IPAC2014 - List of Keywords (niobium)

Paper	Title	Other Keywords	Page
WEPRI002	Status and First Results of Two High Beta Prototype Elliptical Cavities for ESS	cavity, cryomodule, accelerating-gradient, operation	2477
	F. Peauger, P. Bosland, P. Carbonnier, G. Devanz, F. Éozénou, X. Hanus, P. Hardy, V.M. Hennion, J. Plouin, D. Roudier, C. Servouin CEA/DSM/IRFU, France C. Darve, S. Molloy ESS, Lund, Sweden L. Maurice CEA/IRFU, Gif-sur-Yvette, France G. Olivier IPN, Orsay, France
	Two prototypes of elliptical superconducting cavities have been designed and manufactured in the frame of the French-Swedish agreement for ESS. These 5-cell cavities have a beta value of 0.86 and their frequency is 704.42 MHz. The nominal accelerating gradient on the ESS accelerator is 19.9 MV/m at 2K. We present the manufacturing status of the cavities by two different vendors as well as the specific means which have been developed for the cavity treatments performed at CEA after delivery. We emphasis the activities performed on the first bare cavities recently received at CEA such as the RF measurement and tuning operations, the cleaning and chemical treatments and the clean room assembly including high pressure rinsing. Finally, first test results at 2K in vertical cryostat are reported.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI002
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WEPRI005	Processing and Testing of the SRF Photoinjector Cavity for BERLinPro	cavity, SRF, operation, electron	2484
	A. Burrill, W. Anders, A. Frahm, J. Knobloch, A. Neumann HZB, Berlin, Germany G. Ciovati, W.A. Clemens, P. Kneisel, L. Turlington JLab, Newport News, Virginia, USA E.N. Zaplatin FZJ, Jülich, Germany
	Funding: Work supported by German Bundesministerium für Bildung und Forschung, Land Berlin, and grants of Helmholtz Association The BERLinPro project is a compact, c.w. SRF energy recovery linac (ERL) that is being built to develop the accelerator physics and technology required to operate the next generation of high current ERLs. The machine is designed to produce a 50 MeV 100 mA beam, with better than 1 mm-mrad emittance. The electron source for the ERL will be a SRF photoinjector equipped with a multi-alkali photocathode. In order to produce a SRF photoinjector to operate reliably at this beam current HZB has undertaken a 3 stage photoinjector development program to study the operation of SRF photoinjectors in detail. The 1.4 cell cavity being reported on here is the second stage of this development, and represents the first cavity designed by HZB for use with a high quantum efficiency multi-alkali photocathode. This paper will describe the work done to prepare the cavity for RF testing in the vertical testing dewar at Jefferson Laboratory as well as the results of these RF tests.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI005
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WEPRI034	Analysis of BCP Characteristics for SRF Cavities	experiment, SRF, ion, cavity	2549
	Y. Jung, H.J. Kim IBS, Daejeon, Republic of Korea H.H. Lee, H.C. Yang KRICT, Daejoen, Republic of Korea
	A chemical polishing process is well-known critical process for improving superconducting cavities such as a quality factor and an acceleration electric filed with additional temperature treatment. Especially, Buffered Chemical Polishing (BCP) has been widely used in SRF (Superconducting Radio Frequency) cavity processing. We performed BCP experiments with 1:1:1 and 1:1:2 of an etchant ratio (HF:HNO3:H3PO4). In fact, BCP experiments were carried out by using both undeformed (as-receoved) and deformed niobium samples. We will report baseline BCP results by analyzing surface states of niobium samples such as optical photographs, etch rates and AFM (Atomic Force Microscopy) depending on temperature and time.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI034
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WEPRI041	Progress of HOM Couplers for CERN SPL Cavities	HOM, simulation, cavity, factory	2568
	K. Papke, F. Gerigk CERN, Geneva, Switzerland U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	Funding: Work supported by the Wolfgang-Gentner-Programme of the Bundesministerium für Bildung und Forschung (BMBF) In this paper we present the progress of the Higher-Order-Mode (HOM) coupler design for the high beta CERN SPL (Superconducting Proton Linac) cavities. This includes the RF transmission behavior as well as mechanical and thermal requirements and their optimizations. Warm RF measurements are presented for the first four high beta SPL Cavities made of bulk niobium. Moreover the first prototype of a HOMcoupler will be introduced and we discuss its characteristics and its tuning possibilities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI041
