Keyword: experiment
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MOP003 Development of Nb3Sn Cavity Coating at IMP cavity, niobium, SRF, radio-frequency 21
 
  • Z.Q. Yang, H. Guo, Y. He, C.L. Li, Z.Q. Lin, M. Lu, T. Tan, P.R. Xiong, S.H. Zhang, S.X. Zhang
    IMP/CAS, Lanzhou, People’s Republic of China
 
  The A15 superconductor Nb3Sn is one of the most promising alternative materials to standard niobium for SRF applications. In this paper, we report our progress in the development of Nb3Sn cavity coating by vapor diffusion method at IMP. The evolutionary process of nucleation was analyzed. Influence of SnCl2 partial pressure inhomogeneity was studied. Less-nuclear zones were found on the surfaces of nucleation samples. The Nb3Sn film structure and composition were investigated and analyzed. In light of knowledge obtained above, the coating process was optimized. Finally, both 1.3 GHz and 650 MHz single cell cavities were coated and vertically tested both at 4 K and 2 K. Effect of low temperature baking (1000°C for 48 hs) on the RF performance of Nb3Sn cavity was studied. After baking, the Q drop in the low field region was eliminated and the Q in the intermediate field region was increased 8 times. The Q was 10 times larger than that of the Nb cavity at 4.2 K even in the case of the ambient field larger than 20 mGs. This study shows that the low temperature baking is an effective enrichment to the post treatment of the Nb3Sn cavity.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP003  
About • paper received ※ 23 June 2019       paper accepted ※ 03 July 2019       issue date ※ 14 August 2019  
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MOP015 RF Performance Sensitivity to Tuning of Nb3Sn Coated CEBAF Cavities cavity, simulation, SRF, factory 55
 
  • G.V. Eremeev, W. Crahen, J. Henry, F. Marhauser, C.E. Reece
    JLab, Newport News, Virginia, USA
  • U. Pudasaini
    The College of William and Mary, Williamsburg, Virginia, USA
 
  Funding: Co-Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics.
Nb3Sn has the potential to surpass niobium as the material of choice for SRF applications. The potential of this material stems from a larger superconducting energy gap, which leads to expectations of a higher RF critical field and a lower RF surface resistance. The appeal of better superconducting properties is offset by the relative complexity of producing practical Nb3Sn structures, and Nb3Sn sensitivity to lattice disorder challenges the use of the material for practical applications. Such sensitivity is indirectly probed during SRF cavity development, when the cavity is tuned to match the desired accelerator frequency. In the course of recent experiments we have coated and tuned several multi-cell cavities. Cold RF measurements before and after tuning showed degradation in cavity performance after tuning. The results of RF measurement were compared against strain evolution on Nb3Sn surface during tuning based on CST and ANSYS models.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP015  
About • paper received ※ 26 June 2019       paper accepted ※ 01 July 2019       issue date ※ 14 August 2019  
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MOP018 Recent Results From Nb3Sn Single Cell Cavities Coated at Jefferson Lab cavity, SRF, factory, niobium 65
 
  • U. Pudasaini, M.J. Kelley
    The College of William and Mary, Williamsburg, Virginia, USA
  • G. Ciovati, G.V. Eremeev, M.J. Kelley, C.E. Reece
    JLab, Newport News, Virginia, USA
  • I.P. Parajuli, Md.N. Sayeed
    ODU, Norfolk, Virginia, USA
 
  Funding: Partially authored by Jefferson Science Associates under contract no. DE¬AC05¬06OR23177. Supported by Office of High Energy Physics under grants DE-SC-0014475 to the College of William and DE-SC-0018918 to Virginia Tech
Because of superior superconducting properties (Tc ~ 18.3K, Hs h ~ 425 mT and delta ~ 3.1 meV) compared to niobium, Nb3Sn promise better RF performance (Q0 and Eacc) and/or higher operating temperature (2 K Vs 4.2 K) for SRF cavities. Nb3Sn-coated SRF cavities are produced routinely by depositing a few micron-thick Nb3Sn films on the interior surface of Nb cavities via tin vapor diffusion technique. Early results from Nb3Sn cavities coated with this technique exhibited precipi-tous low field Q-slope, also known as Wuppertal slope. Several Nb3Sn single cell cavities coated at JLab ap-peared to exhibit similar Q-slope. RF testing of cavi-ties and materials study of witness samples were con-tinuously used to modify the coating protocol. At best condition, we were able to produce Nb3Sn cavity with Q0 in excess of ~ 5×1010 at 2 K and ~ 2×1010 at 4 K up the accelerating gradient of ~15 MV/m, without any significant Q-slope. In this presentation, we will dis-cuss recent results from several Nb3Sn coated single-cell cavities linked with material studies of witness samples, coating process modifications and the possi-ble causative factors to Wuppertal slope.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP018  
About • paper received ※ 23 June 2019       paper accepted ※ 29 June 2019       issue date ※ 14 August 2019  
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MOP040 Low Temperature Thermal Conductivity of Niobium and Materials for SRF Cavities niobium, SRF, cavity, controls 144
 
  • M. Fouaidy
    IPN, Orsay, France
 
  A test facility, allowing the test of 4 samples simultaneously during each run, was developed for measuring at low temperature (T= 1.5 K - 10 K) the thermal conductivity k(T) of niobium and other materials used for the fabrication of SRF cavities. The measurements are performed using steady-state axial heat flow method with a careful control of heat leaks to the surrounding. Several samples of different materials (industrial Nb sheets, Ti’) were either tested as received or/and subjected to various Heat Treatment (H.T) prior to the experiment then tested. The resulting experimental data are presented and compared to the experimental results previously reported by other groups. As expected, H.T @ 1200°C with Ti gettering improves the Nb RRR by a factor of 3 and consequently k(T). Finally, the correlation between the Niobium RRR and the thermal conductivity. at T=4.2 K is confirmed in good agreement with the Wiedemann-Franz law.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP040  
About • paper received ※ 04 July 2019       paper accepted ※ 05 July 2019       issue date ※ 14 August 2019  
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MOP057 Electropolishing of PIP-II Low Beta Cavity Prototypes cavity, cathode, FEL, linac 194
 
  • M. Bertucci, A. Bosotti, A. D’Ambros, P. Michelato, L. Monaco, C. Pagani, R. Paparella, D. Sertore
    INFN/LASA, Segrate (MI), Italy
  • A. Gresele, A. Visentin
    Ettore Zanon S.p.A., Nuclear Division, Schio, Italy
  • C. Pagani
    Università degli Studi di Milano & INFN, Segrate, Italy
  • D. Rizzetto, M. Rizzi
    Ettore Zanon S.p.A., Schio, Italy
 
