07 Accelerator Technology
T07 Superconducting RF

Paper	Title	Page
MOODA01	Experience with the Cornell ERL Injector SRF Cryomodule during High Beam Current Operation	35
	M. Liepe, D.L. Hartill, G.H. Hoffstaetter, S. Posen, P. Quigley, V. Veshcherevich CLASSE, Ithaca, New York, USA
	Funding: Supported by NSF award DMR-0807731 Cornell University has developed and fabricated a SCRF injector cryomodule for the acceleration of high current, low emittance CW beams. This cryomodule is based on superconducting RF technology with five 2-cell SRF cavities operated in CW mode. Strong Higher-Order-Mode (HOM) damping and high power RF input couplers support accelerating beam currents of tens of mA. The cryomodule is currently under extensive testing in the Cornell ERL injector prototype with CW beam currents exceeding 25 mA. This paper gives an overview of the experience gained during the high beam current operation of the cryomodule, with a focus on the intrinsic cavity quality factors, input coupler performance, and HOM damping.
MOODA02	S1-Global Module Tests at STF/KEK	38
	D. Kostin, K. Jensch, L. Lilje, A. Matheisen, W.-D. Möller, P. Schilling, M. Schmökel, N.J. Walker, H. Weise DESY, Hamburg, Germany C. Adolphsen, C.D. Nantista SLAC, Menlo Park, California, USA M. Akemoto, S. Fukuda, K. Hara, H. Hayano, N. Higashi, E. Kako, H. Katagiri, Y. Kojima, Y. Kondo, T. Matsumoto, H. Matsushita, S. Michizono, T. Miura, H. Nakai, H. Nakajima, K. Nakanishi, S. Noguchi, N. Ohuchi, T. Saeki, M. Satoh, T. Shidara, T. Shishido, T. Takenaka, A. Terashima, N. Toge, K. Tsuchiya, K. Watanabe, S. Yamaguchi, A. Yamamoto, Y. Yamamoto, K. Yokoya KEK, Ibaraki, Japan T.T. Arkan, S. Barbanotti, M.A. Battistoni, H. Carter, M.S. Champion, A. Hocker, R.D. Kephart, J.S. Kerby, D.V. Mitchell, T.J. Peterson, Y.M. Pischalnikov, M.C. Ross, W. Schappert, B.E. Smith Fermilab, Batavia, USA A. Bosotti, C. Pagani, R. Paparella, P. Pierini INFN/LASA, Segrate (MI), Italy
	S1-Global collaborative effort of INFN, DESY, FNAL, SLAC and KEK, recently successfully finished at KEK as a part of ILC GDE, is an important milestone for the ILC. International collaboration of three regions, Asia, North America and Europe, proved to be efficient on the construction and cold tests of the accelerating module consisting of 8 SRF cavities; 2 from FNAL, 2 from DESY and 4 from KEK. Three different cavity tuning systems were tested together with two types of high power couplers. The module was cooled down three times which enabled extensive high power tests with cavities, performance limits investigation, Lorentz force detuning tests, simultaneous multiple cavities operation and other activities such as an operation test of distributed RF scheme with low level RF feedback. The results of this S1-Global module test are presented and discussed.
	Slides MOODA02 [2.982 MB]
MOODA03	First Characterization of a Fully Superconducting RF Photoinjector Cavity	41
	A. Neumann, W. Anders, R. Barday, A. Jankowiak, T. Kamps, J. Knobloch, O. Kugeler, A.N. Matveenko, T. Quast, J. Rudolph, S.G. Schubert, J. Völker HZB, Berlin, Germany P. Kneisel JLAB, Newport News, Virginia, USA R. Nietubyc The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock, Poland J.K. Sekutowicz DESY, Hamburg, Germany J. Smedley BNL, Upton, Long Island, New York, USA V. Volkov BINP SB RAS, Novosibirsk, Russia G. Weinberg FHI, Berlin, Germany I. Will MBI, Berlin, Germany
	As a first step towards a high brightness, high average current electron source for the BERLinPro ERL a fully superconducting photo-injector was developed by HZB in collaboration with JLab, DESY and the A. Soltan Institute. This cavity-injector ensemble is made up of a 1.6-cell superconducting cavity with a superconducting lead cathode deposited on the half-cell backwall. A superconducting solenoid is used for emittance compensation. This system, including a diagnostics beamline, has been installed in the HoBiCaT facility to serve as a testbed for beam dynamics studies and to test the combination SRF cavity and superconducting solenoid. This paper summarizes the characterization of the cavity in this configuration including Q measurements, dark current tests and field-stability analyses.
	Slides MOODA03 [10.343 MB]
MOPC050	Multipacting Analysis for the Superconducting RF Cavity HOM Couplers in ESS	190
	S. Molloy ESS, Lund, Sweden R. Ainsworth Royal Holloway, University of London, Surrey, United Kingdom R.J.M.Y. Ruber Uppsala University, Uppsala, Sweden
	The European Spallation Source (ESS) linac will consist of three families superconducting RF cavities to accelerate protons to the required 5 MW for collision with the target. If it is determined that HOM damping is required to limit the effect of beam induced modes, it is quite likely that HOM couplers will be installed. Multipacting in these couplers is a concern as thermally induced detuning of the fundamental notch filter has limited the achievable gradient in other high power machines. It is therefore important to avoid potential multipacting conditions during the design phase. Presented here are simulations using the Track3P code developed at SLAC. Multipacting regions are highlighted, electron trajectories are shown, and suitability of the proposed HOM coupler design is discussed.
