IPAC2011 - List of Keywords (cryogenics)

Paper	Title	Other Keywords	Page
MOPC007	Cold Photocathode RF Gun	cavity, gun, vacuum, cathode	77
	V. Vogel, K. Flöttmann, S. Schreiber DESY, Hamburg, Germany
	Heating and thermal expansion in the normal conductivity RF-photo electron gun, are the main limitations to achieve high accelerating gradient and consequently a low emittance beam. Some pure materials show a significant increase in thermal conductivity with a small coefficient of temperature expansion at temperatures around 20 degrees Kelvin. Possible materials are Molybdenum, Iridium or Tungsten. However, machining of these materials is very difficult. Therefore we propose a simplified shape for an L-band RF gun. We expect to achieve a significant increase in gradient for similar RF powers as used in the present DESY RF-gun. On the other hand, it would also be possible to increase the duty cycle keeping a moderate gradient. In this report we discuss one possible design of an RF-gun using hard metals and present simulations on thermal properties.

MOPC091	Status of the XFEL 3.9 GHz Injector Section	cavity, cryomodule, linac, status	289
	P. Pierini, M. Bonezzi, A. Bosotti, M. Fusetti, P.M. Michelato, L. Monaco, R. Paparella, D. Sertore INFN/LASA, Segrate (MI), Italy E. Vogel DESY, Hamburg, Germany
	The European XFEL will use a superconducting third harmonic section to achieve the necessary beam quality for the FEL process. The concept has been successfully proven at the FLASH linac in DESY, with a 4 cavity superconducting module contributed by FNAL. The design of the third harmonic system at the XFEL injector is being finalized and prototypes of the components (cavities and couplers) have been fabricated and are currently in the testing stage. The paper will provide a status of the activities.

MOPC103	Cryostat for Testing HIE-ISOLDE Superconducting RF Cavities	cavity, vacuum, cryomodule, niobium	313
	O. Capatina, J.P. Brachet, G. Cuccuru, M. Pasini, T. Renaglia, M. Therasse, B. Vullierme CERN, Geneva, Switzerland
	The High Intensity and Energy ISOLDE (HIE-ISOLDE) project is a major upgrade of the existing ISOLDE and REX-ISOLDE facilities at CERN [1], with the objective of increasing the energy and the intensity of the delivered radioactive ion beams (RIB). This project aims to fill the request for a more energetic post accelerated beam by means of a new superconducting (SC) linac based on Quarter Wave Resonators (QWRs). A research and development program looking at all different aspects of the SC linac has started in 2008 and continued throughout 2010. In particular the R&D effort has focused on the development of the high β cavity (β = 10.3%), for which it has been decided to adopt the Nb sputtered on Cu substrate technology. Two prototype cavities were manufactured and are undergoing RF cold tests. The pre-series cavity fabrication is under way using 3D forged Cu billets. A single vacuum cryostat was designed and built to test these cavities at liquid helium temperatures. The paper details the main design concepts of the test cryostat as well as the results of the cryogenic behavior of the complete set-up including the cryostat, the RF cavity, the tuner and the main coupler.

MOPC111	Progress of ILC High Gradient SRF Cavity R&D at Jefferson Lab	cavity, SRF, niobium, accelerating-gradient	334
	R.L. Geng, J. Dai, G.V. Eremeev, A.D. Palczewski JLAB, Newport News, Virginia, USA
	Funding: US Department of Energy Latest progress of ILC high gradient SRF cavity R&D at Jefferson Lab will be presented. 9 out of 10 real 9-cell cavities reached an accelerating gradient of more than 38 MV/m at a unloaded quality factor of more than 8·10⁹. New understandings of quench limitation in 9-cell cavities are obtained through instrumented studies of cavities at cryogenic temperatures. Our data have shown that present limit reached in 9-cell cavities is predominantly due to localized defects, suggesting that the fundamental material limit of niobium is not yet reached in 9-cell cavities and further gradient improvement is still possible. Some examples of quench-causing defects will be given. Possible solutions to pushing toward the fundamental limit will be described.