  We present the upgrade of the EP facility for the surface treatment of PIP-II low beta cavities. The main process parameters, such as voltage, treatment time, acid throughput and cathode geometry, already optimized on the previous experience of 1.3 GHz Tesla-shape cavities, are discussed taking into account the different cavity size and geometry. The first surface treatments have been performed at Ettore Zanon SpA on single cell cavity prototypes in order to reach good final surface finishing and the required thickness removal. In the meantime, the upgrade of the system for the treatment of multicell PIP-II prototype cavities is presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP057  
About • paper received ※ 23 June 2019       paper accepted ※ 02 July 2019       issue date ※ 14 August 2019  
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MOP064 Performance of First Prototype Multi-Cell Low-Surface-Field Shape Cavity cavity, SRF, electron, niobium 222
 
  • R.L. Geng
    JLab, Newport News, Virginia, USA
  • Y. Fuwa, Y. Iwashita
    Kyoto ICR, Uji, Kyoto, Japan
  • H. Hayano
    KEK, Ibaraki, Japan
  • H. Ito
    Sokendai, Ibaraki, Japan
  • Z. Li
    SLAC, Menlo Park, California, USA
 
  The idea of cavity shaping for higher ultimate acceleration gradients has been proposed for some time, Low Loss/Ichiro and Re-entrant being examples, both seeking a lower Hpk/Eacc at the expense of a higher Epk/Eacc. While experimental verification in single-cell cavities of those shapes was very successful including the record gradient of 59 MV/m, pushing multi-cell cavities of those shapes to higher gradients was prevented by field emission. The Low-Surface-Field (LSF) shape seeks not only a lower Hpk/Eacc but also a lower Epk/Eacc, therefore it has the advantage of raising ultimate gradient at reduced field emission. The first multi-cell LSF shape prototype cavity was built using the standard forming and welding techniques. RF tests have been carried out, following standard ILC TDR baseline surface processing and treatment recipe. Three out of five cells achieved Hpk values corresponding to Eacc 50 MV/m. The current limit is the field emission in end cells. Instrumented testing following end-cell wiping and HPR with larger nozzles is in progress. We will present detailed experimental results and preparation procedures.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP064  
About • paper received ※ 24 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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MOP073 The Study of High Power Couplers for CIADS status, multipactoring, operation, simulation 241
 
  • Z.Q. Lin, Y. He, S.C. Huang, Y.L. Huang, T.C. Jiang, C.L. Li, Y.M. Li, M. Lu, F. Pan, T. Tan, R.X. Wang, Z. Xue, Z.Q. Yang, S.X. Zhang
    IMP/CAS, Lanzhou, People’s Republic of China
 
  High power couplers with high operation reliability are needed for the superconducting cavities used in the Linac of CiADS project at IMP. This paper will report two works on high power coupler. The DC bias structure of the coupler was optimized to suppress the multipacting effect, where the series resistors were introduced to the wire of the DC bias to reduce the field propagating along the DC bias’s wire. For the purpose of significantly decreasing the power needed to condition the coupler, we designed a new RF conditioning scheme, in which the coupler served as a standing wave resonator, and the positions of the crests and troughs of the wave were tunable. The details of the design mentioned above will be depicted.  
poster icon Poster MOP073 [14.677 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP073  
About • paper received ※ 25 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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MOP083 R&D of Copper Electroplating Process for Power Couplers: Effect of Microstructures on RRR SRF, target, electron, ECR 278
 
  • Y. Okii, J. Taguchi
    Nomura Plating Co, Ltd., Osaka, Japan
  • E. Kako, S. Michizono, Y. Yamamoto
    KEK, Ibaraki, Japan
  • H. Takahashi, H. Yasutake
    CETD, Tochigi, Japan
 
  Power couplers for superconducting cavities are required to have both low-thermal conductivity and high-electrical conductivity, because high-thermal conductivity and low-electrical conductivity could generate unexpected increase for heat load. In order to combine these contrary properties, power couplers are made of stainless steel and plated with copper plating. As electrical conductivity of copper layer affects dynamic heat load, it is crucial to optimize plating processes. In this study, we investigated influences of plating parameters (i.e., thickness of copper layer, plating bath composition, bath temperature, heat-treatment conditions) on RRR by collaborative work among Nomura plating, CETD, and KEK. As a result, we obtained high-RRR samples with conditions noted below; (1) electroformed copper plate, (2) copper layer thickness of over 50 µm, and (3) heat-treatment at 200deg-1h, (4) other plating bath composition. In addition, we observed microstructures of several samples, then found that microstructures of copper layer are strongly related to RRR. In this paper, we will present the recent results for this investigation.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP083  
About • paper received ※ 23 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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MOP085 The Destructive Effects to the RF Coupler by the Plasma Discharge plasma, cavity, vacuum, coupling 285
 
  • A.D. Wu, Q.W. Chu, H. Guo, Y. He, S.C. Huang, T.C. Jiang, C.L. Li, Z.Q. Lin, F. Pan, Y.K. Song, T. Tan, W.M. Yue, S.H. Zhang, H.W. Zhao
    IMP/CAS, Lanzhou, People’s Republic of China
 
  The low temperature RF plasma was proved an effec-tive method to clean the niobium surface and relieve the field emission effect for the SRF cavities. In the case of half-wave resonators, these cavities were usually powered via the fundamental coupler with the electric coupling. Thus, coupler antennas were fixed in the intense electric field region, and this region was where the plasma rou-tinely ignited. Therefore, the ceramic window of coupler taken the risk of breakdown under the sputtering of ions and heating loads that may be caused by the plasma drift and diffusion from the electric field region. In this paper, the plasma ignition for surface cleaning on the HWR cavity and its coupler was investigated, and the power transmission, temperature raising and vacuum degradation were tested to characterize the adverse impacts on the ceramic window. Finally, the solution was proposed to figure these issues.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP085  
About • paper received ※ 22 June 2019       paper accepted ※ 02 July 2019       issue date ※ 14 August 2019  
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TUFUA7 Review of Muon Spin Rotation Studies of SRF Materials SRF, niobium, cavity, FEL 360
 
  • T. Junginger
    Lancaster University, Lancaster, United Kingdom
  • R.E. Laxdal
    TRIUMF, Vancouver, Canada
 
  Muons spin rotate in magnetic fields and emit a positron preferentially in spin direction after decay. These properties enable muon spin rotation (muSR) as a precise probe for local magnetism. muSR has been used to characterize SRF materials since 2010. At TRIUMF a so called surface beam implants muons at a material dependent depth of about 150 µm in the bulk. A dedicated spectrometer was developed for field of first vortex penetration and pinning strength measurements of SRF materials in parallel magnetic fields of up to 300 mT. A low energy beam available at PSI implants muons at variable depth in the London layer allowing for direct measurements of the London penetration depth from which the lower critical field and the superheating field can be calculated. This facility is limited to parallel magnetic fields of up to 25 mT. Here, surface and low energy muSR results on SRF materials are reviewed and cross-correlated to each other and to further results from additional experiments. Finally, we present the status of a new facility based on the similar beta-NMR technique enabling measurements in the London layer of SRF materials exposed to parallel magnetic fields above 200 mT.  
slides icon Slides TUFUA7 [4.063 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUA7  
About • paper received ※ 01 July 2019       paper accepted ※ 12 July 2019       issue date ※ 14 August 2019  
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TUFUB3 Mapping Flux Trapping in SRF Cavities to Analyze the Impact of Geometry cavity, HOM, niobium, simulation 364
 
