Energy and temperature dependences of ion-induced electron emission from polycrystalline graphite

The dependences of the yield γ of ion-induced kinetic electron emission from polycrystalline graphite on ion energy E were measured under high-fluence Ar^+ and N^+_2 ion irradiation in energy range 6–30 keV from room temperature to 400 °C. It has been observed that the step-like pattern of temperature dependence γ(T) at the dynamic radiation damage annealing temperature T_a is gradually transformed with decreasing ion energy until γ virtually ceases to depend on temperature. The experimentally obtained energy dependence of the ratio γ(T > T_a)/γ(T < T_a) has been analyzed using the theory of ion-induced kinetic electron emission. Some threshold values of the level of radiation damage v_d measured in dpa under steady state of high-fluence Ar^+ and N^+_2 irradiation have been found. When v becomes less than a threshold value v_d, the graphite lattice is virtually not disordered. It has been found that v_d for Ar^+ ions is greater than v_d for N^+_2 ions.