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WEPRI042	Nb Coated HIE-ISOLDE QWR Superconducting Accelerating Cavities: From Process Development to Series Production	cavity, cryomodule, cathode, SRF	2571
	A. Sublet, I. Aviles Santillana, B. Bártová, S. Calatroni, N.M. Jecklin, I. Mondino, M. Therasse, W. Venturini Delsolaro, P. Zhang CERN, Geneva, Switzerland M. Cantoni EPFL, Lausanne, Switzerland
	The new HIE-ISOLDE accelerator at CERN requires the production of 32 superconducting cavities (20 high-beta and 12 low-beta) in order to increase the energy of the rare isotope beam delivered to the experiments. The Quarter Wave Resonators (QWRs) cavities (0.3m diameter and 0.8m height) are made of OFE 3D-forged copper and are coated by DC-bias diode sputtering with a thin superconducting layer of niobium. Following a preliminary process development phase, the series production of the high-beta cavities has started. An overview of the development phase is presented, describing the key parameters varied to match the HIE-ISOLDE specifications (operation at 4.5 K with an accelerating field of 6 MV/m at 10W RF losses and Q0=4.5x108) and the resulting niobium film characteristics. The first series of cavities, produced using the baseline coating recipe, and their RF performance is reviewed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI042
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WEPRI047	UK Industrial Development of Manufacturing Techniques for Superconducting RF Cavities	cavity, electron, superconducting-RF, PLC	2586
	A.E. Wheelhouse, R.K. Buckley, L.S. Cowie, P. Goudket, A.R. Goulden, P.A. McIntosh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom J.R. Everard, N. Shakespeare Shakespeare Engineering, South Woodham Ferrers, Essex, United Kingdom
	An STFC Innovation Partnership Scheme (IPS) grant, funding Daresbury Laboratory and Shakespeare Engineering Ltd to develop the capability to fabricate, process and test a 9-cell 1.3 GHz superconducting RF cavity in support of enabling UK industry to address the large potential market for superconducting RF structures. At the heart of the development are the repeatability and the reproducibility of the manufacturing process in an effort to reduce the costs. Effort has been spent on developing the techniques to fabricate the niobium half cells and the beam pipes and this paper discusses the manufacturing processes and the results obtained.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI047
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WEPRI050	Development and Test Results of a Quasi-waveguide Multi-cell Resonator	cavity, cathode, impedance, HOM	2595
	Z.A. Conway, A. Barcikowski, S.M. Gerbick, M. Kedzie, M.P. Kelly, J.S. Kerby, S.H. Kim, S.V. Kutsaev, R.C. Murphy, A. Nassiri, P.N. Ostroumov, T. Reid, T.L. Smith, A. Zholents ANL, Argonne, Illinois, USA
	Funding: Work supported by the U.S. Department of Energy, Offices of Nuclear Physics and Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. This paper reports the successful fabrication and test results of a novel 2815 MHz superconducting deflecting cavity operating in a TE-mode trapped in a quasi-waveguide structure with extremely high shunt impedance. The waveguide structure of this cavity allows for the free propagation of all higher order modes (HOMs) out of the cavity via the beam ports, eliminating the need for HOM dampers inside the cavity when operated with high beam current. The absence of HOM dampers greatly simplifies the cavity fabrication and operation at cryogenic temperatures. This cavity with its high shunt impedance is ideal for the spatial rotation of short bunches in a small physical space, a requirement for the generation of sub-picosecond short pulse x-rays in electron storage rings or luminosity upgrades of colliders. Results characterizing the fabrication accuracy and precision, the RF performance at 2 K, and frequency tuning considerations will be discussed here.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI050
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WEPRI054	Medium Field Q-Slope Studies in Low Beta Resonators	cavity, radiation, controls, operation	2608
	O.S. Melnychuk, A. Grassellino, A.I. Sukhanov Fermilab, Batavia, Illinois, USA
	Studies of the phenomenon of Medium field Q-slope (MFQS, 30-80 mT) have been focused predominantly on high beta superconducting cavities. Complementing research on cavity losses with the analysis of low beta cavity data can provide additional insights into the nature of MFQS. We present MFQS measurements of 325MHz β=0.2 single spoke resonators and 650MHz β=0.9 elliptical single cell resonators at vertical test facility at FNAL. We compare our findings with those obtained for high frequency 1.3GHz cavities tested both at the same facility and other laboratories.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI054
