Formation and Heating of Laser Irradiated Solid Particle Plasmas

Abstract

High energy, spherically symmetric, free plasmas are produced by electrically suspending a small, solid, lithium hydride particle in vacuum at the focus of a lens where the particle is vaporized, ionized, and the resulting plasma heated by the focused beam of a Q-spoiled laser. A two-temperature, integated similarity model has been developed for calculation of the plasma time development and gives plasma energies in good agreement with those determined experimentally. Charge collector and expansion velocity measurements show that the plasma expansion is spherically symmetric with a linear velocity profile as assumed in the calculations. While line radiation studies indicate that some recombination occurs in the plasma, from mass spectrometer measurements the plasma consists primarily of Li3+ and H+ for plasma energies above 100 eV. Calculations have been carried out to define the optimum conditions of particle radius, focal spot size, pulse duration, and laser peak power for both maximum plasma energy and maximum plasma quantity at a given energy. Based on the results of these calculations, average plasma energies in excess of 5 keV can be produced with 10 J, 0.1 nsec laser pulses, and a laser system with these characteristics is being developed for high-energy plasma production experiments.