High-$beta$ capture and mirror confinement of laser-produced plasmas. Semiannual report, February 1--July 31, 1973

Abstract

The United Aircraft Research Laboratories are engaged in a program to investigate the use of a dense, mirror-confined, laser-produced plasma as the target for a neutral-injection beam and to examine this technique for establishing and maintaining a high-temperature, high-density, steady-state, mirrorconfined fusion plasma. The program is a direct extension of the current UARL investigations of the capture and confinement of laser-produced plasmas in a minimum-B mirror field. The overall program plan of the UARL Laser-Initiated Target Experiment involves four parts. The first of these is the laser heating of a solid particle positioned within the experiment chamber by an ultrahigh- vacuum suspension system to create a filly ionized plasma of ~10/sup 16/ to 10/ sup 17/ ions and electrons at a temperature of 0.5 to 1 keV. The second part of the program is the capture and confinement of the high-temperature laser-produced plasma to form a stable, high-density (>10/sup13/ cm/sup -3/), mirror-confined target plasma which fills an appreciable fraction of the mirror field volume. Heating of the confined-target plasma to ~10 keV by charge-exchange interaction with an injected energetic neutral beam comprises the third part of the program, and the fourth is the creation of a collisional, steady-state, mirror-confined plasma by ionization of the neutral beam on the energetic target. Experiments have demonstrated the required laser plasma heating, plasma capture, and stable mirror confinement, and initial evidence has been obtained on the field volume filling. Fokker-Planck and rate-equation calculations of the plasma heating and evolution to steady state with neutral-beam injection were carried out, and it was established that this technique can be used to form a steady-state, injection- sustained, mirror-confined 10-keV plasma at a density >10/sup 12/cm/sup -3/ with beam parameters and vacuum conditions that lie within the current state-of-the- art. During the period plasmas with average energies up to ~keV containing more than 10/sup 16/ hydrogen ions have been generated from ~60- mu m-diameter lithium hydride panticles within the baseball coil minimum-B mirror field; development was undertaken of an ultrahigh-vacuum feedback particle suspension system; measurements were made that show effective filling of the containment field by the mirror-confined plasma; the rateequation analysis of the target plasma evolution to a steady state sustained by neutral-beam injection was used to explore the experimental parameters for the injection studies; and detailed design of the beamline system for the injection experiments was carried out, based on a self-consistent analysis of the beamline vacuum conditions and pumping requirements. These experimental and theoretical results are described along with the design of the neutral beam for the injection experiments. (auth)