Contribution of neutral production to ion flux from a vacuum arc source

This article describes studies of the effect of electrode spacing on the performance of vacuum arc plasma sources for ion accelerators and other applications. We measured the time‐resolved emission of neutrals from a compact arc source with a titanium cathode and 100 A drive current and found that the source emitted roughly 100 atoms for each extracted ion. The inferred neutral pressure in the arc gap was about 500 mTorr. The result suggested the possibility of achieving significant ionization in the plasma expansion region by increasing the anode–cathode gap length, thereby forcing the drive current to flow through the gas column. With a new two‐stage trigger, we were able to ignite arcs with gaps as long as 20 cm. Extended gaps doubled the ion flux, gave better output directionality, and helped to stabilize the location of emission spots on the cathode. These improvements, coupled with direct observations of discharge luminosity, support the hypothesis of ionization of the expanding vapor.