SRF2015 - List of Keywords (cathode)

Paper	Title	Other Keywords	Page
MOPB024	SRF Cavity Breakdown Calculation Procedure Using FEA-Software	cavity, simulation, SRF, niobium	140
	R.A. Kostin, A. Kanareykin Euclid TechLabs, LLC, Solon, Ohio, USA I.V. Gonin Fermilab, Batavia, Illinois, USA E.N. Zaplatin FZJ, Jülich, Germany
	SRF cavity thermal breakdown can be analyzed analytically using thermodynamics equation. This technique is suitable for simple geometries when surface magnetic field variation can be omitted. Thermal radiation effect which is crucial for SRF gun calculations is also hard to implement properly because of complicated geometry. All of these can be overcome by using multiphysics FEA-software. This paper shows the procedure of cavity thermal breakdown calculation in coupled multiphysics analysis with dependable parameters.
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MOPB074	CERN’s Bulk Niobium High Gradient SRF Programme: Developments and Recent Cold Test Results	cavity, niobium, radiation, SRF	291
	A. Macpherson, K.G. Hernández-Chahín, C. Jarrige, P. Maesen, F. Pillon, K.M. Schirm, R. Torres-Sanchez, N. Valverde Alonso CERN, Geneva, Switzerland K.G. Hernández-Chahín DCI-UG, León, Mexico
	Recent results from the bulk niobium high-gradient cavity development program at CERN are presented, with particular focus on test results for the 704 MHz bulk niobium 5-cell elliptical cavity prototypes produced for the Superconducting Proton Linac (SPL) project. Successive cold tests of bare cavities have been used to refine the cavity preparation and testing process, with all steps done in-house at CERN. Current performance results are discussed with reference to observables such as ambient magnetic field, field emission levels, and quenches.
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MOPB092	Economics of Electropolishing Niobium SRF Cavities in Eco-Friendly Aqueous Electrolytes Without Hydrofluoric Acid	cavity, SRF, niobium, accelerating-gradient	359
	E.J. Taylor, T.D. Hall, M.E. Inman, S.T. Snyder Faraday Technology, Inc., Clayton, Ohio, USA D. Holmes AES, Medford, New York, USA A.M. Rowe Fermilab, Batavia, Illinois, USA
	A major challenge for industrialization of SRF cavity fabrication and processing is developing a supply chain to meet the high production demands of the ILC prior to establishment of a long term market need. Conventional SRF cavity electropolishing is based on hydrofluoric-sulfuric acid mixtures. In comparison, FARADAYIC® Bipolar EP applies pulse reverse electrolysis in dilute sulfuric acid-water solutions without hydrofluoric acid and offers substantial savings in operating and capital costs. Based on a preliminary economic analysis of the cavity processing requirements associated with the ILC, we project the cost of FARADAYIC® Bipolar EP to be about 27% that of the Baseline EP. In terms of tangible cost savings, the cost per cavity for the FARADAYIC® Bipolar EP and Baseline EP are \1,293 and \4,828, respectively. The “eco-friendly” intangible cost savings are generally accepted although the cost savings in terms of material degradation and maintenance are difficult to quantify at this time. Continued development and validation of FARADAYIC® Bipolar EP on nine cell cavities will contribute greatly to the industrialization of SRF accelerator technology. Work supported by DOE Grant Nos. DE-SC0011235 and DE-SC0011342 and DOE Purchase Order No. 594128.
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MOPB093	Vertical Electropolishing Studies at Cornell	cavity, SRF, niobium, target	364
	F. Furuta, B. Elmore, G.M. Ge, T. Gruber, G.H. Hoffstaetter, D.K. Krebs, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA T.D. Hall, M.E. Inman, S.T. Snyder, E.J. Taylor Faraday Technology, Inc., Clayton, Ohio, USA H. Hayano, T. Saeki KEK, Ibaraki, Japan Y.I. Ida, K.N. Nii MGH, Hyogo-ken, Japan
	Vertical Electro-Polishing (VEP) has been developed and applied on various SRF R&Ds at Cornell as primary surface process of Nb. Recent achievements had been demonstrated with nitrogen doped high-Q cavities for LCLS-II. Five 9-cell cavities processed with VEP and nitrogen doping at Cornell showed the high average Qo value of 3.0·10¹⁰ at 16MV/m, 2K, during vertical test. this achievement satisfied the required cavity specification values of LCLS-II(2.7·10¹⁰ at 16MV/m, 2K). We will report the details of these achievements and new VEP collaboration projects between Cornell and companies.
	Poster MOPB093 [4.364 MB]
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MOPB096	Vertical Electro-Polishing at TRIUMF	cavity, TRIUMF, operation, niobium	378
	J.J. Keir, P.R. Harmer, D. Lang, R.E. Laxdal, T. Shishido, R. Smith TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada T. Shishido KEK, Ibaraki, Japan
	A setup for electropolishing of a superconducting niobium single-cell cavity has been installed at TRIUMF. A vertical method was selected to make the setup compact. To increase removal speed at the equator and remove hydrogen bubbles at the iris surface, 4 cathode paddles were rotated in the cavity cell during electropolishing. We will report on our first electropolishing result.
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MOPB098	Improvement of Temperature Control During Nb 9-Cell SRF Cavity Vertical Electro-Polishing (VEP) and Progress of VEP Quality	cavity, experiment, controls, SRF	381
	K.N. Nii, V. Chouhan, Y.I. Ida, T.Y. Yamaguchi MGH, Hyogo-ken, Japan H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe KEK, Ibaraki, Japan K. Ishimi MGI, Chiba, Japan
	Marui Galvanizing Co.,Ltd. has been developing Nb 9-cell SRF cavity vertical electro-polishing (VEP) facility and technique for mass production in collaboration with KEK. Our first 9-cell cavity VEP facility was not enough to control temperature during VEP, so the polishing quality was not so high. In this article, we will report the progress of temperature distribution and polishing quality due to the improvement of temperature control system of electrolyte and cavity during VEP.
	Poster MOPB098 [0.988 MB]
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MOPB100	Cathode Geometry and Flow Dynamics Impact on Vertical Electropolishing of Superconducting Niobium Cavities	cavity, niobium, simulation, operation	385
	L.M.A. Ferreira CERN, Geneva, Switzerland
	CERN has now a fully operating vertical electropolishing installation, which has been used for the processing of 704 MHz high-beta five-cell Superconducting Proton Linac (SPL) niobium cavities. This installation relies only on the electrolyte circulation (HF/H2SO4) for power dissipation, evacuation of gases and homogeneous finishing; thus, parameters like cathode geometry, electrolyte flow and temperature become even more crucial when compared with horizontal electropolishing installations. Based on computational simulations performed with Comsol Multiphysics® and on a methodology developed at CERN, it is possible to assess the impact of the different cathode geometries as well as of the flow on the etching rate distribution. The data obtained with two different cathode geometries are presented: electrolyte velocity distribution, etching rate distribution, average current density and minimum working potential. One geometry was defined through a purely electrochemical approach while the second was defined to minimise the difference between the maximum and the minimum electrolyte speed inside the cavity; in both cases, the influence of the electrolyte flow was taken into account.
	Poster MOPB100 [1.794 MB]
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MOPB101	Electropolishing of Niobium SRF Cavities in Eco-Friendly Aqueous Electrolytes Without Hydrofluoric Acid	cavity, niobium, SRF, target	390
	M.E. Inman, T.D. Hall, S. Lucatero, S.T. Snyder, E.J. Taylor Faraday Technology, Inc., Clayton, Ohio, USA F. Furuta, G.H. Hoffstaetter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA J.D. Mammosser ORNL, Oak Ridge, Tennessee, USA A.M. Rowe Fermilab, Batavia, Illinois, USA
	Electropolishing of niobium cavities is conventionally conducted in high viscosity electrolytes consisting of concentrated sulfuric and hydrofluoric acids. This use of dangerous and ecologically damaging chemicals requires careful attention to safety protocols to avoid harmful worker exposure and environmental damage. We present an approach for electropolishing of niobium materials based on pulse reverse waveforms, enabling the use of low viscosity aqueous dilute sulfuric acid electrolytes without hydrofluoric acid, or aqueous near-neutral pH salt solutions without any acid. Results will be summarized for both cavity and coupon electropolishing for bulk and final polishing steps. With minimal optimization of pulse reverse waveform parameters we have demonstrated the ability to electropolish single-cell niobium SRF cavities and achieve at least equivalent performance compared to conventionally processed cavities. Cavities are electropolished in a vertical orientation filled with electrolyte and without rotation, offering numerous advantages from an industrial processing perspective. Shielding, external cooling and high surface area cathodes are adaptable to the bipolar EP process. Work supported by DOE Grant Nos. DE-SC0011235 and DE-SC0011342 and DOE Purchase Order No. 594128.
