Loss current minimization during ion extraction from an inductively coupled plasma

In ion sources with a grid-type acceleration system, the output current often decreases with increasing power at a constant extraction voltage despite the fact that the carrier density inside the source increases linearly. At this point, the loss and output currents have the same magnitude. This paper proposes a mechanism for loss current minimization when restrictions are placed on the beam focusing efficiency with increasing rf power. The influence of the plasma potential on the magnitude of the loss current was examined. The beam intensity was found to increase considerably when the plasma potential was sufficiently high to suppress sheath curvature growth.