Intense, pulsed, ion-diode sources and their application to mirror machines

Startup conditions for future mirror fusion experiments require a rapidly formed target plasma of ~0.5 coulomb of ions with energy of 50 to 100 keV. Theory suggests that very intense ion-flux emission satisfying these requirements can be extracted from a pulsed ion diode. Developing such sources would be an ideal CTR application of the high-power, single-shot capability of pulsed power technology. Recent experimental results are reviewed in which ~2 kA/cm² of D⁺ at ~50 keV was extracted. In the experiment, an intense relativistic electron beam undergoes many transits through a solid but range-thin anode foil. With each transit the electrons lose energy, causing their trajectories to collapse toward the anode surface. In so doing, the increased space charge extracts an intense ion flux from the anode foil IS plasma. Observations are reported on the importance of diode stability. The general agreement between theoretical scaling laws and experimental results is also presented.