Source fabrication and lifetime for Li+ ion beams extracted from alumino-silicate sources

Abstract

A space-charge-limited beam with current densities (J ) exceeding 1 mA/cm 2 have been measured from lithium alumino-silicate ion sources at a temperature of ∼1275 • C. At higher extraction voltages, the source appears to become emission limited with J ≥ 1.5 mA/cm 2 , and J increases weakly with the applied voltage. A 6.35 mm diameter source with an alumino-silicate coating, ≤0.25 mm thick, has a measured lifetime of ∼40 hours at ∼1275 • C, when pulsed at 0.05 Hz and with pulse length of ∼6 µs each. At this rate, the source lifetime was independent of the actual beam charge extracted due to the loss of neutral atoms at high temperature. The source lifetime increases with the amount of alumino-silicate coated on the emitting surface, and may also be further extended if the temperature is reduced between pulses.

Advanced neutral alkali beam diagnostics for applications in fusion research (invited)

“…Due to special composition of the emission material and proper heat treatment the extracted ion current reaches 5 mA, corresponding to about 3mA/cm 2 current density. This value is consistent with data from the literature 17 where ion sources operating below 1300 • C are reported to deliver up to 1.5mA/cm 2 current density. The total extractable charge was tested by operating an ion source at a moderate 2 mA ion current continuosly for several hours per day.…”