IPAC2012 - List of Keywords (niobium)

Paper	Title	Other Keywords	Page
MOYBP01	State-of-the-Art and Future Prospects in RF Superconductivity	cavity, SRF, electron, storage-ring	11
	K. Saito KEK, Ibaraki, Japan
	This presentation should recount the remarkable progress in improving the performance of superconducting cavities over the past 50 years and explore future directions, including advances in materials other than Nb, such as MgB2 and novel multi-layer superconductor-insulator systems. This talk should provide an overview of international activities.
	Slides MOYBP01 [10.097 MB]

MOPPD001	Accelerator R&D in the QUASAR Group	antiproton, diagnostics, storage-ring, instrumentation	364
	C.P. Welsch Cockcroft Institute, Warrington, Cheshire, United Kingdom C.P. Welsch The University of Liverpool, Liverpool, United Kingdom
	Funding: Work supported by the Helmholtz Association and GSI under contract VH-NG-328, the EU under contracts PITN-GA-2008-215080, PITN-GA-2011-289191, PITN-GA-2011-289485 and STFC. The QUASAR Group was founded in 2007 with an initial focus on the development and experimental exploitation of a novel electrostatic ultra-low energy storage ring (USR), part of the future facility for low-energy antiproton and ion research (FLAIR). The group's research activities have grown considerably over the past four years and now include also the development of beam diagnostic tools for accelerators and light sources, investigations into superconducting linear accelerators and medical applications, and, most recently, a broad R&D program into laser applications at accelerators. In this contribution, an overview of the QUASAR Group’s research achievements to date is given.

MOPPR020	An Improved Cryogenic Current Comparator for FAIR	pick-up, shielding, cryogenics, ion	822
	R. Geithner, W. Vodel HIJ, Jena, Germany R. Geithner, R. Neubert, P. Seidel FSU Jena, Jena, Germany F. Kurian, H. Reeg, M. Schwickert GSI, Darmstadt, Germany
	Online monitoring of low intensity (below 1 μA) charged particle beams without disturbing the beam and its environment is crucial for any accelerator facility. For the upcoming FAIR project a beam monitor based on the Cryogenic Current Comparator principle with an enhanced resolution was developed. The main focus of research was on the low temperature properties of the ferromagnetic core material of the superconducting pickup coil. The pickup coil transforms the magnetic field of the beam into a current that is detected by a high performance low temperature dc Superconducting QUantum Interference Device (LTS-DC-SQUID). The penetration of the pickup coil by interfering magnetic fields is highly attenuated by a meander shaped superconducting shielding. The Cryogenic Current Comparator is able to measure DC beam currents, e.g. as required for slow extraction from a synchrotron, as well as bunched beams. In this contribution we present first results of the improved Cryogenic Current Comparator working in a laboratory environment.

TUPPD082	Simulations of Multipacting in the Cathode Stalk and FPC of 112 MHz Superconducting Electron Gun	electron, cathode, gun, simulation	1593
	T. Xin, X. Liang Stony Brook University, Stony Brook, USA S.A. Belomestnykh, I. Ben-Zvi, T. Rao, J. Skaritka, E. Wang, Q. Wu BNL, Upton, Long Island, New York, USA X. Chang Far-Tech, Inc., San Diego, California, USA
	Funding: Work is supported at BNL by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. The work at Stony Brook is supported by the US DOE under grant DE-SC0005713. A 112 MHz superconducting quarter-wave resonator electron gun will be used as the injector of the Coherent Electron Cooling (CEC) proof-of-principle experiment at BNL. Furthermore, this electron gun can be used for testing of the performance of various high quantum efficiency photocathodes. In a previous paper, we presented the design of the cathode stalks and a Fundamental Power Coupler (FPC). In this paper we present updated designs of the cathode stalk and FPC. Multipacting in the cathode stalk and FPC was simulated using three different codes, Multipac, CST particle studio and FishPact respectively. All simulation results show no serious multipacting in the cathode stalk structure and FPC.

WEOAB03	An Update on a Superconducting Photonic Band Gap Structure Resonator Experiment	SRF, cavity, HOM, wakefield	2140
	E.I. Simakov, W.B. Haynes, M.A. Madrid, F.P. Romero, T. Tajima, W.M. Tuzel LANL, Los Alamos, New Mexico, USA C.H. Boulware, T.L. Grimm Niowave, Inc., Lansing, Michigan, USA
	Funding: This work is supported by the U.S. Department of Energy (DOE) Office of Science Early Career Research Program. We present an update on the 2.1 GHz superconducting rf (SRF) photonic band gap (PBG) resonator experiment in Los Alamos. The SRF PBG cell was designed to operate at 2.1 GHz. PBG cells have great potential for outcoupling long-range wakefields in SRF accelerator structures without affecting the fundamental accelerating mode. Using PBG structures in superconducting particle accelerators will allow operation at higher frequencies and moving forward to significantly higher beam luminosities thus leading towards a completely new generation of colliders for high energy physics. However, the technology of fabrication of PBG accelerator cells from niobium has not been well developed to date. Here we report the results of our efforts to fabricate a 2.1 GHz PBG cell and to test it at high gradients in a liquid helium bath at the temperature of 2 Kelvin. The high gradient performance of the cell will be evaluated and the results will be compared to simulations with the CST Microwave Studio.
	Slides WEOAB03 [2.061 MB]

WEEPPB011	Analysis of High Field Non-Linear Losses on SRF Surfaces Due to Specific Topographic Roughness	simulation, superconductivity, SRF, feedback	2188
	C. Xu The College of William and Mary, Williamsburg, USA M.J. Kelley, C.E. Reece, C. Xu JLAB, Newport News, Virginia, USA
	Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The high-field performance of SRF cavities will eventually be limited by the realization of fundamental material limits, whether it be Hc1 or Hsh, or some derivative thereof, at which the superconductivity is lost. Before reaching this fundamental field limit at the macro level, it must be encountered at localized, perhaps microscopic, sites of field enhancement due to local topography. If such sites are small enough, they may produce thermally stabilized normal-conducting regions which contribute non-linear losses when viewed from the macro resonant field perspective, and thus produce degradation in Q0. We have undertaken a calculation of local surface magnetic field enhancement from specific fine topographic structure by conformal mapping method and numerically. A solution of the resulting normal conducting volume has been derived and the corresponding RF ohmic loss simulated.

WEEPPB015	Temperature Dependence of the Superheating Field: DC and RF Critical Fields	cavity, electron, superconductivity, SRF	2197
	N.R.A. Valles, M. Liepe CLASSE, Ithaca, New York, USA
	The superheating field is a metastable state at which the Meissner state persists at fields higher than would be predicted from steady-state energy considerations. Previous work demonstrated that a phenomenological approach based on the RF superheating field scaling near the critical temperature is also consistent with low temperature results. This work expands upon the RF results by measuring the DC superheating field, and comparing it to RF results and theoretical predictions.

WEPPC002	Impact of Trapped Flux and Thermal Gradients on the SRF Cavity Quality Factor	cavity, superconducting-cavity, SRF, controls	2203
	O. Kugeler, J. Knobloch, J.M. Vogt HZB, Berlin, Germany S. Aull CERN, Geneva, Switzerland
	The obtained Q0 value of a superconducting niobium cavity is known to depend on various factors like the RRR of the Niobium material, crystallinity, chemical treatment history, the high-pressure rinsing process, or effectiveness of the magnetic shielding. We have observed that spatial thermal gradients over the cavity length during cool-down appear to contribute to a degradation of Q0. Measurements were performed in the Horizontal Bi-Cavity Test Facility (HoBiCaT) at HZB on TESLA type cavities as well as on disc- and rod-shaped niobium samples equipped with thermal, electrical and magnetic diagnostics. Possible explanations for the effect are discussed.

