Evidence for high-velocity solid dust generation induced by runaway electron impact in FTU

TL;DR

This paper presents evidence that runaway electron impacts in FTU generate high-velocity solid dust, which can cause secondary wall damage, with implications for future fusion reactors like ITER and DEMO.

Contribution

It provides the first combined experimental, theoretical, and modeling evidence of high-velocity dust generation from runaway electron impacts in a fusion device.

Findings

High-velocity dust impacts cause crater formation.

Runaway electron impacts produce solid dust during plasma interactions.

Dust impacts can lead to secondary wall damage.

Abstract

Post-mortem and in-situ evidence is presented in favor of the generation of high-velocity solid dust during the explosion-like interaction of runaway electrons with metallic plasma-facing components in FTU. The freshly-produced solid dust is the source of secondary de-localized wall damage through high-velocity impacts that lead to the formation of craters, which have been reproduced in dedicated light gas gun impact tests. This novel mechanism, of potential importance for ITER and DEMO, is further supported by surface analysis, multiple theoretical arguments and dust dynamics modelling.