MOPC053	Mechanical Design and Fabrication Studies for SPL Superconducting RF Cavities	199
	S. Atieh, G. Arnau-Izquierdo, I. Aviles Santillana, O. Capatina, T. Renaglia, T. Tardy, N. Valverde Alonso, W. Weingarten CERN, Geneva, Switzerland
	CERN’s R&D programme on the Superconducting Proton Linac’s (SPL) superconducting radio frequency (SRF) elliptical cavities made from niobium sheets explores new mechanical design and consequently new fabrication methods, where several opportunities for improved optimization were identified. A stainless steel helium vessel is under design rather than a titanium helium vessel using an integrated brazed transition between Nb and the SS helium vessel. Different design and fabrication aspects were proposed and the results are discussed hereafter.
MOPC078	Operation of Superconducting Cavities in a Fast Ramping Electron Storage Ring	253
	A. Roth, W. Hillert ELSA, Bonn, Germany
	Funding: Supported by German Research Foundation through SFB/TR 16. The achievable maximum energy of a medium-sized electron accelerator is mainly limited by the accelerating voltage. Using superconducting (sc) cavities, the energy limitation can be shifted considerably. However, the operation of sc multi-cell cavities in a fast ramping storage ring causes additional problems which were investigated at the 3.5 GeV Electron Stretcher Accelerator ELSA. We studied the use of two 500 MHz sc cavities providing the necessary resonator voltage of up to 14 MV and replacing the normal conducting cavities of PETRA type. A large cavity coupling factor is required, so that using the existing 250 kW klystron, an internal beam of 50 mA can be accelerated up to 5 GeV. In addition, a fast detuning of the resonance frequency of the cavities must be implemented during beam injection and the energy ramp of 4 GeV/s. An appropriate 500 MHz structure is given by a five-cell cavity constructed for the JAERI-FEL-LINAC. Based on this geometry, HOM have been calculated from a numerical simulation. Since all monopole and a larger number of dipole HOM are well above the multibunch instabilities threshold, further studies about beam instabilities damping are essential.
MOPC079	Status of the Low Beta 0.07 Cryomodules for SPIRAL2	256
	P. Bosland, P. Carbonnier, F. Eozénou, P. Galdemard, O. Piquet CEA/DSM/IRFU, France M. Anfreville, C. Madec, L. Maurice CEA/IRFU, Gif-sur-Yvette, France P.-E. Bernaudin, R. Ferdinand GANIL, Caen, France Y. Gomez-Martinez LPSC, Grenoble Cedex, France A. Pérolat CEA, Gif-sur-Yvette, France
	The status of the low beta cryomodules for SPIRAL2, supplied by the Irfu institute of CEA Saclay, is reported in this paper. We summarise in three parts the RF tests performed on the cavities in vertical cryostat, the RF power tests of the qualifying cryomodule performed in 2010 and the RF power tests performed in 2011 on the first cryomodule of the series
MOPC080	First Considerations Concerning an Optimized Cavity Design for the Main Linac of BERLinPro	259
	B. Riemann, T. Weis DELTA, Dortmund, Germany W. Anders, J. Knobloch, A. Neumann HZB, Berlin, Germany H.-W. Glock, C. Potratz, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany F. Marhauser JLAB, Newport News, Virginia, USA
	Funding: work supported by BMBF under contracts 05K10PEA and 05K10HRC The Berlin Energy Recovery Linac Project (BERLinPro) is designed to develop and demonstrate CW linac technology and expertise required to drive next-generation Energy Recovery Linacs. Strongly HOM-damped multicell 1.3 GHz cavities are required for the main linac. The optimization of the cavities presented here is primarily based on the CEBAF 1.5 GHz 5-cell high-current cavity design, including HOM waveguide couplers. The cavity was scaled to 1.3 GHz and extended to 7 cells. Modifications to the end group design have also been studied. An effort was also made to reduce the ratio Epk/Eacc while still permitting HOMs to propagate.
MOPC081	Pulsed Mode Operation and Longitudinal Parameter Measurement of the Rossendorf SRF Gun	262
	J. Teichert, A. Arnold, H. Büttig, M. Justus, U. Lehnert, P. Michel, P. Murcek, Ch. Schneider, R. Schurig, R. Xiang HZDR, Dresden, Germany T. Kamps, J. Rudolph, M. Schenk HZB, Berlin, Germany I. Will MBI, Berlin, Germany
	Funding: The European Community-Research Infrastructure Activity under the FP7 program (EuCARD, contract number 227579) the German Federal Ministry of Education and Research grant 05 ES4BR1/8. The Rossendorf SRF gun with a 3 1/2 cell cavity has been operated since 2007. It has produced CW beam with the electron energy of 3 MeV and the average current up to 16 μA. The electron beam of the gun has successfully injected the ELBE superconducting linac since 2010. The Nb cavity has shown constant quality during the operation and for the Cs2Te photocathode life time of months could be obtained. Recently the gun started to run in the pulsed mode with higher gradient. The longitudinal parameters have been measured in this mode. The dark current arose from the high gradient is studied. The main field emission source has been found to be the half cell. Meanwhile, two modified 3+1/2 cell niobium cavities have been fabricated and tested in Jlab. In this paper the new status of the SRF gun will be presented, and the latest results of the beam experiments will be discussed.
