Electric discharges in laser produced plasmas

Abstract

This thesis describes the results of an investigation of the effects of a medium voltage (0.1-1 kV), low-inductance discharge in a laser produced plasma. Discharging was done in vacuum using coaxial discharge cells of different geometries. The expansion dynamics of the plasma were analysed using various experimental techniques, such as Langmuir ion probes, time-resolved imaging, time- and space- resolved spectroscopy, ion energy spectrum analysis and thin film deposition. A novel technique was used to manipulate ion probe signals, in order to infer the ion density profiles at different times after ablation. This work is separated into two parts: in the first, a laser produced plasma is formed inside the charged coaxial cell, and as the plume expands, electric current begins to flow within the plasma. The effects of this current on the expansion dynamics, ion energy, electron temperature and deposition rate were studied using two discharge cell geometries: open-ended and conical. The second part of this work consisted of driving an electric discharge through a thin plasma column in order to obtain a Z-pinch. An aperture was used to select a portion of the ablation plume in order to control parameters important for pinching (e.g. column diameter and ion line density). Results such as the time to pinch, the final radius after compression and ion line density are compared with current Z-pinch models.