Simulation of negative hydrogen ion production and transport

Negative hydrogen ion production by volume process and its transport in a negative hydrogen ion source has been simulated by a combination of three three-dimensional Monte Carlo codes: (1) neutral transport, (2) negative hydrogen ion production, and (3) negative hydrogen ion transport. Neutral transport code has been used to calculate the spatially resolved density spectrum n(upsilon) of the vibrationally excited H-2 molecules. With the negative hydrogen ion production code, the production and distribution of H- ion density n(-) in the discharge volume has been calculated. And with the negative hydrogen ion transport code, the calculation of the survival probability of H- ions up to the extraction grid has been carried out. In all cases, the experimentally observed plasma parameters, as well as background gas density and temperature profiles, are inputs during trajectory calculation. It has been found that the negative ion density is almost uniform from the ion production zone (driver) to the grid. However, H- ions, which are produced within a few centimeters from the grid, are only able to reach the extraction hole. To compare the code calculation, a zero-dimensional particle balance rate equation is also solved. (C) 2004 American Institute of Physics.