MOPC123	Temperature Dependent Microphonics in the BNL Electron Cooler*	resonance, cavity, electron, linac	370
	P. Jain Stony Brook University, Stony Brook, USA I. Ben-Zvi, C. Schultheiss BNL, Upton, Long Island, New York, USA
	An R&D Energy Recovery Linac (ERL), to be used in the BNL electron cooler, has been operational in a developmental setting. The ERL requires a cryogenic system to supply cooling to a superconducting RF gun and the 5-cell superconducting RF cavity system that is kept cold at 2K. The 2K superfluid bath is produced by pumping on the bath using a sub-atmospheric warm compression system. During a test run in October 2010, a resonance peak corresponding to a noise of 30 Hz was observed at 1.88K. This noise peak, present at all temperatures below 2K, is assumed to be of mechanical origin from the vibration of the cryopump. Another resonance noise peak of 16 Hz, characteristic of the system, was observed at 1.98K, which shifted towards the 30 Hz peak as the temperature of the cryostat varied from 1.98K to 1.88K. The 16 Hz resonance peak upon hitting the 30 Hz resonance peak, sets a resonance condition, thereby the 30 Hz peak getting amplified by more than five times. In this paper we explore the origin of the temperature dependent 16 Hz resonance peak and give a physical explanation of the resonance.

MOPC157	Performance of LLRF System at S1-Global in KEK*	cavity, controls, diagnostics, klystron	451
	S. Michizono, D.A. Arakawa, S. Fukuda, E. Kako, H. Katagiri, T. Matsumoto, T. Miura, Y. Yano KEK, Ibaraki, Japan
	Vector-sum control was carried out at S1-Global. The rf stabilities of 0.007% in amplitude and 17 mdeg. in phase are obtained. Various diagnostics (such as on-line quench pulse detector, dynamic detuning monitor and so on) is implemented. The IF-mixture system, where 3 intermediate frequencies (IF) are used and the number of ADCs can be reduced, was used as rf waveform monitors. These monitors are used for the performance analysis. Quench phenomena observed at the high-gradient operation are also analyzed from the view point of dynamic change in loaded Q and cavity detuning during rf pulse.

TUYA02	LHC Upgrade Plans: Options and Strategy	luminosity, cavity, quadrupole, collider	908
	L. Rossi CERN, Geneva, Switzerland
	Presentation of options for future luminosity and/or energy upgrades of the LHC ring. The presentation should cover the different ideas, short term, medium term and long term, and discuss the research programme that is needed to prepare the upgrades.
	Slides TUYA02 [5.139 MB]

TUPS020	Leak Tightness of LHC Cold Vacuum Systems	vacuum, superconducting-magnet, controls, proton	1566
	P. Cruikshank, S.D. Claudet, W. Maan, L. Mourier, A. Perrier-Cornet, N. Provot CERN, Geneva, Switzerland
	The cold vacuum systems of the LHC machine have been in operation since 2008. While a number of acceptable helium leaks were known to exist prior to cooldown and have not significantly evolved over the last years, several new leaks have occurred which required immediate repair activities or mitigating solutions to permit operation of the LHC. The LHC vacuum system is described together with a summary and timetable of known air and helium leaks and their impact on the functioning of the cryogenic and vacuum systems. Where leaks have been investigated and repaired, the cause and failure mechanism is described. We elaborate the mitigating solutions that have been implemented to avoid degradation of known leaks and minimize their impact on cryogenic operation and LHC availability, and finally a recall of the consolidation program to be implemented in the next LHC shutdown.

TUPS023	Secondary Electron Yield on Cryogenic Surfaces as a Function of Physisorbed Gases	electron, vacuum, gun, insertion	1575
	A. Kuzucan, H. Neupert, M. Taborelli CERN, Geneva, Switzerland H. Stoeri IAP TUW, Wien, Austria
	Electron cloud is a serious limitation for the operation of particle accelerators with intense positively charged beams. It occurs if the secondary electron yield (SEY) of the beam-pipe surface is sufficiently high to induce an electron multiplication. At low surface temperatures, the SEY is strongly influenced by the nature of the physisorbed gases and by the corresponding surface coverage. These conditions occur in many accelerators operating with superconducting magnets and cold vacuum sections such as the LHC and RHIC. In this work, we investigated the variation of the SEY of copper, aluminium and electro-polished copper as a function of physisorbed N2, CO, CO2, CH4, Kr, C2H6 at cryogenic temperatures. The conditioning by electron bombardment of the surface after the physisorption of H2O on electro polished copper will also be presented. The results of the various gases are compared in order to find a rationale for the behaviour of the secondary electrons for the various adsorbates.

