Mitigation of EC breakdown in the gyrotron transmission line of the ITER Collective Thomson Scattering diagnostic via a Split Biased Waveguide

A. W. Larsen*, S. B. Korsholm, B. Gonçalves, H. E. Gutierrez, E. Henriques, V. Infante, T. Jensen, M. Jessen, Esben Bryndt Klinkby, Erik Nonbøl, R. Luis, A. Vale, A. Lopes, Volker Naulin, S.K. Nielsen, Mirko Salewski, J. Rasmussen, A. Taormina, Claus Møllsøe, T. MussenbrockJ. Trieschmann

*Corresponding author for this work

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In this paper we present the results of the R&D work that has been performed on avoiding electron cyclotron (EC) gas breakdown inside the launcher transmission line (TL) of the ITER collective Thomson scattering (CTS) diagnostic, due to encountering the fundamental EC resonance, which is located inside the port plug vacuum for the baseline ITER magnetic field scenario. If an EC breakdown occurs, this can lead to strong local absorption of the CTS gyrotron beam, as well as arcing inside the ITER vacuum vessel, which must be avoided. Due to the hostile, restrictive, and nuclear environment in ITER, it is not possible to implement the standard method for avoiding EC breakdown - a controlled atmosphere at the EC resonance. Instead, the CTS diagnostic will include a longitudinally-split electrically-biased corrugated waveguide (SBWG) in the launcher transmission line. The SBWG works by applying a transverse DC bias voltage across the two electrically-isolated waveguide halves, causing free electrons to diffuse out of the EC resonant region before they can cause an electron-impact ionisation-avalanche, and thus an EC breakdown. Due to insufficient experimental facilities, the functionality of the SBWG is validated through Monte Carlo electron modelling.
Original languageEnglish
Article numberC11009
JournalJournal of Instrumentation
Issue number11
Number of pages11
Publication statusPublished - 2019
Event3rd European Conference on Plasma Diagnostics - Lisbon, Portugal
Duration: 6 May 201910 May 2019
Conference number: 3


Conference3rd European Conference on Plasma Diagnostics


  • Detector design and construction technologies and materials
  • ; Interaction of radiation with matter
  • Nuclear instruments and methods for hot plasma diagnostics
  • Overall mechanics design (support structures and materials, vibration analysis etc)


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