  • F. Kramer, J. Knobloch, O. Kugeler, J.M. Köszegi
    HZB, Berlin, Germany
  • J. Knobloch
    University of Siegen, Siegen, Germany
 
  A combined temperature and magnetic field mapping system was used to investigate the impact of an ambient field on trapped flux and on the resulting local surface resistance. For this, a 1.3 GHz TESLA single cell cavity was cooled through the superconducting transition at different magnetic field angles with respect to the cavity axis. The measurements suggest, that the field is trapped homogeneously over the cavity volume, without changing its orientation. Flux trapped perpendicular the surface contributed significantly more to the surface resistance, than trapped flux parallel to the surface.  
slides icon Slides TUFUB3 [12.777 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUB3  
About • paper received ※ 21 June 2019       paper accepted ※ 01 July 2019       issue date ※ 14 August 2019  
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TUFUB7 Measurement of Surface Resistance Properties with Coaxial Resonators - Review cavity, multipactoring, ECR, SRF 374
 
  • H. Park, S.U. De Silva, J.R. Delayen
    ODU, Norfolk, Virginia, USA
 
  Achieving ever decreasing surface resistance at higher field in superconducting RF accelerating structures is one of most outstanding developments in modern accelerators. The BCS theory has been used widely to estimate the surface resistance and to direct the technology. However, recent research results show that the behavior of the surface resistance further deviates from the BCS theory. So far the study on surface resistance was performed usually with cavities of single frequency which limited the study of frequency dependent surface resistance. The Center for Accelerator Science at Old Dominion University has designed and built several half wave coaxial cavities to study the frequency, temperature, and RF field dependence of surface resistance. TRIUMF in Canada also joined this line of research using such multi frequency quarter wave and half wave coaxial cavities. This type of multi mode cavity will allow us to systematically study the parameters affecting surface resistance on the same cavity surface. In this paper, we review the results ODU and TRIUMF collected so far and proper analysis methods.  
slides icon Slides TUFUB7 [3.551 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUB7  
About • paper received ※ 01 July 2019       paper accepted ※ 12 July 2019       issue date ※ 14 August 2019  
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TUP008 HOMs Extraction Structure Design for HEPS 166.6 MHz Cavities HOM, cavity, extraction, simulation 403
 
  • X.R. Hao
    IHEP, Beijing, People’s Republic of China
 
  Higher order modes (HOMs) may af{}fect beam stability and refrigeration requirements of superconducting cavity such as the 166.6~MHz superconducting(SC) cavity, which is studied at IHEP. Under certain conditions beam-induced HOMs can accumulate suf{}f{}icient energy to destabilize the beam or quench the SC cavities. In order to limit these ef{}fects, we considers the use of coaxial HOM couplers on the cut-of{}f tubes of the SC cavity. However, HOMs cannot be ef{}fectively extracted by HOM couplers. Therefore, it is necessary to design a HOMs extraction structure to introduce the dangerous modes from the cavity into the bundle tube, which are designed to couple to potentially dangerous modes while suf{}ficiently rejecting the fundamental mode. The HOMs extraction structure consists of an enlarged tubes, a coaxial structure, and the petal. The extraction of the dangerous modes and the suppression of the fundamental mode are realized by the petal structure and the coaxial structure. In order to verify the designs, a rapid prototype for the favored structure was fabricated and characterized on a low-power test-stand.  
poster icon Poster TUP008 [1.665 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP008  
About • paper received ※ 22 June 2019       paper accepted ※ 01 July 2019       issue date ※ 14 August 2019  
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TUP012 Evaluation of High Performance Large Grain Medium Purity SRF Cavity From KEK cavity, niobium, SRF, cryogenics 415
 
  • P. Dhakal, G. Ciovati, G.R. Myneni
    JLab, Newport News, Virginia, USA
 
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
We presented the RF measurement on a 1.3 GHz single cell cavity fabricated at KEK using large grain ingot niobium with RRR=107. The cavity reached to 35 MV/m with Q0 = 2.0×10zEhNZeHn at 2.0 K, record performance on the cavity made from medium purity ingot niobium. The cavity was cool down with different temperature gradient along the cavity axis in order to understand the flux expulsion mechanism when the cavity does through the superconducting transition and effect of trap residual magnetic field on the residual resistance. The measurement showed the excellent flux expulsion with the flux trapping sensitivity of 0.29 nΩ/mG for electro polished surface and 0.44 nΩ/mG for cavity followed by low temperature baking at 120°C for 12 hours.
We acknowledge KEK for sending this cavity for evaluations.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP012  
About • paper received ※ 17 June 2019       paper accepted ※ 29 June 2019       issue date ※ 14 August 2019  
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TUP021 Effect of Cathode Rotation and Acid Flow in Vertical Electropolishing of 1.3 GHz Niobium Nine-Cell Cavity cavity, cathode, SRF, niobium 448
 
  • V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi
    MGH, Hyogo-ken, Japan
  • H. Hayano, S. Kato, H. Monjushiro, T. Saeki
    KEK, Ibaraki, Japan
 
  We have been carrying out R&D on vertical electropolishing (VEP) technique to establish it as an alternate of the horizontal EP (HEP) technique used for the surface treatment of niobium (Nb) superconducting RF (SRF) cavities. We have earlier reported on a VEP parameter study for 1.3 GHz single and nine-cell Nb cavities. The optimized VEP parameters and a unique rotating cathode yielded uniform removal and a smooth surface in the single cell cavity. The unique cathode and a dual flow mechanism for acid circulation were applied to improve the removal uniformity in the nine-cell cavity. The vertically electropolished single and nine cell cavities achieved the same RF performance as achieved after the HEP processes. We are making efforts to further improve the removal uniformity in the nine-cell cavity. Here, we report on a VEP of the 1.3 GHz Nb nine-cell cavity at a higher cathode rotation speed of 50 rpm. The VEP results reveal that the speed could be considered for improving the uniformity in removal while maintaining the surface smoothness. Required improvements in the VEP facility and acid flow condition for achieving uniform EP and a smooth surface are also described.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP021  
About • paper received ※ 23 June 2019       paper accepted ※ 02 July 2019       issue date ※ 14 August 2019  
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TUP026 Vibro-tumbling as an Alternative to Standard Mechanical Polishing Techniques for SRF Cavities cavity, SRF, framework, superconductivity 464
 
  • E. Chyhyrynets, O. Azzolini, V.A. Garcia, G. Keppel, C. Pira, F. Stivanello, L. Zanotto
    INFN/LNL, Legnaro (PD), Italy
 