MOPC082	Status of the 325 MHz SC CH-Cavity at IAP Frankfurt	265
	M. Busch, F.D. Dziuba, H. Podlech, U. Ratzinger IAP, Frankfurt am Main, Germany M. Amberg, K. Aulenbacher HIM, Mainz, Germany W.A. Barth, S. Mickat GSI, Darmstadt, Germany
	Funding: BMBF contract no. 06FY161I At the Institute for Applied Physics (IAP), University of Frankfurt, a s.c. 325 MHz CH-Cavity is under development for future beam tests at GSI UNILAC, Darmstadt. The cavity with 7 accelerating cells has a geometrical beta of 0.15 corresponding to 11.4 AMeV. The design gradient is 5 MV/m. The geometry of this resonator was optimized with respect to a compact design, low peak fields, surface processing, power coupling and tuning. Furthermore a new tuning system based on bellow tuners inside the resonator will control the frequency during operation. After rf tests in Frankfurt the cavity will be tested with a 10 mA, 11.4 AMeV beam delivered by the GSI UNILAC. In this paper rf simulations, multipacting analysis as well as thermal calculations will be presented.
MOPC083	Structural Mechanics of Superconducting CH Cavities	268
	M. Amberg, K. Aulenbacher HIM, Mainz, Germany W.A. Barth, S. Mickat GSI, Darmstadt, Germany M. Busch, F.D. Dziuba, H. Podlech, U. Ratzinger IAP, Frankfurt am Main, Germany
	The superconducting CH-structure (Crossbar-H-mode) is a multi-cell drift tube cavity for the low and medium energy range operated in the H21-mode, which has been developed at the Institute for Applied Physics (IAP) of Frankfurt University. With respect to different high power applications two types of superconducting CH-structures (f = 325 MHz, β = 0.16, seven cells and f = 217 MHz, β = 0.059, 15 cells) are presently under construction and accordingly under development. The structural mechanical simulation is a very important aspect of the cavity design. Furthermore, several simulations with ANSYS Workbench have been performed to predict the deformation of the cavity walls due to the cavity cool-down, pressure effects and mechanical vibrations. To readjust the fast frequency changes in consequence of the cavity shape deformation, a new concept for the dynamic frequency tuning has been investigated, including a novel type of bellow-tuner.
MOPC084	The Superconducting cw LINAC Demonstrator for GSI	271
	F.D. Dziuba, M. Busch, H. Podlech, U. Ratzinger IAP, Frankfurt am Main, Germany M. Amberg, K. Aulenbacher HIM, Mainz, Germany W.A. Barth, S. Mickat GSI, Darmstadt, Germany
	Funding: BMBF Contr. No. 06FY9089I, Helmholtz Institut Mainz At GSI a new, superconducting (sc) continuous wave (cw) LINAC is under design in cooperation with the Institute for Applied Physics (IAP) of Frankfurt University and the Helmholtz Institut Mainz (HIM). This proposed LINAC is highly requested by a broad community of future users to fulfill the requirements of nuclear chemistry, nuclear physics, and especially in the research field of Super Heavy Elements (SHE). In this context the preliminary layout of the LINAC has been carried out by IAP. The main acceleration of up to 7.3 AMeV will be provided by nine sc Crossbar-H-mode (CH) cavities operated at 217 MHz. Currently, a prototype of the cw LINAC as a demonstrator is under development. The demonstrator comprises a sc CH-cavity embedded between two sc solenoids mounted in a horizontal cryomodule. A full performance test of the demonstrator in 2013/14 by injecting and accelerating a beam from the GSI High Charge Injector (HLI) is one important milestone of the project. The status of the demonstrator is presented.
MOPC085	Quality Assessment for Industrially Produced High-Gradient Superconducting Cavities	274
	F. Schlander, S. Aderhold, E. Elsen, D. Reschke, M. Wenskat DESY, Hamburg, Germany
	Funding: This work is supported by the Commission of the European Communities under the 7th Framework Programme “Construction of New Infrastructures – Preparatory Phase”, contract number 206711. A series of some 600 superconducting 1.3 GHz cavities will start being delivered to DESY by industry in early 2012. Although a considerably smaller gradient satisfies the needs for the European XFEL the electro-polished cavities (50% of the delivery) are deemed to be suitable for gradients in excess of 35 MV/m, the performance goal of the International Linear Collider (ILC). Specifically 24 cavities will be supplied without helium tank to enable further investigations. The results may serve to improve overall performance; limitations such as field emission and thermal breakdown of superconductivity ("quench") are still under investigation. For this matter the DESY ILC group has developed tools to monitor aspects of the cavity fabrication. An automated optical mapping system (OBACHT) is being commissioned and will be complemented by software for automated cavity surface feature recognition. For cold RF tests a Second Sound setup for locating the positions of the thermal breakdown is routinely used. These diagnostic tools will give guidance on post-processing cavities for best performance. The current status of these projects will be described.
