Ion sputtering, evaporation and arcing in DIVA

Abstract

Experimental studies on the origin of metal impurities in DIVA are described. Three processes of metal impurity release, i.e. ion sputtering, evaporation and arcing, have been identified. Among these processes, ion sputtering is the dominant process in the quiet phase of the discharge, which is characterized by the lack of spikes in the loop voltage as well as by the fact that no heat flux concentration towards a specific part of the first wall takes place. Moreover, it is demonstrated that a honeycomb structure can decrease the metal impurity release.

Heat flux to the material surfaces in a tokamak

“…The other interactions relevant to the release of the metal impurity, such as ion sputtering and arcing, are discussed in Ref. [6].…”

Tokamak experiments at the Japan Atomic Energy Research Institute

“…the first wall [11]. These observations were the first to show the crucial role of controlling the plasma parameters in the scrape-off layer for the reduction of the impurity influx into the main plasma [12].…”

The Role of Electron Phase Coherence in Quantum Transport through Open Ballistic Cavities

“…Lower hybrid wave heating experiments have been carried out on several tokamaks; in several cases the production of fast-ion tails due to RF injection was reported [1][2][3][4][5]. Specifically, the Alcator-A lower hybrid experiment observed the formation of an energetic ion tail in the plasma centre having a tail temperature Tj > 15 keV and extending out to energies E > 50 keV [4,5].…”

“…Our present understanding of the tokamak impurity problem may be briefly summarized as follows: 1) Light impurities (oxygen, carbon) which are the dominant ones up to now can be well controlled by a relevant cleaning technique, for example, titanium gettering [ 1 ] or Taylor discharge cleaning [2]. 2) Ejection of metal impurities into the plasma is mainly caused by sputtering due to the light impurities and by self-sputtering of the first-wall material [3]. Arcing only appears during an unstable discharge phase [4].…”