Impacts of charge-exchange neutrals on degradation of plasma-facing materials

Abstract

This paper reviews the recent data from the PISCES linear plasma facility and the TRIAM-1M tokamak, demonstrating the impacts of energetic charge-exchange particles on surface erosion and bulk damage. High energy neutrals can result in significant surface erosion via sputtering even for tungsten. For the erosion of tungsten it has been emphasized in the PISCES data that oxygen-containing plasma impurities dominate the overall erosion behavior at energies below the sputtering thresholds for hydrogenic species. Radiation damage has been observed in plasma-facing materials in TRIAM-1M due to charge-exchange hydrogen neutrals. The accumulation of dislocation loops has been observed in metals subjected to the bombardment of charge-exchange hydrogen neutrals with energy up to keV. The flux was on the order of 10 18 H atoms/m 2/s, which is comparable with the ITER first wall condition. Severe embrittlement was observed in tungsten after long-term exposure in TRIAM-1M. Due to their strong interaction with lattice defects, helium atoms cause more profound effects on material properties than hydrogen. Defect accumulation by keV helium ions induces significant hardening and embrittlement even at high temperatures. As such, bombardment of energetic neutrals of hydrogen and helium can result in unrecoverable damage in plasma-facing materials and degrade even material bulk properties.