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.
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