WEPPC003	Component Qualification and Final Assembly of the S-DALINAC Injector Upgrade Module	cavity, linac, SRF, shielding	2206
	J. Conrad, R. Eichhorn, T. Kürzeder, A. Richter, S.T. Sievers TU Darmstadt, Darmstadt, Germany
	Funding: This work is supported by the DFG through SFB 634. The injector of the S-DALINAC delivers currently electron beams of up to 10 MeV with a current of up to 60 μA. With the new cryostat-module an increase of both parameters, energies ranging to 14 MeV and currents up to 150 μA, are expected. For acceleration, the module houses two 20 cell elliptical niobium cavities which are used at a frequency of 3 GHz in liquid helium at 2 K. The RF power is delivered to the cavities through the different temperature stages by a WR-284 transition line which is connected to the resonator by a new waveguide-to-coax power coupler (being one of the major changes compared to the design of the existing module). We review on the design of the module and present the results of the first cool-down. Also, a report on additional new design features, e.g. piezo actuators for tuning at 2 K, and the production of the cavities will be given.

WEPPC005	Parts Management during Fabrication at the European XFEL	controls, undulator, cavity, cryomodule	2212
	L. Hagge, J.A. Dammann, S. Eucker, A. Herz, J. Kreutzkamp, D. Käfer, D. Szepielak, N. Welle DESY, Hamburg, Germany
	This presentation describes policies and methods for parts management during fabrication at the European XFEL. The objective is to provide procedures for reliably gathering, recording, processing and archiving the complete mandatory fabrication information. The solution is a foundation for conducting Quality Assurance and Quality Control (QA/QC), as it ensures that acceptance tests are recorded, signed-off and followed-up in a reliable and orderly way. It achieves compliance with legal regulations in certain areas. One example is the pressurized equipment directive (PED), which for certain (parts of) equipment requires that the complete fabrication and usage history is tracked throughout the entire lifespan of the XFEL facility. In addition, the solution provides a basis for building the necessary documentation for later installation, operation and maintenance activities. The solution is established in the series production of several accelerator components. It uses DESY’s Engineering Data Management System as central collaboration and documentation platform.

WEPPC021	Development of Superconducting Radio Frequency Cavities at SINAP	cavity, superconducting-cavity, electron, HOM	2248
	J.F. Liu, H.T. Hou, C.W. Lu, C. Luo, Z.Y. Ma, D.Q. Mao, J. Shi, Zh.G. Zhang, S.J. Zhao, X. Zheng SINAP, Shanghai, People's Republic of China Z.Q. Feng, Z. Li, J.F. Liu, Y.L. Wei, K. Xu, Y.B. Zhao Shanghai KEY Laboratory of Cryogenics & Superconducting RF Technology, Shanghai, People's Republic of China H. Yu Graduate School of the Chinese Academy of Sciences, Beijing, People's Republic of China
	This paper presents the development of superconducting radio frequency cavities at Shanghai Institute of Applied Physics (SINAP) mainly focused on the 500MHz band. Firstly, Two KEKB type 500MHz single cell niobium cavities have been fabricated and one of them has been vertical tested successfully in 2010. The highest accelerating gradient of the fabricated cavity higher than 10MV/m was obtained while the quality factor was better than 4·10⁸ at 4.2K. Secondly, a new type of 500MHz single cell cavity has been designed which adopts the fluted beam pipe for higher order modes propagation and a coaxial type high power input coupler. Thirdly, a 500MHz 5-cell superconducting cavity with large aperture, enlarged beam pipe for HOM propagation and high r/Q value has been optimized which can be a candidate cavity for high current FEL and ERL.

WEPPC032	Analysis of the Four Rod Crab Cavity for HL-LHC	cavity, multipactoring, simulation, luminosity	2275
	B.D.S. Hall, P.K. Ambattu, G. Burt, D. Doherty, C. Lingwood Cockcroft Institute, Lancaster University, Lancaster, United Kingdom P. Goudket STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	The Hi-Lumi Upgrade to the LHC will utilise crab cavities to increase the peak luminosity and provide luminosity levelling at the increased crossing angle. A transversely compact design is required to fit within the limited space between opposing beamlines. In this paper a four rod TEM deflecting cavity (4RCC) is shown to be suitable for LHC. The variation of the deflecting voltage with radial offset has been minimised by careful design and an aluminium prototype has been constructed and beadpull measurements are compared to simulations. Multipacting simulations have been performed on the cavity geometry and it is predicted that the growth rate is less than unity for a clean surface. Pressure variations in the LHe can result in deformation of the complex shape which will alter the resonant frequency. Mechanical simulations have also been performed to assess the sensitivity of the frequency to pressure. In order to reduce the impact of these cavities on the LHC beam low impedance is required for the HOMs as well as the fundamental monopole mode. The couplers for the 4RCC cavity have been optimised to provide effective damping of these modes while rejecting the operating mode.

WEPPC033	RF and Surface Properties of Bulk Niobium and Niobium Film Samples	electron, quadrupole, collider, photon	2278
	T. Junginger, W. Weingarten CERN, Geneva, Switzerland R. Seviour University of Huddersfield, Huddersfield, 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. Different models accounting for the field depended surface resistance are being confronted by the experimental results. The RF results are being correlated to surface analyses measurements carried out on the same samples.

WEPPC057	Design of SSR1 Single Spoke Resonators for PXIE	cavity, SRF, cryomodule, coupling	2342
	L. Ristori, M.H. Awida, I.V. Gonin, M. Merio, D. Passarelli, V.P. Yakovlev Fermilab, Batavia, USA
	Funding: Operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy. The Project X Injector Experiment (PXIE) at Fermilab contains one cryomodule of Single Spoke Resonators operating at 325 MHz with a geometrical beta of 0.2. Two prototypes have been tested successfully at high gradients in the Fermilab Vertical Test Stand (VTS). We have welded a Stainless Steel helium vessel on the first prototype and tested it in the spoke-dedicated Test Cryostat. With excellent results in hand, an order for ten bare resonators was placed with US industry. A new design for the helium vessel was developed for these resonators with the main goal of reducing the sensitivity of the resonator to variations of the helium pressure to meet the requirements of PXIE. A new tuner was developed despite the good results of the first prototype. The new design was inevitable due to the different behavior of the resonator in the new helium vessel. Other aspects were improved such as the maintainability of the tuner motor and piezoelectric actuators allowing their replacement from access ports on the cryomodule's vacuum vessel.

WEPPC058	Development at ANL of a Copper-brazed Joint for the Coupling of the Niobium Cavity End Wall to the Stainless Steel Helium Vessel in the Fermilab SSR1 Resonator	cavity, vacuum, coupling, SRF	2345
	L. Ristori Fermilab, Batavia, USA W.F. Toter ANL, Argonne, USA
	Funding: Operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy. In order to reduce the sensitivity of the Fermilab SSR1 resonator to helium pressure variations, it was concluded that the cavity and helium vessel end-walls needed to be structurally coupled by means of a transition ring. With the materials to be connected being Niobium and Stainless Steel, it was decided to utilize the same technology already developed for the cavity flanges which consists of a furnace-brazed joint utilizing oxygen-free electrolytic copper. Small-scale and full-scale annular samples have been constructed at Argonne National Laboratory and subject to tensile tests, thermal cycling and visual inspections to qualify the joint. The transition ring is electron-beam welded to the cavity and TIG welded to the helium vessel, the process is explained in detail.