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MOPB102	Comments on Electropolishing at Ettore Zanon SpA at the End of EXFEL Production	cavity, niobium, controls, acceleration	394
	M. Rizzi, G. Corniani Ettore Zanon S.p.A., Schio, Italy A. Matheisen DESY, Hamburg, Germany P. Michelato INFN/LASA, Segrate (MI), Italy
	In 2013 a new horizontal Electropolishing facility was developed and implemented by Ettore Zanon SpA (EZ) for the treatment of cavities for the European XFEL series production. More than 300 cavities have been treated. Electropolishing has been used for two applications: bulk removal and recovering of cavities with surface defects. Treatment settings have been analysed and compared with cavities performances to verify possible influences of the various parameters. Main parameters considered are treatment time, voltage and current, that together define average thickness removal. We present here the results of these investigation. The facility and process in use are also presented, together with possible next upgrade of the system, facing the new production of cavities for the LCLSII project.
	Poster MOPB102 [1.535 MB]
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MOPB105	Symmetric Removal of Niobium Superconducting RF Cavity in Vertical Electropolishing	cavity, experiment, accumulation, niobium	409
	V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi MGH, Hyogo-ken, Japan H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe KEK, Ibaraki, Japan K. Ishimi MGI, Chiba, Japan
	Vertical electropolishing (VEP) leads several advantages over horizontal EP in respect of easy operation and mechanism of an EP system resulting in lower cost. However, till yet VEP always resulted inhomogeneous removal of a niobium (Nb) cavity along its length and bubble traces especially on the top iris of a vertically set cavity. In this work we performed lab EP and VEP experiments in order to study and solve these two problems. A coupon cavity which contains 6 disk type Nb coupons positioned at beam pipes, irises and equator was vertically electropolished to optimize VEP parameters so as to get almost uniform removal of Nb and a smooth surface of the cavity without bubble traces. Our patented unique i-Ninja cathode having 4 wings was used with an optimized rotation speed to get homogeneous removal of Nb. The homogeneous removal and the surface without bubble traces might be result of a uniform thickness of a viscous layer on the surface of the cavity cell and no accumulation of hydrogen bubbles on the top iris surface. The surfaces of the coupons were studied in detail with surface analytical tools.
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MOPB110	The Transfer of Improved Cavity Processing Protocols to Industry for LCLS-II: N-Doping and Electropolishing	cavity, niobium, controls, superconductivity	418
	C.E. Reece, F. Marhauser, A.D. Palczewski JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 with supplemental funding from the LCLS-II Project U.S. DOE Contract No. DE-AC02-76SF00515. Based on the R&D efforts of colleagues at FNAL, Cornell, and JLab, the LCLS-II project adopted a modification to the rather standard niobium SRF cavity surface processing protocol that incorporates a high temperature diffusion doping with nitrogen gas. This change was motivated by the resulting higher Q0 and the prospect of significantly lower cryogenic heat load for LCLS-II. JLab is responsible for managing the cavity procurement for the LCLS-II project. The first phase of the procurement action is to transfer the nitrogen-doping protocol to the industrial vendors. We also seek to exploit improvements in understanding of the niobium electropolishing process as part of the production processing of the TESLA-style LCLS-II cavities. We report on the technology transfer activities and progress toward the envisaged performance demonstration of vendor-processed cavities.
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TUPB003	Cavity Procurement and Qualification Plan for LCLS-II	cavity, controls, hardware, site	529
	F. Marhauser, E. Daly, J.A. Fitzpatrick JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 with supplemental funding from the LCLS-II Project U.S. DOE Contract No. DE-AC02-76SF00515. The LCLS-II project aims to build 35 accelerating cryomodules, which are based on the European XFEL design but modified for operation in CW mode. Each cryomodule houses eight TESLA-style nine-cell superconducting radio-frequency cavities. The activities to assemble the first two prototype cryomodules are ongoing at FNAL and JLab. 264 cavities worth of cavities for the remaining 33 cryomodules will be procured from two industrial vendors in similar quantity considering the option to produce spares. The assembly of cavities into the production cryomodules will be distributed among FNAL (16 cryomodules) and JLab (17 cryomodules). In this paper the cavity procurement and qualification plan for the LCLS-II project is detailed.
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TUPB010	Plug Transfer System for GaAs Photocathodes	gun, SRF, operation, vacuum	553
	P. Murcek, A. Arnold, P.N. Lu, J. Teichert, H. Vennekate, R. Xiang HZDR, Dresden, Germany A. Burrill HZB, Berlin, Germany
	The transport and exchange technology of Cs2Te photocathode for the ELBE superconducting rf photoinjector (SRF gun) has been successfully developed and tested at HZDR. The next goal is to realize the transport of GaAs photocathode into SRF gun, which will need a new transfer system with XHV 10^-11 mbar. The key component of the system is the transfer chamber and the load-lock system that will be connected to the SRF-gun. In the carrier four small plugs will be transported, and one of them will be plug on the cathode-body and inserted into the cavity. The new transport chamber allows the transfer and exchange of plugs between HZDR, HZB and other cooperating institutes. In HZDR this transfer system will also provide a direct connection between the SRFGUN and the GaAs preparation chamber in the Elbe-accelerator hall.
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TUPB027	Developments on SRF Coatings at CERN	cavity, SRF, plasma, simulation	617
	A. Sublet, S. Aull, B. Bártová, S. Calatroni, T. Richard, G.J. Rosaz, M. Taborelli, M. Therasse, W. Venturini Delsolaro, P. Zhang CERN, Geneva, Switzerland
	The thin films techniques applied to Superconducting RF (SRF) has a long history at CERN. A large panel of cavities have been coated from LEP, to LHC. For the current and future projects (HIE-ISOLDE, HL-LHC, FCC) there is a need for further higher RF-performances with focus on minimizing residual resistance Rres and maximizing quality factor Q0 of the cavities. This paper will present CERN’s developments on thin films to achieve these goals through the following main axes of research: The first one concerns the application of different coating techniques for Nb (DC-bias diode sputtering, magnetron sputtering and HiPIMS). Another approach is the investigation of alternative materials like Nb3Sn. These lines of development will be supported by a material science approach to characterize and evaluate the layer properties by means of FIB-SEM, TEM, XPS, XRD, etc. In addition a numerical tool for plasma simulation will be exploited to develop adapted coating systems and optimize the coating process, from plasma generation to thin film growth.
	Poster TUPB027 [1.070 MB]
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TUPB032	Energetic Condensation Growth of Nb on Cu SRF Cavities	cavity, niobium, SRF, plasma	629
	K.M. Velas, S.F. Chapman, I. Irfan, M. Krishnan AASC, San Leandro, California, USA
	Funding: This research is supported by the US DOE via and SBIR grant: DE-SC0011371 Alameda Applied Sciences Corporation (AASC) grows Nb thin films via Coaxial Energetic Deposition (CED) from a cathodic arc plasma. The plasma from the cathode consists exclusively of 60-120eV Nb ions (Nb+ and Nb2+) that penetrate a few monolayers into the substrate and enable sufficient surface mobility to ensure that the lowest energy state (crystalline structure with minimal defects) is accessible to the film. AASC is coating 1.3 GHz SRF cavities using a graded anode to ensure uniform film thickness in the beam tube and elliptical regions. Copper cavities are centrifugal barrel polished and electropolished (done for us by the Fermilab Technical Division, Superconducting RF Development Department and by Thomas Jefferson National Accelerator Facility (JLAB)) before coating, to ensure good adhesion and improved film quality. The Nb coated copper cavities will undergo RF tests at JLAB and at Fermilab to measure Qo vs. E.
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TUPB034	Bulk Niobium Polishing and Electropolishing Steps for Thinfilm Coated Copper SRF Cavities	cavity, SRF, ion, plasma	633
	M. Krishnan, S.F. Chapman, I. Irfan, K.M. Velas AASC, San Leandro, California, USA J.K. Spradlin, H. Tian JLab, Newport News, Virginia, USA