  Funding: Work supported by the INFN V group experiment TEFEN, Agreement N. KE2722/BE/FCC and from the European Union’s H2020 Framework Programme under grant agreement no. 764879 (EASITrain)
Centrifugal Barrel Polishing (CBP) is a common tool in the Nb bulk SC cavities production, prior to elec-tropolishing (EP). Indeed, the mechanical polishing is fun-damental also in the superconducting thin film resonant cavities in which one of the main issues that limits the per-formances is the surface preparation. A promising vi-bro-tumbling technique is being studied and implemented with a possibility to replace or improve mechanical treat-ment steps (grinding, barrel polishing). The simplic-ity of the technology allows it to adapt to any cavity geom-etry, both for Nb and Cu materials. The presented work contains last results on 6 GHz cavities obtained at LNL-INFN, both Nb bulk and Cu cavities.
 
poster icon Poster TUP026 [5.584 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP026  
About • paper received ※ 21 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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TUP027 Vertical Electropolishing of Niobium Nine-Cell Cavity with a Cavity Flipping System for Uniform Removal cavity, cathode, niobium, SRF 467
 
  • K.N. Nii, V. Chouhan, Y.I. Ida, T.Y. Yamaguchi
    MGH, Hyogo-ken, Japan
  • H. Hayano, S. Kato, H. Monjushiro, T. Saeki
    KEK, Ibaraki, Japan
 
  Marui Galvanizing Co., Ltd. has been developing vertical electropolishing (VEP) technology for single and nine-cell niobium superconducting radio frequency cavities using a unique cathode namely Ninja cathode in collaboration with KEK. The VEP process usually results in non-uniform removal with a large asymmetry along the cavity length. In order to suppress the asymmetry in removal, we are making different approaches. Flipping of the cavity during the VEP process is one of the approaches applied so far. A unique VEP setup, which allows the flipping of a multi-cell cavity, has been developed as reported earlier. Here, we report the improvement in the setup with automation for cavity flipping. VEP experiments were conducted with the improved system. VEP parameters were studied and the VEP results including the removal trend are discussed in detail.  
poster icon Poster TUP027 [1.347 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP027  
About • paper received ※ 24 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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TUP045 Ab Initio Calculations on Impurity Doped Niobium and Niobium Surfaces niobium, scattering, electron, lattice 523
 
  • N. Sitaraman, T. Arias
    Cornell University, Ithaca, New York, USA
  • R.G. Farber, S.J. Sibener, R.D. Veit
    The University of Chicago, Chicago, Illinois, USA
  • M. Liepe, J.T. Maniscalco
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Funding: This work was funded by the Center for Bright Beams
We develop and apply new tools to understand Nb surface chemistry and fundamental electronic processes using theoretical ab initio methods. We study the thermodynamics of impurities and hydrides in the near-surface region as well as their effect on the surface band gap. This makes it possible for experimentalists to relate changes in STM dI/dV measurements resulting from different preparations to changes in subsurface structure. We also calculate matrix elements for electron-impurity scattering in Nb for common impurities O, N, C, and H. By transforming these matrix elements into a Wannier function basis, we calculate lifetimes for a dense set of states on the Fermi surface and determine the mean free path as a function of impurity density. This technique can be generalized to calculate other scattering amplitudes and timescales relevant to SRF theory.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP045  
About • paper received ※ 02 July 2019       paper accepted ※ 03 July 2019       issue date ※ 14 August 2019  
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TUP049 Maximum Performance of Cavities Affected by the High-field Q-slope (HFQS) cavity, SRF, niobium, radio-frequency 533
 
  • G. Ciovati
    JLab, Newport News, Virginia, USA
  • A.V. Gurevich, I.P. Parajuli
    ODU, Norfolk, Virginia, USA
 
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The work of I. P. and A. G. is supported by NSF Grant PHY 100614-010.
The performance of high-purity, bulk niobium SRF cavities treated by chemical processes such as BCP or EP is limited by the so-called high-field Q-slope (HFQS). Several models and experimental studies have been proposed and performed over the years to understand the origin of these anomalous losses but a general consensus on what these orgins are is yet to be established. In this contribution, we present the results from the RF tests of several 1.3 GHz single-cell cavities limited by the HFQS and tested using a variable input coupler. This allowed to maintain close to critical coupling even at high field and the data showed that the HFQS did not saturate and that in some cases a power dissipation of up to 200 W at 2 K could be sustained without quench.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP049  
About • paper received ※ 21 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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TUP052 Design and Commissioning of a Magnetic Field Scanning System for SRF Cavities cavity, SRF, cryogenics, data-acquisition 547
 
  • I.P. Parajuli, J.R. Delayen, A.V. Gurevich, J. Nice
    ODU, Norfolk, Virginia, USA
  • G. Ciovati, W.A. Clemens, J.R. Delayen
    JLab, Newport News, Virginia, USA
 
  Funding: Work supported by NSF Grant 100614-010. G. C. is supported by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Trapped magnetic vortices are one of the leading sources of residual losses in SRF cavities. Mechanisms of flux pinning depend on the materials treatment and cool-down conditions. A magnetic field scanning system using flux-gate magnetometers and Hall probes has been designed and built to allow measuring the local magnetic field of trapped vortices normal to the outer surface of 1.3 GHz single-cell SRF cavities at cryogenic temperatures. Such system will allow inferring the key information about the distribution and magnitude of trapped flux in the SRF cavities for different material, surface preparations and cool-down conditions.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP052  
About • paper received ※ 22 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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TUP053 Optimal Thermal Gradient for Flux Expulsion in 600°C Heat-treated CEBAF 12 GeV Upgrade Cavities cavity, HOM, niobium, controls 550
 
  • R.L. Geng, F. Marhauser, P.D. Owen
    JLab, Newport News, Virginia, USA
 
  We will present results on measurement of flux expulsion in CEBAF 12 GeV upgrade cavities and original CEBAF cavities and the search for optimal thermal gradient for reducing the trapped flux in cavities installed in CEBAF linacs. Preliminary measurements of one C100 cavities has shown that a nearly perfect flux expulsion can be achieved at an optimal thermal gradient - a surprising result contrary to the expectation of zero flux expulsion for 600°C heat treated niobium cavities. These results could lead to a cost-effective path for improving the quality factor of cavities installed in CEBAF and ultimately saving accelerator operation cost.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP053  
About • paper received ※ 24 June 2019       paper accepted ※ 29 June 2019       issue date ※ 14 August 2019  
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TUP054 How Is Flux Expulsion Affected by Geometry: Experimental Evidence and Model cavity, niobium, SRF, accelerating-gradient 555
 
  • D. Longuevergne
    IPN, Orsay, France
 
  Measurements of magnetic sensitivity to trapped flux on several type of cavity geometries have been performed at IPNO showing a clear geometrical effect. Magnetic sensitivity depends not only on material quality but also on the cavity geometry and on the residual magnetic field orientation. A presentation of experimental data will be done. These will be as well compared to the theoretical magnetic sensitivities calculated thanks to a simple Labview routine  
poster icon Poster TUP054 [1.312 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP054  
About • paper received ※ 03 July 2019       paper accepted ※ 04 July 2019       issue date ※ 14 August 2019  
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TUP058 Characterization of Small AMR Sensors in Liquid Helium to Measure Residual Magnetic Field on Superconducting Samples SRF, cavity, controls, site 576
 