WEPPC066	Niobium Reaction Kinetics: An Investigation into the Reactions Between Buffered Chemical Polish and Niobium and the Impact on SRF Cavity Etching	cavity, SRF, superconducting-RF	2360
	I.M. Malloch, L.J. Dubbs, K. Elliott, R. Oweiss, L. Popielarski FRIB, East Lansing, Michigan, USA
	Funding: Work supported by US DOE Cooperative Agreement DE-SC0000661 and Michigan State University. In the SRF community, there is no definitive agreement on the precise reaction mechanism in the etching of niobium cavities by buffered chemical polish (BCP) mixtures. As a consequence, it is difficult to predict the heat produced during cavity etching. To gain a better understanding of the reaction kinetics of niobium and BCP, calorimetry experiments were performed to establish an experimental heat of reaction, and research was performed to determine a reasonable reaction scheme to allow for calculation of the theoretical heat of reaction. The results of the calorimetry experiments were in excellent agreement with one another and with the theoretical value. These results will allow for more accurate estimation of etch removal amounts on cavities without the need to perform time-intensive etch rate tests. Applying the experimental data to pre and post cavity etch ultrasonic thickness measurements has shown a significant improvement in the predictability of etch removal amounts in Facility for Rare Isotope Beams (FRIB) half-wave and quarter-wave resonators, and will allow for more reliable heat removal and prevention of Q-disease during other cavity etching procedures.

WEPPC067	Dewar Testing of Coaxial Resonators at MSU	linac, cryomodule, SRF, cavity	2363
	J. Popielarski, E.C. Bernard, A. Facco, M. Hodek, F. Marti, D. Norton, G.J. Velianoff, J. Wlodarczak FRIB, East Lansing, Michigan, USA A. Burrill, G.K. Davis JLAB, Newport News, Virginia, USA
	Funding: Work supported by US DOE Cooperative Agreement DE-SC0000661 and Michigan State University Michigan State University is currently testing prototype and production cavities for two accelerator projects. 80.5 MHz β=0.085 quarter wave resonators (QWR) are being produced as part of a cryomodule for ReA3. 322 MHz β=0.53 half wave resonators (HWR) are being prototyped for a driver linac for the Facility for Rare Isotope Beams. This paper will discuss test results and how different cavity preparations effect cavity performs. Also various diagnostics methods have been developed, such as second sound quench location determination, and temperature mapping to determine hot spots from defects and multipacting location.

WEPPC068	Multipacting Simulation and Analysis for the FRIB β = 0.085 Quarter Wave Resonators using Track3P	cavity, simulation, resonance, linac	2366
	L. Ge, C. Ko, Z. Li SLAC, Menlo Park, California, USA J. Popielarski FRIB, East Lansing, Michigan, USA
	Funding: Work supported by DOE Office of Science under Cooperative Agreement DE- SC0000661, DOE Contract No. DE-AC02-76SF00515, and used resources of NERSC supported by DOE Contract No. DE-AC02- 05CH11231. The drive linac for the Facility for Rare Isotope Beams (FRIB) utilizes several types of low beta superconducting resonators to accelerate the ion beams from 0.3 MeV per nucleon to 200 MeV per nucleon. Multipacting is an issue of concern for such superconducting resonators as they have unconventional shapes. We have used the parallel codes Tack3P and Omega3P, developed at SLAC under the support of the DOE SciDAC program, to analyze the multipacting barriers of such resonators. In this paper, we will present the simulation results for the β(v/c) = 0.085 Quarter Wave Resonator (QWR) for the FRIB project. Experimental data will also be presented to benchmark with the simulation results.

WEPPC078	Recent Developments in the Cornell Nb3Sn Initiative	cavity, linac, SRF, accelerating-gradient	2390
	S. Posen, G.H. Hoffstaetter, M. Liepe, Y. Xie CLASSE, Ithaca, New York, USA
	Superconducting accelerator cavities coated with Nb3Sn have already demonstrated significantly higher unloaded quality factors than standard niobium cavities at surface magnetic fields <30 mT. Theoretical predictions suggest that the maximum critical field of such cavities could be twice that of niobium cavities. Significant facilities have been developed at Cornell University to fabricate Nb3Sn using the vapor diffusion technique. In this paper, recent progress is presented from our Nb3Sn program. The first RF results from a test of a Nb3Sn sample in a TE pillbox sample cavity are presented as well as first images of the newly constructed apparatus for coating full 1.3 GHz single cell cavities.

WEPPC082	First Results on Cornell TE-type Sample Host Cavities	cavity, coupling, vacuum, pick-up	2402
	Y. Xie, M. Liepe CLASSE, Ithaca, New York, USA
	Funding: Work supported by NSF and Alfred P. Sloan Foundation. In order to measure surface resistance of new materials other than niobium such as Nb3Sn and MgB2, two sample host niobium cavities operating at TE modes have been developed at Cornell University. The first one is a 6GHz pillbox TE011 cavity modified from an older vision enabling testing 2.75'' diameter flat sample plates. The second one is an optimized mushroom-shape niobium cavity operating at both 5GHz TE012 and 6GHz TE013 modes for 3.75'' diameter flat sample plates . First results from the commissioning of the two TE cavities will be reported.

WEPPC083	Tunable 28 MHz Superconducting Cavity for RHIC	cavity, superconducting-cavity, site, superconducting-RF	2405
	C.H. Boulware, T.L. Grimm Niowave, Inc., Lansing, Michigan, USA S.A. Belomestnykh, I. Ben-Zvi BNL, Upton, Long Island, New York, USA
	Funding: This research has been supported by a Department of Energy Small Business Innovative Research Phase II grant through the Nuclear Physics program office, contract #DE-SC0001215. Replacement of the normal conducting 28 MHz accelerating cavities in the RHIC ring with superconducting structures offers a number of advantages for the machine operation, including reduction of the number of cavities required and improved HOM performance. A prototype folded quarter wave structure is under construction at Niowave, Inc. to meet this need. This novel cavity geometry achieves the very low resonant frequency required with a relatively compact structure, and can provide the large tuning range required (~1% of the cavity frequency). Progress of the cavity fabrication will be presented along with room temperature RF measurements.

WEPPC084	Development of a Superconducting 500 MHz Multi-Spoke Cavity for Electron Linacs	cavity, cryomodule, electron, SRF	2408
	D. Gorelov, C.H. Boulware, T.L. Grimm Niowave, Inc., Lansing, Michigan, USA S.U. De Silva, J.R. Delayen, C.S. Hopper, R.G. Olave ODU, Norfolk, Virginia, USA
	Funding: This work is supported by the US Department of Energy SBIR/STTR program through the Office of Nuclear Physics. Multi-spoke cavities are well-known options for acceleration of heavy and light ions. A recently developed multi-spoke cavity for β=1 presents an attractive opportunity to use this cavity type for electron accelerators. One of the main attractive features of this cavity type is its compactness for relatively low frequency. A simplified design at 500 MHz allowed building of a multi-spoke cavity and cryomodule in a 2-year time frame with confidence and development of effective manufacturing techniques. It also constitutes an important step in proving the usefulness of this kind of cavity design for new applications in the electron machines. Niowave is now in a position to build on the success of this cavity to help advance the design of superconducting electron accelerators. Accelerating voltage of more then 4.3 MV in a single cavity at 4.5 K is expected with peak electric field of less then 21.7 MV/m, and peak magnetic field of less then 80 mT. The paper discusses the fabrication challenges of the complete cavity and the cryomodule, as well as room temperature and cryogenic test results.

WEPPC085	Engineering of a Superconducting 400 MHz Crabbing Cavity for the LHC HiLumi Upgrade	cavity, luminosity, collider, SRF	2411
	D. Gorelov, T.L. Grimm Niowave, Inc., Lansing, Michigan, USA S.U. De Silva, J.R. Delayen ODU, Norfolk, Virginia, USA
	Funding: This work is supported by the US DOE-HEP SBIR/STTR program and the US DOE through the US LHC Accelerator Research Program (LARP). The recently developed new simplified design for the 400 MHz LHC crabbing cavity presents attractive properties compared to conventional designs. The proposed approach can be equally compact in both transverse dimensions and allows horizontal as well as vertical deflection of the beam in the collider. The significant modification of the parallel-bar design with the bars merged to the side walls of the cavity gives improved properties, such as better mode separation and reduced surface fields. A transverse deflecting voltage of 3 to 5 MV in a single cavity can be expected with the peak surface electric field lower then 50 MV/m and peak magnetic field below 100 mT. This paper presents engineering issues of the proof-of-concept crabbing cavity design and discusses the manufacturing techniques. The paper discusses present status of the project including fabrication of the niobium cavity, as well as room temperature and cryogenic testing. J.R. Delayen, S.U. De Silva, "Design of Superconducting Parallel-Bar Deflecting/Crabbing Cavities with Improved Properties," Proc. of 2011 PAC, New York, NY, USA, 2011, p. 10²¹.