	Funding: Research supported at AASC by the US DOE via SBIR grant: DE-SC0011371. The JLab effort was provided by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 Alameda Applied Sciences Corporation (AASC) grows Nb thin films via Coaxial Energetic Deposition (CED) from a cathodic arc plasma. The plasma consists of 60-120eV Nb ions (Nb+ and Nb++) [1] that penetrate a few monolayers into the substrate [2] and enable sufficient surface mobility to ensure that the lowest energy state (crystalline structure with minimal defects) is accessible to the film [3]. One limitation of CED thinfilms is the presence of Nb macroparticles (~0.1-10 microns) that could be deleterious to high field performance of the SRF cavity. One way to remove such macroparticles [4] is to grow a thick film (~3-5 microns), followed by mechanical polishing (MP) using the finest media as might be applied in Centrifugal Barrel Polishing (CBP) to achieve a 0.4 micron surface figure, and an electropolishing (EP) step to remove ~1 micron of Nb that also removes all traces of embedded media in the film. The residual 2-4 micron Nb film should more nearly resemble the surface of a bulk Nb cavity that has been subjected to the same steps. This paper describes experiments conducted on Cu coupons as a prelude to an SRF Cu cavity coating.
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TUPB047	Next Generation of SRF-Guns: Low Secondary Electron Yield Based on a Thin Film Approach	electron, target, gun, SRF	673
	C. Schlemper, X. Jiang, M. Vogel University Siegen, Siegen, Germany
	Multipacting is a common issue in the context of cathode units of superconducting radiofrequency photoinjectors (SRF-guns) utilized in linear accelerators under resonant conditions. In this study, Titanium Nitride (TiN) and Carbon thin films have been prepared by DC and RF magnetron sputtering in a Nitrogen and Argon plasma discharge, respectively. Films featuring a thickness of about 600 nm were produced under various deposition conditions on substrates such as Copper, Molybdenum, and Silicon. Materials characterization was carried out utilizing SEM, Raman and FTIR spectroscopy, XRD and AFM. In order to evaluate the SEY a new device is introduced, which is capable of quasi in-situ measurements. The latter is realized by connecting the coating-, the SEY- and a contamination chamber into one setup allowing sample transfer under UHV conditions. Even after an exposure to air carbon shows SEY values down to 0.69. This value, however, turns out to be quite sensitive with respect to the actual surface morphology. Clean TiN surfaces, on the other hand, displayed a SEY value as low as 1.4. In this case the SEY value is strongly affected by potential surface contamination.
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TUPB077	The Influence of Cooldown Conditions at Transition Temperature on the Quality Factor of Niobium Sputtered Quarter-Wave Resonators for HIE-ISOLDE	cavity, niobium, accelerating-gradient, linac	765
	P. Zhang, G.J. Rosaz, A. Sublet, M. Therasse, W. Venturini Delsolaro CERN, Geneva, Switzerland
	Funding: This work has been supported partly by a Marie Curie Early Initial Training Network Fellowship of the European Community’s 7th Programme under contract number PITN-GA-2010-264330-CATHI. Superconducting quarter-wave resonators (QWRs) are to be used in the ongoing linac upgrade of the ISOLDE facility at CERN. The cavities are made of niobium sputtered on copper substrates. They will be operated at 101.28 MHz at 4.5 K providing 6 MV/m accelerating gradient with 10 W power dissipation. In recent measurements, we found the thermal gradient along the cavity during the niobium superconducting transition has an impact on the cavity quality factor. On the other hand, the speed of the cooling down through the superconducting transition turned out to have no influence on the cavity Q-factor.
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THAA02	SRF Gun Development Overview	gun, cavity, SRF, electron	994
	J.K. Sekutowicz DESY, Hamburg, Germany
	The most demanding component of a continuous wave (cw) injector is cw operating RF-gun, delivering highly populated low emittance bunches. RF-guns, both working at room temperature and superconducting, when they generate highly populated low emittance bunches have to be operated at high accelerating gradients to suppress space charge effects diluting emittance. Superconducting RF-guns are technically superior to the normal conducting devices because they dissipate orders of magnitude less power when operating at very high gradients in cw mode. In this contribution progress since 2013 in the R&D programs, designing and operation of the SRF-injectors at KEK, HZB, HZDR, PKU and DESY will be discussed.
	Slides THAA02 [6.107 MB]
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THAA03	SRF Gun at BNL: First Beam and Other Commissioning Results	gun, SRF, cavity, electron	1001
	W. Xu, Z. Altinbas, S.A. Belomestnykh, I. Ben-Zvi, L. DeSanto, S. Deonarine, D.M. Gassner, R.C. Gupta, H. Hahn, L.R. Hammons, C. Ho, J.P. Jamilkowski, P. K. Kankiya, D. Kayran, R. Kellermann, N. Laloudakis, R.F. Lambiase, C.J. Liaw, V. Litvinenko, G.J. Mahler, L. Masi, G.T. McIntyre, T.A. Miller, D. Phillips, V. Ptitsyn, T. Rao, T. Seda, B. Sheehy, K.S. Smith, A.N. Steszyn, T.N. Tallerico, R. Than, J.E. Tuozzolo, E. Wang, D. Weiss, M. Wilinski, A. Zaltsman, Z. Zhao BNL, Upton, Long Island, New York, USA S.A. Belomestnykh, I. Ben-Zvi, V. Litvinenko Stony Brook University, Stony Brook, USA
	The talk shall cover two SRF photoemission electron guns under commissioning at BNL: a 704 MHz elliptical ERL gun and a 112 MHz quarter-wave gun for coherent electron cooling experiment. In particular, the speaker shall report on generating first photoemission beam current from the 704 MHz SRF gun, multipacting issues in the SRF guns, photocathode behavior as well as other commissioning experiences and results.
	Slides THAA03 [2.215 MB]
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THBA02	Recent Development in Vertical Electropolishing	cavity, experiment, ion, SRF	1024
	V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi MGH, Hyogo-ken, Japan H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe KEK, Ibaraki, Japan K. Ishimi MGI, Chiba, Japan
	Horizontal electropolishing (HEP) is being used for final surface treatment of niobium SRF cavities. However a HEP system is equipped with complicated mechanism that makes it expensive and enhances cost of surface treatment of cavities especially when mass production is considered. Vertical electropolishing (VEP) has been introduced by other labs and the research is being carried out to establish the VEP technique. The VEP system requires simple mechanism and has advantages over HEP setup. Positive results have been obtained from the VEPed cavities also as shown by other labs. However further improvement in a VEP setup, cathode and VEP parameters is required. Marui Galvanizing Co., Ltd in collaboration with KEK has been working for development of VEP system, optimization of cathode and VEP parameters to obtain uniform Nb removal with a smooth surface of a cavity. Here we report our recent development of VEP system, unique Ninja cathode and parameter optimization with a 1-cell coupon cavity containing 6 Nb disk coupons at the beam pipes, irises and equator. The coupon surfaces were analyzed to obtain detail of the cavity surface.
	Slides THBA02 [5.703 MB]
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THPB047	Analysis of a 750 MHz SRF Dipole Cavity	cavity, dipole, simulation, cryogenics	1200
	A. Castilla, J.R. Delayen ODU, Norfolk, Virginia, USA A. Castilla, J.R. Delayen JLab, Newport News, Virginia, USA A. Castilla DCI-UG, León, Mexico
	Funding: Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177. There is a growing interest in using rf transverse deflecting structures for a plethora of applications in the current and future high performance colliders. In this paper, we present the results of a proof of principle superconducting rf dipole, designed as a prototype for a 750 MHz crabbing corrector for the Medium Energy Electron-Ion Collider (MEIC), which has been successfully tested at 4.2 K and 2 K at the Jefferson Lab’s Vertical Testing Area (VTA). The analysis of its rf performance during cryogenic testing, along with Helium pressure sensitivity, Lorentz detuning, surface resistance, and multipacting processing analysis are presented in this work. Detailed calculations of losses at the port flanges are included for completeness of the cavity’s cryogenic performance studies.
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THPB048	Design of a Compact Superconducting Crab-Cavity for LHC Using Nb-on-Cu-Coating Technique	cavity, impedance, HOM, SRF	1205
	A. Grudiev, S. Atieh, R. Calaga, S. Calatroni, O. Capatina, F. Carra, G. Favre, L.M.A. Ferreira, J.-F. Poncet, T. Richard, A. Sublet, C. Zanoni CERN, Geneva, Switzerland
	The design of a compact superconducting crab-cavity for LHC using Nb-on-Cu-coating technique is presented. The cavity shape is based on the ridged waveguide resonator with wide open apertures to provide access to the inner surface of the cavity for coating. It also provides natural damping for HOMs and rather low longitudinal and transverse impedances. The results of the cavity shape optimization taking into account RF performance, coating, and thermo-mechanical considerations as well as the design and fabrication plans of the first prototype for coating and cold tests are presented.
