An Efficient Ionizer for Polarized H- Formation

An ionizer is under development for a polarized H-source based on the resonant charge exchange reaction HH#x02192°+D- H#x02192-+D°. The H#x02192° beam passes through the center of a magnetron surface-plasma source having an annular geometry, where it crosses a high current (~0.5 A), 200 eV D-beam. Calculations predict an H°H#x02192- ionization efficiency of ~ 7%, 1 more than an order of magnitude higher than that obtained on present ground state atomic beam sources. In initial experiments using an unpolarized H° beam, H- currents in excess of 100 µA have been measured. While the ionization efficiency is now only about the same as other methods (Cs beam, for example), the results are encouraging since it appears that by injecting positive ions to improve the space-charge neutralization, and by improving the extraction optics, considerable gains in intensity will be made. We will then use this ionizer with a polarized H' beam, and measure the polarization of the resulting H-beam. If no depolarization is observed this ionizer will be combined with an atomic beam, cooled to 5-6 K, 2 to give a polarized H- beam expected to be in the milliampere range for use in the AGS.