Combined impact of transient heat loads and steady-state plasma exposure on tungsten

Abstract

Cracking thresholds and crack patterns in tungsten targets have been studied in recent experiments after repetitive ITER-like ELM heat pulses in combination with plasma exposure in PSI-2 (Γtarget=2.5–4.0×1021m−2s−1, ion energy on surface Eion=60eV, Te≈10eV). The heat pulses were simulated by laser irradiation. A Nd:YAG laser with energy per pulse of up to 32J and a duration of 1ms at the fundamental wavelength (λ=1064nm, repetition rate 0.5Hz) was used to irradiate ITER-grade W samples with repetitive heat loads.In contrast to pure thermal exposure with a laser beam where the damage threshold under pure heat loads for ITER-grade W lies between 0.38 and 0.76GW/m2, the experiments with pre-loaded W-samples as well as under combined loading conditions show a lower damage threshold of 0.3GW/m2. This is probably due to deuterium embrittlement and/or a higher defect concentration in a region close to the surface due to supersaturation with deuterium. A pronounced increase in the D retention (more than a factor of five) has been observed during the combined transient heat loads and plasma exposure.Enhanced blister formation has been observed under these combined loading conditions.