	Poster THPB048 [0.534 MB]
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THPB055	RF Performance Results of the 2nd ELBE SRF Gun	gun, SRF, cavity, electron	1227
	A. Arnold, M. Freitag, P.N. Lu, P. Murcek, J. Teichert, H. Vennekate, R. Xiang HZDR, Dresden, Germany G. Ciovati, P. Kneisel, M. Stirbet, L. Turlington JLab, Newport News, Virginia, USA
	As in 2007 the first 3.5 cell superconducting radio frequency (SRF) gun was taken into operation at Helmholtz-Zentrum Dresden-Rossendorf, it turned out that the specified performance to realize an electron energy of 9.4 MeV has not been achieved. Instead, the resonator of the gun was limited by field emission to about one third of this value and the measured beam parameters remained significantly below its expectations. However, to demonstrate the full potential of this electron source for the ELBE linear accelerator, a second and slightly modified SRF gun was developed and built in collaboration with Thomas Jefferson National Accelerator Facility. We will report on commissioning of this new SRF gun and present a full set of RF performance results. Additionally, investigations are shown that try to explain a particle contamination that happened recently during our first cathode transfer.
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THPB056	SRF Gun Cavity R&D at DESY	cavity, SRF, gun, operation	1231
	D. Kostin, C. Albrecht, A. Brinkmann, Th. Buettner, J. Eschke, T. Feldmann, A. Gössel, D. Klinke, A. Matheisen, W.-D. Möller, D. Reschke, M. Schmökel, J.K. Sekutowicz, W. Singer, X. Singer, N. Steinhau-Kühl, J. Ziegler, B. van der Horst DESY, Hamburg, Germany M. Barlak, J.A. Lorkiewicz, R. Nietubyć NCBJ, Świerk/Otwock, Poland
	SRF Gun Cavity is an ongoing accelerator R&D project at DESY, being developed since several years. Currently several SRF Gun cavity prototypes were simulated, built and tested in our Lab and elsewhere. Lately the 1.6 cells Pb thin film cathode niobium cavity was tested in a vertical cryostat with a different cathode plug configurations. Cathode plug design was improved, as well as SRF Gun Cavity cleaning procedures. Results of the last cavity performance tests are presented and discussed.
	Poster THPB056 [1.257 MB]
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THPB057	ELBE SRF Gun II - Emittance Compensation Schemes	emittance, gun, focusing, SRF	1235
	H. Vennekate, A. Arnold, D. Janssen, P.N. Lu, P. Murcek, J. Teichert, R. Xiang HZDR, Dresden, Germany P. Kneisel JLab, Newport News, Virginia, USA
	In May 2014 the first SRF photo injector at HZDR has been replaced by a new gun, featuring a new resonator and cryostat. The intention for this upgrade has been to reach for higher beam energies, bunch charges and therefore an increased average beam current, which is to be injected into the superconducting, CW ELBE accelerator, where it can be used for multiple purposes, such as THz generation or Compton backscattering. Because of the increased bunch charge of this injector compared to its predecessor, it demands upgrades of the existing and/or novel approaches to alleviate the transverse emittance growth. One of these methods is the integration of a superconducting solenoid into the cryostat. Another method, the so called RF focusing, is realized by displacing the photo cathode's tip and retracting it from the last cell of the resonator. In this case, part of the accelerating field is sacrificed for a better focus of the electron bunch right at the start of its generation. Besides particle tracking simulations, a recent study, investigating on the exact position of the cathode tip with respect to the cell's back plane after tuning and cool down, has been performed.
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THPB058	Commissioning of the 112 MHz SRF Gun	gun, SRF, electron, laser	1240
	S.A. Belomestnykh, I. Ben-Zvi, J.C. Brutus, T. Hayes, V. Litvinenko, K. Mernick, G. Narayan, P. Orfin, I. Pinayev, T. Rao, F. Severino, J. Skaritka, K.S. Smith, R. Than, J.E. Tuozzolo, E. Wang, Q. Wu, B. P. Xiao, A. Zaltsman BNL, Upton, Long Island, New York, USA S.A. Belomestnykh, I. Ben-Zvi, V. Litvinenko, T. Xin Stony Brook University, Stony Brook, USA
	Funding: Work is supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE. A 112 MHz superconducting RF photoemission gun was designed, fabricated and installed in RHIC for the Coherent electron Cooling Proof-of-Principle (CeC PoP) experiment at BNL. The gun was commissioned first without beam. This was followed by generating the first photoemission beam from a multi-alkali cathode. The paper presents the commissioning results.
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THPB059	Design, Fabrication and Performance of SRF-Gun Cavity	cavity, gun, SRF, target	1243
	T. Konomi, E. Kako, Y. Kobayashi, K. Umemori, S. Yamaguchi KEK, Ibaraki, Japan R. Matsuda Mitsubishi Heavy Industries Ltd. (MHI), Takasago, Japan T. Yanagisawa MHI, Hiroshima, Japan
	The development of superconducting RF gun has been started at KEK. The performance targets are that average current is 100 mA, normalized emittance is less than 1 μm.rad, beam energy is 2 MeV and energy spread is less than 0.1 %. The SRF gun consists of 1.3 GHz and 1.5 cell elliptical cavity and backward illuminated photocathode. The cavity shape was designed by using SUPERFISH and GPT. The cavity has been fabricated by Japanese industry. Accelerating field tuning and vertical test without cathode plug was done. The surface peak electric field reached 66 MV/m, and this meet the target value 42 MV/m sufficiently. For next vertical test, cathode rod without photocathode is in preparation. In the workshop, the SRF-Gun concepts and vertical test results will be reported.
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THPB083	Energetic Copper Coating on Stainless Steel Power Couplers for SRF Application	SRF, plasma, laser, ion	1330
	I. Irfan, S.F. Chapman, M. Krishnan, K.M. Velas AASC, San Leandro, California, USA W. Kaabi LAL, Orsay, France
	Funding: This research is supported by the US DOE via and SBIR grant: DE-SC0009581 Delivering RF power from the outside (at room temperature) to the inside of SRF cavities (at ~4 K temperature), requires a power coupler to be thermally isolating, while still electrically conducting on the inside. Stainless steel parts that are coated on the insides with a few skin depths of copper can meet these conflicting requirements. The challenge has been the adhesion strength of copper coating on stainless steel coupler parts when using electroplating methods. These methods also require a nickel flash layer that is magnetic and can therefore pose problems. Alameda Applied Sciences Corporation (AASC) uses Coaxial Energetic Deposition (CED) from a cathodic arc plasma to grow copper films directly on stainless steel coupler parts with no Ni layer and no electrochemistry. The vacuum arc plasma consists of ~100 eV Cu ions that penetrate a few monolayers into the stainless steel substrate to promote growth of highly adhesive films with crystalline structure. Adhesion strength and coating quality of copper coatings on complex stainless steel tubes, bellows, mock coupler parts and an actual Tesla Test Facility (TTF) type coupler part, are discussed. * Adhesion and Cu quality testing were done for us by the Fermilab Technical Division, Superconducting RF Development Department
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FRBA03	SRF, Compact Accelerators for Industry & Society	cavity, SRF, electron, gun	1467
	R.D. Kephart, B.E. Chase, I.V. Gonin, A. Grassellino, S. Kazakov, T.N. Khabiboulline, S. Nagaitsev, R.J. Pasquinelli, S. Posen, O.V. Pronitchev, A. Romanenko, V.P. Yakovlev Fermilab, Batavia, Illinois, USA S. Biedron, S.V. Milton, N. Sipahi CSU, Fort Collins, Colorado, USA S. Chattopadhyay Northern Illinois Univerity, Dekalb, Illinois, USA P. Piot Northern Illinois University, DeKalb, Illinois, USA
	Accelerators developed for Science now are used broadly for industrial, medical, and security applications. Over 30,000 accelerators touch over $500B/yr in products producing a major impact on our economy, health, and well being. Industrial accelerators must be cost effective, simple, versatile, efficient, and robust. Many industrial applications require high average beam power. Exploiting recent advances in Superconducting Radio Frequency (SRF) cavities and RF power sources as well as innovative solutions for the SRF gun and cathode system, a collaboration of Fermilab-CSU-NIU has developed a design for a compact SRF high-average power electron linac. Capable of 5-50 kW average power and continuous wave operation this accelerator will produce electron beam energies up to 10 MeV and small and light enough to mount on mobile platforms, such accelerators will enable new in-situ environmental remediation methods and new applications involving in-situ crosslinking of materials. More importantly, we believe this accelerator will be the first of a new class of simple, turn-key SRF accelerators that will find broad application in industry, medicine, security, and science.
	Slides FRBA03 [2.342 MB]
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Paper