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WEPRI060	Investigation of Thermocurrents Limiting the Performance of Superconducting Cavities	cavity, shielding, linac, framework	2621
	R.G. Eichhorn, C.G. Daly, F. Furuta, A. Ganshin Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	As the surface resistance of superconducting cavities approach the theoretical limits parasitic effects limiting the performance came into focus of current research. One of these effects is that the quality factor of a cavity is impacted by the cooldown rate. We will present results from recent investigations on thermocurrents, driven by the temperature difference between the two material interfaces between the superconducting Niobium cavity and its Titanium helium-vessel, leading to the presence of a magnetic field while the cavity transits to the superconducting state.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI060
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WEPRI063	Flux Trapping in Nitrogen-Doped and 120 C Baked Cavities	cavity, SRF, linac, vacuum	2631
	D. Gonnella, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: United States Department of Energy It is well known that external magnetic fields can cause higher residual resistance in superconducting RF cavities if the field is present during cooldown. However, the effect of cavity preparation and surface mean free path on the resulting residual resistance from magnetic field is less well studied. In this paper, we report on recent studies at Cornell in which two SRF cavities (one nitrogen-doped and one 120oC baked) were cooled through Tc in an applied uniform external magnetic field. Trapped flux and residual resistance were measured for a variety of cooldowns and applied magnetic fields. It was found that the residual resistance due to trapped flux in the nitrogen-doped cavity was three times larger than in the 120oC baked cavity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI063
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WEPRI064	New Insights into Heat Treatment of SRF Cavities in a Low-pressure Nitrogen Atmosphere	cavity, SRF, vacuum, resonance	2634
	D. Gonnella, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: United States Department of Energy Recent results from Cornell and FNAL have shown that superconducting RF cavities given a heat treatment in a nitrogen atmosphere of a few mTorr display an increase in Q0 with increasing accelerating field, opposite to the medium field Q slope usually observed. Three cavities was prepared at Cornell using this method and subsequently tested after different amounts of material removal. Cavity performance and material properties were extracted for each cavity and correlated with material removal. This has given new insights into how material properties and the anti-Q slope depend on cavity preparation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI064
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WEPRI065	SRF Material Performance Studies using a Sample Host Cavity	cavity, coupling, SRF, controls	2638
	D.L. Hall, D. Gonnella, M. Liepe, I.S. Madjarov Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	A sample-host TE-mode cavity developed at Cornell for the purposes of studying novel superconducting materials has undergone further testing using a niobium sample plate. In initial testing the peak field achieved on the sample plate was (45 ± 4.5) mT, although this was limited by the amount of input power available. New tests have been performed using both an improved RF power system and a temperature mapping system for precision measurements of surface resistance as a function of location on the sample plate. Results of the most recent test, in which the cavity achieved a peak sample plate field of (81 ± 4) mT using a high-RRR niobium sample plate, are presented and future work on the cavity is discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI065
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WEPRI066	Recent Progress in Nb3Sn SRF Cavity Development at Cornell	cavity, SRF, accelerating-gradient, cryogenics	2641
	S. Posen, D. Gonnella, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Nb₃Sn coatings on niobium SRF cavities have the potential to significantly reduce cryogenic costs due to their extremely small surface resistance (R_s). In this paper, we present new results showing the repeatability of Cornell's fabrication process, which produces high Q₀ cavities that reach medium fields with minimal Q-slope. We also show the results of attempts to smooth RF surfaces and reduce defects via material removal. However, both HF rinsing and centrifugal barrel polishing resulted in strong performance degradation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI066
