A Pulsed Negative Hydrogen Source for Currents up to One Ampere

During the 2nd Symposium on Ion Sources and Formation of Ion Beams, we reported on the development of our Mk II pulsed double slit magnetron source for the production of negative hydrogen ions.1 The source was capable of yielding beam currents up to 125 milliamperes, corresponding to current densities of 1.25 A/cm2. In order to increase negative hydrogen beam intensities by an order of magnitude (this would be quite useful for initial high energy neutral injector systems on Tokamaks), a larger, Mk III magnetron has been constructed, with the number of slits increased up to six. The idea was to utilize in a more efficient way the plasma width. In addition, such a source geometry will be more adaptable for beam formation and acceleration than single slit structures. With three extraction slits, we obtained a negative hydrogen yield of 300 mA with current densities of 1.2 A/cm2; preliminary results with six extraction slits showed beam currents in excess of half an ampere with averaged current densities in excess of 0.75 A/cm2.