Measurement of electron-ion recombination rate in noble gases at high-pressure with application to high-power gas lasers

Two separate studies which are related to X-ray preionized discharge-pumped XeCl lasers comprise this dissertation. In Part I, results of analytic examination of the space-charge field effect in the vicinity of an electrostatic probe and experimental investigation using a parallel plate probe for determining the electron-ion recombination coefficient {dollar}alpha{dollar} in noble gases at high pressure (p = 10 atm) are presented. Experimental measurements were made by observing the electric current decay after the termination of an X-ray preionization pulse in a gas mixture of Ar/Xe = 9/1. With a specially designed detection circuit, the large interference of the electromagnetic noise generated by the X-ray preionizer can be totally avoided. Based on a theoretical model which divides the ionized gas sample into a plasma region and a cathode layer, and with the numerical solutions of the Boltzmann equation, the drift velocity of electrons in the plasma region are solved. By simulating the detected signal voltage, the value of the electron-ion recombination coefficient is determined to be 6 {dollar}times{dollar} 10{dollar}sp{lcub}-6{rcub}{dollar} cm{dollar}sp3{dollar}/s at room temperature. This conclusion suggests that both the two- and three-body electron-ion recombination processes are important at high gas pressures. The theoretical analyses also show that the probe can be used for measurement of the volume recombination rate coefficients only at low values of E{dollar}sb0{dollar}/n (ratio of the externally applied electric field in the plasma region to the neutral molecule number density).; In Part II, some important experimental results on high-current-density (up to 15 kA/cm{dollar}sp2{dollar}) discharge-pumped XeCl laser are also presented. In collaboration with D. Lo, high net gain coefficient (g = 0.61 cm{dollar}sp{lcub}-1{rcub}{dollar}), high power laser action ({dollar}sim{dollar}3.1MW), and high specific energy output ({dollar}sim{dollar}20 mJ/cm{dollar}sp3{dollar}, or {dollar}sim{dollar}20 J/liter, assuming that such intense discharge is scalable to large excitation volumes) are observed in a 3.8 cm{dollar}sp3{dollar} effective volume discharge. However, the laser pulse duration ({dollar}sim{dollar}25 ns) was much shorter than the {dollar}sim{dollar}1 {dollar}mu{dollar}s ringing period of the discharge current pulse. The total stored electrical energy in the pulse forming network was, therefore, not efficiently utilized. Theoretical analyses by T. Ishihara, and Prof. S. C. Lin indicate that the short laser pulse duration was due to rapid depletion of HCl; and during the brief period of peak laser power output, the intrinsic efficiency of the XeCl laser was very high ({dollar}sim{dollar}15%). By shortening the discharge current pulse, it may be possible to operate an intensely-pumped XeCl laser at very high specific power output while maintaining high energy-conversion efficiency.