Plasma density measurements in a magnetically insulated ion diode

Summary form only given. An applied-B/sub r/ magnetically insulated ion diode is used at Los Alamos for thin film deposition. The authors have measured the radial line-integrated (1 /spl theta/ 5 cm) electron densities n(z,t) at various z locations within the AK (anode-cathode) gap with two (0.63 and 3.39 /spl mu/m) heterodyne quadrature laser interferometers. During ion beam emission, no measurable nl (< 10/sup 14/ cm/sup -2/) is observed, except very near K. This suggests that impedance collapses are not caused by A or K plasma closures. At the z location closest (0.3 cm) to K, nl starts to rise 0.1-0.2 /spl mu/s after beam onset and reaches about 10/sup 15/ cm/sup -2/ by beam fall. These density releases correlate with beam current densities and are delayed with anodes of reduced (2.5 cm) annular thickness. Hence, they appear to be beam-induced K plasmas. After beam emission, large nl´s are observed through the entire AK gap. Near K, peak nl´s of (2-3) /spl times/ 10/sup 16/ cm/sup -2/ are measured 1 /spl mu/s after beam fall. These plasmas appear to propagate from K towards A with average speeds of 0.5 cmspl mu/s. near A, peak nl´s reach (6-8) /spl times/ 10/sup 16/ cm/sup -2/. These data are consisted with avalanche ionization of flashover-produced neutrals.