Magnetically Insulated Ion Diode with a Gas-Breakdown Plasma Anode

摘要

An active anode plasma source was operated on the LONGSHOT annular magnetically insulated ion diode. This source uses an inductive voltage from a single turn coil to break 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 as a well-defined surface after about 300 ns to form a plasma anode layer defined by magnetic fields. An ion beam is then extracted from this plasma layer by applying typically a 150 kV, 1 microsecond 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 microsecond duration 75 to 150 keV ion beam pulses with greater than 100 A/sq cm peak ion current density over an area of about 400 sq cm. Up to 5 J/sq cm was collected by a 4 sq cm calimeter. 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 equal to or less than 3 degrees, but under certain operating conditions, large excursions in mean aiming angle on time scales of 20 to 200 ns. These and other operating characteristics of the gas-breakdown diode are discussed.