Progress in the development of rf driven H−/D− sources for neutral beam injection

Recent experiments with a radio frequency (rf) driven ion source for the production of negative hydrogen ions have shown that the previously observed improvement in the H- ion current by the admixture of argon is a beam optics effect, rather than an ion production effect. The plasma flow from the driver to the expansion volume causes a pressure gradient in the source. In a caesiated source the efficiency is no longer a function of the source pressure, but low pressure operation is limited by rf coupling. Using an internal coil to provide the filter field required in negative ion sources has no negative effect on source efficiency. (C) 2004 American Institute of Physics.