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WEPRI069	Reproducibility of High-Q SRF Cavities by High Temperature Heat Treatment	cavity, vacuum, SRF, induction	2651
	P. Dhakal, G. Ciovati, P. Kneisel, G.R. Myneni JLab, Newport News, Virginia, USA
	Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 Recent work on high-temperature (> 600 °C) heat treatment of ingot Nb cavities in a customized vacuum furnace for several hours showed the possibility of achieving Q0-values of up to ~5×10¹⁰ at 2.0 K, 1.5 GHz and accelerating gradients of ~20 MV/m. This contribution presents results on further studies of the heat treatment process to produce cavities with high Q0 values for continuous-wave accelerator application. Single-cell cavities of different Nb purity have been processed through few cycles of heat-treatments and chemical etching. Measurements of Q0 as a function of temperature at low RF field and of Q0 as a function of the RF field at or below 2.0 K have been made after each treatment. Measurements by TOF-SIMS of the impurities’ depth profiles were made on samples heat treated with the cavities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI069
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WEPRI070	Mechanical Properties of Ingot Nb Cavities	cavity, SRF, radio-frequency, network	2654
	G. Ciovati, P. Dhakal, P. Kneisel, J.D. Mammosser, J. Matalevich, G.R. Myneni JLab, Newport News, Virginia, USA
	Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. This contribution presents the results of measurements of the resonant frequency and of strain along the contour of a single-cell cavity made of ingot Nb subjected to increasing uniform differential pressure, up to 6 atm. The data were used to infer mechanical properties of this material after cavity fabrication, by comparison with the results from simulation calculations done with ANSYS. The objective is to provide useful information about the mechanical properties of ingot Nb cavities which can be used in the design phase of SRF cavities intended to be built with this material.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI070
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WEPRI078	Development of a Quarter-wave Coaxial Coupler for 1.3 GHz Superconducting Cavities	cavity, coupling, HOM, SRF	2675
	Y. Xie, A. Kanareykin Euclid TechLabs, LLC, Solon, Ohio, USA N. Solyak, V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	Superconducting ILC-type cavities have an rf coupler that is welded on. A detachable coupler will reduce conditioning time (can be conditioned separately), reduce cost and improve reliability. The problem with placing an extra flange in the superconducting cavity is creating a possible quench spot. Euclid Techlabs LLC designed a coupler and optimized its geometry that yielding an area on the surface with zero magnetic field (hence zero surface current). By placing a flange in that area we are able to avoid disturbing surface currents that typically lead to a quench. The coupler is optimized to preserve the axial symmetry of the cavity and rf field. The rf test results of this type coupler with a 1.3 GHz ILC-type single-cell cavity at Fermilab will be reported and discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI078
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THPME122	A SQUID-based Beam Current Monitor for FAIR	pick-up, cryogenics, electronics, ion	3524
	R. Geithner, T. Stöhlker, W. Vodel HIJ, Jena, Germany R. Geithner, R. Neubert, P. Seidel FSU Jena, Jena, Germany F. Kurian, H. Reeg, M. Schwickert GSI, Darmstadt, Germany T. Stöhlker IOQ, Jena, Germany
	A Cryogenic Current Comparator (CCC) was developed for the upcoming FAIR-Project, providing a non-destructive online monitoring of the beam current in the nA-range. The CCC was optimized for a lowest possible noise-limited current resolution together with a high system bandwidth. Therefore, the low temperature properties of ferromagnetic core materials used in the pick-up coil were investigated and different SQUID-systems were tested. In this contribution we present results of the completed Cryogenic Current Comparator for FAIR working in a laboratory environment, regarding the improvements in resolution and bandwidth due to the use of suitable ferromagnetic core materials and optimized SQUID-system components.
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Paper

