Keyword: superconducting-RF
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TUPTEV009 Seamless 1.3 GHz Copper Cavities for Nb Coatings: Cold Test Results of Two Different Approaches cavity, SRF, niobium, ISOL 498
  • L. Vega Cid, S. Atieh, L.M.A. Ferreira, L. Laín-Amador, C. Pereira Carlos, G.J. Rosaz, K. Scibor, W. Venturini Delsolaro, P. Vidal García
    CERN, Meyrin, Switzerland
  • S.B. Leith
    University Siegen, Siegen, Germany
  A necessary condition for high SRF performances in thin film coated cavities is the absence of substrate defects. For instance, in the past, defects originated around electron beam welds in high magnetic field areas have been shown to be the cause of performance limitations in Nb/Cu cavities. Seamless cavities are therefore good candidates to allow an optimization of the coating parameters without the pitfalls of a changing substrate. In this work, we present the first results of two different methods to produce seamless cavities applied to 1.3 GHz copper single cells coated with thin Nb films by means of HIPIMS. A first method consists in electroplating the copper resonator on precisely machined aluminum mandrels, which are then dissolved chemically. As an alternative and a cross check, one cavity was machined directly from the bulk. Both cavities were coated with HIPIMS Nb films using the same coating parameters and the SRF performance was measured down to 1.8 K with a variable coupler to minimize the measurement uncertainty.  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2021-TUPTEV009  
About • Received ※ 21 June 2021 — Revised ※ 28 October 2021 — Accepted ※ 18 November 2021 — Issue date ※ 10 February 2022
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WEPFDV010 Structural Investigation of Nitrogen-Doped Niobium for SRF Cavities cavity, niobium, SRF, linac 581
  • M. Major, L. Alff, M. Arnold, J. Conrad, S. Flege, R. Grewe, N. Pietralla
    TU Darmstadt, Darmstadt, Germany
  Funding: Work supported by the German Federal Ministry for Education and Research (BMBF) through grant 05H18RDRB2 and the German Research Foundation (DFG) via the AccelencE Research Training Group (GRK 2128).
Niobium is the standard material for superconducting RF (SRF) cavities for particle acceleration. Superconducting materials with higher critical temperature or higher critical magnetic field allow cavities to work at higher operating temperatures or higher accelerating fields, respectively. One direction of search for new materials with better properties is the modification of bulk niobium by nitrogen doping. In the Nb-N phase diagram, the cubic delta-phase of NbN has the highest critical temperature. Niobium samples were annealed and doped with nitrogen in the high-temperature furnace at TU Darmstadt and investigated at its Materials Research Department with respect to structural modifications. X-ray diffraction (XRD) confirmed the appearance of Nb4N3 and Nb2N phases on the surface of the samples. A single cell cavity was annealed under optimized doping conditions. The test samples treated together with the cavity showed almost single Nb4N3 phase. XRD pole figures also showed grain growth during sample annealing.
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2021-WEPFDV010  
About • Received ※ 22 June 2021 — Revised ※ 18 August 2021 — Accepted ※ 17 November 2021 — Issue date ※ 19 November 2021
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FROFDV01 Systematic Investigation of Mid-T Furnace Baking for High-Q Performance cavity, niobium, vacuum, SRF 881
  • H. Ito, A. Araki, K. Umemori
    KEK, Ibaraki, Japan
  • K. Takahashi
    Sokendai, Ibaraki, Japan
  We report on an investigation of the effect of a new baking process called "furnace baking" on the quality factor. Furnace baking is performed as the final step of the cavity surface treatment; the cavities are heated in a vacuum furnace in a temperature range of 200-800C for 3 h, followed by high-pressure rinsing and radio-frequency measurement. We find the anti-Q-slope for cavities furnace-baked at a temperature range of 250 to 400C and a reduction in the residual resistance for all cavities. In particular, an extremely high Q value of 5·1010 at 16 MV/m and 2.0 K is obtained for cavities furnace-baked at 300C.  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2021-FROFDV01  
About • Received ※ 21 June 2021 — Accepted ※ 24 February 2022 — Issue date ※ 30 April 2022  
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