ion Mass Spectroscopy SLAC Stanford Linear Accelerator Centre

S‐LHC‐PP Large Hadron Collider upgrade Preparatory Phase SNS Superconducting spallation source at Oak Ridge National Laboratory, TN

(USA) SRF Superconducting RF

Superconducting energy gap

Energy that an electron gains when interacting with another electron to form a Copper pair

Supratech Technological premises located at IPN Orsay devoted to develop sc cavities relevant for high intensity proton or deuteron beams in close coordination

with CEA‐Saclay (France) TEM Transmission Electron Microscopy

TESLA TeV electron superconducting linear accelerator and the technology that goes with it

TIARA Test Infrastructure and Accelerator Research Area TJLAB Thomas Jefferson Accelerator Lab at Newport News, VA (USA) TTC TESLA Technology Collaboration UHV Ultra high vacuum

UPWR Ultrapure water rinsing at low pressure (~ 6 bar) US Ultrasound

XFEL X‐ray free electron laser at DESY, Hamburg (Germany)

34

Acknowledgments

The work is co‐funded by the European Commission within the Framework Program 7 Capacities Specific Program, Grant Agreement 227579 – EuCARD.

This report would not have been possible without the information and valuable comments received from many individuals, whom I want to thank with gratitude. Particularly important were the comments by the participants of the RFTech meetings and by D. Proch (DESY), as to the contents, and the contributions by S. Chel (CEA‐Saclay), R. Eichhorn (University Darmstadt), P. McIntosh (Cockcroft Institute), W.‐D. Möller (DESY) , G. Müller (University of Wuppertal), G. Olry (IPN Orsay),V. Palmieri (INFN Legnaro), U. Ratzinger (University Frankfurt), and J. Teichert (HZDR), as to the equipment available in their respective laboratories.

35

AN

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SRF

rela

ted

sp

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qu

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ent a

vail

able

in E

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Lab

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Tab

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: Gen

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pu

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La

bora

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El

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on b

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Shap

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00 °C

) for

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(S

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the

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trea

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(Ger

man

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36

Tab

le 2

: Sp

ecif

ic m

anu

fact

ure

/ass

emb

ly fa

cili

ties

an

d in

spec

tion

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tin

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Cl

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ss tu

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of 7

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z ca

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var

ious

bet

as

‐ ISO

7 ~6

x5 m

2 ‐IS

O5

~8x5

m2 in

clud

ing

UPW

R ‐IS

O4

~8x1

4 m

2 incl

udin

g ca

vity

was

her,

HPW

R, U

PWR

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7 2x

5m2

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5 6x

5 m

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cle

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ity

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stit

ute

(UK)

‐b

ead

pull

appa

ratu

s in

side

tem

pera

ture

an

d hu

mid

ity c

ontr

olle

d en

clos

ure

‐ISO

4 6x

4 m

2 ‐IS

O5

4x8

m2 in

clud

ing

UPW

R an

d H

PWR

‐mov

eabl

e IS

O4‐

6 cl

ean

room

s (2

x2 to

4x4

m2 )

‐par

ticle

cou

nter

s, s

low

pum

ping

sta

tions

, ion

izin

g ai

r gu

ns

DES

Y (G

erm

any)

‐t

unin

g m

achi

ne in

ded

icat

ed la

b ‐s

emi a

utom

atic

tuni

ng m

achi

nes

for

XFEL

‐a

utom

atis

ed R

F m

easu

rem

ent m

achi

ne fo

r ha

lf‐ce

lls &

dum

b‐be

lls (H

AZE

MEM

A)

‐ Bld

. 28,

ISO

4 20

m2 to

51

m2 w

ith 3

oil

free

pum

p st

atio

ns; 1

sl

ow p

umpi

ng, s

low

ven

ting

equi

pmen

t; in

clud

ing

UPW

R, 2

x H

PWR

‐ ISO

5 62

m2 to

81

m2

‐ ISO

6 ‐s

tand

ard

ISO

6 &

loca

l ISO

4

‐cle

an r

oom

Bld

. 47

‐ISO

5 40

m2 w

ith 1

oil

free

pum

ping

uni

t, U

P W

R H

PWR,

dry

ic

e cl

eani

ng

‐”Ky

oto”

cam

era

‐3D

mec

hani

cal i

nspe

ctio

n ‐m

icro

stru

ctur

e ‐e

ddy

curr

ent s

cann

ing

‐ten

sile

test

‐h

ardn

ess

‐ int

erst

itial

impu

rity

ana

lysi

s (H

,N,O

, C)

‐ met

allic

impu

ritie

s an

alys

is b

y SE

M (F

e,

Ni e

tc.)

