Abstract

The Vacuum Spark is a small scale device which allows the achievement of plasma conditions leading to radiative collapse on a nanosecond timescale. This paper reports on the plasma formations in a Vacuum Spark operated in the hybrid mode when driven from a 1.5 Ohm coaxial pulse forming line with a maximum current of 140 kA in a 120 ns pulse. A comparatively low power Nd:YAG laser pulse incident onto the cathode initiates the discharge. The evolution of the titanium plasma electron density and temperature is followed both in the visible and the soft x-ray part of the spectrum. The plasma electron density dynamics are followed using a novel micro holographic interferometric technique, based on the Mach-Zehnder interferometer, permitting a spatial resolution better than 20 ?m. This technique is compared with simultaneous results from image plane interferometric holograms. The probing beam is a 1 ns frequency doubled Nd:YAG laser.