Title: High beta capture and mirror confinement of laser produced plasmas. Semiannual report, February 1, 1975--June 30, 1975

Separate abstracts were prepared for the 4 included sections. (MOW)

The Laser Initiated Target Experiment (LITE) at the United Technologies Research Center is designed to address the target plasma buildup approach to a steady state mirror fusion device. A dense, mirror confined, target plasma is produced by high power laser irradiation of a solid lithium hydride particle, electrically suspended in a vacuum at the center of an established minimum-B magnetic field. Following expansion in and capture by the magnetic field, this target plasma is irradiated by an energetic neutral hydrogen beam. Charge exchange collisions with energetic beam particles serve to heat the confined plasma while ionization of the neutral beammore » atoms and trapping in the mirror magnetic field add particles to the confined plasma. For sufficiently high beam intensities, confined plasmas losses will be offset so that buildup of the plasma density occurs, thus demonstrating sustenance and fueling as well as the heating by neutral beam injection of a steady state mirror fusion device. Investigations of the decay of the magnetically confined target plasmas and initial studies of energetic neutral beam injection into confined target plasmas, conducted during this report period, are presented. Additional development of the LITE experimental systems including improvements in the laser plasma production facility, the energetic neutral beam line, and the heavy ion probe diagnostic is reported. A series of calculations on enhanced scattering and classical decay for plasma mirror confined in a LITE type system are discussed.« less

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-more » 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)« less

The LITE research program is addressing two aspects of mirror confinement physics. ECRH heating of the confined LITE plasma is being investigated as a means for producing a local electrostatic well to trap cold ions within the plasma and provide DCLC stabilization without the energy drain effects obtained with a cold stabilizing stream. Concurrently, the heavy ion beam probe diagnostic being developed in LITE to experimentally measure the space potential within a minimum-B mirror plasma. During the period, 10-A beam injection focused on the target location has been achieved with the neutral beam source; investigations of hot ion building havemore » been carried out with both a laser produced and a washer gun target; calculations modeling the ECRH stabilization have been performed, the experimental program defined, and preparations for the ECRH stabilization investigation undertaken; and the high current cesium source and high resolution electrostatic analyzer have been developed for the heavy ion beam probe. The physics of the ECRH stabilization model is studied, and conditions necessary to produce a local potential well for trapping cold ions are examined. An analysis of the stabilizing effect of this potential dip on the DCLC mode is presented. The heavy ion probe, under development for direct measurement of the mirror plasma space potential, is discussed. Using Thomson scattering measurements to calibrate the complex response of an electron cyclotron resonance microwave radiometer, measurements have been made of the time history of the electron temperature for the decaying mirror confined laser plasma target with and without streaming plasma stabilization and are reported.« less