Wall conditioning in fusion devices with superconducting coils

Abstract

Wall conditioning is essential in tokamak and stellarator research to achieve plasma performance and reproducibility. This paper presents an overview of recent conditioning results, both from experiments in present devices and modelling, in view of devices with superconducting coils, with focus on W7-X, JT-60SA and ITER. In these devices, the coils stay energised throughout an experimental day or week which demands for new conditioning techniques that work in presence of the nominal field, in addition to the proven conditioning methods such as baking, glow discharge conditioning (GDC) and low-Z wall coating through GDC-plasma, which do not work under such condition. The discussed techniques are RF conditioning without plasma current, both in the ion cyclotron and electron cyclotron range of frequencies, and diverted conditioning plasmas with nested magnetic flux surfaces.

First experiments on ICRF discharge generation by a W7-X-like antenna in the Uragan-2M stellarator

“…2017; Wauters et al. 2020) studies. Following these studies, separate plasma production stages can be identified that are characterized by different physical pictures.…”

Design and Application of Glow Discharge Cleaning at Uragan-2m Stellarator

“…Various methods are used for wall conditioning [1,2]. To create plasma in cleaning modes, various types of cleaning discharges, both stationary and pulsed, are used.…”

“…Glow discharge [1,2] and various types of highfrequency discharges [1][2][3][4][5][6][7] are widely used for cleaning the inner surfaces of vacuum chambers of tokamaks and stellarators. High-frequency discharges in various frequency ranges (electron-cyclotron frequency [1][2][3], ion-cyclotron frequency [1][2][3], ultrashort waves [6,7]) are used mainly in the presence of a magnetic field. on the contrary Glow discharge cleaning (GDC), is used mainly without a magnetic field, although, in principle, the discharge can also burn in a magnetic field.…”

Observation of Arc Trails with Significant Damage due to Glow Discharge Wall Conditioning in the Large Helical Device

“…Glow discharge conditioning (GDC) is an essential wall conditioning technique in tokamaks and stellarators to produce high performance plasma [1]. Physical or chemical sputtering by impacts of accelerated ions release impurities absorbed in the material.…”