Author: Pietralla, N.
Paper Title Page
TUOFAV01
Recent Achievements at S-DALINAC*  
 
  • M. Arnold, L. Alff, A. Brauch, J. Conrad, M. Dutine, J. Enders, M. Fischer, R. Grewe, L.E. Jürgensen, M. Major, M.G. Meier, J. Pforr, N. Pietralla, F. Schließmann, D. Schneider, N. Schäfer, M. Steinhorst, L. Stobbe, S. Weih
    TU Darmstadt, Darmstadt, Germany
 
  Funding: *Work supported by DFG (GRK 2128), BMBF (05H18RDRB2), State of Hesse (Cluster Project ELEMENTS and LOEWE Research Cluster Nuclear Photonics)
The superconducting Darmstadt linear accelerator S-DALINAC is a 130 MeV thrice-recirculating linac for electrons, running at 3 GHz in cw [1]. It can be operated in a conventional acceleration scheme for an experimental program in nuclear physics and as an energy recovery linac (ERL) [2]. Since 1991, the S-DALINAC was mainly developed and operated by students and junior researchers, e.g., within their thesis works. Recent upgrades include measures for improved beam quality and diagnostics. The previous five-cell capture cavity in the superconducting injector with a beta of 1 was, for example, replaced by a 6-cell capture cavity with an injection-matched beta of 0.86. Other projects address the treatment and development of SRF cavities (N-doping, surface preparation, Nb3Sn coating) or the improvement of diagnostics, including the installation of a diagnosis beam-line upstream of the injector and dedicated RF control for the quantification of ERL performance. An overview on the facility and recent projects will be given. Latest operational experience on the conventional and on the ERL mode will be presented. A focus will be on the 6-cell cavity from design to commissioning.
[1] N. Pietralla, Nuclear Physics News, Vol. 28, No. 2, 4 (2018).
[2] M. Arnold et al., Phys. Rev. Accel. Beams 23, 020101 (2020).
 
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WEPFDV010 Structural Investigation of Nitrogen-Doped Niobium for SRF Cavities 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 ※ https://doi.org/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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WEPCAV007 Status and First Tests of the Reduced-Beta Capture Cavity for the S-DALINAC 597
 
  • S. Weih, M. Arnold, M. Dutine, J. Enders, R. Grewe, L.E. Jürgensen, N. Pietralla, F. Schließmann, M. Steinhorst
    TU Darmstadt, Darmstadt, Germany
 
  Funding: work supported by German research council (DFG) through GRK 2128 ’AccelencE’ and the state of Hesse through the LOEWE research project Nuclear Photonics and the Collaborative Research Cluster ELEMENTS
The superconducting part of the injector section of the superconducting Darmstadt electron linear accelerator (S-DALINAC) [1] consisted of one five-cell capture cavity and two 20-cell cavities at 3 GHz resonance frequency. All of them were geometrically adapted to electron velocities with a beta of 1, while the thermionic gun provides electrons with a beta of 0.74. This mismatch resulted in an insufficient capture process for optimum beam quality. For this reason, a new six-cell capture cavity with a beta of 0.86 has been designed and built. Field flatness tuning, a test in the vertical bath cryostat, and a UHV furnace treatment have been carried out in-house to finalize the cavity processing. The cryostat module was adapted to house the new cavity, which has been recently installed. Following the module assembly, a first RF test run was conducted at the S-DALINAC. We report on these latest advancements towards the implementation of the injector upgrade.
* N. Pietralla, Nuclear Physics News, Vol. 28, No. 2, 4 (2018).
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-WEPCAV007  
About • Received ※ 20 June 2021 — Revised ※ 22 December 2021 — Accepted ※ 27 February 2022 — Issue date ※ 01 March 2022
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