WEPPC091	A Path to Higher Q0 with Large Grain Niobium Cavities	cavity, SRF, accelerating-gradient, induction	2426
	P. Dhakal, G. Ciovati, G.R. Myneni JLAB, Newport News, Virginia, USA
	The improvement of the quality factor Q0 of superconducting radio-frequency (SRF) cavities at medium accelerating gradients (~ 20 MV/m) is important in order to reduce the cryogenic losses in continuous wave accelerators for a variety of applications. In recent years, SRF cavities fabricated from ingot niobium have become a viable alternative to standard high-purity fine-grain Nb for the fabrication of high-performing SRF cavities with the possibility of significant cost reduction. Initial studies,, demonstrated the improvement of Q0 at medium field in cavities heat treated at 800-1000 °C without subsequent chemical etching. To further explore this treatment procedure, a new induction furnace with an all-niobium hot-zone was commissioned. A single-cell 1.5 GHz cavity fabricated from ingot material from CBMM, Brazil, with RRR~200, was heat treated with the new furnace in the temperature range 600-1400 °C for several hours. Residual resistance values below 5 nano Ω have been consistently achieved on this cavity as well as Q0 values above 4.5×1010 at 2 K and 100 mT peak surface magnetic field. Q0-values of the order of 1011 have been measured at 1.5 K. G. Ciovati, et al., Phys. Rev. ST Accel. Beams 13, 022002 (2010). ** G. Ciovati, et al., Proc. of the 15th Int. Conf. on RF Superconductivity, Chicago, July 25-29, 2011, paper TUPO051

WEPPC096	Exploring the Effect of AL2O3 ALD Coating on a High Gradient ILC Single-Cell Cavity	cavity, SRF, electron, site	2441
	G.V. Eremeev, A-M. Valente-Feliciano, A.T. Wu JLAB, Newport News, Virginia, USA D. Gu ODU, Norfolk, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Encouraged by work at Argonne National Lab, we investigated atomic layer deposition technique for high gradient superconducting RF cavities at JLab with an ALD coating system of Old Dominion University located on the JLab site. The goal of this study was to look into the possibility of coating a dielectric layer on top of RF niobium surface at a lower temperature of 120 C as compared to ANL coatings at 200 C in order to preserve niobium pentooxide on niobium surface. The initial coatings showed complete, but non-uniform coatings of the surface with several areas exhibiting discoloration, which was probably due to the temperature variation during coatings. The initial coating showed a high RF losses, which were improved after discolored areas on the beam tubes were removed with HF rinse of the beam tubes only. The best result was 2·10⁹ low field Q0 and Eacc = 18 MV/m limited by available power.

WEPPC101	Characteristics and Fabrication of a 499 MHz Superconducting Deflecting Cavity for the Jefferson Lab 12 GeV Upgrade	cavity, vacuum, electron, target	2450
	H. Park, S.U. De Silva JLAB, Newport News, Virginia, USA J.R. Delayen ODU, Norfolk, Virginia, USA
	A 499 MHz parallel bar superconducting deflecting cavity has been designed and optimized for a possible implementation at the Jefferson Lab 12 GeV upgrade. This paper will present the analysis of the mechanical characteristics of the cavity (pressure sensitivity and tunability) and will detail the fabrication process. The unique geometry of the cavity–which is currently being fabricated at Jefferson Lab–and its required mechanical strength present interesting manufacturing challenges.

WEPPC104	Tomography as a Diagnostic Tool for Plasma Etching of SRF Cavities	plasma, SRF, cavity, diagnostics	2459
	M. Nikolić, A.L. Godunov, S. Popović, A. Samolov, L. Vušković ODU, Norfolk, Virginia, USA F. Čučkov Old Dominion University, Norfolk, USA
	Plasma based surface modification is a promising alternative for etching of superconductive radio frequency (SRF) cavities. A plasma processed SRF cavity presents a plasma reactor with limited or distorted symmetry. We are developing a tomographic reconstruction of local plasma parameters, as a diagnostic tool in the plasma etching setting of SRF cavities. The method is non-invasive and provides deep insight into the fundamental processes and phenomena during the plasma treatment of SRF cavities’ surfaces. Here we report on our progress in developing tomographic numerical method, based on 2D inverse Radon formula. We tested it on supersonic flowing microwave discharge maintained in the cylindrical quartz tube. Due to the model’s sensitivity to the noise signal in the experiment, an automated measurement system has been built with the aim to increase the overall precision of data acquisition as well as to stream line the measurement process.

WEPPC115	High Q0 in Superconducting Niobium Cavities: Progress at FNAL and Future Plans	cavity, SRF, factory, vacuum	2492
	A. Grassellino, L.D. Cooley, C.M. Ginsburg, A. Romanenko, A.M. Rowe, V.P. Yakovlev Fermilab, Batavia, USA
	Consistent improvement in the quality factors of SRF cavities at medium surface fields of about 70 mT represents a direct cost savings factor for the proposed Project X CW linac and other SRF accelerator projects based on CW operation. Current state-of-the-art in SRF does not provide processing recipes to maximize the Q0 at those fields since a complete understanding of the mechanisms governing the quality factor at non-negligible surface fields is not yet developed. In this contribution we present results of the FNAL effort in both scientific understanding and practical improvements and discuss the directions we are pursuing for future research.

WEPPC116	Depth Distribution of Losses in Superconducting Niobium Cavities	cavity, SRF, positron, vacuum	2495
	A. Romanenko, A. Grassellino, J.P. Ozelis Fermilab, Batavia, USA H. Padamsee CLASSE, Ithaca, New York, USA
	In order to optimize performances of superconducting niobium cavities it is crucial to understand the structure of near-surface few tens of nanometers of the material. In particular, superconducting properties of niobium, which depend on the presence of impurities and/or defects, may be non-uniform in the magnetic field penetration depth. A few cavity experiments based on oxypolishing* and anodizing,* provided some insight into the problem, but the definitive understanding is not developed yet. In this contribution we report on the "depth profiling" of the near-surface RF layer using an alternative technique based on the hydrofluoric acid (HF) rinsing. Tumbled, electropolished and buffered chemical polished cavities have been investigated and tentative nanostructural interpretation is discussed. * P. Kneisel, Proc. of the 1999 SRF Workshop, Santa Fe, USA G. Eremeev and H. Padamsee, Physica C 441 No. 1-2 (2006) 62 * G. Ciovati, P. Kneisel and A. Gurevich, PRSTAB 10 (2007) 062002

THPPC093	SRF Cavity Surface Topography Characterization Using Replica Techniques	cavity, SRF, superconductivity, radio-frequency	3497
	C. Xu, M.J. Kelley The College of William and Mary, Williamsburg, USA C.E. Reece JLAB, Newport News, Virginia, USA
	Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. To better understand the roll of topography on SRF cavity performance, we seek to obtain detailed topographic information from the curved practical cavity surfaces. Replicas taken from a cavity interior surface provide internal surface molds for fine Atomic Force Microscopy (AFM) and stylus profilometry. In this study, we confirm the replica resolution both on surface local defects such as grain boundary and etching pits and compare the surface uniform roughness with the aid of Power Spectral Density (PSD) where we can statistically obtain roughness parameters at different scales. A series of sampling locations are at the same magnetic field chosen at the same latitude on a single cell cavity to confirm the uniformity. Another series of sampling locations at different magnetic field amplitudes are chosen for this replica on the same cavity for later power loss calculation. We also show that application of the replica followed by rinsing does not adversely affect the cavity performance.

