Effect of high energy electrons on H− production and destruction in a high current DC negative ion source for cyclotron

Recently, a filament driven multi-cusp negative ion source has been developed for proton cyclotrons in medical applications. In this study, numerical modeling of the filament arc-discharge source plasma has been done with kinetic modeling of electrons in the ion source plasmas by the multi-cusp arc-discharge code and zero dimensional rate equations for hydrogen molecules and negative ions. In this paper, main focus is placed on the effects of the arc-discharge power on the electron energy distribution function and the resultant H− production. The modelling results reasonably explains the dependence of the H− extraction current on the arc-discharge power in the experiments.