  • G. Martinet
    IPN, Orsay, France
 
  Trapped residual magnetic flux is responsible of residual resistance degradation on superconducting materials used in SRF technologies. To characterize this effect on superconducting samples, compact sensors are required to mount on sample characterization devices. In this paper, we present results on AMR sensors supplied from different manufacturers in the temperature range from 4.2 K up to 300 K.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP058  
About • paper received ※ 23 June 2019       paper accepted ※ 03 July 2019       issue date ※ 14 August 2019  
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TUP059 Investigation of Trapped Flux Dynamics via DC-Magnetic Quenching cavity, superconducting-cavity, ECR, SRF 580
 
  • P. Nuñez von Voigt, J. Knobloch, O. Kugeler
    HZB, Berlin, Germany
  • J. Knobloch
    University of Siegen, Siegen, Germany
 
  Trapped magnetic flux increases the surface resistance in superconducting radio-frequency cavities. A better understanding of its behaviour could help to develop a method of expelling trapped flux from the superconducting surface. Using a superconducting coil with ferrite core attached to a 3 GHz sample Niobium cavity fully immersed in liquid Helium, we were able to subject the cavity walls to unusually large magnetic fields (estimated > 150 mT) and create magnetic quenches. With Fluxgate sensors attached in three spatial directions inside the cavity, we were able to monitor the quench dynamics and extract parameters of the flux dynamics from the hysteretic behaviour of the measured fields resulting from the applied coil current. First results of manipulation of the trapped flux with high magnetic fields are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP059  
About • paper received ※ 24 June 2019       paper accepted ※ 05 July 2019       issue date ※ 14 August 2019  
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TUP068 Study of Surface Treatment of 1.3 GHz Single-cell Copper Cavity for Niobium Sputtering cavity, SRF, niobium, MMI 605
 
  • F.Y. Yang, J. Dai, P. He, Z.Q. Li, Y. Ma, P. Zhang
    IHEP, Beijing, People’s Republic of China
 
  Funding: This work has been supported in part by PAPS project and National Key Programme for S&T Research and Development (Grant NO.: 2016YFA0400400)
A R&D program on niobium sputtering on copper cavities has started at IHEP in 2017. Single-cell 1.3 GHz copper cavity has been chosen as a substrate. A chemical polishing system has subsequently developed and commissioned recently to accommodate the etching of both copper samples and a cavity. Different polishing agents have been tested on copper samples and later characterized. The results of these surface treatment tests are presented.
 
poster icon Poster TUP068 [1.228 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP068  
About • paper received ※ 20 June 2019       paper accepted ※ 03 July 2019       issue date ※ 14 August 2019  
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TUP075 New Progress for Nb Sputtered 325 MHz QWR Cavities in IMP cavity, target, SRF, niobium 621
 
  • F. Pan, H. Guo, Y. He, T.C. Jiang, C.L. Li, M. Lu, T. Tan
    IMP/CAS, Lanzhou, People’s Republic of China
 
  Comparing with bulk niobium cavities, the Nb/Cu cavities feature a much better stability at 4.5 K. Last year, two 325 MHz QWR copper cavities coated with biased DC diode sputterred Nb for CiADS has been accomplished at IMP. But vertical tests showed the cavities had low Q0 at 4 K. To solve the issue, a new coating system was designed and built. The sputtering target was redesigned and manufactured. The coating parameters were selected again and auxiliary heating was used to control the coating temperature in the process of sputtering. The power and Ar pressure during coating were also carefully selected. The paper covers resulting film characters, vertical tests with the evolution of the sputtering process, and improvements we made since last year.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP075  
About • paper received ※ 22 June 2019       paper accepted ※ 14 August 2019       issue date ※ 14 August 2019  
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TUP077 Nb3Sn Thin Film Coating Method for Superconducting Multilayered Structure site, SRF, cavity, target 628
 
  • R. Ito, T. Nagata
    ULVAC, Inc, Chiba, Japan
  • H. Hayano, R. Katayama, T. Kubo, T. Saeki
    KEK, Ibaraki, Japan
  • H. Ito
    Sokendai, Ibaraki, Japan
  • Y. Iwashita
    Kyoto ICR, Uji, Kyoto, Japan
 
  S-I-S (superconductor-insulator-superconductor) multilayered structure has been proposed in order to increase the maximum acceleration gradient of SRF cavities. Nb3Sn is the material most expected as a superconducting layer of the S-I-S multilayered structure because it offers both a large critical temperature and large predicted Hsh. Most important in fabricating Nb3Sn thin films is the stoichiometry of the material produced, and the lack of tin leads to performance degradation. We have launched a new in-house DC magnetron sputtering apparatus for Nb3Sn deposition. Nb and Sn layers were alternately and repeatedly deposited on Si wafer while adjusting the film thickness of each layer, so we successfully obtained Nb-Sn films having appropriate composition ratio. The as-deposited films were annealed under the temperature of 600 degree C for 1 hour to generate the Nb3Sn phase. The characteristics of Nb-Sn films evaluated by XRD, XRF, FE-SEM, and so on. We also measured critical temperature of the annealed films. In this paper, the detail of the Nb3Sn coating method and the measurement result of the Nb-Sn films will be reported.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP077  
About • paper received ※ 02 July 2019       paper accepted ※ 03 July 2019       issue date ※ 14 August 2019  
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TUP085 Operation of an SRF Cavity Tuner Submerged into Liquid He cavity, SRF, resonance, operation 660
 
  • Y.M. Pischalnikov, D.J. Bice, A. Grassellino, T.N. Khabiboulline, O.S. Melnychuk, R.V. Pilipenko, S. Posen, O.V. Pronitchev, A.S. Romanenko
    Fermilab, Batavia, Illinois, USA
 
  To precisely control the resonance of 1.3 GHz SRF cavities during testing at the FNAL’s Vertical Test Facility, we install for the first time a double lever tuner and operate it when submerged into the liquid He bath. Both active components of the tuner: electromechanical actuator (stepper motor) and piezo-actuators are operated inside superfluid helium. Accuracy in controlling the SRF cavity resonance frequency will be presented. Specifics of the tuner operation when submerged into liquid He will be discussed.  
poster icon Poster TUP085 [2.164 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP085  
About • paper received ※ 23 June 2019       paper accepted ※ 02 July 2019       issue date ※ 14 August 2019  
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TUP100 Thermal Load Studies on the Photocathode Insert with Exchangeable Plug for the BERLinPro SRF-Photoinjector cathode, SRF, gun, cavity 705
 
  • J. Kühn, N. Al-Saokal, M. Bürger, M. Dirsat, A. Frahm, A. Jankowiak, T. Kamps, G. Klemz, S. Mistry, A. Neumann, H. Plötz
    HZB, Berlin, Germany
 