TUPS027	Characterization of Carbon Coatings with Low Secondary Electron Yield	electron, vacuum, ion, gun	1587
	C. Yin Vallgren, S. Calatroni, P. Costa Pinto, A. Kuzucan, H. Neupert, M. Taborelli CERN, Geneva, Switzerland
	Amorphous carbon (a-C) coatings can reliably be produced with a maximum secondary electron yield (SEY) close to 1 at room temperature. Measurements at low temperature (LHe) are in progress. Analysis by X-ray Photoemission Spectroscopy (XPS) shows a correlation between the lineshape of C1s spectrum in XPS and maximum SEY of the investigated samples. The initial level of oxygen on the surface of the various samples does not seem to be related to the initial maximum SEY value. However, the increase of the SEY with air exposure time on each individual sample is related to the amount of oxygen containing adsorbates. Storage in different environments has been investigated (static vacuum, aluminum foil, dry nitrogen and desiccators) and shows significant differences in the “aging” behavior. Aging is very moderate when storing samples wrapped in aluminum foil in air. Samples which have undergone aging due to inappropriate storage can be recovered nearly to the initial value of the SEY by typical surface treatments as ion bombardment, annealing under vacuum and conditioning by electron beam. However, an enhanced sensitivity to air exposures is observed for most of these curing methods.

TUPS106	Absorber Materials at Room and Cryogenic Temperatures*	HOM, cavity, damping, electron	1792
	F. Marhauser, T.S. Elliott, A.T. Wu JLAB, Newport News, Virginia, USA E.P. Chojnacki CLASSE, Ithaca, New York, USA E. Savrun Sienna Technologies Inc., Woodinville, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. We recently reported on investigations of RF absorber materials at cryogenic temperatures conducted at Jefferson Laboratory (JLab). The work was initiated to find a replacement material for the 2 Kelvin low power waveguide Higher Order Mode (HOM) absorbers employed within the original cavity cryomodules of the Continuous Electron Beam Accelerator Facility (CEBAF). This effort eventually led to suitable candidates as reported in this paper. Furthermore, though constrained by small funds for labor and resources, we have analyzed a variety of lossy ceramic materials, several of which could be usable as HOM absorbers for both normal conducting and superconducting RF structures, e.g. as loads in cavity waveguides and beam tubes either at room or cryogenic temperatures and, depending on cooling measures, low to high operational power levels.

WEPO036	Design of a Cryogenic Regulation Valve Box for SRF Operation at TPS	SRF, cavity, feedback, coupling	2475
	M.H. Chang, L.-H. Chang, L.J. Chen, F.-T. Chung, F. Z. Hsiao, M.-C. Lin, Y.-H. Lin, C.H. Lo, H.H. Tsai, Ch. Wang, T.-T. Yang, M.-S. Yeh, T.-C. Yu NSRRC, Hsinchu, Taiwan L.L. Han, M.H. Tsai NTUT, Taiwan
	A 3-GeV light source named Taiwan Photon Source (TPS) at National Synchrotron Radiation Research Center (NSRRC) is under construction, and is scheduled for commissioning in 2013/2014. An SRF module of KEKB type has been selected for the TPS as the accelerating cavity of its storage ring. The SRF valve boxes, as part of the cryogenic transfer system, stabilize the cryogenic operational conditions required for various needs of SRF operation. The SRF operation requires a large dynamic variation in the cryogenic loading that challenges appropriate sizing of the cryogenic regulation valves to minimize the pressure drop and concurrently to maintain a fine regulation of pressure. Here, we report our design considerations for an SRF valve box with emphasis on highly stabilizing the helium pressure for SRF operation with a dual-return valve scheme. The estimated fluctuations of pressure due to finite accuracy of the valve opening decrease to a tenth of what is obtained from the conventional single return-valve scheme.

WEPS094	Dynamic Vacuum Stability in SIS100	ion, vacuum, extraction, beam-losses	2724
	P. Puppel, U. Ratzinger IAP, Frankfurt am Main, Germany P.J. Spiller GSI, Darmstadt, Germany
	SIS100 is the main synchrotron of the FAIR project. It is designed to accelerate high intensity intermediate charge state uranium beams from 200 MeV/u up to 2.7 GeV/u. Intermediate charge state heavy ions are exposed to a high probability of charge exchange due to collisions with residual gas molecules. Since the charge exchange process changes the magnetic rigidity, the involved ions are lost behind dispersive elements, and an energy-dependent gas desorption takes place. The StrahlSim code has been used to predict the stability of the residual gas pressure in SIS100 under beam loss driven dynamic conditions. The results show, that a stable operation at highest U²⁸⁺ intensities is possible, under the constraint that the vacuum chambers of the ion catcher system are cold enough to pump hydrogen. Furthermore, in order to determine the load to the cryogenic system, the average beam energy deposition onto the ion catcher system has been calculated.