Title

Other Keywords

Page

MOPB024

SRF Cavity Breakdown Calculation Procedure Using FEA-Software

cavity, simulation, SRF, niobium

140

R.A. Kostin, A. Kanareykin
Euclid TechLabs, LLC, Solon, Ohio, USA
I.V. Gonin
Fermilab, Batavia, Illinois, USA
E.N. Zaplatin
FZJ, Jülich, Germany

SRF cavity thermal breakdown can be analyzed analytically using thermodynamics equation. This technique is suitable for simple geometries when surface magnetic field variation can be omitted. Thermal radiation effect which is crucial for SRF gun calculations is also hard to implement properly because of complicated geometry. All of these can be overcome by using multiphysics FEA-software. This paper shows the procedure of cavity thermal breakdown calculation in coupled multiphysics analysis with dependable parameters.

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MOPB074

CERN’s Bulk Niobium High Gradient SRF Programme: Developments and Recent Cold Test Results

cavity, niobium, radiation, SRF

291

A. Macpherson, K.G. Hernández-Chahín, C. Jarrige, P. Maesen, F. Pillon, K.M. Schirm, R. Torres-Sanchez, N. Valverde Alonso
CERN, Geneva, Switzerland
K.G. Hernández-Chahín
DCI-UG, León, Mexico

Recent results from the bulk niobium high-gradient cavity development program at CERN are presented, with particular focus on test results for the 704 MHz bulk niobium 5-cell elliptical cavity prototypes produced for the Superconducting Proton Linac (SPL) project. Successive cold tests of bare cavities have been used to refine the cavity preparation and testing process, with all steps done in-house at CERN. Current performance results are discussed with reference to observables such as ambient magnetic field, field emission levels, and quenches.

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MOPB092

Economics of Electropolishing Niobium SRF Cavities in Eco-Friendly Aqueous Electrolytes Without Hydrofluoric Acid

cavity, SRF, niobium, accelerating-gradient

359

E.J. Taylor, T.D. Hall, M.E. Inman, S.T. Snyder
Faraday Technology, Inc., Clayton, Ohio, USA
D. Holmes
AES, Medford, New York, USA
A.M. Rowe
Fermilab, Batavia, Illinois, USA

A major challenge for industrialization of SRF cavity fabrication and processing is developing a supply chain to meet the high production demands of the ILC prior to establishment of a long term market need. Conventional SRF cavity electropolishing is based on hydrofluoric-sulfuric acid mixtures. In comparison, FARADAYIC® Bipolar EP applies pulse reverse electrolysis in dilute sulfuric acid-water solutions without hydrofluoric acid and offers substantial savings in operating and capital costs. Based on a preliminary economic analysis of the cavity processing requirements associated with the ILC, we project the cost of FARADAYIC® Bipolar EP to be about 27% that of the Baseline EP. In terms of tangible cost savings, the cost per cavity for the FARADAYIC® Bipolar EP and Baseline EP are \1,293 and \4,828, respectively. The “eco-friendly” intangible cost savings are generally accepted although the cost savings in terms of material degradation and maintenance are difficult to quantify at this time. Continued development and validation of FARADAYIC® Bipolar EP on nine cell cavities will contribute greatly to the industrialization of SRF accelerator technology.
Work supported by DOE Grant Nos. DE-SC0011235 and DE-SC0011342 and DOE Purchase Order No. 594128.

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MOPB093

Vertical Electropolishing Studies at Cornell

cavity, SRF, niobium, target

364

F. Furuta, B. Elmore, G.M. Ge, T. Gruber, G.H. Hoffstaetter, D.K. Krebs, J. Sears
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
T.D. Hall, M.E. Inman, S.T. Snyder, E.J. Taylor
Faraday Technology, Inc., Clayton, Ohio, USA
H. Hayano, T. Saeki
KEK, Ibaraki, Japan
Y.I. Ida, K.N. Nii
MGH, Hyogo-ken, Japan

Vertical Electro-Polishing (VEP) has been developed and applied on various SRF R&Ds at Cornell as primary surface process of Nb. Recent achievements had been demonstrated with nitrogen doped high-Q cavities for LCLS-II. Five 9-cell cavities processed with VEP and nitrogen doping at Cornell showed the high average Qo value of 3.0·10¹⁰ at 16MV/m, 2K, during vertical test. this achievement satisfied the required cavity specification values of LCLS-II(2.7·10¹⁰ at 16MV/m, 2K). We will report the details of these achievements and new VEP collaboration projects between Cornell and companies.

Poster MOPB093 [4.364 MB]

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MOPB096

Vertical Electro-Polishing at TRIUMF

cavity, TRIUMF, operation, niobium

378

J.J. Keir, P.R. Harmer, D. Lang, R.E. Laxdal, T. Shishido, R. Smith
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
T. Shishido
KEK, Ibaraki, Japan

A setup for electropolishing of a superconducting niobium single-cell cavity has been installed at TRIUMF. A vertical method was selected to make the setup compact. To increase removal speed at the equator and remove hydrogen bubbles at the iris surface, 4 cathode paddles were rotated in the cavity cell during electropolishing. We will report on our first electropolishing result.

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MOPB098

Improvement of Temperature Control During Nb 9-Cell SRF Cavity Vertical Electro-Polishing (VEP) and Progress of VEP Quality

cavity, experiment, controls, SRF

381

K.N. Nii, V. Chouhan, Y.I. Ida, T.Y. Yamaguchi
MGH, Hyogo-ken, Japan
H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe
KEK, Ibaraki, Japan
K. Ishimi
MGI, Chiba, Japan

Marui Galvanizing Co.,Ltd. has been developing Nb 9-cell SRF cavity vertical electro-polishing (VEP) facility and technique for mass production in collaboration with KEK. Our first 9-cell cavity VEP facility was not enough to control temperature during VEP, so the polishing quality was not so high. In this article, we will report the progress of temperature distribution and polishing quality due to the improvement of temperature control system of electrolyte and cavity during VEP.

Poster MOPB098 [0.988 MB]

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MOPB100

Cathode Geometry and Flow Dynamics Impact on Vertical Electropolishing of Superconducting Niobium Cavities

cavity, niobium, simulation, operation

385

L.M.A. Ferreira
CERN, Geneva, Switzerland

CERN has now a fully operating vertical electropolishing installation, which has been used for the processing of 704 MHz high-beta five-cell Superconducting Proton Linac (SPL) niobium cavities. This installation relies only on the electrolyte circulation (HF/H2SO4) for power dissipation, evacuation of gases and homogeneous finishing; thus, parameters like cathode geometry, electrolyte flow and temperature become even more crucial when compared with horizontal electropolishing installations. Based on computational simulations performed with Comsol Multiphysics® and on a methodology developed at CERN, it is possible to assess the impact of the different cathode geometries as well as of the flow on the etching rate distribution. The data obtained with two different cathode geometries are presented: electrolyte velocity distribution, etching rate distribution, average current density and minimum working potential. One geometry was defined through a purely electrochemical approach while the second was defined to minimise the difference between the maximum and the minimum electrolyte speed inside the cavity; in both cases, the influence of the electrolyte flow was taken into account.

Poster MOPB100 [1.794 MB]

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MOPB101

Electropolishing of Niobium SRF Cavities in Eco-Friendly Aqueous Electrolytes Without Hydrofluoric Acid

cavity, niobium, SRF, target

390

M.E. Inman, T.D. Hall, S. Lucatero, S.T. Snyder, E.J. Taylor
Faraday Technology, Inc., Clayton, Ohio, USA
F. Furuta, G.H. Hoffstaetter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
J.D. Mammosser
ORNL, Oak Ridge, Tennessee, USA
A.M. Rowe
Fermilab, Batavia, Illinois, USA

Electropolishing of niobium cavities is conventionally conducted in high viscosity electrolytes consisting of concentrated sulfuric and hydrofluoric acids. This use of dangerous and ecologically damaging chemicals requires careful attention to safety protocols to avoid harmful worker exposure and environmental damage. We present an approach for electropolishing of niobium materials based on pulse reverse waveforms, enabling the use of low viscosity aqueous dilute sulfuric acid electrolytes without hydrofluoric acid, or aqueous near-neutral pH salt solutions without any acid. Results will be summarized for both cavity and coupon electropolishing for bulk and final polishing steps. With minimal optimization of pulse reverse waveform parameters we have demonstrated the ability to electropolish single-cell niobium SRF cavities and achieve at least equivalent performance compared to conventionally processed cavities. Cavities are electropolished in a vertical orientation filled with electrolyte and without rotation, offering numerous advantages from an industrial processing perspective. Shielding, external cooling and high surface area cathodes are adaptable to the bipolar EP process.
Work supported by DOE Grant Nos. DE-SC0011235 and DE-SC0011342 and DOE Purchase Order No. 594128.