MOPC086	Description and First Experience with the RF Measurement Procedure for the European XFEL SC Cavity Production	277
	A.A. Sulimov, Th. Buettner, A. Gössel, D. Kostin, G. Kreps, W.-D. Möller, D. Reschke, J.H. Thie, K. Twarowski DESY, Hamburg, Germany
	Cavity production for the European XFEL was recently started with first Nb sheets arriving. From this stage to the accelerating module being ready for the linac installation, many critical RF measurements are necessary. During the mechanical cavity fabrication the cavity half-cells, dumb-bells and end-groups are measured and sorted. The cavity spectrum and field profiles are measured and tuned. The HOM (Higher Oder Modes) couplers filter tuning, vertical cavity RF tests, cavity checks during the string assembly and final cavity performance measurements in the module as well as the fundamental mode and HOM RF spectra measurements complete the sequence. We present the procedures of the RF measurements and discuss the first results for the XFEL prototype modules with special attention for the cavity tuning.
	Poster MOPC086 [0.515 MB]
MOPC088	Bead-pull Measurement using Phase-Shift Technique in Multi-cell Elliptical Cavity	280
	S. Ghosh, A. Mandal, S. Seth, S.S. Som DAE/VECC, Calcutta, India
	The project on the development of high-beta multi-cell elliptical shape superconducting rf linac cavity at around 704 MHz has been funded at VECC, Kolkata, India. A full-scale copper prototype cavity has been designed and fabricated. There are 5 distinct modes exist in the cavity and the accelerating mode is pi-mode in which each cell operates at same frequency with phase difference of 180 degrees between two neighboring cells. A fully automated bead-pull measurement setup has been developed for analyzing these modes and field profile distribution at different modes in such type of linac cavity. A special measurement method inside the cavity using phase-shift technique is proposed in this paper, which describes the development of mechanical setup comprising pulleys and stepper motor–gear arrangement, PC-based control system for precise movement of bead using stepper motor, measurement using VNA, development of software for data acquisition & automation and measurement results for the 5-cell copper prototype cavity.
MOPC089	RF Simulations for the QWR Cavities of PIAVE-ALPI	283
	M. Comunian, F. Grespan, A. Palmieri INFN/LNL, Legnaro (PD), Italy
	The PIAVE-ALPI linac is composed of several families of QWR cavities. In order to have a thorough description of the accelerator in terms of beam dynamics, a detailed field mapping of the accelerating cavities is necessary, including non-linear behavior of the off-axis fields, as well as the steering and dispersion effects due to transverse components. For such a purpose, a set of RF simulation was accomplished, with the codes HFSS and COMSOL. The details about these simulations and the main outcomes and results will be described in this article.
MOPC090	Tuner Performance in the S1-global Cryomodule	286
	R. Paparella, A. Bosotti, C. Pagani INFN/LASA, Segrate (MI), Italy C. Albrecht, K. Jensch, L. Lilje DESY, Hamburg, Germany S. Barbanotti, Y.M. Pischalnikov, W. Schappert Fermilab, Batavia, USA H. Hayano, E. Kako, S. Noguchi, N. Ohuchi, Y. Yamamoto KEK, Ibaraki, Japan
	S1-Global is a collaborative effort of INFN, DESY, FNAL, SLAC and KEK, in the framework of the ILC global collaboration. For this project two cryomodules, 6 meter long and hosting four SC cavities each, were realized and successfully cold tested at KEK-STF. Three different cavity tuning systems, provided with fast tuning capability through piezoelectric actuators (piezo), were installed, and fully characterized in static and dynamic operation: Blade Tuner from INFN/FNAL, Saclay Tuner from DESY, Slide Jack Tuner from KEK. Finally, Lorenz Force Detuning (LFD) active compensation has been successfully achieved during high power cavity tests in pulsed RF regime, where active control of the LFD disturbance up to Hz-level residual detuning has been achieved with each type of tuning system up to the maximum gradient of each cavity. The installation procedures, together with the relevant results and their analyses are summarized in the paper.
MOPC091	Status of the XFEL 3.9 GHz Injector Section	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.
MOPC092	Effect of Current Densities on Sulfur Generation at Electropolished Niobium Surface	292
	P.V. Tyagi Sokendai, Ibaraki, Japan H. Hayano, S. Kato, M. Nishiwaki, T. Noguchi, T. Saeki, M. Sawabe KEK, Ibaraki, Japan
	We conducted a series of electropolishing (EP) experiments in aged EP acid with high (≈50 mA/cm2) and low (≈30 mA/cm2) current densities on Nb surfaces. The experiments were carried out both for laboratory coupons and a real Nb single cell cavity with six witness samples located at three typical positions (equator, iris and beam pipe). All the samples surface were investigated by XPS (x-ray photoelectron spectroscopy), SEM (scanning electron microscope) and EDX (energy dispersive x-ray spectroscopy). The surface analysis showed the EP with a high current density produced a huge amount sulfate particles at Nb surface whereas the EP with a low current density is very helpful to mitigate sulfate at Nb surface in both the experiments.