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MOYBP01

State-of-the-Art and Future Prospects in RF Superconductivity

cavity, SRF, electron, storage-ring

11

K. Saito
KEK, Ibaraki, Japan

This presentation should recount the remarkable progress in improving the performance of superconducting cavities over the past 50 years and explore future directions, including advances in materials other than Nb, such as MgB2 and novel multi-layer superconductor-insulator systems. This talk should provide an overview of international activities.

Slides MOYBP01 [10.097 MB]

MOPPD001

Accelerator R&D in the QUASAR Group

antiproton, diagnostics, storage-ring, instrumentation

364

C.P. Welsch
Cockcroft Institute, Warrington, Cheshire, United Kingdom
C.P. Welsch
The University of Liverpool, Liverpool, United Kingdom

Funding: Work supported by the Helmholtz Association and GSI under contract VH-NG-328, the EU under contracts PITN-GA-2008-215080, PITN-GA-2011-289191, PITN-GA-2011-289485 and STFC.
The QUASAR Group was founded in 2007 with an initial focus on the development and experimental exploitation of a novel electrostatic ultra-low energy storage ring (USR), part of the future facility for low-energy antiproton and ion research (FLAIR). The group's research activities have grown considerably over the past four years and now include also the development of beam diagnostic tools for accelerators and light sources, investigations into superconducting linear accelerators and medical applications, and, most recently, a broad R&D program into laser applications at accelerators. In this contribution, an overview of the QUASAR Group’s research achievements to date is given.

MOPPR020

An Improved Cryogenic Current Comparator for FAIR

pick-up, shielding, cryogenics, ion

822

R. Geithner, W. Vodel
HIJ, Jena, Germany
R. Geithner, R. Neubert, P. Seidel
FSU Jena, Jena, Germany
F. Kurian, H. Reeg, M. Schwickert
GSI, Darmstadt, Germany

Online monitoring of low intensity (below 1 μA) charged particle beams without disturbing the beam and its environment is crucial for any accelerator facility. For the upcoming FAIR project a beam monitor based on the Cryogenic Current Comparator principle with an enhanced resolution was developed. The main focus of research was on the low temperature properties of the ferromagnetic core material of the superconducting pickup coil. The pickup coil transforms the magnetic field of the beam into a current that is detected by a high performance low temperature dc Superconducting QUantum Interference Device (LTS-DC-SQUID). The penetration of the pickup coil by interfering magnetic fields is highly attenuated by a meander shaped superconducting shielding. The Cryogenic Current Comparator is able to measure DC beam currents, e.g. as required for slow extraction from a synchrotron, as well as bunched beams. In this contribution we present first results of the improved Cryogenic Current Comparator working in a laboratory environment.

TUPPD082

Simulations of Multipacting in the Cathode Stalk and FPC of 112 MHz Superconducting Electron Gun

electron, cathode, gun, simulation

1593

T. Xin, X. Liang
Stony Brook University, Stony Brook, USA
S.A. Belomestnykh, I. Ben-Zvi, T. Rao, J. Skaritka, E. Wang, Q. Wu
BNL, Upton, Long Island, New York, USA
X. Chang
Far-Tech, Inc., San Diego, California, USA

Funding: Work is supported at BNL by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. The work at Stony Brook is supported by the US DOE under grant DE-SC0005713.
A 112 MHz superconducting quarter-wave resonator electron gun will be used as the injector of the Coherent Electron Cooling (CEC) proof-of-principle experiment at BNL. Furthermore, this electron gun can be used for testing of the performance of various high quantum efficiency photocathodes. In a previous paper, we presented the design of the cathode stalks and a Fundamental Power Coupler (FPC). In this paper we present updated designs of the cathode stalk and FPC. Multipacting in the cathode stalk and FPC was simulated using three different codes, Multipac, CST particle studio and FishPact respectively. All simulation results show no serious multipacting in the cathode stalk structure and FPC.

WEOAB03

An Update on a Superconducting Photonic Band Gap Structure Resonator Experiment

SRF, cavity, HOM, wakefield

2140

E.I. Simakov, W.B. Haynes, M.A. Madrid, F.P. Romero, T. Tajima, W.M. Tuzel
LANL, Los Alamos, New Mexico, USA
C.H. Boulware, T.L. Grimm
Niowave, Inc., Lansing, Michigan, USA

Funding: This work is supported by the U.S. Department of Energy (DOE) Office of Science Early Career Research Program.
We present an update on the 2.1 GHz superconducting rf (SRF) photonic band gap (PBG) resonator experiment in Los Alamos. The SRF PBG cell was designed to operate at 2.1 GHz. PBG cells have great potential for outcoupling long-range wakefields in SRF accelerator structures without affecting the fundamental accelerating mode. Using PBG structures in superconducting particle accelerators will allow operation at higher frequencies and moving forward to significantly higher beam luminosities thus leading towards a completely new generation of colliders for high energy physics. However, the technology of fabrication of PBG accelerator cells from niobium has not been well developed to date. Here we report the results of our efforts to fabricate a 2.1 GHz PBG cell and to test it at high gradients in a liquid helium bath at the temperature of 2 Kelvin. The high gradient performance of the cell will be evaluated and the results will be compared to simulations with the CST Microwave Studio.

Slides WEOAB03 [2.061 MB]

WEEPPB011

Analysis of High Field Non-Linear Losses on SRF Surfaces Due to Specific Topographic Roughness

simulation, superconductivity, SRF, feedback

2188

C. Xu
The College of William and Mary, Williamsburg, USA
M.J. Kelley, C.E. Reece, C. Xu
JLAB, Newport News, Virginia, USA

Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The high-field performance of SRF cavities will eventually be limited by the realization of fundamental material limits, whether it be Hc1 or Hsh, or some derivative thereof, at which the superconductivity is lost. Before reaching this fundamental field limit at the macro level, it must be encountered at localized, perhaps microscopic, sites of field enhancement due to local topography. If such sites are small enough, they may produce thermally stabilized normal-conducting regions which contribute non-linear losses when viewed from the macro resonant field perspective, and thus produce degradation in Q0. We have undertaken a calculation of local surface magnetic field enhancement from specific fine topographic structure by conformal mapping method and numerically. A solution of the resulting normal conducting volume has been derived and the corresponding RF ohmic loss simulated.

WEEPPB015

Temperature Dependence of the Superheating Field: DC and RF Critical Fields

cavity, electron, superconductivity, SRF

2197

N.R.A. Valles, M. Liepe
CLASSE, Ithaca, New York, USA

The superheating field is a metastable state at which the Meissner state persists at fields higher than would be predicted from steady-state energy considerations. Previous work demonstrated that a phenomenological approach based on the RF superheating field scaling near the critical temperature is also consistent with low temperature results. This work expands upon the RF results by measuring the DC superheating field, and comparing it to RF results and theoretical predictions.

WEPPC002

Impact of Trapped Flux and Thermal Gradients on the SRF Cavity Quality Factor

cavity, superconducting-cavity, SRF, controls

2203

O. Kugeler, J. Knobloch, J.M. Vogt
HZB, Berlin, Germany
S. Aull
CERN, Geneva, Switzerland

The obtained Q0 value of a superconducting niobium cavity is known to depend on various factors like the RRR of the Niobium material, crystallinity, chemical treatment history, the high-pressure rinsing process, or effectiveness of the magnetic shielding. We have observed that spatial thermal gradients over the cavity length during cool-down appear to contribute to a degradation of Q0. Measurements were performed in the Horizontal Bi-Cavity Test Facility (HoBiCaT) at HZB on TESLA type cavities as well as on disc- and rod-shaped niobium samples equipped with thermal, electrical and magnetic diagnostics. Possible explanations for the effect are discussed.