Title

Other Keywords

Page

WEPRI002

Status and First Results of Two High Beta Prototype Elliptical Cavities for ESS

cavity, cryomodule, accelerating-gradient, operation

2477

F. Peauger, P. Bosland, P. Carbonnier, G. Devanz, F. Éozénou, X. Hanus, P. Hardy, V.M. Hennion, J. Plouin, D. Roudier, C. Servouin
CEA/DSM/IRFU, France
C. Darve, S. Molloy
ESS, Lund, Sweden
L. Maurice
CEA/IRFU, Gif-sur-Yvette, France
G. Olivier
IPN, Orsay, France

Two prototypes of elliptical superconducting cavities have been designed and manufactured in the frame of the French-Swedish agreement for ESS. These 5-cell cavities have a beta value of 0.86 and their frequency is 704.42 MHz. The nominal accelerating gradient on the ESS accelerator is 19.9 MV/m at 2K. We present the manufacturing status of the cavities by two different vendors as well as the specific means which have been developed for the cavity treatments performed at CEA after delivery. We emphasis the activities performed on the first bare cavities recently received at CEA such as the RF measurement and tuning operations, the cleaning and chemical treatments and the clean room assembly including high pressure rinsing. Finally, first test results at 2K in vertical cryostat are reported.

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WEPRI005

Processing and Testing of the SRF Photoinjector Cavity for BERLinPro

cavity, SRF, operation, electron

2484

A. Burrill, W. Anders, A. Frahm, J. Knobloch, A. Neumann
HZB, Berlin, Germany
G. Ciovati, W.A. Clemens, P. Kneisel, L. Turlington
JLab, Newport News, Virginia, USA
E.N. Zaplatin
FZJ, Jülich, Germany

Funding: Work supported by German Bundesministerium für Bildung und Forschung, Land Berlin, and grants of Helmholtz Association
The BERLinPro project is a compact, c.w. SRF energy recovery linac (ERL) that is being built to develop the accelerator physics and technology required to operate the next generation of high current ERLs. The machine is designed to produce a 50 MeV 100 mA beam, with better than 1 mm-mrad emittance. The electron source for the ERL will be a SRF photoinjector equipped with a multi-alkali photocathode. In order to produce a SRF photoinjector to operate reliably at this beam current HZB has undertaken a 3 stage photoinjector development program to study the operation of SRF photoinjectors in detail. The 1.4 cell cavity being reported on here is the second stage of this development, and represents the first cavity designed by HZB for use with a high quantum efficiency multi-alkali photocathode. This paper will describe the work done to prepare the cavity for RF testing in the vertical testing dewar at Jefferson Laboratory as well as the results of these RF tests.

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WEPRI034

Analysis of BCP Characteristics for SRF Cavities

experiment, SRF, ion, cavity

2549

Y. Jung, H.J. Kim
IBS, Daejeon, Republic of Korea
H.H. Lee, H.C. Yang
KRICT, Daejoen, Republic of Korea

A chemical polishing process is well-known critical process for improving superconducting cavities such as a quality factor and an acceleration electric filed with additional temperature treatment. Especially, Buffered Chemical Polishing (BCP) has been widely used in SRF (Superconducting Radio Frequency) cavity processing. We performed BCP experiments with 1:1:1 and 1:1:2 of an etchant ratio (HF:HNO3:H3PO4). In fact, BCP experiments were carried out by using both undeformed (as-receoved) and deformed niobium samples. We will report baseline BCP results by analyzing surface states of niobium samples such as optical photographs, etch rates and AFM (Atomic Force Microscopy) depending on temperature and time.