‐ sur

face

rou

ghne

ss

‐the

rmal

con

duct

ivity

IN

FN L

egna

ro

(Ita

ly)

‐bea

d pu

ll ap

para

tus

insi

de th

erm

osta

tic

cham

ber

‐are

a of

150

m2 IS

O7

and

15 m

2 of c

lean

roo

m IS

O6

‐dig

ital c

amer

a an

d sy

stem

for

insp

ectio

n in

side

mon

o‐ce

ll ca

vitie

s

IPN‐O

rsay

(F

ranc

e)

‐IS

O4

(45m

²) in

clud

ing

HPW

R (1

00 b

ar)

‐vid

eo‐s

cope

for

insp

ectio

n of

inne

r su

rfac

e ca

vity

37

Tab

le 3

: Su

rfac

e tr

eatm

ent/

coat

ing/

fin

al c

lean

ing

Labo

rato

ry

Surf

ace

trea

tmen

t

Surf

ace

coat

ing/

proc

essi

ng e

quip

men

t

Fina

l cle

anin

g

CEA‐S

acla

y (F

ranc

e)

‐hor

izon

tal E

P fo

r sm

all N

b ca

vitie

s an

d ve

rtic

al E

P fo

r al

l cav

ities

‐2

fully

aut

omat

ed B

CP s

tatio

ns a

nd 2

CP

stat

ions

for

cavi

ties

‐sev

eral

US

degr

easi

ng ta

nks

(larg

est =

250

l)

‐mag

netr

on s

putt

erin

g ap

para

tus

for N

b de

posi

tion

on s

mal

l cav

ities

‐H

PWR

100

bar,

18

MO

hmcm

(in

clea

n ro

om)

CERN

(S

wit

zerl

and)

‐C

u‐CP

LEP

‐LH

C ca

vity

siz

e

‐Cu‐

EP 1

.3‐1

.5 G

Hz

cavi

ties

‐ver

tical

Nb

EP 7

04 M

Hz

5‐ce

ll ca

vitie

s ‐U

S de

grea

sing

16x

0.6

m2

‐US

degr

easi

ng 7

x2 m

2

‐Nb

coat

ing

for 1

.3÷1

.5 G

Hz

cavi

ties

‐Nb

coat

ing

for L

HC

cavi

ties

(400

MH

z m

ono‐

cell)

‐N

b co

atin

g fo

r HIE‐IS

OLD

E ca

vitie

s (1

01 M

Hz

QW

R)

‐HPW

R 10

0 ba

r 18

MO

hmcm

‐U

PWR

6 ba

r 18

MO

hmcm

Cock

crof

t In

stit

ute

(UK)

‐H

PWR

100

bar,

18

MO

hmcm

in IS

O4

clea

n ro

om fo

r si

ngle

and

mul

ti‐ce

ll ca

vitie

s D

ESY

(Ger

man

y)

‐clo

sed‐

circ

uit N

b‐CP

in IS

O7

clea

n ro

om

‐clo

sed‐

circ

uit N

b‐EP

‐H

PR 1

00 b

ar in

ISO

4 cl

ean

room

‐H

PR 2

00 b

ar in

ISO

4 cl

ean

room

‐b

akin

g TE

SLA

cav

ities

@ 1

20 °C

in in

ert g

as

atm

osph

ere

‐bak

ing

TESL

A c

aviti

es @

120

°C in

iner

t gas

at

mos

pher

e an

d IS

O5

clea

n ro

om

‐UPW

R an

d U

S cl

eani

ng in

sta

ndar

d IS

O6

& lo

cal I

SO4

clea

n ro

oms

‐cen

trifu

gal b

arre

l pol

ishi

ng

‐H

PWR:

100

bar

, 18

MO

hmcm

in IS

O5

clea

n ro

om fo

r 9‐

cell

cavi

ty

‐150

bar

18

MO

hmcm

, 3‐c

ell c

avity

‐h

oriz

onta

l dry‐ic

e cl

eani

ng o

f 3‐c

ell

INFN

Leg

naro

(I

taly

) ‐C

P, E

P, tu

mbl

ing

& g

rind

ing,

all

for

QW

R an

d fo

r m

ono‐

cells

and

thre

e ce

lls 1

.3/1

.5 G

Hz

cavi

ties

‐thi

n fil

ms

synt

hesi

s by

mea

ns o

f RF

and

puls

ed D

C m

agne

tron

spu

tter

ing

‐ion

impl

ante

r (ne

w h

eavy

ion

acce

lera

tor

with

ene

rgie

s up

to 2

00 k

eV)

