K+ diode for the LLNL heavy ion recirculator accelerator experiment

An 80 keV K+ diode source that will deliver up to 9 mA of beam current has been developed for the LLNL Small Recirculator experiment. The diode consists of a hot plate alumino-silicate (Zeolite) source, a graphite Pierce electrode, and an exit extraction electrode. The K+ source emitting surface is planar, and one inch in diameter. A fine (70 line/inch) high transparency (90%) mesh is placed in the exit beam extraction electrode. The exit mesh reduces the sensitivity of the diode optics to possible variations in the diode gap and exit aperture shape, without a growth in the beam emittance. Numerical EGUN simulations were used for the diode physics design. The simulations showed that the diode can deliver a uniform 9 mA K+ beam with a normalized emittance of about 0.05 mm-mr, resulting mainly from the source temperature at 1000 °C. The beam at the diode exit is aperture to a diameter of 11 mm to meet the recirculator experiment requirements of a 2 mA beam with 0.01 mm-mr normalized emittance. The 80 kV source acceleration potential is provided by a thyratron switched, 4 μS long 8-section PFN which drives a 1:10 step-up pulse transformer. We shall report on the source performance including measurements of the beam total current, current density profile, phase space profile, angular divergence, and transverse emittance