THPC080	Making Engineering Data Available at the European XFEL	cavity, survey, LLRF, photon	3077
	L. Hagge, J. Bürger, J.A. Dammann, S. Eucker, A. Herz, J. Kreutzkamp, S. Panto, S. Sühl, D. Szepielak, N. Welle DESY, Hamburg, Germany
	One of the essential success factors for the European XFEL is up-to-date, complete and consistent engineering data which is readily accessible throughout the project. Such data include for example civil construction drawings of tunnels and buildings; integrated 3D models of accelerator sections; definitions of fabrication processes and test procedures; inspection sheets, test data, standards, contracts and other technical documentation. The data is kept in the DESY Engineering Data Management System (EDMS). The DESY EDMS is the central information platform for the European XFEL and provides procedures for e.g. review & approvals and change management. The poster presents an overview of Engineering Data Management and its benefits at the European XFEL.

THPC149	Development of PrFeB Cryogenic Undulator (CPMU) at SOLEIL	undulator, vacuum, permanent-magnet, storage-ring	3233
	C. Benabderrahmane, P. Berteaud, N. Béchu, L. Chapuis, M.-E. Couprie, J.P. Daguerre, J.-M. Filhol, C. Herbeaux, A. Lestrade, M. Louvet, J.L. Marlats, K. Tavakoli, M. Valléau, D. Zerbib SOLEIL, Gif-sur-Yvette, France
	A R&D programme for the construction of a 2 m long 18 mm period CPMU is under progress at SOLEIL. The cryogenic undulator will provide photons in the region of 1.4 to 30 keV. It will be installed in the next few months on the long straight section (SDL13) of the storage ring, and could be used later on to produce photons for the NANOSCOPIUM beamline. The use of PrFeB which features a 1.35 T remanence (Br) at room temperature enables to increase the peak magnetic field at 5.5 mm minimum gap, from 1.04 T at room temperature to 1.15 T at a cryogenic temperature of 77 K. Praseodymium was chosen instead of Neodymium magnetic material, because it is more resistant against the appearance of the Spin Reorientation Transition. Different corrections were performed first at room temperature to adjust the phase error, the electron trajectory and to reduce the multipolar components. The mounting inside the vacuum chamber enables the fitting of a dedicated magnetic measurement bench to check the magnetic performance of the undulator at low temperature. The results of the magnetic measurements at low temperature and the comparison with the measurement at room temperature are reported.

THPC155	Modification of the BESSY II Optic for the Implementation of a Small Gap Undulator	undulator, optics, quadrupole, sextupole	3251
	J. Bahrdt, K.B. Bürkmann-Gehrlein, V. Dürr, W. Frentrup, A. Gaupp, A. Jankowiak, P. Kuske, J. Rahn, M. Scheer, P.O. Schmid, G. Wüstefeld HZB, Berlin, Germany
	At BESSY there is an increasing demand for photons in the range from 60 eV to 8 keV available at the same experimental station. The photons will be produced by a combination of two adjacent undulators, one of them will be a small period cryogenic undulator. Several optics schemes for the 1.7 GeV BESSY II storage ring are discussed to install the undulators. Two types of straight sections exist. A high beta straight with betax_min=15 m and betay_min=4.5 m and a low beta straight with betax_min=betay_min=1 m. We discuss the present plan, which clearly favours a small detuning of an existing low beta straight to shift the low beta waist to the centre of the low gap undulator, with only minor impact to the machine.

THPC178	Superconducting Planar Undulator Development in the UK	undulator, cryomodule, vacuum, radiation	3320
	J.A. Clarke, D.J. Scott, B.J.A. Shepherd STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom V. Bayliss, T.W. Bradshaw, A.J. Brummitt, G.W. Burton, M.J.D. Courthold, M.J. Hills, S.R. Watson, M.L. Woodward STFC/RAL, Chilton, Didcot, Oxon, United Kingdom
	Superconducting undulators promise higher peak fields on axis than any other technology but they are still not a mainstream solution for 3rd or 4th generation light sources. A team within the UK is developing the design of a short period, narrow aperture, superconducting undulator that is planned to be installed and tested in the Diamond Light Source (DLS) in 2014. This paper will describe the main parameters of the undulator and the key design choices that have been made. Recent progress is then described in the areas of magnet modelling, mechanical design, cryogenic design, and prototyping. Finally, the next steps are described.

