DuoPIGatron II ion source

Abstract

The DuoPIGatron ion source concept at Oak Ridge has proven itself capable of providing multiampere beams at tens of kilovolts. The DuoPIGatron II operates very reliably at 6–8 A total output current in the 25–35 kV range. Impurity level is easily maintained below 0.4% and the 0.2 sec pulses show no appreciable wear on the copper accel–decel electrode system after thousands of pulses with duty cycles up to 10%. The 7 cm diam grids are 50% transparent and optimum curvature of the grids allows about 60%–65% of the current to be incident on a 9 cm diam target 100 cm from the source. Beam ion and neutral species fractions have been measured as a function of total source current. Studies of the ion source plasma show an m=1 helical instability to be present. Probe measurements show a density variation of about 25%–30% across the extraction grid. Instantaneous density variations from ± 10% to ± 40%, depending on radius, are observed to be driven by the instability at 250–400 kHz. A stabilizer has been developed which reduces the oscillation amplitude by about an order of magnitude. Studies at extraction voltages up to 10 kV show that the use of the stabilizer yields a less divergent beam and higher current output through a single aperture either on axis or 1.8 cm from the source axis.