WEPPC003

Component Qualification and Final Assembly of the S-DALINAC Injector Upgrade Module

cavity, linac, SRF, shielding

2206

J. Conrad, R. Eichhorn, T. Kürzeder, A. Richter, S.T. Sievers
TU Darmstadt, Darmstadt, Germany

Funding: This work is supported by the DFG through SFB 634.
The injector of the S-DALINAC delivers currently electron beams of up to 10 MeV with a current of up to 60 μA. With the new cryostat-module an increase of both parameters, energies ranging to 14 MeV and currents up to 150 μA, are expected. For acceleration, the module houses two 20 cell elliptical niobium cavities which are used at a frequency of 3 GHz in liquid helium at 2 K. The RF power is delivered to the cavities through the different temperature stages by a WR-284 transition line which is connected to the resonator by a new waveguide-to-coax power coupler (being one of the major changes compared to the design of the existing module). We review on the design of the module and present the results of the first cool-down. Also, a report on additional new design features, e.g. piezo actuators for tuning at 2 K, and the production of the cavities will be given.

WEPPC005

Parts Management during Fabrication at the European XFEL

controls, undulator, cavity, cryomodule

2212

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

This presentation describes policies and methods for parts management during fabrication at the European XFEL. The objective is to provide procedures for reliably gathering, recording, processing and archiving the complete mandatory fabrication information. The solution is a foundation for conducting Quality Assurance and Quality Control (QA/QC), as it ensures that acceptance tests are recorded, signed-off and followed-up in a reliable and orderly way. It achieves compliance with legal regulations in certain areas. One example is the pressurized equipment directive (PED), which for certain (parts of) equipment requires that the complete fabrication and usage history is tracked throughout the entire lifespan of the XFEL facility. In addition, the solution provides a basis for building the necessary documentation for later installation, operation and maintenance activities. The solution is established in the series production of several accelerator components. It uses DESY’s Engineering Data Management System as central collaboration and documentation platform.

WEPPC021

Development of Superconducting Radio Frequency Cavities at SINAP

cavity, superconducting-cavity, electron, HOM

2248

J.F. Liu, H.T. Hou, C.W. Lu, C. Luo, Z.Y. Ma, D.Q. Mao, J. Shi, Zh.G. Zhang, S.J. Zhao, X. Zheng
SINAP, Shanghai, People's Republic of China
Z.Q. Feng, Z. Li, J.F. Liu, Y.L. Wei, K. Xu, Y.B. Zhao
Shanghai KEY Laboratory of Cryogenics & Superconducting RF Technology, Shanghai, People's Republic of China
H. Yu
Graduate School of the Chinese Academy of Sciences, Beijing, People's Republic of China

This paper presents the development of superconducting radio frequency cavities at Shanghai Institute of Applied Physics (SINAP) mainly focused on the 500MHz band. Firstly, Two KEKB type 500MHz single cell niobium cavities have been fabricated and one of them has been vertical tested successfully in 2010. The highest accelerating gradient of the fabricated cavity higher than 10MV/m was obtained while the quality factor was better than 4·10⁸ at 4.2K. Secondly, a new type of 500MHz single cell cavity has been designed which adopts the fluted beam pipe for higher order modes propagation and a coaxial type high power input coupler. Thirdly, a 500MHz 5-cell superconducting cavity with large aperture, enlarged beam pipe for HOM propagation and high r/Q value has been optimized which can be a candidate cavity for high current FEL and ERL.

WEPPC032

Analysis of the Four Rod Crab Cavity for HL-LHC

cavity, multipactoring, simulation, luminosity

2275

B.D.S. Hall, P.K. Ambattu, G. Burt, D. Doherty, C. Lingwood
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
P. Goudket
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

The Hi-Lumi Upgrade to the LHC will utilise crab cavities to increase the peak luminosity and provide luminosity levelling at the increased crossing angle. A transversely compact design is required to fit within the limited space between opposing beamlines. In this paper a four rod TEM deflecting cavity (4RCC) is shown to be suitable for LHC. The variation of the deflecting voltage with radial offset has been minimised by careful design and an aluminium prototype has been constructed and beadpull measurements are compared to simulations. Multipacting simulations have been performed on the cavity geometry and it is predicted that the growth rate is less than unity for a clean surface. Pressure variations in the LHe can result in deformation of the complex shape which will alter the resonant frequency. Mechanical simulations have also been performed to assess the sensitivity of the frequency to pressure. In order to reduce the impact of these cavities on the LHC beam low impedance is required for the HOMs as well as the fundamental monopole mode. The couplers for the 4RCC cavity have been optimised to provide effective damping of these modes while rejecting the operating mode.

WEPPC033

RF and Surface Properties of Bulk Niobium and Niobium Film Samples

electron, quadrupole, collider, photon

2278

T. Junginger, W. Weingarten
CERN, Geneva, Switzerland
R. Seviour
University of Huddersfield, Huddersfield, 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. Different models accounting for the field depended surface resistance are being confronted by the experimental results. The RF results are being correlated to surface analyses measurements carried out on the same samples.

WEPPC057

Design of SSR1 Single Spoke Resonators for PXIE

cavity, SRF, cryomodule, coupling

2342

L. Ristori, M.H. Awida, I.V. Gonin, M. Merio, D. Passarelli, V.P. Yakovlev
Fermilab, Batavia, USA

Funding: Operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.
The Project X Injector Experiment (PXIE) at Fermilab contains one cryomodule of Single Spoke Resonators operating at 325 MHz with a geometrical beta of 0.2. Two prototypes have been tested successfully at high gradients in the Fermilab Vertical Test Stand (VTS). We have welded a Stainless Steel helium vessel on the first prototype and tested it in the spoke-dedicated Test Cryostat. With excellent results in hand, an order for ten bare resonators was placed with US industry. A new design for the helium vessel was developed for these resonators with the main goal of reducing the sensitivity of the resonator to variations of the helium pressure to meet the requirements of PXIE. A new tuner was developed despite the good results of the first prototype. The new design was inevitable due to the different behavior of the resonator in the new helium vessel. Other aspects were improved such as the maintainability of the tuner motor and piezoelectric actuators allowing their replacement from access ports on the cryomodule's vacuum vessel.

WEPPC058

Development at ANL of a Copper-brazed Joint for the Coupling of the Niobium Cavity End Wall to the Stainless Steel Helium Vessel in the Fermilab SSR1 Resonator

cavity, vacuum, coupling, SRF

2345

L. Ristori
Fermilab, Batavia, USA
W.F. Toter
ANL, Argonne, USA

Funding: Operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.
In order to reduce the sensitivity of the Fermilab SSR1 resonator to helium pressure variations, it was concluded that the cavity and helium vessel end-walls needed to be structurally coupled by means of a transition ring. With the materials to be connected being Niobium and Stainless Steel, it was decided to utilize the same technology already developed for the cavity flanges which consists of a furnace-brazed joint utilizing oxygen-free electrolytic copper. Small-scale and full-scale annular samples have been constructed at Argonne National Laboratory and subject to tensile tests, thermal cycling and visual inspections to qualify the joint. The transition ring is electron-beam welded to the cavity and TIG welded to the helium vessel, the process is explained in detail.

WEPPC066

Niobium Reaction Kinetics: An Investigation into the Reactions Between Buffered Chemical Polish and Niobium and the Impact on SRF Cavity Etching

cavity, SRF, superconducting-RF

2360

I.M. Malloch, L.J. Dubbs, K. Elliott, R. Oweiss, L. Popielarski
FRIB, East Lansing, Michigan, USA

Funding: Work supported by US DOE Cooperative Agreement DE-SC0000661 and Michigan State University.
In the SRF community, there is no definitive agreement on the precise reaction mechanism in the etching of niobium cavities by buffered chemical polish (BCP) mixtures. As a consequence, it is difficult to predict the heat produced during cavity etching. To gain a better understanding of the reaction kinetics of niobium and BCP, calorimetry experiments were performed to establish an experimental heat of reaction, and research was performed to determine a reasonable reaction scheme to allow for calculation of the theoretical heat of reaction. The results of the calorimetry experiments were in excellent agreement with one another and with the theoretical value. These results will allow for more accurate estimation of etch removal amounts on cavities without the need to perform time-intensive etch rate tests. Applying the experimental data to pre and post cavity etch ultrasonic thickness measurements has shown a significant improvement in the predictability of etch removal amounts in Facility for Rare Isotope Beams (FRIB) half-wave and quarter-wave resonators, and will allow for more reliable heat removal and prevention of Q-disease during other cavity etching procedures.

