Anode plasma dynamics in an extraction applied-B ion diode: Effects on divergence, ion species and parasitic load

Analysis of data from the LION (1.2MV, 300kA, 40ns) extraction applied-B diode [1] allows a number of inferences regarding the effects of anode plasma dynamics on ion beam divergence, ion species composition, and diode impedance and power coupling. Ingap emission spectroscopy and beam diagnostics [1] have been used to investigate the mechanisms which determine anode plasma dynamics and its effects on diode performance. The two dominant features of anode plasma dynamics observed on LION are (1) expansion away from the solid anode surface and into the accelerating gap during the beam pulse, and (2) evolution of the composition of the plasma during the pulse, with a strong increase of both neutrals and high charge states of heavier ion species during the latter part of the pulse. A previous paper [1] has presented the data that support conclusion (2). In this paper, we present data characterizing the plasma expansion, and suggest a possible picture of the mechanism of the plasma dynamics that could produce these basic features.