Paper

Title

Other Keywords

Page

MOPC007

Cold Photocathode RF Gun

cavity, gun, vacuum, cathode

77

V. Vogel, K. Flöttmann, S. Schreiber
DESY, Hamburg, Germany

Heating and thermal expansion in the normal conductivity RF-photo electron gun, are the main limitations to achieve high accelerating gradient and consequently a low emittance beam. Some pure materials show a significant increase in thermal conductivity with a small coefficient of temperature expansion at temperatures around 20 degrees Kelvin. Possible materials are Molybdenum, Iridium or Tungsten. However, machining of these materials is very difficult. Therefore we propose a simplified shape for an L-band RF gun. We expect to achieve a significant increase in gradient for similar RF powers as used in the present DESY RF-gun. On the other hand, it would also be possible to increase the duty cycle keeping a moderate gradient. In this report we discuss one possible design of an RF-gun using hard metals and present simulations on thermal properties.

MOPC091

Status of the XFEL 3.9 GHz Injector Section

cavity, cryomodule, linac, status

289

P. Pierini, M. Bonezzi, A. Bosotti, M. Fusetti, P.M. Michelato, L. Monaco, R. Paparella, D. Sertore
INFN/LASA, Segrate (MI), Italy
E. Vogel
DESY, Hamburg, Germany

The European XFEL will use a superconducting third harmonic section to achieve the necessary beam quality for the FEL process. The concept has been successfully proven at the FLASH linac in DESY, with a 4 cavity superconducting module contributed by FNAL. The design of the third harmonic system at the XFEL injector is being finalized and prototypes of the components (cavities and couplers) have been fabricated and are currently in the testing stage. The paper will provide a status of the activities.

MOPC103

Cryostat for Testing HIE-ISOLDE Superconducting RF Cavities

cavity, vacuum, cryomodule, niobium

313

O. Capatina, J.P. Brachet, G. Cuccuru, M. Pasini, T. Renaglia, M. Therasse, B. Vullierme
CERN, Geneva, Switzerland

The High Intensity and Energy ISOLDE (HIE-ISOLDE) project is a major upgrade of the existing ISOLDE and REX-ISOLDE facilities at CERN [1], with the objective of increasing the energy and the intensity of the delivered radioactive ion beams (RIB). This project aims to fill the request for a more energetic post accelerated beam by means of a new superconducting (SC) linac based on Quarter Wave Resonators (QWRs). A research and development program looking at all different aspects of the SC linac has started in 2008 and continued throughout 2010. In particular the R&D effort has focused on the development of the high β cavity (β = 10.3%), for which it has been decided to adopt the Nb sputtered on Cu substrate technology. Two prototype cavities were manufactured and are undergoing RF cold tests. The pre-series cavity fabrication is under way using 3D forged Cu billets. A single vacuum cryostat was designed and built to test these cavities at liquid helium temperatures. The paper details the main design concepts of the test cryostat as well as the results of the cryogenic behavior of the complete set-up including the cryostat, the RF cavity, the tuner and the main coupler.

MOPC111

Progress of ILC High Gradient SRF Cavity R&D at Jefferson Lab

cavity, SRF, niobium, accelerating-gradient

334

R.L. Geng, J. Dai, G.V. Eremeev, A.D. Palczewski
JLAB, Newport News, Virginia, USA

Funding: US Department of Energy
Latest progress of ILC high gradient SRF cavity R&D at Jefferson Lab will be presented. 9 out of 10 real 9-cell cavities reached an accelerating gradient of more than 38 MV/m at a unloaded quality factor of more than 8·10⁹. New understandings of quench limitation in 9-cell cavities are obtained through instrumented studies of cavities at cryogenic temperatures. Our data have shown that present limit reached in 9-cell cavities is predominantly due to localized defects, suggesting that the fundamental material limit of niobium is not yet reached in 9-cell cavities and further gradient improvement is still possible. Some examples of quench-causing defects will be given. Possible solutions to pushing toward the fundamental limit will be described.