MOPC093	Novel Field Emission Scanner for Surface Study of Niobium SRF Cavity	295
	S. Kato, M. Nishiwaki, T. Noguchi KEK, Ibaraki, Japan V. Chouhan GUAS, Kanagawa, Japan P.V. Tyagi Sokendai, Ibaraki, Japan
	It is mandatory to investigate field emission on Nb SRF cavity systematically since strong field emission often limits the cavity performance. The field emission strength and the number of emission sites strongly depend on Nb surface properties which are determined by its surface treatment and handling. Field emission scanner (FES) developed allows us to measure a distribution of the field emitting sites over a sample surface at a given field strength along with its FE-SEM observation and energy dispersive x-ray analysis. FES consists of an anode needle driven by precise 3D stepping motors and an eucentric sample stage. The compact scanner was installed into the space between the object lens and the SEM sample holder. In addition, this system was newly equipped with a sample load-lock system for existing UHV suitcases. Therefore a sample coupon to be observed is hardly exposed to contaminants and dust particles during the transportation. In-situ heating of a sample coupon can be done during an experiment to simulate a baking process of a SRF cavity. This article describes development of the field emission scanner and its preliminary results of the application to niobium samples.
MOPC095	Superconducting Cavity R&D for ILC at MHI	298
	H. Hitomi, H. Hara, F. Inoue, K. Kanaoka, K. Sennyu, T. Yanagisawa MHI, Kobe, Japan
	We have developed and manufactured some superconducting RF cavity for STF project in KEK. In recent vertical test in KEK, the MHI-#12 cavity which is one of cavities for STF phase 2 project reached ILC specification(max Eacc was about 40MV/m). So techniques for manufacturing cavity is making steady progress in MHI. To be realized ILC project, we also try to decrease the manufacturing cost by using some new techniques, for example Laser Beam Welding, deep drawing, seamless dumbbell, etc. In this meeting, we will report recent MHI's activities for ILC.
MOPC096	Design and Fabrication of a 5-Cell High Current Superconducting Cavity	301
	Y.M. Li, K.X. Liu, S.W. Quan, F. Zhu PKU/IHIP, Beijing, People's Republic of China R. Nassiri ANL, Argonne, USA
	Funding: National High Technology Research and Development program 863 (2009AA03Z206) Energy recovery linacs (ERL) is promising to achieve high average current with superior beam quality. The key component for accelerating such high current beams is the superconducting radio frequency (SRF) cavity. The design of a 1.3 GHz 5-cell high current superconducting cavity has been carried out under the cooperation between Peking University (PKU) and Argonne National Laboratory (ANL). RF properties, damping of the HOMs, multipacting and mechanical features of this cavity have been discussed and the final design is presented.
MOPC101	Vertical Test of PEFP Prototype SRF Cavity	307
	H.S. Kim, Y.-S. Cho, H.-J. Kwon KAERI, Daejon, Republic of Korea
	Funding: This work was supported by Ministry of Education, Science and Technology of the Korean Government. The PEFP Proton linac is a 100-MeV machine which consists of a proton injector, a 3-MeVRFQ and 100-MeV DTL. For the extension of the machine beyond 100 MeV, SRF technology is under consideration. As a prototyping activity, a superconducting RF cavity with a geometrical beta of 0.42 and a resonant frequency of 700 MHz has been designed, fabricated and tested. The cavity is an elliptical shape with 5 cells stiffened by double-ring structure. A design accelerating gradient is 8.0 MV/m at the operating temperature of 4.2 K and maximum duty factor is 9%. For the vertical test of the cavity, a cryostat with a vacuum jacket and multi-layer insulation was prepared. The RF system for driving the cavity is based on PLL to track the resonant frequency. In case of lack of RF power, a two-way RF power combiner based on splitted coaxial transmission line is considered. The details of the vertical test setup and test results will be presented in this paper.
MOPC102	RF and Surface Properties of Superconducting Samples	310
	T. Junginger, W. Weingarten CERN, Geneva, Switzerland T. Junginger MPI-K, Heidelberg, Germany R. Seviour Lancaster University, Lancaster, United Kingdom C.P. Welsch Cockcroft Institute, Warrington, Cheshire, United Kingdom
	Funding: Work supported by the German Doctoral Students program of the Federal Ministry of Education and Research (BMBF) The surface resistance Rs of superconducting cavities can be obtained from the unloaded quality factor Q0. Since Rs varies strongly over the cavity surface its value must be interpreted as averaged over the whole cavity surface. A more convenient way to investigate the surface resistance of superconducting materials is therefore to examine small samples, because they can be manufactured cheaply, duplicated easily and used for further surface analyses. At CERN a compact Quadrupole Resonator has been developed for the RF characterization of superconducting samples at different frequencies. In this contribution, results from measurements on bulk niobium and niobium film on copper samples are presented. It is shown how different contributions to the surface resistance depend on temperature, applied RF magnetic field and frequency. Furthermore, measurements of the maximum RF magnetic field as a function of temperature and frequency in pulsed and CW operation are presented. The study is accompanied by measurements of the surface properties of the samples by various techniques.
MOPC103	Cryostat for Testing HIE-ISOLDE Superconducting RF Cavities	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.
MOPC104	HIE-ISOLDE SRF Development Activities at CERN	316
	M. Therasse, O. Brunner, S. Calatroni, J.K. Chambrillon, B. Delaup, M. Pasini CERN, Geneva, Switzerland
	The HIE-ISOLDE project has initiated a new development phase on the SRF domain at CERN. In particular, the HIE-ISOLDE project aims at the construction of the 32 Quarter Wave Resonators (QWRs) using the Nb on Cu sputtering technology. The paper describes the refurbishment of the test infrastructure and the activities from the cavity production to the cold test, including quality assurance procedure for the correct handling of the resonators.