WEPPC067

Dewar Testing of Coaxial Resonators at MSU

linac, cryomodule, SRF, cavity

2363

J. Popielarski, E.C. Bernard, A. Facco, M. Hodek, F. Marti, D. Norton, G.J. Velianoff, J. Wlodarczak
FRIB, East Lansing, Michigan, USA
A. Burrill, G.K. Davis
JLAB, Newport News, Virginia, USA

Funding: Work supported by US DOE Cooperative Agreement DE-SC0000661 and Michigan State University
Michigan State University is currently testing prototype and production cavities for two accelerator projects. 80.5 MHz β=0.085 quarter wave resonators (QWR) are being produced as part of a cryomodule for ReA3. 322 MHz β=0.53 half wave resonators (HWR) are being prototyped for a driver linac for the Facility for Rare Isotope Beams. This paper will discuss test results and how different cavity preparations effect cavity performs. Also various diagnostics methods have been developed, such as second sound quench location determination, and temperature mapping to determine hot spots from defects and multipacting location.

WEPPC068

Multipacting Simulation and Analysis for the FRIB β = 0.085 Quarter Wave Resonators using Track3P

cavity, simulation, resonance, linac

2366

L. Ge, C. Ko, Z. Li
SLAC, Menlo Park, California, USA
J. Popielarski
FRIB, East Lansing, Michigan, USA

Funding: Work supported by DOE Office of Science under Cooperative Agreement DE- SC0000661, DOE Contract No. DE-AC02-76SF00515, and used resources of NERSC supported by DOE Contract No. DE-AC02- 05CH11231.
The drive linac for the Facility for Rare Isotope Beams (FRIB) utilizes several types of low beta superconducting resonators to accelerate the ion beams from 0.3 MeV per nucleon to 200 MeV per nucleon. Multipacting is an issue of concern for such superconducting resonators as they have unconventional shapes. We have used the parallel codes Tack3P and Omega3P, developed at SLAC under the support of the DOE SciDAC program, to analyze the multipacting barriers of such resonators. In this paper, we will present the simulation results for the β(v/c) = 0.085 Quarter Wave Resonator (QWR) for the FRIB project. Experimental data will also be presented to benchmark with the simulation results.

WEPPC078

Recent Developments in the Cornell Nb3Sn Initiative

cavity, linac, SRF, accelerating-gradient

2390

S. Posen, G.H. Hoffstaetter, M. Liepe, Y. Xie
CLASSE, Ithaca, New York, USA

Superconducting accelerator cavities coated with Nb3Sn have already demonstrated significantly higher unloaded quality factors than standard niobium cavities at surface magnetic fields <30 mT. Theoretical predictions suggest that the maximum critical field of such cavities could be twice that of niobium cavities. Significant facilities have been developed at Cornell University to fabricate Nb3Sn using the vapor diffusion technique. In this paper, recent progress is presented from our Nb3Sn program. The first RF results from a test of a Nb3Sn sample in a TE pillbox sample cavity are presented as well as first images of the newly constructed apparatus for coating full 1.3 GHz single cell cavities.

WEPPC082

First Results on Cornell TE-type Sample Host Cavities

cavity, coupling, vacuum, pick-up

2402

Y. Xie, M. Liepe
CLASSE, Ithaca, New York, USA

Funding: Work supported by NSF and Alfred P. Sloan Foundation.
In order to measure surface resistance of new materials other than niobium such as Nb3Sn and MgB2, two sample host niobium cavities operating at TE modes have been developed at Cornell University. The first one is a 6GHz pillbox TE011 cavity modified from an older vision enabling testing 2.75'' diameter flat sample plates. The second one is an optimized mushroom-shape niobium cavity operating at both 5GHz TE012 and 6GHz TE013 modes for 3.75'' diameter flat sample plates . First results from the commissioning of the two TE cavities will be reported.

WEPPC083

Tunable 28 MHz Superconducting Cavity for RHIC

cavity, superconducting-cavity, site, superconducting-RF

2405

C.H. Boulware, T.L. Grimm
Niowave, Inc., Lansing, Michigan, USA
S.A. Belomestnykh, I. Ben-Zvi
BNL, Upton, Long Island, New York, USA

Funding: This research has been supported by a Department of Energy Small Business Innovative Research Phase II grant through the Nuclear Physics program office, contract #DE-SC0001215.
Replacement of the normal conducting 28 MHz accelerating cavities in the RHIC ring with superconducting structures offers a number of advantages for the machine operation, including reduction of the number of cavities required and improved HOM performance. A prototype folded quarter wave structure is under construction at Niowave, Inc. to meet this need. This novel cavity geometry achieves the very low resonant frequency required with a relatively compact structure, and can provide the large tuning range required (~1% of the cavity frequency). Progress of the cavity fabrication will be presented along with room temperature RF measurements.

WEPPC084

Development of a Superconducting 500 MHz Multi-Spoke Cavity for Electron Linacs

cavity, cryomodule, electron, SRF

2408

D. Gorelov, C.H. Boulware, T.L. Grimm
Niowave, Inc., Lansing, Michigan, USA
S.U. De Silva, J.R. Delayen, C.S. Hopper, R.G. Olave
ODU, Norfolk, Virginia, USA

Funding: This work is supported by the US Department of Energy SBIR/STTR program through the Office of Nuclear Physics.
Multi-spoke cavities are well-known options for acceleration of heavy and light ions. A recently developed multi-spoke cavity for β=1 presents an attractive opportunity to use this cavity type for electron accelerators. One of the main attractive features of this cavity type is its compactness for relatively low frequency. A simplified design at 500 MHz allowed building of a multi-spoke cavity and cryomodule in a 2-year time frame with confidence and development of effective manufacturing techniques. It also constitutes an important step in proving the usefulness of this kind of cavity design for new applications in the electron machines. Niowave is now in a position to build on the success of this cavity to help advance the design of superconducting electron accelerators. Accelerating voltage of more then 4.3 MV in a single cavity at 4.5 K is expected with peak electric field of less then 21.7 MV/m, and peak magnetic field of less then 80 mT. The paper discusses the fabrication challenges of the complete cavity and the cryomodule, as well as room temperature and cryogenic test results.

WEPPC085

Engineering of a Superconducting 400 MHz Crabbing Cavity for the LHC HiLumi Upgrade

cavity, luminosity, collider, SRF

2411

D. Gorelov, T.L. Grimm
Niowave, Inc., Lansing, Michigan, USA
S.U. De Silva, J.R. Delayen
ODU, Norfolk, Virginia, USA

Funding: This work is supported by the US DOE-HEP SBIR/STTR program and the US DOE through the US LHC Accelerator Research Program (LARP).
The recently developed new simplified design for the 400 MHz LHC crabbing cavity presents attractive properties compared to conventional designs. The proposed approach can be equally compact in both transverse dimensions and allows horizontal as well as vertical deflection of the beam in the collider. The significant modification of the parallel-bar design with the bars merged to the side walls of the cavity gives improved properties, such as better mode separation and reduced surface fields*. A transverse deflecting voltage of 3 to 5 MV in a single cavity can be expected with the peak surface electric field lower then 50 MV/m and peak magnetic field below 100 mT. This paper presents engineering issues of the proof-of-concept crabbing cavity design and discusses the manufacturing techniques. The paper discusses present status of the project including fabrication of the niobium cavity, as well as room temperature and cryogenic testing.
* J.R. Delayen, S.U. De Silva, "Design of Superconducting Parallel-Bar Deflecting/Crabbing Cavities with Improved Properties," Proc. of 2011 PAC, New York, NY, USA, 2011, p. 10²¹.

