CATHODE PLASMA FORMATION IN MAGNETICALLY-INSULATED TRANSMISSION LINES.

Cathode plasma formation in magnetically insulated transmission lines (MITLs) using time-resolved laser holography, visible light photography, and emission spectroscopy was studied. Bare and graphite-coated aluminum cathode surfaces were tested. Results indicate that the cathode plasma density at 40 to 70 ns is typically peaked at the cathode at 3 to 7 multiplied by 10**1**5 cm** minus **3 and drops by an order of magnitude in 0. 03 to 0. 05 cm. A luminous plasma extends much farther into the anode-cathode gap, expanding to 0. 3 cm in 40 ns. Spectroscopic scans from 300 to 700 nm show that the H alpha (656. 3 nm) and H beta (486. 1 nm) lines are the major contributors to the cathode plasma luminosity. A one-dimensional simulation of cathode plasma expansion is consistent with the holographic density measurements, but indicates that some process other than direct cathode plasma expansion is responsible for the low density luminous plasma extending several millimeters into the gap.