Extraction of an intense neutralized ion beam from a plasma

If ions are to be used for pellet fusion, it is essential that the ions start the acceleration process with low initial angular momentum. This implies that the ions be extracted from a plasma with low ion temperatures. Two types of target plasmas have been utilized: a pulsed hollow cathode discharge in a low pressure background gas of helium, and a plasma formed by the ablation of a nylon mesh attached to the downstream side of the anode. The anode was pulsed positive by a Nereus accelerator to ~ 400 kV. Time-of-flight data from biased probes and scintillators indicate average ion energies close to that of the anode voltage. By using a crude focussing geometry, we have also observed the ions to focus to roughly 1 cm in diameter. Some evidence for temporal focussing (bunching) has been observed.