Plasma ignition schemes for the Spallation Neutron Source radio-frequency driven H− source

The H− ion source for the Spallation Neutron Source (SNS) is a cesiated, radio-frequency driven multicusp volume source which operates at a duty cycle of 6%. In pulsed rf driven plasma sources, ignition of the plasma affects the stability of source operation and the antenna lifetime. We report on ignition schemes, based on secondary electron generation by UV light, a hot filament, a low power rf plasma (cw, 13.56 MHz), as well as source operation solely with the high power 2 MHz rf. We find that the dual frequency, single antenna scheme is most attractive for the operating conditions of the SNS H− source.