MOPC123

Temperature Dependent Microphonics in the BNL Electron Cooler*

resonance, cavity, electron, linac

370

P. Jain
Stony Brook University, Stony Brook, USA
I. Ben-Zvi, C. Schultheiss
BNL, Upton, Long Island, New York, USA

An R&D Energy Recovery Linac (ERL), to be used in the BNL electron cooler, has been operational in a developmental setting. The ERL requires a cryogenic system to supply cooling to a superconducting RF gun and the 5-cell superconducting RF cavity system that is kept cold at 2K. The 2K superfluid bath is produced by pumping on the bath using a sub-atmospheric warm compression system. During a test run in October 2010, a resonance peak corresponding to a noise of 30 Hz was observed at 1.88K. This noise peak, present at all temperatures below 2K, is assumed to be of mechanical origin from the vibration of the cryopump. Another resonance noise peak of 16 Hz, characteristic of the system, was observed at 1.98K, which shifted towards the 30 Hz peak as the temperature of the cryostat varied from 1.98K to 1.88K. The 16 Hz resonance peak upon hitting the 30 Hz resonance peak, sets a resonance condition, thereby the 30 Hz peak getting amplified by more than five times. In this paper we explore the origin of the temperature dependent 16 Hz resonance peak and give a physical explanation of the resonance.

MOPC157

Performance of LLRF System at S1-Global in KEK*

cavity, controls, diagnostics, klystron

451

S. Michizono, D.A. Arakawa, S. Fukuda, E. Kako, H. Katagiri, T. Matsumoto, T. Miura, Y. Yano
KEK, Ibaraki, Japan

Vector-sum control was carried out at S1-Global. The rf stabilities of 0.007% in amplitude and 17 mdeg. in phase are obtained. Various diagnostics (such as on-line quench pulse detector, dynamic detuning monitor and so on) is implemented. The IF-mixture system, where 3 intermediate frequencies (IF) are used and the number of ADCs can be reduced, was used as rf waveform monitors. These monitors are used for the performance analysis. Quench phenomena observed at the high-gradient operation are also analyzed from the view point of dynamic change in loaded Q and cavity detuning during rf pulse.

TUYA02

LHC Upgrade Plans: Options and Strategy

luminosity, cavity, quadrupole, collider

908

L. Rossi
CERN, Geneva, Switzerland

Presentation of options for future luminosity and/or energy upgrades of the LHC ring. The presentation should cover the different ideas, short term, medium term and long term, and discuss the research programme that is needed to prepare the upgrades.

Slides TUYA02 [5.139 MB]

TUPS020

Leak Tightness of LHC Cold Vacuum Systems

vacuum, superconducting-magnet, controls, proton

1566

P. Cruikshank, S.D. Claudet, W. Maan, L. Mourier, A. Perrier-Cornet, N. Provot
CERN, Geneva, Switzerland

The cold vacuum systems of the LHC machine have been in operation since 2008. While a number of acceptable helium leaks were known to exist prior to cooldown and have not significantly evolved over the last years, several new leaks have occurred which required immediate repair activities or mitigating solutions to permit operation of the LHC. The LHC vacuum system is described together with a summary and timetable of known air and helium leaks and their impact on the functioning of the cryogenic and vacuum systems. Where leaks have been investigated and repaired, the cause and failure mechanism is described. We elaborate the mitigating solutions that have been implemented to avoid degradation of known leaks and minimize their impact on cryogenic operation and LHC availability, and finally a recall of the consolidation program to be implemented in the next LHC shutdown.

TUPS023

Secondary Electron Yield on Cryogenic Surfaces as a Function of Physisorbed Gases

electron, vacuum, gun, insertion

1575

A. Kuzucan, H. Neupert, M. Taborelli
CERN, Geneva, Switzerland
H. Stoeri
IAP TUW, Wien, Austria

Electron cloud is a serious limitation for the operation of particle accelerators with intense positively charged beams. It occurs if the secondary electron yield (SEY) of the beam-pipe surface is sufficiently high to induce an electron multiplication. At low surface temperatures, the SEY is strongly influenced by the nature of the physisorbed gases and by the corresponding surface coverage. These conditions occur in many accelerators operating with superconducting magnets and cold vacuum sections such as the LHC and RHIC. In this work, we investigated the variation of the SEY of copper, aluminium and electro-polished copper as a function of physisorbed N2, CO, CO2, CH4, Kr, C2H6 at cryogenic temperatures. The conditioning by electron bombardment of the surface after the physisorption of H2O on electro polished copper will also be presented. The results of the various gases are compared in order to find a rationale for the behaviour of the secondary electrons for the various adsorbates.

