On temperature bifurcation of beryllium and lithium plasma facing components

The mechanism of temperature bifurcation of plasma contacting surfaces due to recycling of the ionized surface material vapor is considered. It is shown that this mechanism can lead to overheating of beryllium and lithium plasma facing components (in particular, in fusion devices) prior to the thermionic electron emission mechanism. The surface temperatures and the plasma parameters, at which the considered mechanism triggers the local overheating of beryllium and lithium components, are evaluated. The increase in the surface heat load due to secondary electron emission is also considered. It is shown that the combined effects of energy and impact angle distributions of the plasma electrons can increase the averaged secondary electron emission yield to values higher than unity and can lower the average electron energy, at which such yields are achieved.