Temperature Effects on Relief Pressure of Helium Bubbles in Tungsten

Tungsten, the current material of choice for tokamak divertors, is known to develop a network of tendrils, dubbed ``fuzz,'' when exposed to helium plasma. The formation of helium bubbles below the surface is an important part of the process of fuzz formation. This study utilizes molecular dynamics to analyze the effects of temperature on the pressure at which dislocation loop-punching and/or helium bubble bursting occurs. As expected, raising the temperature lowers the pressure at which bubbles of a given size at a given depth from the surface will burst or loop-punch, but the magnitude of the change decreases as the temperature increases. The relief pressure also falls off near the surface: the relief pressure at all tested temperatures is generally well-described by an empirical equation of the form $P_r = P_b(1-e^{-Cd}),$ where $P_r$ is the relief pressure, $P_b$ is the bulk loop-punching pressure at the same temperature, $d$ is the depth of the bubble, and $C$ is a constant to be determined.