TUPS027

Characterization of Carbon Coatings with Low Secondary Electron Yield

electron, vacuum, ion, gun

1587

C. Yin Vallgren, S. Calatroni, P. Costa Pinto, A. Kuzucan, H. Neupert, M. Taborelli
CERN, Geneva, Switzerland

Amorphous carbon (a-C) coatings can reliably be produced with a maximum secondary electron yield (SEY) close to 1 at room temperature. Measurements at low temperature (LHe) are in progress. Analysis by X-ray Photoemission Spectroscopy (XPS) shows a correlation between the lineshape of C1s spectrum in XPS and maximum SEY of the investigated samples. The initial level of oxygen on the surface of the various samples does not seem to be related to the initial maximum SEY value. However, the increase of the SEY with air exposure time on each individual sample is related to the amount of oxygen containing adsorbates. Storage in different environments has been investigated (static vacuum, aluminum foil, dry nitrogen and desiccators) and shows significant differences in the “aging” behavior. Aging is very moderate when storing samples wrapped in aluminum foil in air. Samples which have undergone aging due to inappropriate storage can be recovered nearly to the initial value of the SEY by typical surface treatments as ion bombardment, annealing under vacuum and conditioning by electron beam. However, an enhanced sensitivity to air exposures is observed for most of these curing methods.

TUPS106

Absorber Materials at Room and Cryogenic Temperatures*

HOM, cavity, damping, electron

1792

F. Marhauser, T.S. Elliott, A.T. Wu
JLAB, Newport News, Virginia, USA
E.P. Chojnacki
CLASSE, Ithaca, New York, USA
E. Savrun
Sienna Technologies Inc., Woodinville, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
We recently reported on investigations of RF absorber materials at cryogenic temperatures conducted at Jefferson Laboratory (JLab). The work was initiated to find a replacement material for the 2 Kelvin low power waveguide Higher Order Mode (HOM) absorbers employed within the original cavity cryomodules of the Continuous Electron Beam Accelerator Facility (CEBAF). This effort eventually led to suitable candidates as reported in this paper. Furthermore, though constrained by small funds for labor and resources, we have analyzed a variety of lossy ceramic materials, several of which could be usable as HOM absorbers for both normal conducting and superconducting RF structures, e.g. as loads in cavity waveguides and beam tubes either at room or cryogenic temperatures and, depending on cooling measures, low to high operational power levels.

WEPO036

Design of a Cryogenic Regulation Valve Box for SRF Operation at TPS

SRF, cavity, feedback, coupling

2475

M.H. Chang, L.-H. Chang, L.J. Chen, F.-T. Chung, F. Z. Hsiao, M.-C. Lin, Y.-H. Lin, C.H. Lo, H.H. Tsai, Ch. Wang, T.-T. Yang, M.-S. Yeh, T.-C. Yu
NSRRC, Hsinchu, Taiwan
L.L. Han, M.H. Tsai
NTUT, Taiwan

A 3-GeV light source named Taiwan Photon Source (TPS) at National Synchrotron Radiation Research Center (NSRRC) is under construction, and is scheduled for commissioning in 2013/2014. An SRF module of KEKB type has been selected for the TPS as the accelerating cavity of its storage ring. The SRF valve boxes, as part of the cryogenic transfer system, stabilize the cryogenic operational conditions required for various needs of SRF operation. The SRF operation requires a large dynamic variation in the cryogenic loading that challenges appropriate sizing of the cryogenic regulation valves to minimize the pressure drop and concurrently to maintain a fine regulation of pressure. Here, we report our design considerations for an SRF valve box with emphasis on highly stabilizing the helium pressure for SRF operation with a dual-return valve scheme. The estimated fluctuations of pressure due to finite accuracy of the valve opening decrease to a tenth of what is obtained from the conventional single return-valve scheme.

WEPS094

Dynamic Vacuum Stability in SIS100

ion, vacuum, extraction, beam-losses

2724

P. Puppel, U. Ratzinger
IAP, Frankfurt am Main, Germany
P.J. Spiller
GSI, Darmstadt, Germany

SIS100 is the main synchrotron of the FAIR project. It is designed to accelerate high intensity intermediate charge state uranium beams from 200 MeV/u up to 2.7 GeV/u. Intermediate charge state heavy ions are exposed to a high probability of charge exchange due to collisions with residual gas molecules. Since the charge exchange process changes the magnetic rigidity, the involved ions are lost behind dispersive elements, and an energy-dependent gas desorption takes place. The StrahlSim code has been used to predict the stability of the residual gas pressure in SIS100 under beam loss driven dynamic conditions. The results show, that a stable operation at highest U²⁸⁺ intensities is possible, under the constraint that the vacuum chambers of the ion catcher system are cold enough to pump hydrogen. Furthermore, in order to determine the load to the cryogenic system, the average beam energy deposition onto the ion catcher system has been calculated.

