Simulations for the generation and extraction of negative hydrogen ions in RF-driven ion sources

The injection of energetic neutral hydrogen atoms plays an important part for plasma heating in fusion experiments. In order to fulfill the requirements of the ITER neutral beam injection (NBI), a RF‐driven ion source based on the generation of negative ions prior to neutralization has been successfully developed at IPP Garching. Negative hydrogen ions are generated on a cesiated converter surface (plasma grid) by neutral particles and positive ions and are then transported to the extraction apertures, where the ion beam formation process takes place. Numerical models are necessary to include the relevant physical aspects of these processes. The Monte Carlo transport code CSFLOW is used to describe the dynamical behavior of the cesium distribution on the source walls during vacuum operation. The negative ion transport process is simulated by means of the probabilistic ion transport code TRAJAN, focussing on the effects of aperture diameter variations in mono‐ and multiaperture extraction systems. A simula...