Behaviors of Fast Primary Electrons with Collisional Effects Including Production of Vibrationally Excited Hydrogen Molecules in a Hydrogen Negative Ion Source for a NBI System

Abstract

The relationship between enhancement of H- negative ion volume production and behaviors of fast primary electros are studied. Trajectories of fast primary electrons are calculated numerically, including collisional effects with hydrogen molecules. Taking into account our experimental study, following two main targets are discussed: (1) Effect of field intensity of the magnetic filter (MF) and a filament position on active region of fast primary electrons, and (2) combination effect of the field intensity of the MF and the filament position for controlling behaviors of fast electrons.Active region of fast electrons depends strongly on the field intensity of the MF and filament position. Therefore, spatial distributions of ionization and vibrational excitation collision points are also changed in the same manner although number of vibrational excitation collision points is lower than that of ionization collision points due to longer mean free path. According to the results and discussions including transport of produced vibrationally excited molecules and H- ions, for enhancement of H- production, it is desired that fast electrons should approach the MF position and move into the downstream region as deep as possible without destruction of H- ions. To realize these conditions, good combination between filament position and the intensity of the MF should be required.