Lithium ion sources

Abstract

A 10.9cm diameter lithium alumino-silicate ion source has been chosen as a source of ∼100mA lithium ion current for the Neutralized Drift Compression Experiment (NDCX-II) at LBNL. Research and development was carried out on lithium alumino-silicate ion sources prior to NDCX-II source fabrication. Space-charge-limited emission with the current density exceeding 1mA/cm2 was measured with 0.64cm diameter lithium alumino-silicate ion sources at 1275°C. The beam current density is less for the first 10.9cm diameter NDCX-II source, and it may be due to an issue of surface coverage. The lifetime of a thin coated (on a tungsten substrate) source is varied, roughly 40–50h, when pulsed at 0.05Hz and with pulse length of 6μs each, i.e., a duty factor of 3×10−7, at an operating temperature of 1250–1275°C. The 10.9cm diameter source lifetime is likely the same as of a 0.64cm source, but the lifetime of a source with a 2mm diameter (without a tungsten substrate) is 10–15h with a duty factor of 1 (DC extraction). The lifetime variation is dependent on the amount of deposition of β-eucryptite mass, and the surface temperature. The amount of mass deposition does not significantly alter the current density. More ion source work is needed to improve the large source performance.