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MOPB102

Comments on Electropolishing at Ettore Zanon SpA at the End of EXFEL Production

cavity, niobium, controls, acceleration

394

M. Rizzi, G. Corniani
Ettore Zanon S.p.A., Schio, Italy
A. Matheisen
DESY, Hamburg, Germany
P. Michelato
INFN/LASA, Segrate (MI), Italy

In 2013 a new horizontal Electropolishing facility was developed and implemented by Ettore Zanon SpA (EZ) for the treatment of cavities for the European XFEL series production. More than 300 cavities have been treated. Electropolishing has been used for two applications: bulk removal and recovering of cavities with surface defects. Treatment settings have been analysed and compared with cavities performances to verify possible influences of the various parameters. Main parameters considered are treatment time, voltage and current, that together define average thickness removal. We present here the results of these investigation. The facility and process in use are also presented, together with possible next upgrade of the system, facing the new production of cavities for the LCLSII project.

Poster MOPB102 [1.535 MB]

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MOPB105

Symmetric Removal of Niobium Superconducting RF Cavity in Vertical Electropolishing

cavity, experiment, accumulation, niobium

409

V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi
MGH, Hyogo-ken, Japan
H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe
KEK, Ibaraki, Japan
K. Ishimi
MGI, Chiba, Japan

Vertical electropolishing (VEP) leads several advantages over horizontal EP in respect of easy operation and mechanism of an EP system resulting in lower cost. However, till yet VEP always resulted inhomogeneous removal of a niobium (Nb) cavity along its length and bubble traces especially on the top iris of a vertically set cavity. In this work we performed lab EP and VEP experiments in order to study and solve these two problems. A coupon cavity which contains 6 disk type Nb coupons positioned at beam pipes, irises and equator was vertically electropolished to optimize VEP parameters so as to get almost uniform removal of Nb and a smooth surface of the cavity without bubble traces. Our patented unique i-Ninja cathode having 4 wings was used with an optimized rotation speed to get homogeneous removal of Nb. The homogeneous removal and the surface without bubble traces might be result of a uniform thickness of a viscous layer on the surface of the cavity cell and no accumulation of hydrogen bubbles on the top iris surface. The surfaces of the coupons were studied in detail with surface analytical tools.

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MOPB110

The Transfer of Improved Cavity Processing Protocols to Industry for LCLS-II: N-Doping and Electropolishing

cavity, niobium, controls, superconductivity

418

C.E. Reece, F. Marhauser, A.D. Palczewski
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 with supplemental funding from the LCLS-II Project U.S. DOE Contract No. DE-AC02-76SF00515.
Based on the R&D efforts of colleagues at FNAL, Cornell, and JLab, the LCLS-II project adopted a modification to the rather standard niobium SRF cavity surface processing protocol that incorporates a high temperature diffusion doping with nitrogen gas. This change was motivated by the resulting higher Q0 and the prospect of significantly lower cryogenic heat load for LCLS-II. JLab is responsible for managing the cavity procurement for the LCLS-II project. The first phase of the procurement action is to transfer the nitrogen-doping protocol to the industrial vendors. We also seek to exploit improvements in understanding of the niobium electropolishing process as part of the production processing of the TESLA-style LCLS-II cavities. We report on the technology transfer activities and progress toward the envisaged performance demonstration of vendor-processed cavities.

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TUPB003

Cavity Procurement and Qualification Plan for LCLS-II

cavity, controls, hardware, site

529

F. Marhauser, E. Daly, J.A. Fitzpatrick
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 with supplemental funding from the LCLS-II Project U.S. DOE Contract No. DE-AC02-76SF00515.
The LCLS-II project aims to build 35 accelerating cryomodules, which are based on the European XFEL design but modified for operation in CW mode. Each cryomodule houses eight TESLA-style nine-cell superconducting radio-frequency cavities. The activities to assemble the first two prototype cryomodules are ongoing at FNAL and JLab. 264 cavities worth of cavities for the remaining 33 cryomodules will be procured from two industrial vendors in similar quantity considering the option to produce spares. The assembly of cavities into the production cryomodules will be distributed among FNAL (16 cryomodules) and JLab (17 cryomodules). In this paper the cavity procurement and qualification plan for the LCLS-II project is detailed.

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TUPB010

Plug Transfer System for GaAs Photocathodes

gun, SRF, operation, vacuum

553

P. Murcek, A. Arnold, P.N. Lu, J. Teichert, H. Vennekate, R. Xiang
HZDR, Dresden, Germany
A. Burrill
HZB, Berlin, Germany

The transport and exchange technology of Cs2Te photocathode for the ELBE superconducting rf photoinjector (SRF gun) has been successfully developed and tested at HZDR. The next goal is to realize the transport of GaAs photocathode into SRF gun, which will need a new transfer system with XHV 10^-11 mbar. The key component of the system is the transfer chamber and the load-lock system that will be connected to the SRF-gun. In the carrier four small plugs will be transported, and one of them will be plug on the cathode-body and inserted into the cavity. The new transport chamber allows the transfer and exchange of plugs between HZDR, HZB and other cooperating institutes. In HZDR this transfer system will also provide a direct connection between the SRFGUN and the GaAs preparation chamber in the Elbe-accelerator hall.

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TUPB027

Developments on SRF Coatings at CERN

cavity, SRF, plasma, simulation

617

A. Sublet, S. Aull, B. Bártová, S. Calatroni, T. Richard, G.J. Rosaz, M. Taborelli, M. Therasse, W. Venturini Delsolaro, P. Zhang
CERN, Geneva, Switzerland

The thin films techniques applied to Superconducting RF (SRF) has a long history at CERN. A large panel of cavities have been coated from LEP, to LHC. For the current and future projects (HIE-ISOLDE, HL-LHC, FCC) there is a need for further higher RF-performances with focus on minimizing residual resistance Rres and maximizing quality factor Q0 of the cavities. This paper will present CERN’s developments on thin films to achieve these goals through the following main axes of research: The first one concerns the application of different coating techniques for Nb (DC-bias diode sputtering, magnetron sputtering and HiPIMS). Another approach is the investigation of alternative materials like Nb3Sn. These lines of development will be supported by a material science approach to characterize and evaluate the layer properties by means of FIB-SEM, TEM, XPS, XRD, etc. In addition a numerical tool for plasma simulation will be exploited to develop adapted coating systems and optimize the coating process, from plasma generation to thin film growth.

Poster TUPB027 [1.070 MB]

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TUPB032

Energetic Condensation Growth of Nb on Cu SRF Cavities

cavity, niobium, SRF, plasma

629

K.M. Velas, S.F. Chapman, I. Irfan, M. Krishnan
AASC, San Leandro, California, USA

Funding: This research is supported by the US DOE via and SBIR grant: DE-SC0011371
Alameda Applied Sciences Corporation (AASC) grows Nb thin films via Coaxial Energetic Deposition (CED) from a cathodic arc plasma. The plasma from the cathode consists exclusively of 60-120eV Nb ions (Nb+ and Nb2+) that penetrate a few monolayers into the substrate and enable sufficient surface mobility to ensure that the lowest energy state (crystalline structure with minimal defects) is accessible to the film. AASC is coating 1.3 GHz SRF cavities using a graded anode to ensure uniform film thickness in the beam tube and elliptical regions. Copper cavities are centrifugal barrel polished and electropolished (done for us by the Fermilab Technical Division, Superconducting RF Development Department and by Thomas Jefferson National Accelerator Facility (JLAB)) before coating, to ensure good adhesion and improved film quality. The Nb coated copper cavities will undergo RF tests at JLAB and at Fermilab to measure Qo vs. E.

