One-dimensional analysis of the effect of the ambipolar potential on the H^- ion density recovery after a laser photodetachment in the high density regime

In order to analyse the effect of the ambipolar potential on the H ^- ion density recovery in the measurement of the H^- ion temperature by the two-laser photodetachment diagnostic technique, the particle-in-cell simulation with a one-dimensional slab model is performed. In particular, a high H^- ion density regime with n_-0/n ₊₀ > 0.1 (n_-0 : H^- ion density, n ₊₀ : H⁺ ion density before the laser shot) has been studied. The recovery time of the H^- ion density becomes shorter as the density ratio n_-0/n₊₀ increases. The ambipolar potential formed after the laser shot is almost proportional to the density ratio n_-0/n₊₀. Due to the H^- ion acceleration by this ambipolar potential, the H^- ion temperature T_-d deduced from the H^- ion density recovery tends to be larger than the actual temperature T_-0. The temperature ratio T_-d/T _-0 increases with the density ratio n_-0/n₊₀ and the deduced temperature T_-d becomes about 1.5 times larger than the actual temperature T_-0 for n_-0/n₊₀ ≤ 0.9.