Negative Ions from magnetically insulated diodes

In previous work¹ using a 1 MV, 50 ns, 7 Ω pulse line we have measured −35 A/cm² H⁻ current density from a cylindrical diode with a polyethylene-titanium hydride cathode. Recently we have modified the system to permit radial diagnostics and the extraction of beams through four access ports. A 125 kV, 1 µs external bipolar prepulse can be used prior to the main pulse. The insulation field can be up to ∼3 Tesla and the diagnostics include Faraday cups and CR-39 track recording plastic. Cathodes constructed of different density polyethylene and polyethylene-titanium hydride composites are under study. With the new configuration we have observed 100 A/cm² H⁻ using the polyethylene-titanium hydride cathode. In an effort to generate longer pulse duration ion beams the diode is now driven by a 650 kV, 1µs, Marx generator. We have designed and done preliminary tests on a beam forming diode which uses fiber emitters to assist surface flashover and stabilize impedance.