THPC080

Making Engineering Data Available at the European XFEL

cavity, survey, LLRF, photon

3077

L. Hagge, J. Bürger, J.A. Dammann, S. Eucker, A. Herz, J. Kreutzkamp, S. Panto, S. Sühl, D. Szepielak, N. Welle
DESY, Hamburg, Germany

One of the essential success factors for the European XFEL is up-to-date, complete and consistent engineering data which is readily accessible throughout the project. Such data include for example civil construction drawings of tunnels and buildings; integrated 3D models of accelerator sections; definitions of fabrication processes and test procedures; inspection sheets, test data, standards, contracts and other technical documentation. The data is kept in the DESY Engineering Data Management System (EDMS). The DESY EDMS is the central information platform for the European XFEL and provides procedures for e.g. review & approvals and change management. The poster presents an overview of Engineering Data Management and its benefits at the European XFEL.

THPC149

Development of PrFeB Cryogenic Undulator (CPMU) at SOLEIL

undulator, vacuum, permanent-magnet, storage-ring

3233

C. Benabderrahmane, P. Berteaud, N. Béchu, L. Chapuis, M.-E. Couprie, J.P. Daguerre, J.-M. Filhol, C. Herbeaux, A. Lestrade, M. Louvet, J.L. Marlats, K. Tavakoli, M. Valléau, D. Zerbib
SOLEIL, Gif-sur-Yvette, France

A R&D programme for the construction of a 2 m long 18 mm period CPMU is under progress at SOLEIL. The cryogenic undulator will provide photons in the region of 1.4 to 30 keV. It will be installed in the next few months on the long straight section (SDL13) of the storage ring, and could be used later on to produce photons for the NANOSCOPIUM beamline. The use of PrFeB which features a 1.35 T remanence (Br) at room temperature enables to increase the peak magnetic field at 5.5 mm minimum gap, from 1.04 T at room temperature to 1.15 T at a cryogenic temperature of 77 K. Praseodymium was chosen instead of Neodymium magnetic material, because it is more resistant against the appearance of the Spin Reorientation Transition. Different corrections were performed first at room temperature to adjust the phase error, the electron trajectory and to reduce the multipolar components. The mounting inside the vacuum chamber enables the fitting of a dedicated magnetic measurement bench to check the magnetic performance of the undulator at low temperature. The results of the magnetic measurements at low temperature and the comparison with the measurement at room temperature are reported.

THPC155

Modification of the BESSY II Optic for the Implementation of a Small Gap Undulator

undulator, optics, quadrupole, sextupole

3251

J. Bahrdt, K.B. Bürkmann-Gehrlein, V. Dürr, W. Frentrup, A. Gaupp, A. Jankowiak, P. Kuske, J. Rahn, M. Scheer, P.O. Schmid, G. Wüstefeld
HZB, Berlin, Germany

At BESSY there is an increasing demand for photons in the range from 60 eV to 8 keV available at the same experimental station. The photons will be produced by a combination of two adjacent undulators, one of them will be a small period cryogenic undulator. Several optics schemes for the 1.7 GeV BESSY II storage ring are discussed to install the undulators. Two types of straight sections exist. A high beta straight with betax_min=15 m and betay_min=4.5 m and a low beta straight with betax_min=betay_min=1 m. We discuss the present plan, which clearly favours a small detuning of an existing low beta straight to shift the low beta waist to the centre of the low gap undulator, with only minor impact to the machine.

THPC178

Superconducting Planar Undulator Development in the UK

undulator, cryomodule, vacuum, radiation

3320

J.A. Clarke, D.J. Scott, B.J.A. Shepherd
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
V. Bayliss, T.W. Bradshaw, A.J. Brummitt, G.W. Burton, M.J.D. Courthold, M.J. Hills, S.R. Watson, M.L. Woodward
STFC/RAL, Chilton, Didcot, Oxon, United Kingdom

Superconducting undulators promise higher peak fields on axis than any other technology but they are still not a mainstream solution for 3rd or 4th generation light sources. A team within the UK is developing the design of a short period, narrow aperture, superconducting undulator that is planned to be installed and tested in the Diamond Light Source (DLS) in 2014. This paper will describe the main parameters of the undulator and the key design choices that have been made. Recent progress is then described in the areas of magnet modelling, mechanical design, cryogenic design, and prototyping. Finally, the next steps are described.