Erosion yield of graphite and B4C irradiated by high flux deuterium beams

To investigate the erosion of graphite and B4C under high particle flux loading, such as in a fusion reactor, two types of specimen, i.e. isotropic graphite PD330S and conversion B4C, were irradiated by a high flux neutral beam generator. The erosion yield wlas estimated from the weight loss of specimens, as measured by a microbalance. A neutral deuterium beam with an energy of 5.5 kV was irradiated on the specimens. The beam power measured by a calorimeter array was 4.5 MW m−2. The main composition of the beam was D3, so that the average particle energy was about 1.5 keV and the particle flux of the beam was 1.5 × 1022 m−2 s−1. The duration of the single-beam pulse was 0.72 s and the surface temperature of the specimens rose by about 300 K during each beam irradiation. To investigate the temperature dependence of the erosion yield, the experiments were performed at initial specimen temperatures of 523, 773 and 973 K. For investigation of the impurity dependence of erosion, the oxygen impurity contents in the beam were chosen as 15.5% and 6.5%. The lower oxygen content was attained by ion source conditioning. The following results were obtained. (1) Graphite showed a maximum erosion yield at 773 K. The erosion yield of B4C did not show such a peak and gradually increased with temperature; it was about 30% less than that of graphite at 773 K. (2) The erosion yield of B4C was almost independent of the oxygen impurity content. (3) The erosion yields of graphite and B4C irradiated with a high flux beam of 1.5 × 1022 m−2 s−1 were 30%–40% less than those of low flux (1019–1020 m−2 s−1) irradiation experiments.