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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.

The focused 20-MW giant pulse beam of a Q-spoiled ruby laser has been used to form a high-temperature, high-density plasma from a single 10- to 20-μ-diam solid particle of lithium hydride suspended by a set of ac electric fields in a vacuum environment. Charge collection measurements show that total ionization of the 1015 atoms in the lithium hydride particle is achieved in the plasma produced. Time-of-flight studies of the expanding plasma yield plasma energies of more than 100 eV. Measurements have been carried out which show that the mass and energy density of the expanding plasma are isotropically distributed in space. The results obtained are in good agreement with a simple model of the plasma formation and expansion. Further studies of these laser-irradiated, single particle plasmas are in progress and include measurements of the lifetime of the plasma in magnetic confinement fields.

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