Numerical modeling of excited hydrogen atoms and their transport in hydrogen negative ion sources

Improvements are made of a Monte Carlo neutral transport code for the analysis of negative ion sources. These improvements make it possible to calculate the density of excited atoms, and to compare the numerical results with spectroscopic measurements, such as the H-alpha Balmer spectrum (n = 3 --> n = 2, n: principle number). The line-integrated intensities of the H-alpha spectrum in a tandem-type negative ion source are investigated. The excited hydrogen atoms in the n = 3 level are populated by excitation, mutual neutralization (H- + H+ --> H(n) + H), and dissociation of H-2, etc. The simulation results show that mutual neutralization greatly contributes to the intensity of the H. spectrum, especially in the extraction region. In addition, near the filament in the driver region, the excitation process due to the fast electrons greatly contributes to the intensity of the H-alpha spectrum. (C) 2004 American Institute of Physics.