A PLASMA GUN DRIVER FOR THE SNS ION SOURCE

The original ion source developed for the Spallation Neutron Source* (SNS) was an RF-driven, multi-cusp source based on an internal antenna (plasma - immersed) and designed to produce ~ 40 mA of H - with a ~7% duty- factor. To date, the ion source has demonstrated very reliable operation during commissioning of the SNS accelerator and early operations at low duty-factors of ~0.1%. Endurance tests performed at high duty-factors ~7% suggest internal antennas are subject to failure effectively limiting lifetime. We are therefore developing RF sources based on external antennas which have comparatively much longer operational lifetimes. Recently, we found the H - yield from this type of RF source could be dramatically increased with the introduction of streaming plasma particles injected into the primary RF plasma from a hemispherical glow discharge chamber located in the rear of the source. In some cases, a ~50% increase in the H- beam current was observed. The system also eliminated the need for other plasma ignition systems like a secondary low-power RF generator. This report details the design and operational characteristics of the plasma gun driver.