  For the operation of an SRF photoinjector a well-functioning and efficient cooling system of the photocathode is necessary. A test experiment was set up of the photocathode cooling system based on the original components, which we call thermal contact experiment (TCX). We present the results of our thermal load studies on the photocathode insert with exchangeable photocathode plug. The goal was to test all components before they are installed in the cold string of the BERLinPro SRF-Photoinjector to ensure the operation of very sensitive semiconductor photocathodes. The tests include the investigation of the cooling performance, the thermal load management and the mechanical stability of the photocathode insert.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP100  
About • paper received ※ 23 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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WETEB7 A Ferroelectric Fast Reactive Tuner for Superconducting Cavities cavity, controls, linac, superconducting-cavity 781
 
  • N.C. Shipman, J. Bastard, M.R. Coly, F. Gerigk, A. Macpherson, N. Stapley
    CERN, Geneva, Switzerland
  • I. Ben-Zvi
    BNL, Upton, New York, USA
  • G. Burt, A. Castilla
    Lancaster University, Lancaster, United Kingdom
  • C.-J. Jing, A. Kanareykin
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • S. Kazakov
    Fermilab, Batavia, Illinois, USA
  • E. Nenasheva
    Ceramics Ltd., St. Petersburg, Russia
 
  A prototype FerroElectric Fast Reactive Tuner (FE-FRT) for superconducting cavities has been developed, which allows the frequency to be controlled by application of a potential difference across a ferroelectric residing within the tuner. This technique has now become practically feasible due to the recent development of a new extremely low loss ferroelectric material. In a world first, CERN has tested the prototype FE-FRT with a superconducting cavity, and frequency tuning has been successfully demonstrated. This is a significant first step in the development of an entirely new class of tuner. These will allow electronic control of cavity frequencies, by a device operating at room temperature, within timescales that will allow active compensation of microphonics. For many applications this could eliminate the need to use over-coupled fundamental power couplers, thus significantly reducing RF amplifier power.  
slides icon Slides WETEB7 [21.570 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-WETEB7  
About • paper received ※ 23 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THFUA2 Evaluation of the Superconducting Characteristics of Multi-Layer Thin-Film Structures of NbN and SiO2 on Pure Nb Substrate linac, DTL 807
 
  • R. Katayama, H. Hayano, T. Kubo, T. Saeki
    KEK, Ibaraki, Japan
  • C.Z. Antoine
    CEA-IRFU, Gif-sur-Yvette, France
  • H. Ito
    Sokendai, Ibaraki, Japan
  • R. Ito
    ULVAC, Inc, Chiba, Japan
  • Y. Iwashita, H. Tongu
    Kyoto ICR, Uji, Kyoto, Japan
  • T. Nagata
    ULVAC, Inc., Tsukuba, Japan
 
  In recent years, it has been pointed out that the maximum accelerating gradient of a superconducting RF cavity can be increased by coating the inner surface of the cavity with a multilayer thin-film structure consisting of alternating insulating and superconducting layers. In this structure, the principal parameter that limits the performance of the cavity is the critical magnetic field or effective Hc1 at which vortices begin penetrating into the superconductor layer. This is predicted to depend on the combination of the film thickness. We made samples that have a NbN/SiO2 thin-film structure on a pure Nb substrate with several layers of NbN film deposited using DC magnetron sputtering method. Here, we report the measurement results of effective Hc1 of NbN/SiO2(30 nm)/Nb multilayer samples with thicknesses of NbN layers in the range from 50 nm to 800 nm by using the third-harmonic voltage method. Experimental results show that an optimum thickness exists, which increases the effective Hc1 by 23.8 %.  
slides icon Slides THFUA2 [2.333 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THFUA2  
About • paper received ※ 03 July 2019       paper accepted ※ 05 July 2019       issue date ※ 14 August 2019  
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THFUA6 Nb3Sn Films for SRF Cavities: Genesis and RF Properties cavity, niobium, SRF, interface 810
 
  • U. Pudasaini, M.J. Kelley
    The College of William and Mary, Williamsburg, Virginia, USA
  • J.W. Angle, M.J. Kelley, J. Tuggle
    Virginia Polytechnic Institute and State University, Blacksburg, USA
  • G.V. Eremeev, M.J. Kelley, C.E. Reece
    JLab, Newport News, Virginia, USA
 
  Funding: Partially authored by Jefferson Science Associates under contract no. DE¬AC05¬06OR23177. Supported by Office of High Energy Physics under grants DE-SC-0014475 to the College of William and DE-SC-0018918 to Virginia Tech.
Understanding of Nb3Sn nucleation and growth is essential to the progress with Nb3Sn vapor diffusion coatings of SRF cavities. Samples representing different stages of Nb3Sn formation have been produced and examined to elucidate the effects of nucleation, growth, process conditions, and impurities. Nb3Sn films from few hundreds of nm up to ~15 µm were grown and characterized using AFM, SEM/EDS, XPS, EBSD, SIMS, and SAM. Microscopic examinations of samples suggest the mechanisms behind Nb3Sn thin film nucleation and growth. RF measurements of coated cavities were combined with material characterization of witness samples to adapt the coating process in "Siemens" coating configuration. Understanding obtained from sample studies, applied to cavities, resulted in Nb3Sn cavity with quality factor 2 ×1010 at 15 MV/m accelerating gradient at 4 K, without "Wuppertal" Q-slope. We discuss the genesis of the Nb3Sn thin film in a typical tin vapor diffusion process, and its consequences to the coating of SRF cavities.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THFUA6  
About • paper received ※ 23 June 2019       paper accepted ※ 29 June 2019       issue date ※ 14 August 2019  
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THP003 Results on Bulk Niobium Surface Resistance Measurement With Pillbox Cavity on TE011 and TE012 Modes cavity, niobium, coupling, SRF 833
 
  • G. Martinet
    IPN, Orsay, France
 
  Surface measurement of superconducting samples is required to characterize processes of bulk niobium preparation for SRF resonators. In order to reduce characterization cost and improve measurement performances, a pill-box cavity has been developed at IPN Orsay. Using TE011 and TE012 modes, we describe the latest results based on calorimetric method.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP003  
About • paper received ※ 23 June 2019       paper accepted ※ 03 July 2019       issue date ※ 14 August 2019  
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THP007 In-Situ EXAFS Investigations of Nb-Treatments in N2 at Elevated Temperatures niobium, cavity, vacuum, lattice 842
 
  • P. Rothweiler, B. Bornmann, J. Klaes, D. Lützenkirchen-Hecht, R. Wagner, S. von Polheim
    University of Wuppertal, Wuppertal, Germany
 
  Funding: We gratefully acknowledge financial support by the German Federal Ministry of Education and Research (BMBF) under project No. 05H15PXRB1.
Smooth polycrystalline Nb metal foils were exposed to dilute N2 and Kr atmospheres at elevated temperatures of up to 900°C. Transmission mode X-ray absorption spectroscopy (EXAFS) experiments were used to study the resulting changes of the atomic short range order structure in-situ. EXAFS data were collected prior to any heat treatment as well as during the different process steps at elevated temperatures with a time resolution of about 1 s, and the samples were also studied after cooling to room temperature. In general, only very small changes of the Nb-EXAFS data could be detected after the processing in N2-atmospheres, and no evidence for bulk formation of Nb-nitrides was found. In contrast, the quantitative EXAFS data evaluation revealed slightly distorted Nb-Nb coordinations, suggesting that N-atoms are increasingly incorporated on octahedral interstitial sites in the host lattice with increasing N2-exposure. For the treatments in Kr-atmospheres, simultaneous measurements are feasible at both the K-edge of the Nb host and the Kr dopant. Those studies gave clear evidence for a Kr uptake during the heat treatment, and will be discussed in more detail at the conference.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP007  
About • paper received ※ 23 June 2019       paper accepted ※ 01 July 2019       issue date ※ 14 August 2019  
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THP009 Pulse Laser Annealing of Niobium Film on Copper for SRF Cavities laser, niobium, cavity, interface 848
 
