Computational studies on ion source plasmas of the neutral beam injection system

A three-dimensional particle code taking into account the collision terms between fast electrons and hydrogen molecules is developed, where the elastic, ionization, excitation, and vibrational excitation collisions are calculated. This code is applied to investigate plasma generation and behavior in an ion source of the neutral beam injection system. It is found that the distribution of collision points is affected by grad-B drift when the gas pressure becomes lower. The sheath region around the filament is also taken into account, making it possible to optimize the filament shape and position in a plasma generator. (C) 2000 American Institute of Physics. [S0034-6748(00)65002-5].