The effect of high-flux H plasma exposure with simultaneous transient heat loads on tungsten surface damage and power handling

Abstract

The performance of the full-W ITER divertor may be significantly affected by the interplay between steady-state plasma exposure and transient events. To address this issue, the effect of a high-flux H plasma on the thermal shock response of W to ELM-like transients has been investigated. Transient heating of W targets is performed by means of a high-power Nd:YAG laser with simultaneous exposure to H plasma in the linear device Magnum-PSI. The effects of simultaneous exposure to laser and plasma has been compared to those sequentially and to laser only. Transient melting is found to be aggravated during plasma exposure and to occur at lower heat flux parameters. Roughness and grain growth are observed to be driven by peak temperature, rather than by the loading conditions. The temperature evolution of the W surface under a series of transients is recorded by fast infrared thermography. By accounting for changes in the reflectivity at the damaged surface as measured by ellipsometry, a reduction in power handling capabilities of the laser/plasma affected W is concluded. The evidence of reduced power handling of the W surface under conditions as described here is of great concern with respect to the durability of W PFCs for application in fusion devices.

Self-Regulated Plasma Heat Flux Mitigation Due to Liquid Sn Vapor Shielding

“…DOI: 10.1103/PhysRevLett.116.135002 Designing an efficacious interface between an intense plasma flux and a solid material has been a challenge for many decades and is among the top issues in realizing fusion energy as a viable energy source on Earth. Plasmasolid interactions under fusion divertor conditions cause continuous material erosion and may result in performance degradation of the plasma-facing components [1][2][3]. An alternative path is opened by exploiting liquid metals as an interface between the plasma and solid material world [4]; this could potentially alleviate many of the problems of heat exhaust in the divertor.…”

Characterizing the recovery of a solid surface after tungsten nano-tendril formation

“…The temperature rise for subsequent pulses and the average for the total number of pulses are lower than for the initial pulse but difficult to quantify accurately as the absorbance and emissivity of the surfaces can change as the surface morphology evolves. More details on the temperature measurement techniques can be found in [14] and [15].…”

Surface damage of W exposed to combined stationary D plasma and ELMs-like pulsed plasma

“…Therefore, it is important to study the surface damage behavior of W material under combined D plasma and ELMs-like transient heat loads condition. Many studies have been carried out in this field in recent years [13][14][15][16][17][18][19][20][21] , but experimental conditions were different in each study, and were also not same as the working condition of divertor in ITER. For instance, in some studies, W samples were sequentially (not simultaneously) exposed to D plasma and transient heat loads [13,14,[19][20][21] ; in some other studies, ELMs-like heat loads were simulated by laser beam [13][14][15][16][17][18] or electron beam [19,20] , but ELMs were transient plasma events in ITER.…”