MOPC105	Design of the High Beta Cryomodule for the HIE-ISOLDE Upgrade at CERN	319
	L.R. Williams, A.P. Bouzoud, N. Delruelle, J. Gayde, Y. Leclercq, M. Pasini, J.Ph. G. L. Tock, G. Vandoni CERN, Geneva, Switzerland
	The major upgrade of the energy and intensity of the radioactive ion beams of the existing ISOLDE and REX-ISOLDE facilities at CERN will, in the long term, require downstream of the existing machine, the installation of four high-β and two low-β cryo-modules. The first stage of this upgrade, involving the design, construction, installation and commissioning of two high-β cryo-modules is approved and design work is underway at CERN. The high-β cryo-module houses five high-β superconducting cavities and one superconducting solenoid. As well as providing optimum conditions for physics, where the internal active components must remain aligned within tight tolerances, the cryo-modules need to function under stringent common vacuum and cryogenic conditions. To preserve the RF cavity performance their assembly and sub-system testing will need to be carried out using specifically designed tooling in a class 100 clean-room. We present the determining factors constraining the design of the high-β cryo-module together with the design choices that these factors have imposed.
MOPC106	Study of the Variation of Transverse Voltage in the 4 Rod Crab Cavity for LHC	322
	B.D.S. Hall, P.K. Ambattu, G. Burt, C. Lingwood Cockcroft Institute, Lancaster University, Lancaster, United Kingdom P. Goudket, C. Hill STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	The planned high luminosity upgrade to LHC will utilise crab cavities to rotate the beam in order to increase the luminosity in the presence of a finite crossing angle. A compact design is required in order for the cavities to fit between opposing beam-lines. In this paper we discuss we discuss one option for the LHC crab cavity based on a 4 rod TEM deflecting cavity. Due to the large transverse size of the LHC beam the cavity is required to have a large aperture while maintaining a constant transverse voltage across the aperture. The cavity has been optimised to minimise the variation of the transverse voltage while keeping the peak surface electric and magnetic fields low for a given kick. This is achieved while fitting within the strict design space of the LHC. The variation of deflecting voltage across the aperture has been studied numerically and compared with numerical and analytical estimates of other deflecting cavity types. Performance measurements an aluminium prototype of this cavity are presented and compared to the simulated design.
MOPC107	HOM and FP Coupler Design for the NLSF High Gradient SC Cavity	325
	R.M. Jones, N. Juntong UMAN, Manchester, United Kingdom
	The design of both higher order mode (HOM) and fundamental power (FP) couplers for the New Low Surface Field (NLSF) cavity* is presented. Here we study using the ILC baseline couplers for this new superconducting cavity. A Balleyguier method** of calculating external quality factor is used and the results validated using both Microwave studio and HFSS. * N. Juntong and R.M. Jones, SRF2009, THPPO024, 2009. ** P. Balleyguier, LINAC98, MO4037, 1998
MOPC108	Cornell SRF New Materials Program*	328
	S. Posen, M. Liepe, Y. Xie CLASSE, Ithaca, New York, USA
	Funding: Work supported by NSF Career award PHY-0841213, DOE award ER41628, and the Alfred P. Sloan Foundation The SRF group at Cornell has recently pioneered an extensive program to investigate alternative materials for superconducting cavities. We have developed facilities to fabricate Nb3Sn, a superconductor which will theoretically be able to reach more than twice the maximum accelerating field of Nb in a cavity under the same operating conditions. In addition, with the critical temperature of Nb3Sn being twice that of Nb, Nb3Sn would allow operation of SRF cavities with a much higher cryogenic efficiency. We have also manufactured two TE cavities that measure the RF properties of small, flat samples, ideal for material fabrication methods in development. This paper presents an overview of the materials research program. First results from tests of Nb3Sn samples are presented.
MOPC109	Suppression of Coupler Kicks in 7-Cell Main Linac Cavities for Cornell's ERL	331
	N.R.A. Valles, M. Liepe, V.D. Shemelin CLASSE, Ithaca, New York, USA
	Funding: Supported by NSF award DMR-0807731 Cornell is developing a 5 GeV Energy Recovery Linac operating at 100 mA with very small emittances (~30 pm at 77 pC bunch charge) in the horizontal and vertical directions. We investigate the effect of the fundamental RF power couplers of the main linac SRF cavities on the beam using the ACE3P software package. The cavities in the ERL main linac will be operated at very high loaded quality factors of up to 6.5·107, corresponding to a full bandwidth of only 20 Hz. Cavity microphonics will detune the cavities by more than one bandwidth during operation, thereby causing a time dependent change of the coupler kick in addition to its fast oscillation at the RF frequency. In order to investigate the dependence of the coupler kick on the cavity frequency, we calculate the coupler kick given to the beam for the case of a detuned RF cavity. We show that a compensation stub geometry located opposite to the input coupler port can be optimized to reduce the overall kick given to the beam and the emittace growth caused by its time dependence.
MOPC111	Progress of ILC High Gradient SRF Cavity R&D at Jefferson Lab	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.
MOPC112	Fabrication and Testing Status of CEBAF 12 GeV Upgrade Cavities	337
	F. Marhauser, A. Burrill, G.K. Davis, D. Forehand, C. Grenoble, J. Hogan, R.B. Overton, A.V. Reilly, R.A. Rimmer, M. Stirbet JLAB, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The 12 GeV upgrade of the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Laboratory (JLab) is under way. All cavities have been built by industry and are presently undergoing post-processing and final low and high power qualification before cryomodule assembly. The status is reported including fabrication-related experiences, observations and issues throughout production, post-processing and qualification.
