High-purity intense lithium-ion-beam sources using glow-discharge cleaning techniques

High purity, 1 MV, 50 ns, 300 A/cm2 lithium beams have been produced using an extraction diode driven by Cornell’s Light Ion Accelerator. Both passive and active anodes were studied with the highest-purity beams being generated by active anodes. These anodes were approximately 200 cm2 in area and consisted of 0.1 μm films of Al and LiF evaporated onto a glass substrate. The anode plasma was formed by using a plasma opening switch to divert 50 kA from the main power pulse through the Al foil for 20 ns. Without glow-discharge cleaning, the ion beam produced by the LiF Al anode was over 55% hydrogen and only 20% Li+. In order to remove impurities, especially the hydrogen, the anodes were cleaned with a 110 mA, 33 W, 60 Hz glow discharge. The stoichiometry of the ion beam after discharge cleaning was 65% Li+, 20% Al+2, and 15% H+. The results are presented and a model of the cleaning mechanism is discussed.