Extraction applied-B ion diode experiments on HELIA

Summary form only given. Experiments are in progress on the 16-Ω HELIA linear induction accelerator (3.2 MV, 200 kA) to support the development of a high-impedance extraction geometry light ion driver module for the proposed DOE Laboratory Microfusion Facility (LMF). Ion beam extraction requires that HELIA operate in positive polarity, where each of the four induction cavity voltage adder sections contributes a group of electrons of unique energy to saturate flow in the magnetically insulated transmission line (MlTL). A primary goal of this study is to determine how such electron flow, couples to a magnetically insulated extraction ion diode. This diode will also provide a testbed for development of intense lithium beams. During initial experiments with an epoxy flashover anode and uniform magnetic insulation with the separatrix near midgap, the HELIA ion diode operated at extracted ion current efficiencies of 50-70% consistent with results obtained with a similar diode on the 4-Ω MITE accelerator. For a less uniformly insulating magnetic field geometry having the separatrix near the anode surface. lower extracted ion efficiencies of 45-60% were observed. These initial experiments emphasized the need for better voltage diagnostics