MOPC113	Results of Cavity Series Fabrication at Jefferson Laboratory for the Cryomodule “R100”	340
	F. Marhauser, W.A. Clemens, M.A. Drury, D. Forehand, J. Henry, S. Manning, R.B. Overton, R.S. Williams JLAB, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. A series production of eight superconducting RF cavities for the cryomodule R100 was conducted at JLab in 2010. The cavities underwent chemical post-processing prior to vertical high power testing and routinely exceeded the envisaged performance specifications. After cryomodule assembly, cavities were successfully high power acceptance tested. In this paper, we present the achievements paving the way for the first demonstration of 100 MV (and beyond) in a single cryomodule to be operated at CEBAF.
MOPC114	Design, Fabrication and Testing of Medium-Beta 650 MHz SRF Cavity Prototypes for Project-X	343
	F. Marhauser, W.A. Clemens, J. Henry, P. Kneisel, R. Martin, R.A. Rimmer, G. Slack, L. Turlington, R.S. Williams JLAB, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. A new type of superconducting radio frequency (SRF) cavity shape with a shallow equator dome to reduce electron impact energies for suppressing multipacting barriers has been proposed. The shape is in consideration for the first time in the framework of Project-X to design a potential multi-cell cavity candidate for the medium-beta section of the SRF proton CW linac operating at 650 MHz. Rationales covering the design of the multi-cell cavity, the manufacture, post-processing and high power testing of two single-cell prototypes are presented.
MOPC115	JLab SRF Cavity Fabrication Errors, Consequences and Lessons Learned	346
	F. Marhauser JLAB, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 Today, elliptical superconducting RF (SRF) cavities are preferably made from deep-drawn niobium sheets as pursued at Jefferson Laboratory (JLab). The fabrication of a cavity incorporates various cavity cell machining, trimming and electron beam welding (EBW) steps as well as surface chemistry that add to forming errors creating geometrical deviations of the cavity shape from its design. An analysis of in-house built cavities over the last years revealed significant errors in cavity production. Past fabrication flaws are described and lessons learned applied successfully to the most recent in-house series production of multi-cell cavities.
MOPC116	Development of Nb and Alternative Material Thin Films Tailored for SRF Applications	349
	A-M. Valente-Feliciano, H.L. Phillips, C.E. Reece, J.K. Spradlin, B. Xiao, X. Zhao JLAB, Newport News, Virginia, USA H. Baumgart, D. Gu ODU, Norfolk, Virginia, USA D. Beringer, R.A. Lukaszew The College of William and Mary, Williamsburg, USA K.I. Seo NSU, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S.DOE Contract No. DE-AC05-06OR23177. Over the years, Nb/Cu technology, despite its shortcomings due to the commonly used magnetron sputtering, has positioned itself as an alternative route for the future of superconducting structures used in accelerators. Recently, significant progress has been made in the development of energetic vacuum deposition techniques, showing promise for the production of thin films tailored for SRF applications. JLab is pursuing energetic condensation deposition via techniques such as Electron Cyclotron Resonance and High Power Impulse Magnetron Sputtering. As part of this project, the influence of the deposition energy on the material and RF properties of the Nb thin film is investigated with the characterization of their surface, structure, superconducting properties and RF response. It has been shown that the film RRR can be tuned from single digits to values greater than 400. This paper presents results on surface impedance measurements correlated with surface and material characterization for Nb films produced on various substrates, monocrystalline and polycrystalline as well as amorphous. A progress report on work on NbTiN and AlN based multilayer structures will also be presented.
MOPC117	Advance in Vertical Buffered Electropolishing on Niobium for Particle Accelerators*	352
	A.T. Wu, S. Jin, J.D. Mammosser, C.E. Reece, R.A. Rimmer JLAB, Newport News, Virginia, USA L. Lin, X.Y. Lu, K. Zhao PKU/IHIP, Beijing, People's Republic of China
	Funding: The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes. Niobium (Nb) is the most popular material that has been employed for making superconducting radio frequency (SRF) cavities to be used in various particle accelerators over the last couple of decades. One of the most important steps in fabricating Nb SRF cavities is the final chemical removal of 150 μm of Nb from the inner surfaces of the SRF cavities. This is usually done by either buffered chemical polishing (BCP) or electropolishing (EP). Recently a new Nb surface treatment technique called buffered electropolishing (BEP) has been developed at Jefferson Lab. It has been demonstrated that BEP can produce the smoothest surface finish on Nb ever reported in the literature while realizing a Nb removal rate as high as 10 μm/min that is more than 25 and 5 times quicker than those of EP and BCP(112) respectively. In this contribution, recent advance in optimizing and understanding BEP treatment technique is reviewed. Latest results from RF measurements on BEP treated Nb single cell cavities by our unique vertical polishing system will be reported. Authored by The Southeastern Universities Research Association, Inc. under U.S. DOE Contract No. DE-AC05-84ER40150.
