Plasma cleaning of ITER first mirrors

L Moser, L. Marot, R. Steiner, R Reichle, F. Leipold, C. Vorpahl, F. Le Guern, U. Walach, S. Alberti, I. Furno, R. Yan, J. Peng, Marwa Ben Yaala, E. Meyer

Research output: Contribution to journalArticlepeer-review

33 Citations (Scopus)

Abstract

Nuclear fusion is an extremely attractive option for future generations to compete with the strong increase in energy consumption. Proper control of the fusion plasma is mandatory to reach the ambitious objectives set while preserving the machine’s integrity, which requests a large number of plasma diagnostic systems. Due to the large neutron flux expected in the International Thermonuclear Experimental Reactor (ITER), regular windows or fibre optics are unusable and were replaced by so-called metallic first mirrors (FMs) embedded in the neutron shielding, forming an optical labyrinth. Materials eroded from the first wall reactor through physical or chemical sputtering will migrate and will be deposited onto mirrors. Mirrors subject to net deposition will suffer from reflectivity losses due to the deposition of impurities. Cleaning systems of metallic FMs are required in more than 20 optical diagnostic systems in ITER. Plasma cleaning using radio frequency (RF) generated plasmas is currently being considered the most promising in situ cleaning technique. An update of recent results obtained with this technique will be presented. These include the demonstration of cleaning of several deposit types (beryllium, tungsten and beryllium proxy, i.e. aluminium) at 13.56 or 60 MHz as well as large scale cleaning (mirror size: 200 × 300 mm2). Tests under a strong magnetic field up to 3.5 T in laboratory and first experiments of RF plasma cleaning in EAST tokamak will also be discussed. A specific focus will be given on repetitive cleaning experiments performed on several FM material candidates.
Original languageEnglish
Article number014047
Number of pages7
JournalPhysica Scripta
Volume2017
Issue numberT170
DOIs
Publication statusPublished - 27 Oct 2017

Keywords

  • first mirror
  • International Thermonuclear Experimental Reactor (ITER)
  • plasma cleaning
  • repetitive cleaning
  • fusion plasma
  • metallic first mirrors (FMs)
  • radio frequency (RF) generated plasmas

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