Deuterium retention in tungsten under combined high cycle ELM-like heat loads and steady-state plasma exposure

Abstract

To investigate the synergistic effects of fuel retention in tungsten, experiments were performed in the linear plasma device PSI-2 where the transient heat loads were applied by a high energy laser during the steady-state plasma operation. The impact on the deuterium (D) retention of simultaneous and sequential exposures to laser and plasma has been investigated. A significant increase of D retention, more than a factor of 12, has been observed during the simultaneous transient heat loads and plasma exposure. Successive exposures to transient heat loads and deuterium plasma also show the increased content of D-atoms by more than a factor of 3.6 in comparison to the pure plasma loading. In both cases the increase is most likely due to enhanced hydrogen clustering by the thermal shock exposures, due to an increased mobility of D atoms along the shock-induced cracks as well as to increased diffusion of D atoms into the W material caused by strong temperature gradients during the laser pulse exposure. Comparison of the NRA and TDS measurements shows that only 34% of the retained deuterium in the tungsten specimen is located inside the near-surface layer (d<4µm) after simultaneous as well as sequential exposures of W to heat load. Enhanced blister formation has been observed under combined loading conditions at power densities close to the threshold for damaging. It is shown that blisters are not mainly responsible for the pronounced increase of the D retention.

Keywords

• Transient heat loads
• Deuterium retention
• Blistering
• Surface modifications
• Tungsten