Magnetically insulated ion diode with a gas-breakdown plasma anode

An active anode plasma source has been developed for use in a magnetically insulated ion diode operated on a 1010-W pulsed power generator. This source uses an inductive voltage from a single turn coil to beak down an annular gas puff produced by a supersonic nozzle. The resulting plasma is magnetically driven toward the radial insulating magnetic field in the diode accelerating gap and stagnates at a well-defined surface after about 300 ns to form a plasma anode layer defined by magnetic flux surfaces. An ion beam is then extracted from this plasma layer by applying a 150-kV, 1-μs pulse to the accelerating gap. Optimization of the timing of the gas puff, the plasma production discharge, and the high voltage pulse has resulted in 1-μs duration 75–150-keV ion beam pulses with >100-A/cm2 peak ion current density over an area of about 400 cm2. Up to 5 J/cm2 has been collected by a 4-cm2 calorimeter. The diode impedance history can be varied so that rising, flat, and falling voltage pulse waveforms can be produced. Streak photographs of beamlets impinging on a scintillator and time integrated targets both show beam divergence angles ≤3°. However, under certain operating conditions, large excursions (∼25°) in mean aiming angle on time scales of 20–200 ns are observed.