‐HPW

R: 1

00 b

ar, 1

8 M

Ohm

cm

IPN‐O

rsay

(F

ranc

e)

‐bak

ing

(120

°C) i

n IS

O4

clea

n ro

om

‐US

degr

easi

ng ta

nk

‐BCP

faci

lity

(2 s

tatio

ns)

‐H

PWR

(100

bar

) in

ISO

4 cl

ean

room

38

Tab

le 4

: War

m t

est

pla

ces

- hig

h p

ower

cou

ple

r La

bora

tory

Te

st p

lace

s

RF

Uti

litie

s CE

A‐S

acla

y (F

ranc

e)

‐SU

PRA

TECH

: pow

er c

oupl

er te

sts

for

sc c

aviti

es

‐sta

nd fo

r te

st o

f 352

MH

z co

uple

rs a

nd w

indo

ws

at h

igh

pow

er

‐704

MH

z 1.

2 M

W 5

0Hz

2ms

klys

tron

‐7

04 M

Hz

80 k

W c

w IO

T ‐1

300

MH

z 1.

5 M

W 1

0Hz

1ms

klys

tron

‐2

x 3

52 M

Hz

CW k

lyst

rons

on

loan

from

CE

RN

‐cle

an p

umpi

ng s

yste

m, w

ater

coo

ling

and

air

cool

ing

of c

oupl

ers

CERN

(S

wit

zerl

and)

‐ SPL

pow

er c

oupl

ers:

704

MH

z ~1

MW

50

Hz

(SM

18)

‐LH

C:40

0MH

z, 3

30kW

CW

‐f

or e

xter

nal r

eque

sts:

352

MH

z 1

MW

DES

Y (G

erm

any)

‐p

ower

cou

pler

test

s ‐5

MW

Kly

stro

n, 1

.3G

Hz,

pul

sed

‐1.7

MW

, 500

MH

z, C

W

TiN

coa

ting

INFN

Leg

naro

(I

taly

)

IPN‐O

rsay

(F

ranc

e)

39

Tab

le 5

: Col

d t

est

pla

ces

- low

pow

er

Labo

rato

ry

Test

pla

ces/

cryo

stat

s

RF

Cryo

‐inst

alla

tion

CE

A‐S

acla

y (F

ranc

e)

‐ver

tical

test

cry

osta

t CV1

, use

ful d

epth

/dia

met

er 1

.9 m

/0.7

m

‐ver

tical

test

cry

osta

t CV2

, use

ful d

epth

/dia

met

er 1

.2 m

/0.5

m

‐700

MH

z –

1.5

GH

z, 2

00 W

cw

‐4

.2 –

8.6

GH

z, 8

0 W

cw

‐7

00 M

Hz

800

W c

w

‐88

MH

z 20

0 W

cw

‐ tem

pera

ture

ope

ratio

n of

CV1

and

CV2

fr

om 4

.4K

to 1

.6K

‐2 p

umpi

ng u

nits

1 g

/s @

13

mba

r

CERN

(Sw

itze

rlan

d)

‐14m

bun

ker

for

hori

zont

al te

sts

4.5

K (2

K)

‐14m

bun

ker

for

hori

zont

al te

sts

4.5

K ‐v

ertic

al te

st c

ryos

tat

4.2

m d

eep/

1.1m

dia

met

er 2

K

‐ver

tical

test

cry

osta

t 2.

5 m

dee

p/1.

1m d

iam

eter

2 K

‐v

ertic

al te

st c

ryos

tat

4.2

m d

eep/

1.1m

dia

met

er 4

.2 K

‐v

ertic

al te

st c

ryos

tat

4.2

m d

eep/

1.1m

dia

met

er 4

.2 K

‐s

mal

l ver

tical

test

cry

osta

t 4.2‐1

.8 K

mon

o‐ce

ll 1.

