| 1. |
- Matejicek, Jiri, et al.
(författare)
-
Interaction of candidate plasma facing materials with tokamak plasma in COMPASS
- 2017
-
Ingår i: Journal of Nuclear Materials. - : ELSEVIER SCIENCE BV. - 0022-3115 .- 1873-4820. ; 493, s. 102-119
-
Tidskriftsartikel (refereegranskat)abstract
- The interaction of tokamak plasma with several materials considered for the plasma facing components of future fusion devices was studied in a small-size COMPASS tokamak. These included mainly tungsten as the prime candidate and chromium steel as an alternative whose suitability was to be assessed. For the experiments, thin coatings of tungsten, P92 steel and nickel on graphite substrates were prepared by arc-discharge sputtering. The samples were exposed to hydrogen and deuterium plasma discharges in the COMPASS tokamak in two modes: a) short exposure (several discharges) on a manipulator in the proximity of the separatrix, close to the central column, and b) long exposure (several months) at the central column, aligned with the other graphite tiles. During the discharges, standard plasma diagnostics were used and a local emission of spectral lines in the visible near ultraviolet regions, corresponding to the material erosion, was monitored. Before and after the plasma exposures, the sample surfaces were observed using scanning electron microscopy, the coatings thickness was measured using Rutherford backscattering spectroscopy, and the concentration profiles of hydrogen and deuterium were measured by elastic recoil detection analysis. The uniformity of the coatings and their thickness was verified before the exposure. After the exposure, no reduction of the thickness was observed, indicating the absence of 'global' erosion. Erosion was observed only in isolated spots, and attributed to unipolar arcing. Slightly larger erosion was found on the steel coatings compared to the tungsten ones. Incorporation of deuterium in a thin surface layer was observed, in dependence on the exposure mode. Additionally, boron enrichment of the long-exposure samples was observed, as a result of the tokamak chamber boronization.
|
|
| 2. |
- Ficker, Ondrej, et al.
(författare)
-
Long slide-away discharges in the COMPASS tokamak
- 2016
-
Ingår i: Proceedings of the 58th Annual Meeting of the APS Division of Plasma Physics. ; 61:18, s. GP10.00101-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this contribution, long runaway electron (RE)dominated discharges achieved in the COMPASS tokamak are presented. The extensivelength is possible due to a low consumption of available volt-seconds of thetokamak transformer in this type of discharge. Energetic electron losses in thisregime seems to be modulated mainly by small oscillations of a radial position (controllersetting) unlike in the RE discharges at higher electron density, where variousMHD phenomena affect the evolution of the losses. The behaviour of the slide-awayplasma is studied using magnetic coils, HXR detectors, ECE system and a pair of3He proportional counters of neutrons. The plasma scenario is also modelled usingFokker-Planck codes.
|
|
