Long pulse, plasma cathode E-gun

A unique, long-pulse E-gun has been developed for high-power tube applications. The Hollow-Cathode-Plasma (HCP) E-gun overcomes the limitations of conventional thermionic-cathode guns that have limited current density (typically ≤10 A/cm²) or field-emission guns that offer high current density but suffer from short pulsewidth capability (typically <1 μsec) because of plasma closure of the accelerating gap. The HCP E-gun provides high-current (>50 A/cm²), long-pulse operation without gap closure, and also requires no cathode-heater power. The gun employs a low-pressure glow discharge inside a hollow cathode (HC) structure to provide a stable, uniform plasma surface from which a high current-density electron beam can be extracted. The plasma density is controlled by a low-voltage HC discharge puiser to produce the desired electron current density at the first grid of a multi-grid accelerator system. A dc high-voltage electron-beam supply accelerates the electrons across the gap, while the HC puiser modulates the beam current to generate arbitrary pulse waveforms. The electron accelerator utilizes a multiaperture array that produces a large area, high perveance (>35 μpervs) beam consisting initially of many individual beamlets. The E-beam is normally operated without an applied magnetic field in the ion-focused regime, where the plasma produced by beam ionization of a background gas space-charge neutralizes the beam, and the Bennett self-pinch compresses the beamlets and increases the current density. The self-pinched beam has been observed to propagate over a meter without beam breakup or instabilities. The HCP E-gun has been operated at voltages up to 150 kV, currents up to 750 A, and pulse lengths of up to 120 μsec.