5 G

Hz

cavi

ties

‐300

W C

W 3

40 –

355

MH

z ‐3

00 W

CW

390

– 4

10 M

Hz

‐300

W C

W 7

00 M

Hz

‐500

W C

W 2

00 W

120

0 M

Hz

‐600

W C

W 1

00 M

Hz

‐101

W C

W 1

‐2 G

Hz

‐6 k

W @

4.5

K, l

ique

fact

ion

capa

city

of 2

6 g/

s ‐h

eliu

m p

umpi

ng u

nits

of 1

8 g/

s at

3 k

Pa (3

0 m

bar)

Cock

crof

t Ins

titu

te

(UK)

‐v

ertic

al te

st c

ryos

tat

3.5

m d

eep/

0.8m

dia

met

er 4

.2 a

nd 2

K

‐2

50W

CW

1.3

GH

z ‐5

00W

CW

1.3

GH

z ‐2

0kW

CW

1.3

GH

z

‐4.2

K a

nd 2

50 m

3 /h r

oots

pum

ping

sta

tion

for

1.5

K

DES

Y (G

erm

any)

‐2

ver

tical

test

cry

osta

t, d

iam

eter

0.6

m

‐2 v

ertic

al te

st c

ryos

tat (

AM

TF, X

FEL)

, dia

met

er 1

.1m

‐2

x 10

00 W

cw

1.3

GH

z ‐2

x 10

00 W

cw

1.3

GH

z ‐2

00W

, 2K

per c

ryos

tat

‐400

W, 2

K pe

r cry

osta

t (A

MTF

, XFE

L)

INFN

Leg

naro

(I

taly

) ‐s

tand

for

6 G

Hz

cavi

ty te

st

‐ver

tical

cry

osta

t for

1.5

/1.3

GH

z m

ono‐

cell

and

mul

ti‐ce

ll ca

vitie

s ‐1

.3/1

.5 G

Hz,

500

W C

W

‐6 G

Hz

200W

CW

‐4

.2 K

and

200

00 m

3 /h r

oots

pum

ping

st

atio

n fo

r 1.8

K

IPN‐O

rsay

(Fra

nce)

‐v

ertic

al c

ryos

tat 2

.5 m

dee

p 0.

8 m

dia

met

er w

ith m

icro

phon

ics

and

acce

lero

met

er te

sts

for b

are

and

jack

eted

cav

ities

‐v

ertic

al c

ryos

tat 2

m d

eep,

0.3

5 m

dia

met

er

‐tw

o ho

rizo

ntal

cry

osta

ts: o

ne fo

r 35

2 M

Hz

and

one

704

MH

z ca

vitie

s

‐250

W @

3 to

6 G

Hz

‐3 k

W @

704

MH

z ‐2

50 W

and

600

W @

350

MH

z ‐2

x1 k

W @

88

MH

z

‐liqu

efie

r, 7

0l/h

rat

e pr

oduc

tion

4K a

nd 2

K op

erat

ing

tem

pera

ture

40

Tab

le 6

: Col

d t

est

pla

ces

- hig

h p

ower

La

bora

tory

Te

st p

lace

s/cr

yost

ats

RF

Cr

yo‐in

stal

lati

on

CEA‐S

acla

y (F

ranc

e)

‐“Cr

yhol

ab”

faci

lity,

hor

izon

tal c

ryos

tat f

or h

igh

pow

er R

F te

sts

at 1

.3

GH

z/70

4 M

Hz

at 1

/8 K

‐ 4.

5 K,

sim

ilar

as o

pera

ted

in a

ccel

erat

or (1

.5

m lo

ng, 0

.7 m

dia

.) ‐p

ower

test

sta

nd fo

r 88

MH

z SP

IRA

L2 c

aviti

es a

nd c

ryo‐

mod

ules

‐1

5 m

bun

ker f

or te

st o

f var

ious

cry

o‐m

odul

es (I

FMIF

, ESS

, …)

‐704

MH

z 1.

2 M

W 5

0Hz

2ms

klys

tron

‐7

04 M

Hz

80 k

W c

w IO

T ‐1

300

MH

z 1.

5 M

W 1

0Hz

1ms

klys

tron

‐2

x 3

52 M

Hz

cw k

lyst

rons

on

loan

from

CER

N

‐88

MH

z 10

kW

cw

sol

id s

tate

am

plifi

er o

n lo

an

from

GA

NIL

‐140

l/h

LHeI

liqu

efie

r 4 g

/s

pum

ping

spe

ed @

13

mba

r

CERN

(S

wit

zerl

and)

‐1

4m b

unke

r fo

r ho

rizo

ntal

test

s 4.

5K 2

K ‐1

4m b

unke

r fo

r ho

rizo

ntal

test

s 4.

