Experimental high heat load surface damage of graphite and refractory materials

Different grades of graphite and refractory material surfaces were exposed to pulsed high heat fluxes between 2 and 60 GW/m². Graphite ablation is reduced by 80 to 95% as a result of the self-protecting nature of the vapor shielding mechanism. Such ablation reduction helps in extending the lifetimes of plasma-facing components for large tokamak designs. The ablation of graphite is approximately the same for both transverse and normal exposure to the incident heat flux. Refractory materials erode at lower rates compared to other metallic surfaces. Molybdenum (sintered or arc cast) has lower erosion rate than titanium. Titanium erosion tends to saturate for incident heat fluxes above 10 GW/m², where the melt-shield is dominant. Cracks are absent from exposed titanium, which may suggest that the internal stresses due to thermal shocks do not exceed the modulus of rigidity. Tungsten has approximately no erosion for incident heat fluxes below 20 GW/m, but surface cracking may occur