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Benign termination of runaway electron beams on ASDEX Upgrade and TCV

Author
Abstract

This paper discusses the development of a benign termination scenario for runaway electron (RE) beams on ASDEX Upgrade and TCV. A systematic study revealed that a low electron density (ne) companion plasma was required to achieve a large MHD instability, which expelled the confined REs over a large wetted area and allowed for the conversion of magnetic energy to radiation. Control of the companion plasma ne was achieved via neutral pressure regulation and was agnostic to material injection method. The neutral pressure required for recombination was found to be dependent on impurity species, quantity and RE current. On TCV, ne increased at neutral pressures above 1 Pa, indicating that higher collisionality between the REs and neutrals may lead to an upper pressure limit. The conversion of magnetic energy to radiated energy was measured on both machines and a decrease in efficiency was observed at high neutral pressure on TCV. The benign termination technique was able to prevent any significant increase in maximum heat flux on AUG from 200 to 600 kA of RE current, highlighting the ability of this approach to handle fully formed RE beams.

Year of Publication
2024
Journal
Plasma Physics and Controlled Fusion
Volume
66
Issue
3
Number of Pages
035003
DOI
10.1088/1361-6587/ad1e31
PId
58a73a2e7a6efdf4495c0e9e3c1abfb2
Alternate Journal
Plasma Phys. Control. Fusion
Label
OA
Journal Article
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