5K

‐1M

W c

w 3

52±1

MH

z ‐1

MW

pul

sed

700

MH

z ‐3

00kW

cw

400

±1 M

Hz

‐6 k

W @

4.5

K, l

ique

fact

ion

capa

city

of 2

6 g/

s ‐h

eliu

m p

umpi

ng u

nits

of 1

8 g/

s at

3 k

Pa

DES

Y (G

erm

any)

‐“

Chec

hia”

faci

lity

for

high

and

low

pow

er o

pera

tion

at 1

.3 G

Hz

of

fully

equ

ippe

d ca

vity

sys

tem

s at

1.8‐2

K

‐CM

TB te

st s

tand

for F

LASH

/ X

FEL

mod

ules

‐A

MTF

with

3 te

st s

tand

s fo

r XFE

L m

odul

es

‐Che

chia

: 5M

W K

lyst

ron

1.3

GH

z

‐CM

TB: 1

0MW

Kly

stro

n 1.

3 G

Hz

‐AM

TF: 3

test

sta

nds

with

5M

W K

lyst

ron

1.3G

Hz

each

‐Che

chia

: <50

W, 2

K ‐C

MTB

: 200

W, 2

K ‐ A

MTF

: 200

W, 2

K ea

ch

INFN

Leg

naro

(I

taly

)

IPN‐O

rsay

(F

ranc

e)

‐tw

o ho

rizo

ntal

cry

osta

ts: o

ne fo

r 35

2 M

Hz

and

one

704

MH

z ca

vitie

s ‐8

8 M

Hz,

2 x

10

kW (S

olid‐s

tate

) cw

‐7

04 M

Hz,

80

kW (I

OT)

cw

‐3

50 M

Hz,

10

kW (2

0 kW

) (so

lid‐s

tate

) cw

‐3

50 M

Hz,

2.8

MW

(Kly

stro

n), p

ulse

d

41

Tab

le 7

: Sam

ple

ch

arac

teri

sati

on a

nd

oth

er te

st/i

nsp

ecti

on e

qu

ipm

ent

Labo

rato

ry

RF S

ampl

e ch

arac

teri

zati

on

DC

Sam

ple

char

acte

risa

tion

O

ther

equ

ipm

ent

CEA‐S

acla

y (F

ranc

e)

‐o

ptic

al m

icro

scop

e an

d ca

mer

a ‐p

reci

sion

sca

les

‐glo

ssm

eter

‐v

ideo

‐end

osco

pe

‐RRR

mea

sure

men

ts o

f sam

ples

at 1

.6 –

300

K ‐m

echa

nica

l coe

ffic

ient

s of

sam

ples

at c

old

(4K)

Sam

ple

prep

arat

ion:

‐s

ampl

e en

caps

ulat

ion

‐mec

hani

cal,

mec

hani

cal &

che

mic

al p

olis

hing

CERN

(S

wit

zerl

and)

‐q

uadr

upol

e re

sona

tor

(400

/120

0 M

Hz

sam

ple

diam

eter

7.5

cm

abo

ve 2

K)

‐sca

nnin

g el

ectr

on m

icro

scop

e co

uple

d w

ith E

DX

com

posi

tion

anal

ysis

‐X‐r

ay d

iffra

ctom

eter

fitt

ed w

ith E

uler

ian

crad

le

‐XPS

che

mic

al s

urfa

ce a

naly

sis

and

Aug

er c

ompo

sitio

n an

alys

is

‐Tc

& R

RR m

easu

rem

ents

‐X‐r

ay fl

uore

scen

ce

DES

Y (G

erm

any)

‐RRR

‐S

EM &

ED

X ‐s

ee a

lso

insp

ectio

n/te

stin

g to

ols

(Tab

le 2

)

Acc

ess

to b

eam

faci

litie

s:

‐XFE

L in

fras

truc

ture

and

TES

LA T

est F

acili

ty

‐FLA

SH w

ith 1

GeV

e‐b

eam

IN

FN L

ASA

M

ilano

(Ita

ly)

Man

ufac

ture

and

des

ign:

‐d

evel

opm

ent a

nd d

esig

n fo

r sc

cavi

ties,

cr

yom

odul

es a

nd a

cces

sori

es

Proc

essi

ng a

nd a

ssem

bly:

‐H

PWR

stat

ions

RF

test

ing:

‐v

ertic

al c

ryos

tat f

or 5

00, 7

04 a

nd 1

300

MH

z, 4

.2 –

1.

