Reduced damage threshold for tungsten using combined steady state and transient sources

Abstract

Divertor wall materials in future fusion devices will be subject to both high flux steady state plasma and transient ELM striking which could limit the lifetime of these plasma facing materials. A pulsed plasma source was therefore developed to reproduce these conditions. Laser irradiation of similar pulse length has been used to disambiguate between the effects of particle and heat loads compared with transient heating alone. A lowered threshold for damage of tungsten was observed in the case of simultaneous transient and steady state loads compared to transients alone, while surface damage was also enhanced with repeated laser irradiation following steady plasma exposure, compared to the two processes individually, indicating a synergistic enhancement of surface modification due to plasma exposure.

High heat flux capabilities of the Magnum-PSI linear plasma device

“…For the lowest laser energy, surface roughening and the development of cracks at grain boundaries can clearly be seen. It should be mentioned that under otherwise similar laser loading conditions, no surface modifications can be observed in the absence of plasma exposure [26], outlining the possible strong role of hydrogen plasma exposure on the surface damage of tungsten as well as the importance of synergistic effects arising during simultaneous plasma/transients exposure [25]. Further studies will be carried out to compare the damage induced by laser and pulsed plasma heating, respectively, and elucidate the role of the increased particle flux during a plasma pulse on the surface response.…”

Plasma–Surface Interactions Under High Heat and Particle Fluxes

“…8c). More details can be found in [20]. However, no clear difference in terms of surface roughening was observed after the laser exposure between samples exposed to different plasma fluences.…”

Morphological and structural damage investigation of nanostructured molybdenum fuzzy surface after pulsed plasma bombardment

“…[21] On the other hand, the lower mechanical and thermal strength of W nanostructure reduce the transient damage threshold. [22] The interactions of fuzzy surfaces with transient loads simulated by plasma gun and laser reveal that the arcing is more prone to occur on fuzzy surfaces during ELMs, leading the impurities and dust to release. [23] As one of the candidate materials for plasma-facing first mirror materials, Mo is a kind of high Z material similar to W. Even a small amount of Mo fuzz injection can contaminate the confined plasma, causing the plasma to cool down and finally threatening the sustainability of controlled fusion.…”