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This contribution describes the latest milestones of a multiyear program to build and operate a compact −300 kV dc high voltage photogun with inverted insulator geometry and alkali-antimonide photocathodes. Photocathode thermal emittance measurements and quantum efficiency charge lifetime measurements at average current up to 4.5 mA are presented, as well as an innovative implementation of ion generation and tracking simulations to explain the benefits of a biased anode to repel beam line ions from the anodecathode gap, to dramatically improve the operating lifetime of the photogun and eliminate the occurrence of micro-arc discharges.

Development of sources for heavy ion fusion motivates study of diode current transients. For the one-dimensional problem a unique applied voltage eliminates transients in the space-charge-dominated case:V(t)=V[4/3 (t/τ)−1/3 (t/τ)4] for t<τ, V(t)=V for t≥τ, where L is diode length, V is steady state diode potential, q/m is charge to mass ratio, and τ=3L(m/2qV)1/2 is a particle transit time through the diode. We derive this result and compare it to computer simulations and experimental results.