Performance and Degradation of Carbonaceous Materials in High-Heat Plasma Conditions

Understanding plasma-material interactions in high heating conditions ~MW/m2 is essential for optimizing a breadth of technology, from advanced spacecraft heat shields to plasma-facing components in fusion power plants. Here we analyze experiments at the DIII-D tokamak to study performance and degradation of carbonaceous materials exposed to steady state plasma heating conditions in the range 1-40 MW/m2. Of specific interest is calculating expected mass loss rates in the reaction-dominated, diffusion-dominated, and sublimation-dominated regimes for porous and glassy carbon spheres, and ATJ graphite cylindrical rods. The plasma heating conditions in each DIII-D experiment were calculated using data from Divertor Thomson Scattering and Langmuir Probes, which indicate electron temperatures 5-40 eV and electron densities 1019-1020 m-3. For each case, semi-empirical equations by Scala [1] will be used to estimate mass loss rates as a function of increasing heat flux. The model predictions will be compared against experimental measurements of mass loss rates using spectroscopy and interferometer diagnostics. This is the first study to test the Scala models in low-pressure, high-heat flux plasma and predict the threshold heat fluxes that lead to transitions across the different ablation regimes.

[1] https://doi.org/10.2514/6.2011-3615

Work supported by EPSCoR FTPP OIA-2148653, DE-SC0023061, DE-SC0024547, DE-FC02-04ER54698, DE-FG02-07ER54917, DE-AC52-07NA27344.