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WEPRI041

Progress of HOM Couplers for CERN SPL Cavities

HOM, simulation, cavity, factory

2568

K. Papke, F. Gerigk
CERN, Geneva, Switzerland
U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

Funding: Work supported by the Wolfgang-Gentner-Programme of the Bundesministerium für Bildung und Forschung (BMBF)
In this paper we present the progress of the Higher-Order-Mode (HOM) coupler design for the high beta CERN SPL (Superconducting Proton Linac) cavities. This includes the RF transmission behavior as well as mechanical and thermal requirements and their optimizations. Warm RF measurements are presented for the first four high beta SPL Cavities made of bulk niobium. Moreover the first prototype of a HOMcoupler will be introduced and we discuss its characteristics and its tuning possibilities.

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WEPRI042

Nb Coated HIE-ISOLDE QWR Superconducting Accelerating Cavities: From Process Development to Series Production

cavity, cryomodule, cathode, SRF

2571

A. Sublet, I. Aviles Santillana, B. Bártová, S. Calatroni, N.M. Jecklin, I. Mondino, M. Therasse, W. Venturini Delsolaro, P. Zhang
CERN, Geneva, Switzerland
M. Cantoni
EPFL, Lausanne, Switzerland

The new HIE-ISOLDE accelerator at CERN requires the production of 32 superconducting cavities (20 high-beta and 12 low-beta) in order to increase the energy of the rare isotope beam delivered to the experiments. The Quarter Wave Resonators (QWRs) cavities (0.3m diameter and 0.8m height) are made of OFE 3D-forged copper and are coated by DC-bias diode sputtering with a thin superconducting layer of niobium. Following a preliminary process development phase, the series production of the high-beta cavities has started. An overview of the development phase is presented, describing the key parameters varied to match the HIE-ISOLDE specifications (operation at 4.5 K with an accelerating field of 6 MV/m at 10W RF losses and Q0=4.5x108) and the resulting niobium film characteristics. The first series of cavities, produced using the baseline coating recipe, and their RF performance is reviewed.

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WEPRI047

UK Industrial Development of Manufacturing Techniques for Superconducting RF Cavities

cavity, electron, superconducting-RF, PLC

2586

A.E. Wheelhouse, R.K. Buckley, L.S. Cowie, P. Goudket, A.R. Goulden, P.A. McIntosh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
J.R. Everard, N. Shakespeare
Shakespeare Engineering, South Woodham Ferrers, Essex, United Kingdom

An STFC Innovation Partnership Scheme (IPS) grant, funding Daresbury Laboratory and Shakespeare Engineering Ltd to develop the capability to fabricate, process and test a 9-cell 1.3 GHz superconducting RF cavity in support of enabling UK industry to address the large potential market for superconducting RF structures. At the heart of the development are the repeatability and the reproducibility of the manufacturing process in an effort to reduce the costs. Effort has been spent on developing the techniques to fabricate the niobium half cells and the beam pipes and this paper discusses the manufacturing processes and the results obtained.

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WEPRI050

Development and Test Results of a Quasi-waveguide Multi-cell Resonator

cavity, cathode, impedance, HOM

2595

Z.A. Conway, A. Barcikowski, S.M. Gerbick, M. Kedzie, M.P. Kelly, J.S. Kerby, S.H. Kim, S.V. Kutsaev, R.C. Murphy, A. Nassiri, P.N. Ostroumov, T. Reid, T.L. Smith, A. Zholents
ANL, Argonne, Illinois, USA

Funding: Work supported by the U.S. Department of Energy, Offices of Nuclear Physics and Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
This paper reports the successful fabrication and test results of a novel 2815 MHz superconducting deflecting cavity operating in a TE-mode trapped in a quasi-waveguide structure with extremely high shunt impedance. The waveguide structure of this cavity allows for the free propagation of all higher order modes (HOMs) out of the cavity via the beam ports, eliminating the need for HOM dampers inside the cavity when operated with high beam current. The absence of HOM dampers greatly simplifies the cavity fabrication and operation at cryogenic temperatures. This cavity with its high shunt impedance is ideal for the spatial rotation of short bunches in a small physical space, a requirement for the generation of sub-picosecond short pulse x-rays in electron storage rings or luminosity upgrades of colliders. Results characterizing the fabrication accuracy and precision, the RF performance at 2 K, and frequency tuning considerations will be discussed here.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI050

