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.

Angular Distribution of Electron Temperature and Density in a Laser-Ablation Plume

“…Initially the expansion of the plume is primarily driven by the plasma pressure gradients [2], but there may be an additional contribution from Coulomb repulsion between the ions if there is significant net loss of the more mobile electrons [3,10]. In any case, when the plume has propagated more than a few hundred mm from the target surface, the major part of the initial thermal energy in the plasma is converted to the directed kinetic energy of the ions, which are much more massive than the electrons [11,12].The energy distribution of the ions has been measured using time-of-flight (TOF) optical spectroscopy [13,14] and ion probes [4,[7][8][9][15][16][17]. Mostly these ion probe measurements have been for the plasma flow close to the normal of the target surface.…”

“…Initially the expansion of the plume is primarily driven by the plasma pressure gradients [2], but there may be an additional contribution from Coulomb repulsion between the ions if there is significant net loss of the more mobile electrons [3,10]. In any case, when the plume has propagated more than a few hundred mm from the target surface, the major part of the initial thermal energy in the plasma is converted to the directed kinetic energy of the ions, which are much more massive than the electrons [11,12].…”

Numerical study of nanosecond laser interactions with micro-sized single droplets and sprays of xenon

“…Following Haught and Polk, 24 we use for each droplet a Gaussian truncated density profile of the form…”

High beta capture and mirror confinement of laser produced plasmas. Semiannual report, August 1, 1974--January 31, 1975

“…. (10) and (11) In these equations for the neutral densities, the electron velocity v and ion velocity v are the root .. mean-square velocities of the Fokker-Planck v~locity distributions. The charge exchange cross section a is obtained from the formula for ex Of ex ( 16) In this·formula, vis the ion speed in each velocity group, while CT {v) is the velocity dependent cross section evaluated from Riviere's formula a~xthe energy E. = ~mr2.…”