Radiation-enhanced sublimation of graphite in PISCES experiments

Radiation enhanced sublimation (RES) of graphite leads to potentially high erosion rates in advanced fusion devices (Compact Ignition Tokamak, CIT) and (the International Thermonuclear Experimental Reactor ITER) and may be important in the ''carbon blooms'' observed in Tokamak Fusion Test Reactor (TFTR) and the Joint European Torus (JET). Erosion rates measured by weight loss are reported for POCO graphite exposed to helium plasmas for a temperature range from 900--2000 degree C, ion energies of 30--300 eV, ion fluxes of 1--6x1018 cm-2 s-1, densities of 2--10x1012 cm-3, and electron temperatures of 4--10 eV. These are the first data on RES at fusion-relevant particle fluxes. The data show little reduction from a direct linear dependence upon flux. For these conditions, the amount of redeposition and carbon self-sputtering was minimal. Over 1700 degree C, there is evidence of electron emission from the sample