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WEPRI054

Medium Field Q-Slope Studies in Low Beta Resonators

cavity, radiation, controls, operation

2608

O.S. Melnychuk, A. Grassellino, A.I. Sukhanov
Fermilab, Batavia, Illinois, USA

Studies of the phenomenon of Medium field Q-slope (MFQS, 30-80 mT) have been focused predominantly on high beta superconducting cavities. Complementing research on cavity losses with the analysis of low beta cavity data can provide additional insights into the nature of MFQS. We present MFQS measurements of 325MHz β=0.2 single spoke resonators and 650MHz β=0.9 elliptical single cell resonators at vertical test facility at FNAL. We compare our findings with those obtained for high frequency 1.3GHz cavities tested both at the same facility and other laboratories.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI054

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WEPRI060

Investigation of Thermocurrents Limiting the Performance of Superconducting Cavities

cavity, shielding, linac, framework

2621

R.G. Eichhorn, C.G. Daly, F. Furuta, A. Ganshin
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

As the surface resistance of superconducting cavities approach the theoretical limits parasitic effects limiting the performance came into focus of current research. One of these effects is that the quality factor of a cavity is impacted by the cooldown rate. We will present results from recent investigations on thermocurrents, driven by the temperature difference between the two material interfaces between the superconducting Niobium cavity and its Titanium helium-vessel, leading to the presence of a magnetic field while the cavity transits to the superconducting state.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI060

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WEPRI063

Flux Trapping in Nitrogen-Doped and 120 C Baked Cavities

cavity, SRF, linac, vacuum

2631

D. Gonnella, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: United States Department of Energy
It is well known that external magnetic fields can cause higher residual resistance in superconducting RF cavities if the field is present during cooldown. However, the effect of cavity preparation and surface mean free path on the resulting residual resistance from magnetic field is less well studied. In this paper, we report on recent studies at Cornell in which two SRF cavities (one nitrogen-doped and one 120oC baked) were cooled through Tc in an applied uniform external magnetic field. Trapped flux and residual resistance were measured for a variety of cooldowns and applied magnetic fields. It was found that the residual resistance due to trapped flux in the nitrogen-doped cavity was three times larger than in the 120oC baked cavity.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI063

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WEPRI064

New Insights into Heat Treatment of SRF Cavities in a Low-pressure Nitrogen Atmosphere

cavity, SRF, vacuum, resonance

2634

D. Gonnella, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: United States Department of Energy
Recent results from Cornell and FNAL have shown that superconducting RF cavities given a heat treatment in a nitrogen atmosphere of a few mTorr display an increase in Q0 with increasing accelerating field, opposite to the medium field Q slope usually observed. Three cavities was prepared at Cornell using this method and subsequently tested after different amounts of material removal. Cavity performance and material properties were extracted for each cavity and correlated with material removal. This has given new insights into how material properties and the anti-Q slope depend on cavity preparation.

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WEPRI065

SRF Material Performance Studies using a Sample Host Cavity

cavity, coupling, SRF, controls

2638

D.L. Hall, D. Gonnella, M. Liepe, I.S. Madjarov
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

A sample-host TE-mode cavity developed at Cornell for the purposes of studying novel superconducting materials has undergone further testing using a niobium sample plate. In initial testing the peak field achieved on the sample plate was (45 ± 4.5) mT, although this was limited by the amount of input power available. New tests have been performed using both an improved RF power system and a temperature mapping system for precision measurements of surface resistance as a function of location on the sample plate. Results of the most recent test, in which the cavity achieved a peak sample plate field of (81 ± 4) mT using a high-RRR niobium sample plate, are presented and future work on the cavity is discussed.

