Initiation Processes and Development of Laser-Induced Low-Pressure Spark Channels

The characteristics of laser-guided discharges have been studied extensively by a number of researchers [1–5]. This technology has application to localized metallic melting and hole boring, to laser-triggered gap switches and to the transport systems for light ion beams. Generally speaking, there are three main stages of the laser-induced discharge. The first stage includes a laser injection and the photoionization of the gas. The second stage, which starts with the application of voltage on the gap, comprises the growth of electron avalanches and the accumulation of space charge. It leads to local field disturbance and the current rise after the filamentary discharge across the gap. The third stage shows a high gas temperature, and when the current rises rapidly, an outward or inward shock wave develops if the hot core of the plasma column expands or contracts rapidly. A schematic drawing of these processes is shown in Fig.l. In general, core radius of spark discharge is a function of the discharge current I and the density of ambient gas ρ1. Considerable progress has already been made about the understanding of their principal process taking place under the low-pressure and high-current case, which is known as the Z-pinch discharge, and under the comparatively high-pressure and moderate current case, which is called spark discharge [6]. However, for the moderate pressure and moderate current case, of interest at present, analysis is not yet well characterized.