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WEYGBF3 | Nb3Sn Multicell Cavity Coating at JLab | 1798 |
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Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics. Following encouraging results with Nb3Sn-coated R&D cavities, the existing coating system was upgraded to allow for Nb3Sn coating of CEBAF accelerator cavities. The upgrade was designed to allow Nb3Sn coating of original CEBAF 5-cell cavities with the vapor diffusion technique. Several CEBAF cavities were coated in the upgraded system to investigate vapor diffusion coatings on extended structures. Witness samples coated along with the cavities were characterized with material science techniques, while coated cavities were measured at 4 and 2 K. The progress, lessons learned, and the pathforward are discussed. |
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Slides WEYGBF3 [2.381 MB] | |
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEYGBF3 | |
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THPAL129 | Magnetron Sputtering of Nb3Sn for SRF Cavities | 3946 |
SUSPL076 | use link to see paper's listing under its alternate paper code | |
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Nb3Sn is a potential candidate for surface material of SRF cavities since it can enable the cavity to operate at higher temperatures with high quality factor and at an increased accelerating gradient. Nb-Sn films were deposited using magnetron sputtering of individual Nb and Sn targets onto Nb and sapphire substrates. The as-deposited films were annealed at 1200 °C for 3 hours. The films were characterized for their structure by X-ray Diffraction (XRD), morphology by Field Emission Scanning Electron Microscopy (FESEM), and composition by Energy Dispersive X-ray Spectroscopy (EDS) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The surface resistivity was measured down to cryogenic temperature to determine the superconducting transition temperature and its width. The composition of the multilayered films was controlled by varying the thickness of the Nb and Sn layers. The films showed crystalline Nb3Sn phases with Tc up to 17.6 K. | ||
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL129 | |
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THPAL130 | Effect of Deposition Temperature and Duration on Nb3Sn Diffusion Coating | 3950 |
SUSPL075 | use link to see paper's listing under its alternate paper code | |
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Funding: Partially authored by Jefferson Science Associates under contract no. DE¬AC05¬06OR23177. Work at College of William & Mary supported by Office of High Energy Physics under grant SC0014475. Nb3Sn is a potential candidate to replace Nb in SRF accelerator cavities to reduce cost and advance perfor-mance. Tin vapor diffusion is the preferred technique to realize such cavities by growing a few microns thick Nb3Sn coating on the interior surface of the niobium cavity. The coating process typically uses temperatures of 1100-1200 °C for 3-6 hours. It is important to better understand the coating process, and optimize the coating parameters to overcome the current limitation on the performance of Nb3Sn coated SRF cavities. We investi-gate Nb3Sn coatings prepared in the temperature range of 900-1200 °C and duration of 3 - 12 hours using various material characterization tools. Variation of these pa-rameters appears to have notable effect on microstructure and topography of the obtained surface. |
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DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL130 | |
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THPAL131 | Studies of Electropolishing and Oxypolishing Treated Diffusion Coated Nb3Sn Surfaces | 3954 |
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The Nb3Sn-coated cavities aim to enhance perfor-mance and significantly reduce cost. Their fabrication involves tin vapor diffusion coating of Nb3Sn on the interior surface of a Nb cavity. Controlled removal of first few layers to obtain a smoother and cleaner surface could be desirable to improve the high field RF perfor-mance. Our first results from the application of elec-tropolishing and oxypolishing techniques on Nb3Sn-coated surfaces indicated reduced surface roughness, and the surface composition appeared nominally unchanged. Systematic studies explore the effect of different polish-ing parameters into the roughness and composition. We present the latest results from SEM/EDS and AFM studies of Nb3Sn-coated samples treated with electropolishing and oxypolishing. | ||
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL131 | |
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THPAL140 | Rework Recipe Development, Analysis and Results of Select 9-Cell Cavities for LCLS-II | 3968 |
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Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The SLAC National Accelerator Laboratory is currently constructing a major upgrade to its accelerator, the Linac Coherent Light Source II (LCLS-II). Several Department of Energy laboratories, including the Thomas Jefferson National Accelerator Facility (JLab) and Fermi National Accelerator Laboratory (FNAL), are collaborating in this project. The cryomodules for this project each consist of eight 1.3-GHz cavities produced by two vendors, Research Instruments GmbH in Germany (RI*) and Ettore Zanon S.p.a. in Italy (EZ*), using niobium cell material from Tokyo Denkai Co., Ltd. (TD) and Ningxia Orient Tantalum Industry Co., Ltd. (OTIC/NX)). During the initial production run, cavity performance from one of the vendors (Vendor A) was far below expectation. All the cavities had low Q0, later attributed to minimal EP as well as high-flux-trapping NX material, early quench behaviour below 18 MV/m, with many having Q0 roll-off at 12-16 MV/m. Production was stopped multiple times over the following 6 months, with test batches of cavities being made to ascertain the root cause of the problem. The final root cause of the problem was found to be inappropriate grinding of the RF surface prior to welding which left normal conducting inclusions in the surface. In addition, most cavities showed internal and external weld spatter which required post weld grinding and a very rough surface from operating the electropolishing machine in an etching rather than polishing regime. All issues have been corrected on new cavities and rework is underway on the originally effected cavities. |
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DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL140 | |
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THPAL142 | Surface Characterization of NbTiN Films for Accelerator Applications | 3975 |
SUSPL069 | use link to see paper's listing under its alternate paper code | |
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Funding: Work supported by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The development of next-generation SRF cavities requires the deployment of innovative material solutions with RF performance beyond bulk Nb. Theoretical interest has stimulated efforts to grow and characterize thin multi-layer superconductor/insulator/superconductor (SIS) structures for their potential capability of supporting otherwise inaccessible surface magnetic fields in SRF cavities *. The ternary B1-compound NbTiN is among the candidate superconducting materials for SIS structures. Single crystal NbTiN films with thicknesses below 15 nm are also of interest for the development of high resolution, high sensitivity (SNSPD) detectors for particle physics application. Using DC reactive magnetron sputtering, NbTiN can be deposited with nominal superconducting parameters. This contribution presents the on-going material surface and superconducting properties characterization in order to optimize the NbTiN films for each application. * A Gurevich, "Maximum screening fields of superconducting multilayer structures", AIP ADVANCES 5, 017112 (2015) |
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DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL142 | |
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THPAL143 | Commissioning of JLab Vertical Cavity Processing System for SRF Nb Single Cell and Multicell Cavity With HF-Free Pulse-Reverse Electopolishing | 3978 |
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Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177 Pulse reversed electropolishing of niobium SRF cavities, using a dilute aqueous H2SO4 electrolyte without HF yields equivalent RF performance with traditional EP. Comparing with present EP process for Nb SRF cavity which uses 1:10 volume ratio of HF (49%) and H2SO4 (98%), pulse reverse EP (also known as bipolar EP (BPEP)) is ecologically friendly and uses relatively benign electrolyte options for cavity processing. In this study, we report the commissioning of a new vertical cavity processing system for SRF Nb single cell and multi-cell cavities with HF-free pulse-reverse electropolishing at Jefferson Lab, together with RF test of cavities being processed. We report the scale-up challenges and interpretations from process R&D to implementation. |
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DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL143 | |
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