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TUPB034

Bulk Niobium Polishing and Electropolishing Steps for Thinfilm Coated Copper SRF Cavities

cavity, SRF, ion, plasma

633

M. Krishnan, S.F. Chapman, I. Irfan, K.M. Velas
AASC, San Leandro, California, USA
J.K. Spradlin, H. Tian
JLab, Newport News, Virginia, USA

Funding: Research supported at AASC by the US DOE via SBIR grant: DE-SC0011371. The JLab effort was provided by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
Alameda Applied Sciences Corporation (AASC) grows Nb thin films via Coaxial Energetic Deposition (CED) from a cathodic arc plasma. The plasma consists of 60-120eV Nb ions (Nb+ and Nb++) [1] that penetrate a few monolayers into the substrate [2] and enable sufficient surface mobility to ensure that the lowest energy state (crystalline structure with minimal defects) is accessible to the film [3]. One limitation of CED thinfilms is the presence of Nb macroparticles (~0.1-10 microns) that could be deleterious to high field performance of the SRF cavity. One way to remove such macroparticles [4] is to grow a thick film (~3-5 microns), followed by mechanical polishing (MP) using the finest media as might be applied in Centrifugal Barrel Polishing (CBP) to achieve a 0.4 micron surface figure, and an electropolishing (EP) step to remove ~1 micron of Nb that also removes all traces of embedded media in the film. The residual 2-4 micron Nb film should more nearly resemble the surface of a bulk Nb cavity that has been subjected to the same steps. This paper describes experiments conducted on Cu coupons as a prelude to an SRF Cu cavity coating.

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TUPB047

Next Generation of SRF-Guns: Low Secondary Electron Yield Based on a Thin Film Approach

electron, target, gun, SRF

673

C. Schlemper, X. Jiang, M. Vogel
University Siegen, Siegen, Germany

Multipacting is a common issue in the context of cathode units of superconducting radiofrequency photoinjectors (SRF-guns) utilized in linear accelerators under resonant conditions. In this study, Titanium Nitride (TiN) and Carbon thin films have been prepared by DC and RF magnetron sputtering in a Nitrogen and Argon plasma discharge, respectively. Films featuring a thickness of about 600 nm were produced under various deposition conditions on substrates such as Copper, Molybdenum, and Silicon. Materials characterization was carried out utilizing SEM, Raman and FTIR spectroscopy, XRD and AFM. In order to evaluate the SEY a new device is introduced, which is capable of quasi in-situ measurements. The latter is realized by connecting the coating-, the SEY- and a contamination chamber into one setup allowing sample transfer under UHV conditions. Even after an exposure to air carbon shows SEY values down to 0.69. This value, however, turns out to be quite sensitive with respect to the actual surface morphology. Clean TiN surfaces, on the other hand, displayed a SEY value as low as 1.4. In this case the SEY value is strongly affected by potential surface contamination.

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TUPB077

The Influence of Cooldown Conditions at Transition Temperature on the Quality Factor of Niobium Sputtered Quarter-Wave Resonators for HIE-ISOLDE

cavity, niobium, accelerating-gradient, linac

765

P. Zhang, G.J. Rosaz, A. Sublet, M. Therasse, W. Venturini Delsolaro
CERN, Geneva, Switzerland

Funding: This work has been supported partly by a Marie Curie Early Initial Training Network Fellowship of the European Community’s 7th Programme under contract number PITN-GA-2010-264330-CATHI.
Superconducting quarter-wave resonators (QWRs) are to be used in the ongoing linac upgrade of the ISOLDE facility at CERN. The cavities are made of niobium sputtered on copper substrates. They will be operated at 101.28 MHz at 4.5 K providing 6 MV/m accelerating gradient with 10 W power dissipation. In recent measurements, we found the thermal gradient along the cavity during the niobium superconducting transition has an impact on the cavity quality factor. On the other hand, the speed of the cooling down through the superconducting transition turned out to have no influence on the cavity Q-factor.

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THAA02

SRF Gun Development Overview

gun, cavity, SRF, electron

994

J.K. Sekutowicz
DESY, Hamburg, Germany

The most demanding component of a continuous wave (cw) injector is cw operating RF-gun, delivering highly populated low emittance bunches. RF-guns, both working at room temperature and superconducting, when they generate highly populated low emittance bunches have to be operated at high accelerating gradients to suppress space charge effects diluting emittance. Superconducting RF-guns are technically superior to the normal conducting devices because they dissipate orders of magnitude less power when operating at very high gradients in cw mode. In this contribution progress since 2013 in the R&D programs, designing and operation of the SRF-injectors at KEK, HZB, HZDR, PKU and DESY will be discussed.

Slides THAA02 [6.107 MB]

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THAA03

SRF Gun at BNL: First Beam and Other Commissioning Results

gun, SRF, cavity, electron

1001

W. Xu, Z. Altinbas, S.A. Belomestnykh, I. Ben-Zvi, L. DeSanto, S. Deonarine, D.M. Gassner, R.C. Gupta, H. Hahn, L.R. Hammons, C. Ho, J.P. Jamilkowski, P. K. Kankiya, D. Kayran, R. Kellermann, N. Laloudakis, R.F. Lambiase, C.J. Liaw, V. Litvinenko, G.J. Mahler, L. Masi, G.T. McIntyre, T.A. Miller, D. Phillips, V. Ptitsyn, T. Rao, T. Seda, B. Sheehy, K.S. Smith, A.N. Steszyn, T.N. Tallerico, R. Than, J.E. Tuozzolo, E. Wang, D. Weiss, M. Wilinski, A. Zaltsman, Z. Zhao
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh, I. Ben-Zvi, V. Litvinenko
Stony Brook University, Stony Brook, USA

The talk shall cover two SRF photoemission electron guns under commissioning at BNL: a 704 MHz elliptical ERL gun and a 112 MHz quarter-wave gun for coherent electron cooling experiment. In particular, the speaker shall report on generating first photoemission beam current from the 704 MHz SRF gun, multipacting issues in the SRF guns, photocathode behavior as well as other commissioning experiences and results.

Slides THAA03 [2.215 MB]

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THBA02

Recent Development in Vertical Electropolishing

cavity, experiment, ion, SRF

1024

V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi
MGH, Hyogo-ken, Japan
H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe
KEK, Ibaraki, Japan
K. Ishimi
MGI, Chiba, Japan

Horizontal electropolishing (HEP) is being used for final surface treatment of niobium SRF cavities. However a HEP system is equipped with complicated mechanism that makes it expensive and enhances cost of surface treatment of cavities especially when mass production is considered. Vertical electropolishing (VEP) has been introduced by other labs and the research is being carried out to establish the VEP technique. The VEP system requires simple mechanism and has advantages over HEP setup. Positive results have been obtained from the VEPed cavities also as shown by other labs. However further improvement in a VEP setup, cathode and VEP parameters is required. Marui Galvanizing Co., Ltd in collaboration with KEK has been working for development of VEP system, optimization of cathode and VEP parameters to obtain uniform Nb removal with a smooth surface of a cavity. Here we report our recent development of VEP system, unique Ninja cathode and parameter optimization with a 1-cell coupon cavity containing 6 Nb disk coupons at the beam pipes, irises and equator. The coupon surfaces were analyzed to obtain detail of the cavity surface.

Slides THBA02 [5.703 MB]

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THPB047

Analysis of a 750 MHz SRF Dipole Cavity

cavity, dipole, simulation, cryogenics

1200

A. Castilla, J.R. Delayen
ODU, Norfolk, Virginia, USA
A. Castilla, J.R. Delayen
JLab, Newport News, Virginia, USA
A. Castilla
DCI-UG, León, Mexico

Funding: Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177.
There is a growing interest in using rf transverse deflecting structures for a plethora of applications in the current and future high performance colliders. In this paper, we present the results of a proof of principle superconducting rf dipole, designed as a prototype for a 750 MHz crabbing corrector for the Medium Energy Electron-Ion Collider (MEIC), which has been successfully tested at 4.2 K and 2 K at the Jefferson Lab’s Vertical Testing Area (VTA). The analysis of its rf performance during cryogenic testing, along with Helium pressure sensitivity, Lorentz detuning, surface resistance, and multipacting processing analysis are presented in this work. Detailed calculations of losses at the port flanges are included for completeness of the cavity’s cryogenic performance studies.

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THPB048

Design of a Compact Superconducting Crab-Cavity for LHC Using Nb-on-Cu-Coating Technique

cavity, impedance, HOM, SRF

1205

A. Grudiev, S. Atieh, R. Calaga, S. Calatroni, O. Capatina, F. Carra, G. Favre, L.M.A. Ferreira, J.-F. Poncet, T. Richard, A. Sublet, C. Zanoni
CERN, Geneva, Switzerland

The design of a compact superconducting crab-cavity for LHC using Nb-on-Cu-coating technique is presented. The cavity shape is based on the ridged waveguide resonator with wide open apertures to provide access to the inner surface of the cavity for coating. It also provides natural damping for HOMs and rather low longitudinal and transverse impedances. The results of the cavity shape optimization taking into account RF performance, coating, and thermo-mechanical considerations as well as the design and fabrication plans of the first prototype for coating and cold tests are presented.