8 K

300

m3 /h

gH

e pu

mpi

ng s

tatio

n IN

FN L

egna

ro

(Ita

ly)

‐ n

ucle

ar te

chni

ques

with

ion

beam

s (R

BS, E

RD, P

IXE,

NRA

) X‐r

ay

ener

gy a

naly

sis;

‐s

cann

ing

elec

tron

mic

rosc

opy

(SEM

) ‐m

icro‐s

crat

ch‐t

este

r ‐X‐r

ay d

iffra

ctom

etry

42

IPN‐O

rsay

(F

ranc

e)

‐TE 0

11 c

avity

for

surf

ace

resi

stan

ce m

easu

rem

ents

(3

.88

& 5

.12

GH

z) s

ampl

e on

dis

c of

125

mm

di

amet

er (1

10 m

m o

f ef

fect

ive

diam

eter

)

‐RRR

(100

mm

x 3

.5 m

m) i

n cr

yost

at w

ith 0

.15

m d

iam

eter

0.9

m

deep

‐t

herm

al c

ondu

ctiv

ity o

f iso

latin

g an

d co

nduc

ting

mat

eria

ls 4

.2 ‐

300

K ‐K

apitz

a re

sist

ance

1.7

– 2

.1 K

(0.5

mm

thic

k, <

80

mm

dia

met

er)

Acc

ess

to b

eam

faci

litie

s:

‐ ALT

O, 1

0 –

50 M

eV, 1

0 µA

e‐b

eam

‐ T

AN

DEM

Van

de

Gra

af, 1

5 M

V H‐ io

ns, a

ggre

gate

io

n be

ams

LAL‐

Ors

ay

(Fra

nce)

W

arm

test

pla

ces:

‐1

300

MH

z 5

MW

‐7

904

MH

z, b

oth

in fu

ll re

flect

ion

and

unde

r m

atch

ed c

ondi

tions

‐A

r di

scha

rge

clea

ning

43

Specific SRF related equipment available elsewhere Institution/University Equipment

Cockcroft Institute Daresbury/Universitie

s of Lancaster, Liverpool and

Manchester (UK)

Processing and assembly: ‐ISO6 7x9 m2 clean room ‐3x4m2 clean room

RF testing: ‐20 kW 1.3 GHz IOT ‐300 W 1.3 GHz

‐250 kW 500 MHz Klystron ‐6 MWpk (12 kWavg) 2998 MHz klystron (6μs pulse)

Cryogenics: ‐150W @ 1.8 K‐120W @ 4.5 K

Sample characterisation: ‐XPS/SEM

‐ultrasonic force microscopy Access to beam facilities:

‐ALICE IR‐ERL 13 �A 35 MeV e‐beam ‐EMMA NS‐FFAG 10 – 20 MeV e‐beam

Darmstadt Institut für Kernphysik (Germany)

Processing and assembly: ‐ISO5 clean room

‐chemical polishing facility ‐temperature annealing of samples and small size cavities in UHV furnace: max. sample diameter: 120 mm, max. sample length: 1400 mm, max. temperature:

1800°C, min. pressure: 10‐8 mbar, sample chamber built of reactor grade niobium RF testing:

‐bath cryostat testing area Access to beam facilities:

‐S‐DALINAC e‐recyclotron 60 �A 2.5 – 130 MeV Frankfurt University Institute of Applied

Physics

Processing and assembly: ‐ISO7 clean room

RF testing: 3 m high vertical cryostat, transport dewar, helium recovery system, 150 W cryo plant at 4K, 3000 l helium storage, 330‐370 MHz amp. 2 kW cw, 325 MHz 40 kW

pulsed, 2 ms, 5 Hz (200 W cw), 50‐1000 MHz, 50 W cw, concrete test cave 5 x 4.5 x 3.5 m3, LLRF 100‐400 MHz

HZB Berlin (Germany) RF testing: ‐power coupler tests

‐solid state amplifiers, klystron and IOT 1300 MHz 200 W‐30 kW CW ‐“HoBiCaT” test facility for high and low power simultaneous test of fully equipped

cavity systems 3.5 m long 1.1 m useful diameter‐1.8‐2.2 K@ 4 g/s 80 W‐180 l/ h 4.5 K TCF50 helium refrigeration plant at BESSYII

Access to beam facilities: ‐BESSY FEL

HZDR Dresden (Germany)

RF testing: ‐power coupler tests 1300 MHz CPI klystron 10 kW CW RF power

Access to beam facilities: ‐ELBE radiation source 40 MeV 1 mA average beam current

Wuppertal FB Physik (Germany)

Sample characterisation: ‐DC field emission scanning microscope and spectrometer

‐surface roughness measurements on Nb samples (optical profilometer, atomic force microscope)

44