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WEPRI066

Recent Progress in Nb3Sn SRF Cavity Development at Cornell

cavity, SRF, accelerating-gradient, cryogenics

2641

S. Posen, D. Gonnella, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Nb₃Sn coatings on niobium SRF cavities have the potential to significantly reduce cryogenic costs due to their extremely small surface resistance (R_s). In this paper, we present new results showing the repeatability of Cornell's fabrication process, which produces high Q₀ cavities that reach medium fields with minimal Q-slope. We also show the results of attempts to smooth RF surfaces and reduce defects via material removal. However, both HF rinsing and centrifugal barrel polishing resulted in strong performance degradation.

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WEPRI069

Reproducibility of High-Q SRF Cavities by High Temperature Heat Treatment

cavity, vacuum, SRF, induction

2651

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

Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
Recent work on high-temperature (> 600 °C) heat treatment of ingot Nb cavities in a customized vacuum furnace for several hours showed the possibility of achieving Q0-values of up to ~5×10¹⁰ at 2.0 K, 1.5 GHz and accelerating gradients of ~20 MV/m. This contribution presents results on further studies of the heat treatment process to produce cavities with high Q0 values for continuous-wave accelerator application. Single-cell cavities of different Nb purity have been processed through few cycles of heat-treatments and chemical etching. Measurements of Q0 as a function of temperature at low RF field and of Q0 as a function of the RF field at or below 2.0 K have been made after each treatment. Measurements by TOF-SIMS of the impurities’ depth profiles were made on samples heat treated with the cavities.

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WEPRI070

Mechanical Properties of Ingot Nb Cavities

cavity, SRF, radio-frequency, network

2654

G. Ciovati, P. Dhakal, P. Kneisel, J.D. Mammosser, J. Matalevich, G.R. Myneni
JLab, Newport News, Virginia, USA

Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
This contribution presents the results of measurements of the resonant frequency and of strain along the contour of a single-cell cavity made of ingot Nb subjected to increasing uniform differential pressure, up to 6 atm. The data were used to infer mechanical properties of this material after cavity fabrication, by comparison with the results from simulation calculations done with ANSYS. The objective is to provide useful information about the mechanical properties of ingot Nb cavities which can be used in the design phase of SRF cavities intended to be built with this material.

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WEPRI078

Development of a Quarter-wave Coaxial Coupler for 1.3 GHz Superconducting Cavities

cavity, coupling, HOM, SRF

2675

Y. Xie, A. Kanareykin
Euclid TechLabs, LLC, Solon, Ohio, USA
N. Solyak, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA

Superconducting ILC-type cavities have an rf coupler that is welded on. A detachable coupler will reduce conditioning time (can be conditioned separately), reduce cost and improve reliability. The problem with placing an extra flange in the superconducting cavity is creating a possible quench spot. Euclid Techlabs LLC designed a coupler and optimized its geometry that yielding an area on the surface with zero magnetic field (hence zero surface current). By placing a flange in that area we are able to avoid disturbing surface currents that typically lead to a quench. The coupler is optimized to preserve the axial symmetry of the cavity and rf field. The rf test results of this type coupler with a 1.3 GHz ILC-type single-cell cavity at Fermilab will be reported and discussed.

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THPME122

A SQUID-based Beam Current Monitor for FAIR

pick-up, cryogenics, electronics, ion

3524

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

A Cryogenic Current Comparator (CCC) was developed for the upcoming FAIR-Project, providing a non-destructive online monitoring of the beam current in the nA-range. The CCC was optimized for a lowest possible noise-limited current resolution together with a high system bandwidth. Therefore, the low temperature properties of ferromagnetic core materials used in the pick-up coil were investigated and different SQUID-systems were tested. In this contribution we present results of the completed Cryogenic Current Comparator for FAIR working in a laboratory environment, regarding the improvements in resolution and bandwidth due to the use of suitable ferromagnetic core materials and optimized SQUID-system components.

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