Poster THPB048 [0.534 MB]

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THPB055

RF Performance Results of the 2nd ELBE SRF Gun

gun, SRF, cavity, electron

1227

A. Arnold, M. Freitag, P.N. Lu, P. Murcek, J. Teichert, H. Vennekate, R. Xiang
HZDR, Dresden, Germany
G. Ciovati, P. Kneisel, M. Stirbet, L. Turlington
JLab, Newport News, Virginia, USA

As in 2007 the first 3.5 cell superconducting radio frequency (SRF) gun was taken into operation at Helmholtz-Zentrum Dresden-Rossendorf, it turned out that the specified performance to realize an electron energy of 9.4 MeV has not been achieved. Instead, the resonator of the gun was limited by field emission to about one third of this value and the measured beam parameters remained significantly below its expectations. However, to demonstrate the full potential of this electron source for the ELBE linear accelerator, a second and slightly modified SRF gun was developed and built in collaboration with Thomas Jefferson National Accelerator Facility. We will report on commissioning of this new SRF gun and present a full set of RF performance results. Additionally, investigations are shown that try to explain a particle contamination that happened recently during our first cathode transfer.

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THPB056

SRF Gun Cavity R&D at DESY

cavity, SRF, gun, operation

1231

D. Kostin, C. Albrecht, A. Brinkmann, Th. Buettner, J. Eschke, T. Feldmann, A. Gössel, D. Klinke, A. Matheisen, W.-D. Möller, D. Reschke, M. Schmökel, J.K. Sekutowicz, W. Singer, X. Singer, N. Steinhau-Kühl, J. Ziegler, B. van der Horst
DESY, Hamburg, Germany
M. Barlak, J.A. Lorkiewicz, R. Nietubyć
NCBJ, Świerk/Otwock, Poland

SRF Gun Cavity is an ongoing accelerator R&D project at DESY, being developed since several years. Currently several SRF Gun cavity prototypes were simulated, built and tested in our Lab and elsewhere. Lately the 1.6 cells Pb thin film cathode niobium cavity was tested in a vertical cryostat with a different cathode plug configurations. Cathode plug design was improved, as well as SRF Gun Cavity cleaning procedures. Results of the last cavity performance tests are presented and discussed.

Poster THPB056 [1.257 MB]

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THPB057

ELBE SRF Gun II - Emittance Compensation Schemes

emittance, gun, focusing, SRF

1235

H. Vennekate, A. Arnold, D. Janssen, P.N. Lu, P. Murcek, J. Teichert, R. Xiang
HZDR, Dresden, Germany
P. Kneisel
JLab, Newport News, Virginia, USA

In May 2014 the first SRF photo injector at HZDR has been replaced by a new gun, featuring a new resonator and cryostat. The intention for this upgrade has been to reach for higher beam energies, bunch charges and therefore an increased average beam current, which is to be injected into the superconducting, CW ELBE accelerator, where it can be used for multiple purposes, such as THz generation or Compton backscattering. Because of the increased bunch charge of this injector compared to its predecessor, it demands upgrades of the existing and/or novel approaches to alleviate the transverse emittance growth. One of these methods is the integration of a superconducting solenoid into the cryostat. Another method, the so called RF focusing, is realized by displacing the photo cathode's tip and retracting it from the last cell of the resonator. In this case, part of the accelerating field is sacrificed for a better focus of the electron bunch right at the start of its generation. Besides particle tracking simulations, a recent study, investigating on the exact position of the cathode tip with respect to the cell's back plane after tuning and cool down, has been performed.

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THPB058

Commissioning of the 112 MHz SRF Gun

gun, SRF, electron, laser

1240

S.A. Belomestnykh, I. Ben-Zvi, J.C. Brutus, T. Hayes, V. Litvinenko, K. Mernick, G. Narayan, P. Orfin, I. Pinayev, T. Rao, F. Severino, J. Skaritka, K.S. Smith, R. Than, J.E. Tuozzolo, E. Wang, Q. Wu, B. P. Xiao, A. Zaltsman
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh, I. Ben-Zvi, V. Litvinenko, T. Xin
Stony Brook University, Stony Brook, USA

Funding: Work is supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE.
A 112 MHz superconducting RF photoemission gun was designed, fabricated and installed in RHIC for the Coherent electron Cooling Proof-of-Principle (CeC PoP) experiment at BNL. The gun was commissioned first without beam. This was followed by generating the first photoemission beam from a multi-alkali cathode. The paper presents the commissioning results.

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THPB059

Design, Fabrication and Performance of SRF-Gun Cavity

cavity, gun, SRF, target

1243

T. Konomi, E. Kako, Y. Kobayashi, K. Umemori, S. Yamaguchi
KEK, Ibaraki, Japan
R. Matsuda
Mitsubishi Heavy Industries Ltd. (MHI), Takasago, Japan
T. Yanagisawa
MHI, Hiroshima, Japan

The development of superconducting RF gun has been started at KEK. The performance targets are that average current is 100 mA, normalized emittance is less than 1 μm.rad, beam energy is 2 MeV and energy spread is less than 0.1 %. The SRF gun consists of 1.3 GHz and 1.5 cell elliptical cavity and backward illuminated photocathode. The cavity shape was designed by using SUPERFISH and GPT. The cavity has been fabricated by Japanese industry. Accelerating field tuning and vertical test without cathode plug was done. The surface peak electric field reached 66 MV/m, and this meet the target value 42 MV/m sufficiently. For next vertical test, cathode rod without photocathode is in preparation. In the workshop, the SRF-Gun concepts and vertical test results will be reported.

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THPB083

Energetic Copper Coating on Stainless Steel Power Couplers for SRF Application

SRF, plasma, laser, ion

1330

I. Irfan, S.F. Chapman, M. Krishnan, K.M. Velas
AASC, San Leandro, California, USA
W. Kaabi
LAL, Orsay, France

Funding: This research is supported by the US DOE via and SBIR grant: DE-SC0009581
Delivering RF power from the outside (at room temperature) to the inside of SRF cavities (at ~4 K temperature), requires a power coupler to be thermally isolating, while still electrically conducting on the inside. Stainless steel parts that are coated on the insides with a few skin depths of copper can meet these conflicting requirements. The challenge has been the adhesion strength of copper coating on stainless steel coupler parts when using electroplating methods. These methods also require a nickel flash layer that is magnetic and can therefore pose problems. Alameda Applied Sciences Corporation (AASC) uses Coaxial Energetic Deposition (CED) from a cathodic arc plasma to grow copper films directly on stainless steel coupler parts with no Ni layer and no electrochemistry. The vacuum arc plasma consists of ~100 eV Cu ions that penetrate a few monolayers into the stainless steel substrate to promote growth of highly adhesive films with crystalline structure. Adhesion strength and coating quality of copper coatings on complex stainless steel tubes, bellows, mock coupler parts and an actual Tesla Test Facility (TTF) type coupler part, are discussed.
* Adhesion and Cu quality testing were done for us by the Fermilab Technical Division, Superconducting RF Development Department

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FRBA03

SRF, Compact Accelerators for Industry & Society

cavity, SRF, electron, gun

1467

R.D. Kephart, B.E. Chase, I.V. Gonin, A. Grassellino, S. Kazakov, T.N. Khabiboulline, S. Nagaitsev, R.J. Pasquinelli, S. Posen, O.V. Pronitchev, A. Romanenko, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA
S. Biedron, S.V. Milton, N. Sipahi
CSU, Fort Collins, Colorado, USA
S. Chattopadhyay
Northern Illinois Univerity, Dekalb, Illinois, USA
P. Piot
Northern Illinois University, DeKalb, Illinois, USA

Accelerators developed for Science now are used broadly for industrial, medical, and security applications. Over 30,000 accelerators touch over $500B/yr in products producing a major impact on our economy, health, and well being. Industrial accelerators must be cost effective, simple, versatile, efficient, and robust. Many industrial applications require high average beam power. Exploiting recent advances in Superconducting Radio Frequency (SRF) cavities and RF power sources as well as innovative solutions for the SRF gun and cathode system, a collaboration of Fermilab-CSU-NIU has developed a design for a compact SRF high-average power electron linac. Capable of 5-50 kW average power and continuous wave operation this accelerator will produce electron beam energies up to 10 MeV and small and light enough to mount on mobile platforms, such accelerators will enable new in-situ environmental remediation methods and new applications involving in-situ crosslinking of materials. More importantly, we believe this accelerator will be the first of a new class of simple, turn-key SRF accelerators that will find broad application in industry, medicine, security, and science.

Slides FRBA03 [2.342 MB]

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