Experimental Validation of Graphite Mass Loss Equations in High Heat Plasma Conditions

Understanding plasma interactions with materials in high heating conditions is essential to the development of heatshields for spacecraft and supersonic flights, as well as the development and testing of plasma-facing components for fusion power plants. Here, we examine data from Frontiers experiments at the DIII-D tokamak, which studied the degradation and ablation of carbonaceous materials exposed to high-heat plasma conditions. Two types of experiments are considered: (i) cm-sized retrievable graphite samples exposed to edge plasma regions with a heat flux of ~30-40MW/m^2 and (ii) um-sized and mm-sized carbon pellets injected in the core plasma regions with a heat flux of ~0.5-1 GW/m^2. The former heating conditions are comparable to Pioneer's entry into Venus, while the latter approach the heat flux experienced during Galileo probe's entry into Jupiter. For each experimental condition, the observed material mass loss rates are compared against semi-empirical expressions for carbon mass loss rates developed by Scala [1]. Specifically, we test the validity of the equations guiding mass loss in the reaction-rate-controlled, diffusion-controlled, and sublimation regimes. [1] https://doi.org/10.2514/6.2011-3615