Influence of helium plasma on the structural state of the surface carbide layer of tungsten

This paper presents the results of the experimental studies of the helium plasma interaction with a surface carbide layer of tungsten. The experiments were carried out on a plasma beam installation (PBI) at a constant energy of incoming ions of 2 keV and at a surface temperature of the tungsten carbide layer of ~905 and ~1750 ℃. The local parameters (T_e, n₀) of the helium plasma were evaluated using the probe method and spectrometric analysis of the plasma composition. The helium plasma irradiated two types of the carbide layer on the tungsten surface, WC and W₂C. The mechanisms of changing the tungsten surface morphology in the result of the plasma irradiation have been described. The study of the surface structure of the tungsten samples with a carbide layer of two types (WC, W₂C) after the exposure to the helium plasma has revealed two different types of the formation of helium bubbles and changes in the surface morphology. The physical mechanism of the formation of helium bubbles consists in the capture of helium atoms by the thermal vacancies generated at high temperature by the material surface. However, with a significant increase in temperature to 1750 ℃, the formation of the bubbles was no longer observed and the sample surface had a developed coral-like structure with crystallographically oriented grains.