MOPC118	Effects of the Thickness of Niobium Surface Oxide Layers on Field Emission*	355
	A.T. Wu, S. Jin, J.D. Mammosser, R.A. Rimmer JLAB, Newport News, Virginia, USA X.Y. Lu, K. Zhao PKU/IHIP, Beijing, People's Republic of China
	Funding: The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes. Field emission on the inner surfaces of niobium superconducting radio frequency cavities is still one of the major obstacles for reaching high accelerating gradients for SRF community. Our previous experimental results* seemed to imply that the threshold of field emission was related to the thickness of Nb surface oxide layers. In this contribution, a more detailed study on the influences of the surface oxide layers on the field emission on Nb surfaces will be reported. By anodization technique, the thickness of the surface pentoxide layer was artificially fabricated from 3 nm up to 460 nm. A home-made scanning field emission microscope was employed to perform the scans on the surfaces. Emitters were characterized using a scanning electron microscope together with an energy dispersive x-ray analyzer. The SFEM experimental results were analyzed in terms of surface morphology and oxide thickness of Nb samples and chemical composition and geographic shape of the emitters. A model based on the classic electromagnetic theory was developed trying to understand the experimental results. Possibly implications for Nb SRF cavity applications from this study will be discussed. * A.T. Wu et al., Proc. of IPAC 2010, Kyoto, Japan, WEPEC081, p. 3067 (2010). Authored by The Southeastern Universities Research Association, Inc. under U.S. DOE Contract No. DE-AC05-84ER40150.
MOPC119	Fastest Electropolishing Technique on Niobium for Particle Accelerators*	358
	A.T. Wu, S. Jin, R.A. Rimmer JLAB, Newport News, Virginia, USA X.Y. Lu, K. Zhao PKU/IHIP, Beijing, People's Republic of China
	Funding: The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes. Field emission on the inner surfaces of niobium (Nb) superconducting radio frequency (SRF) cavities is still one of the major obstacles for reaching high accelerating gradients for SRF community. Our previous experimental results [1] seemed to imply that the threshold of field emission was related to the thickness of Nb surface oxide layers. In this contribution, a more detailed study on the influences of the surface oxide layers on the field emission on Nb surfaces will be reported. By anodization technique, the thickness of the surface pentoxide layer was artificially fabricated from 3nm up to 460nm. A home-made scanning field emission microscope (SFEM) was employed to perform the scans on the surfaces. Emitters were characterized using a scanning electron microscope together with an energy dispersive x-ray analyzer. The experimental results could be understood by a simple model calculation based on classic electromagnetic theory as shown in Ref.1. Possibly implications for Nb SRF cavity applications from this study will be discussed. Authored by The Southeastern Universities Research Association, Inc. under U.S. DOE Contract No. DE-AC05-84ER40150.
MOPC120	Design of Superconducting Parallel-bar Deflecting/Crabbing Cavities	361
	J.R. Delayen, S.U. De Silva ODU, Norfolk, Virginia, USA
	The superconducting parallel-bar cavity is a deflecting/crabbing cavity with attractive properties, compared to other conventional designs, that is being considered for a number of applications. We present an analysis of several designs of parallel-bar cavities and their electromagnetic properties.
MOPC121	Design of Low-frequency Superconducting Spoke Cavities for High-velocity Applications	364
	J.R. Delayen, C.S. Hopper ODU, Norfolk, Virginia, USA R.G. Olave Old Dominion University, Norfolk, Virginia, USA
	Superconducting single- and multi-spoke cavities have been designed to-date for particle velocities from β~0.15 to β~0.65. Superconducting spoke cavities may also be of interest for higher-velocity, low-frequency applications, either for hadrons or electrons. We present the design of 325 and 352 MHz spoke cavities optimized for β=0.8 and β=1.
MOPC122	Etching of Niobium Sample Placed on Superconducting Radio Frequency Cavity Surface in Ar/CL2 Plasma	367
	J. Upadhyay, M. Nikolić, S. Popović, L. Vušković ODU, Norfolk, Virginia, USA H.L. Phillips, A-M. Valente-Feliciano JLAB, Newport News, Virginia, USA
	Plasma based surface modification is a promising alternative to wet etching of superconducting radio frequency (SRF) cavities. It has been proven with flat samples that the bulk Niobium (Nb) removal rate and the surface roughness after the plasma etchings are equal to or better than wet etching processes. To optimize the plasma parameters, we are using a single cell cavity with 20 sample holders symmetrically distributed over the cell. These holders serve the purpose of diagnostic ports for the measurement of the plasma parameters and for the holding of the Nb sample to be etched. The plasma properties at RF (100 MHz) and MW (2.45 GHz) frequencies are being measured with the help of electrical and optical probes at different pressures and RF power levels inside of this cavity. The niobium coupons placed on several holders around the cell are being etched simultaneously. The etching results will be presented at this conference.
MOPC123	Temperature Dependent Microphonics in the BNL Electron Cooler*	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.
TUZB01	Superconducting RF Technology for Proton and Ion Accelerators	966
	G. Devanz CEA/DSM/IRFU, France
	The worldwide status of superconducting RF cavities and cryomodules for low velocity ion and proton particles is reviewed, with emphasis on the construction and tests of prototypes. A number of different multicell structures at a range of operating frequencies have been successfully realized. This review will cover the progress of several facilities under construction or being proposed: Spiral2, IFMIF-EVEDA, SPL, ESS, FRIB and ADS drivers.
	Slides TUZB01 [10.630 MB]