  • Y. Yang, X.Y. Lu, W.W. Tan, L. Xiao, D. Xie, L. Zhu
    PKU, Beijing, People’s Republic of China
 
  Thin film cavities were proposed as the most promis-ing next generation superconducting cavities. The chal-lenges are improving the surface superconducting per-formance and reducing defects of the coating film, which can be greatly solved by laser annealing. Laser annealing system has been set up in Peking University, and experi-ments with niobium thin film sample have been carried out. Superconducting performance and other properties of Nb/Cu samples before and after annealing were com-pared. Recrystallization happened and surface structure improved a lot according to the results.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP009  
About • paper received ※ 22 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THP029 Towards Real-time Data Processing using FPGA Technology for High-speed Data Acquisition System at MHz Repetition Rates FPGA, detector, laser, electron 905
 
  • M. Bawatna, A. Arnold, J.-C. Deinert, B.W. Green, S. Kovalev
    HZDR, Dresden, Germany
 
  Accelerator-based light sources, in particular, those based on linear accelerators, are intrinsically less stable than lasers or other more conventional light sources because of their large scale. In order to achieve optimal data quality, the properties of each light pulse need to be detected and implemented into the analysis of each experiment. Such schemes are of particular advantage in 4th generation light sources based on superconducting radiofrequency (SRF) technology, since here the combination of pulse-resolved detection schemes with high-repetition-rate is particularly fruitful. Implementation of several different purpose-built CMOS linear array detector will enable to perform arrival-time measurements at MHz repetition rates. An architecture based on FPGA technology will allow an online analysis of the measured data at MHz repetition rate and will decrease the amount of data throughput and disk capacity for storing the data by orders of magnitude. In this contribution, we will outline how the pulse-resolved data acquisition scheme of the TELBE user facility shall be upgraded to allow operation at MHz repetition rates and sub-femtosecond timing precision.  
poster icon Poster THP029 [1.616 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP029  
About • paper received ※ 23 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THP036 An Insight on the Thermal and Mechanical Numerical Evaluations for the High-Luminosity LHC Crab Cavities cavity, pick-up, coupling, electromagnetic-fields 929
 
  • E. Cano-Pleite, A. Amorim Carvalho, K. Artoos, R. Calaga, O. Capatina, T. Capelli, F. Carra, L. Dassa, M. Garlasché, R. Leuxe, E. Montesinos
    CERN, Geneva, Switzerland
  • J.A. Mitchell
    Lancaster University, Lancaster, United Kingdom
  • S. Verdú-Andrés
    BNL, Upton, New York, USA
 
  Funding: Research supported by the HL-LHC project
One of the key devices of the HL-LHC project are SRF crab cavities. A cryomodule with two Double Quarter Wave (DQW) crab cavities has been successfully fabricat-ed and tested with beam at CERN whereas the Radio Frequency Dipole (RFD) crab cavities are currently on its fabrication process. The paper provides an insight on the multiple calculations carried out to evaluate the thermal and mechanical performance of the DQW and RFD cavi-ties and its components. In some cases, the presence of RF fields inside the cavity volume requires the use of mul-tiphysics numerical models capable of coupling these fields with the thermal and mechanical domains. In fact, the RF field presents a strong dependency on the cavity shape, whereas the mechanical, thermal and electrical properties of the materials may substantially vary as a function of temperature, which in turn depends on the RF field. The results presented in this paper, using both cou-pled and uncoupled models, allowed elucidating the importance of physics coupling on the numerical evalua-tion of RF cavities and its components. Analyses were also of great support for the design evaluation and im-provement of future prototypes.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP036  
About • paper received ※ 21 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THP042 Initial Results from Investigations into Different Surface Peparation Techniques of OFHC Copper for SRF Applications site, cavity, ECR, SRF 941
 
  • S.B. Leith, X. Jiang, Z. Khalil, A.S.H. Mohamed, M. Vogel
    University Siegen, Siegen, Germany
 
  Funding: This work forms part of the EASITrain research programme. This Marie Sklodowska-Curie Action (MSCA) Innovative Training Networks (ITN) has received funding from the European Union’s H2020 Framework Programme under Grant Agreement no. 764879
As part of efforts to improve the performance of thin film coated accelerating cavities, improvement of the topography of the surface of copper is being pursued. This is known to strongly affect the properties of the deposited superconducting thin film. This study focuses on determining the optimal procedure to enhance homogeneity and smoothness of the copper surface. OFHC copper substrates have been processed using mechanical polishing (MP), chemical polishing (CP) and electropolishing (EP) procedures as well as a combina-tion thereof. The parameters of each of the procedures have been tested and optimised to produce the smoothest surface possible. The resulting samples have been analysed using a scanning electron microscope, a laser profilometer and a confocal microscope. Results indicate the superior per-formance of electrochemical polishing over chemical polishing in terms of planarization efficiency, while a combination of mechanical polishing followed by electropolishing provides the most homogeneous and smooth surface when utilising the critical current density of the electrolyte.
 
poster icon Poster THP042 [1.190 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP042  
About • paper received ※ 22 June 2019       paper accepted ※ 29 June 2019       issue date ※ 14 August 2019  
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THP048 Characterization of Flat Multilayer Thin Film Superconductors dipole, superconducting-magnet, SRF, site 968
 
  • D. Turner, A.J. May
    STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
  • G. Burt, L. Gurran
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • K.D. Dumbell, N. Pattalwar, S.M. Pattalwar
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • T. Junginger, O.B. Malyshev
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
 
  The maximum accelerating gradient of SRF cavities can be increased by raising the field of initial flux penetration, Hvp. Thin alternating layers of superconductors and insulators (SIS) can potentially increase Hvp. Magnetometry is commercially available but consists of limitations, such as SQUID measurements apply a field over both superconducting layers, so Hvp through the sample cannot be measured. If SIS structures are to be investigated a magnetic field must be applied locally, from one plane of the sample, with no magnetic field on the opposing side to allow Hvp to be measured. A magnetic field penetration experiment has been developed at Daresbury laboratory, where a VTI has been created for a cryostat where Hvp of a sample can be measured. The VTI has been designed to allow flat samples to be measured to reduce limitations such as edge effects by creating a DC magnetic field smaller than the sample. A small, parallel magnetic field is produced on the sample by the use of a ferrite yoke. The field is increased to determine Hvp by using 2 hall probes either side of the sample.  
poster icon Poster THP048 [0.327 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP048  
About • paper received ※ 23 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THP050 Measurement of the Magnetic Field Penetration into Superconducting Thin Films solenoid, SRF, cavity, FEL 978
 
