Effect of primary electron distribution on ion species yield in an ion source

Effect of primary electron distribution on ion species yield is studied using a semicylindrical, multicusp plasma generator. Experimentally obtained, ion species yields were correlated with primary electron orbits estimated by computer simulation in several magnetic field configurations, where primary electron distributions were considered to be different. The result showed that a magnetic field configuration which produced lower proton yield had denser primary electron orbits in the neighborhood of the plasma grid. The floating potential of the plasma grid was also measured to suppose a distribution of the primary electrons. As a result, the proton yield increases with an increase of the floating potential of the plasma grid. These results lead us to confirm that the proton yield is determined by distribution of the primary electrons in the neighborhood of the plasma grid, in addition to the ratio of the plasma volume and the effective ion loss area. The highest proton yield of 93% and the lowest proton yield of 83% were obtained at the floating potential of the plasma grid of −5 and −21 V with respect to the anode potential, respectively, at an extraction current density of 150 mA/cm2.