WEPPC091

A Path to Higher Q0 with Large Grain Niobium Cavities

cavity, SRF, accelerating-gradient, induction

2426

P. Dhakal, G. Ciovati, G.R. Myneni
JLAB, Newport News, Virginia, USA

The improvement of the quality factor Q0 of superconducting radio-frequency (SRF) cavities at medium accelerating gradients (~ 20 MV/m) is important in order to reduce the cryogenic losses in continuous wave accelerators for a variety of applications. In recent years, SRF cavities fabricated from ingot niobium have become a viable alternative to standard high-purity fine-grain Nb for the fabrication of high-performing SRF cavities with the possibility of significant cost reduction. Initial studies*,**, demonstrated the improvement of Q0 at medium field in cavities heat treated at 800-1000 °C without subsequent chemical etching. To further explore this treatment procedure, a new induction furnace with an all-niobium hot-zone was commissioned. A single-cell 1.5 GHz cavity fabricated from ingot material from CBMM, Brazil, with RRR~200, was heat treated with the new furnace in the temperature range 600-1400 °C for several hours. Residual resistance values below 5 nano Ω have been consistently achieved on this cavity as well as Q0 values above 4.5×1010 at 2 K and 100 mT peak surface magnetic field. Q0-values of the order of 1011 have been measured at 1.5 K.
* G. Ciovati, et al., Phys. Rev. ST Accel. Beams 13, 022002 (2010).
** G. Ciovati, et al., Proc. of the 15th Int. Conf. on RF Superconductivity, Chicago, July 25-29, 2011, paper TUPO051

WEPPC096

Exploring the Effect of AL2O3 ALD Coating on a High Gradient ILC Single-Cell Cavity

cavity, SRF, electron, site

2441

G.V. Eremeev, A-M. Valente-Feliciano, A.T. Wu
JLAB, Newport News, Virginia, USA
D. Gu
ODU, Norfolk, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Encouraged by work at Argonne National Lab, we investigated atomic layer deposition technique for high gradient superconducting RF cavities at JLab with an ALD coating system of Old Dominion University located on the JLab site. The goal of this study was to look into the possibility of coating a dielectric layer on top of RF niobium surface at a lower temperature of 120 C as compared to ANL coatings at 200 C in order to preserve niobium pentooxide on niobium surface. The initial coatings showed complete, but non-uniform coatings of the surface with several areas exhibiting discoloration, which was probably due to the temperature variation during coatings. The initial coating showed a high RF losses, which were improved after discolored areas on the beam tubes were removed with HF rinse of the beam tubes only. The best result was 2·10⁹ low field Q0 and Eacc = 18 MV/m limited by available power.

WEPPC101

Characteristics and Fabrication of a 499 MHz Superconducting Deflecting Cavity for the Jefferson Lab 12 GeV Upgrade

cavity, vacuum, electron, target

2450

H. Park, S.U. De Silva
JLAB, Newport News, Virginia, USA
J.R. Delayen
ODU, Norfolk, Virginia, USA

A 499 MHz parallel bar superconducting deflecting cavity has been designed and optimized for a possible implementation at the Jefferson Lab 12 GeV upgrade. This paper will present the analysis of the mechanical characteristics of the cavity (pressure sensitivity and tunability) and will detail the fabrication process. The unique geometry of the cavity–which is currently being fabricated at Jefferson Lab–and its required mechanical strength present interesting manufacturing challenges.

WEPPC104

Tomography as a Diagnostic Tool for Plasma Etching of SRF Cavities

plasma, SRF, cavity, diagnostics

2459

M. Nikolić, A.L. Godunov, S. Popović, A. Samolov, L. Vušković
ODU, Norfolk, Virginia, USA
F. Čučkov
Old Dominion University, Norfolk, USA

Plasma based surface modification is a promising alternative for etching of superconductive radio frequency (SRF) cavities. A plasma processed SRF cavity presents a plasma reactor with limited or distorted symmetry. We are developing a tomographic reconstruction of local plasma parameters, as a diagnostic tool in the plasma etching setting of SRF cavities. The method is non-invasive and provides deep insight into the fundamental processes and phenomena during the plasma treatment of SRF cavities’ surfaces. Here we report on our progress in developing tomographic numerical method, based on 2D inverse Radon formula. We tested it on supersonic flowing microwave discharge maintained in the cylindrical quartz tube. Due to the model’s sensitivity to the noise signal in the experiment, an automated measurement system has been built with the aim to increase the overall precision of data acquisition as well as to stream line the measurement process.

WEPPC115

High Q0 in Superconducting Niobium Cavities: Progress at FNAL and Future Plans

cavity, SRF, factory, vacuum

2492

A. Grassellino, L.D. Cooley, C.M. Ginsburg, A. Romanenko, A.M. Rowe, V.P. Yakovlev
Fermilab, Batavia, USA

Consistent improvement in the quality factors of SRF cavities at medium surface fields of about 70 mT represents a direct cost savings factor for the proposed Project X CW linac and other SRF accelerator projects based on CW operation. Current state-of-the-art in SRF does not provide processing recipes to maximize the Q0 at those fields since a complete understanding of the mechanisms governing the quality factor at non-negligible surface fields is not yet developed. In this contribution we present results of the FNAL effort in both scientific understanding and practical improvements and discuss the directions we are pursuing for future research.

WEPPC116

Depth Distribution of Losses in Superconducting Niobium Cavities

cavity, SRF, positron, vacuum

2495

A. Romanenko, A. Grassellino, J.P. Ozelis
Fermilab, Batavia, USA
H. Padamsee
CLASSE, Ithaca, New York, USA

In order to optimize performances of superconducting niobium cavities it is crucial to understand the structure of near-surface few tens of nanometers of the material. In particular, superconducting properties of niobium, which depend on the presence of impurities and/or defects, may be non-uniform in the magnetic field penetration depth. A few cavity experiments based on oxypolishing* and anodizing**,*** provided some insight into the problem, but the definitive understanding is not developed yet. In this contribution we report on the "depth profiling" of the near-surface RF layer using an alternative technique based on the hydrofluoric acid (HF) rinsing. Tumbled, electropolished and buffered chemical polished cavities have been investigated and tentative nanostructural interpretation is discussed.
* P. Kneisel, Proc. of the 1999 SRF Workshop, Santa Fe, USA
** G. Eremeev and H. Padamsee, Physica C 441 No. 1-2 (2006) 62
*** G. Ciovati, P. Kneisel and A. Gurevich, PRSTAB 10 (2007) 062002

THPPC093

SRF Cavity Surface Topography Characterization Using Replica Techniques

cavity, SRF, superconductivity, radio-frequency

3497

C. Xu, M.J. Kelley
The College of William and Mary, Williamsburg, USA
C.E. Reece
JLAB, Newport News, Virginia, USA

Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
To better understand the roll of topography on SRF cavity performance, we seek to obtain detailed topographic information from the curved practical cavity surfaces. Replicas taken from a cavity interior surface provide internal surface molds for fine Atomic Force Microscopy (AFM) and stylus profilometry. In this study, we confirm the replica resolution both on surface local defects such as grain boundary and etching pits and compare the surface uniform roughness with the aid of Power Spectral Density (PSD) where we can statistically obtain roughness parameters at different scales. A series of sampling locations are at the same magnetic field chosen at the same latitude on a single cell cavity to confirm the uniformity. Another series of sampling locations at different magnetic field amplitudes are chosen for this replica on the same cavity for later power loss calculation. We also show that application of the replica followed by rinsing does not adversely affect the cavity performance.