  • I.H. Senevirathne, G. Ciovati, J.R. Delayen
    ODU, Norfolk, Virginia, USA
  • G. Ciovati, J.R. Delayen
    JLab, Newport News, Virginia, USA
 
  The magnetic field at which first flux penetrates is a fundamental parameter characterizing superconducting materials for SRF cavities. Therefore, an accurate technique is needed to measure the penetration of the magnetic field directly. The conventional magnetometers are inconvenient for thin superconducting film measurements because these measurements are strongly influenced by orientation, edge and shape effects. In order to measure the onset of field penetration in bulk, thin films and multi-layered superconductors, we have designed, built and calibrated a system combining a small superconducting solenoid capable of generating surface magnetic field higher than 500 mT and Hall probe to detect the first entry of vortices. This setup can be used to study various promising alternative materials to Nb, especially SIS multilayer coatings on Nb that have been recently proposed to delay the vortex penetration in Nb surface. In this paper, the system will be described and calibration will be presented.  
poster icon Poster THP050 [1.201 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP050  
About • paper received ※ 20 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THP064 The Cryostat Results of Carbon Contamination and Plasma Cleaning for the Field Emission on the SRF Cavity cavity, plasma, SRF, cryogenics 1038
 
  • A.D. Wu, Q.W. Chu, H. Guo, Y. He, S.C. Huang, C.L. Li, F. Pan, Y.K. Song, T. Tan, P.R. Xiong, W.M. Yue, S.H. Zhang, H.W. Zhao
    IMP/CAS, Lanzhou, People’s Republic of China
 
  The field emission effect is the mainly limitation for the operating of SRF cavities in higher gradient with stability. In this paper, the experiments were performed to evaluate the impact of the carbon contaminants and plasma cleaning on the performance of SRF cavity. Contamination mechanism was classified into cryogenic adsorption with weak strength and chemical deposition with strong strength. For the weak strength condition, the methane was injected into the SRF cavity during vertical test to make a cryogenic adsorption layer on the inner surface of the cavity. The results revealed that the performance of SRF cavity degraded by methane physical adsorption, but the performance can be recovered by thermal cycle the cavity to 300K and pump methane out. For the strong strength condition, the chemical deposited dirty layer of carbon contamination was produced by using of Ar/CH4 mixed PECVD method, and the SRF cavity performance was deteriorated by the severe field emission. Finally, carbon deposited cavity was treated by the Ar/O2 plasma, and its results revealed that the field emission removed greatly and the gradient was increased.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP064  
About • paper received ※ 20 June 2019       paper accepted ※ 01 July 2019       issue date ※ 14 August 2019  
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THP083 Quadrupole Scan Transverse Emittance Measurements at HZDR ELBE quadrupole, emittance, focusing, electron 1100
 
  • S. Ma, A. Arnold, A.A. Ryzhov, J. Schaber, J. Teichert, R. Xiang, K. Zhou
    HZDR, Dresden, Germany
 
  Two quadrupoles and one screen are used for beam transverse emittance measurements at HZDR ELBE. In this paper, the emittance calculated with two different methods, one with thin-lens approximation and the other one without this approximation, are compared and analized. To analyze the measurement error, quadrupole calibration is need. Two aspects about quadrupole analysis are made. The first one is quadrupole’s effective length and strength and the second one is quadrupole’s converged or diverged ability in reality.  
poster icon Poster THP083 [1.726 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP083  
About • paper received ※ 25 June 2019       paper accepted ※ 03 July 2019       issue date ※ 14 August 2019  
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THP095 Direct Measurement of Thermoelectric Currents During Cool Down cavity, simulation, niobium, coupling 1139
 
  • A.E. Ivanov, F. Gerigk, A. Macpherson
    CERN, Geneva, Switzerland
 
  In recent years there has been much discussion on thermoelectric effects and their role in flux expulsion during cool down of SRF cavities. Magnetic field is often measured to asses both flux expulsion as the cavity undergoes superconducting transition, and thermoelectric currents due to spatial thermal gradients. As a complementary view, in this paper we show direct measurement of the thermoelectric current independent from the expulsion measurement of the magnetic field. In our setup the azimuthally symmetric cavity is vertically installed and the thermal gradient is along the symmetry axis allowing to describe the cool down behavior of the thermoelectric current using simple coupled simulations.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP095  
About • paper received ※ 21 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THP105 Thermal Mapping of SRF Cavities by Second Sound Detection With Transition Edge Sensors and Oscillating Superleak Transducers cavity, SRF, diagnostics, luminosity 1182
 
  • G. Vandoni, T. Koettig, A. Macpherson, K. Turaj, L. Vega Cid
    CERN, Meyrin, Switzerland
  • H. Furci
    EPFL, Lausanne, Switzerland
 
  The SRF cavity testing facilities at CERN include four vertical cryostat stations in SM18 and a cryostat for small cavities in the Cryolab. A large range of structures are tested, from Nb thin film cavities for HIE-Isolde and LHC, to bulk Nb crab cavities for HiLumi or 704 MHz 5-cell high-gradient cavities. To cope with different shapes and small series tests, thermal mapping diagnostics is deployed by sensing second sound in superfluid helium. A new type of Transition Edge Sensors (TES) has been developed in the last 2 years. These are miniature resistors of thin-film superconducting alloys, micro-produced on insulating wafers. An extensive campaign of optimization of design, fabrication process and composition was accompanied by qualification in a calibration cryostat. Reproducibility, stability, then intensity, distance and angular dependence of the response were assessed and compared to Oscillating Superleak Transducers (OST). The TES were then installed in a vertical cryostat for tests of a prototype crab cavity for HiLumi. TES are now applied to quench localization on high gradient cavities, for which the most recent results will be presented, together with the OST results.  
poster icon Poster THP105 [2.186 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP105  
About • paper received ※ 23 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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FRCAB6 The Effect of Helium Processing and Plasma Cleaning for Low Beta HWR Cavity cavity, plasma, SRF, ion-effects 1228
 
  • S.C. Huang, Q.W. Chu, Y. He, C.L. Li, A.D. Wu, S.X. Zhang
    IMP/CAS, Lanzhou, People’s Republic of China
 
  The commissioning of the 25 MeV high power and high intensity proton Linac demo for CiADS showed that the performance of the SRF cavities was mainly limited by field emission inside the cavities. Therefore, the techniques of helium processing and reactive oxygen plasma cleaning have been developed to mitigate field emission issues. We performed an experiment with a low beta HWR cavity exposed to air directly and processed by helium and reactive oxygen. In this paper, the details of the experiment will be described, the efficiency of helium processing and plasma cleaning will be compared and discussed  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-FRCAB6  
About • paper received ※ 23 June 2019       paper accepted ※ 01 July 2019       issue date ※ 14 August 2019  
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