Monte Carlo simulation of secondary electron emission from plasma facing materials

Abstract

A Monte Carlo simulation is performed to study secondary electron emission from Be, C, Mo and W due to impact of low-energy (100 eV–4 keV) electrons. The dependence of the secondary electron yield on the primary energy E p is characterized in terms of the maximum yield and the E p at which it occurs, and it is in good agreement with Kollath's empirical formula, except for C, for low E p's where the formula can be applied. At low E p, the energy distribution of secondary electrons largerly depends on E p, in particular for W; whereas at high E p, the distribution approaches the E p – independent theoretical curve derived by Chung. In magnetic confinement fusion devices, secondary electrons emitted from plasma facing materials (PFM) gyrate in a sheath, which is in the interface between an edge plasma and the PFM surface. As a result, some of them return to the surface within their first gyration, which results in low effective electron yield of the PFM. Due to larger Lorentz force, the higher the energies of the secondary electrons, the more the secondary electrons return to the surface. This causes a low-energy shift of the energy distribution of electrons entering into the plasma.