High beta capture and mirror confinement of laser produced plasmas. Semiannual report, April 1, 1977--September 30, 1977

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 have 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

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

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

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

Experimental studies aimed at improving the reproducibility of the dense, laser produced plasmas were performed. Efforts in this area were concerned with the positioning of the target particle more accurately in the laser focal region and with preventing the premature displacement of the particle from the focal region. To address this latter problem, the single beam laser system of the previous experiments was modified to permit the simultaneous irradiation of the lithium hydride pellet by two opposed laser beams. In addition, the diagnostic capabilities of the present experiment were augmented so that more detailed measurements of the plasma lifetime, density, and energy can be made. A 4 mm microwave interferometer was installed to follow the plasma decay from higher densities. The measured density decay histories were analyzed to give estimates of the plasma lifetime and energy. Independent measures of the time dependence of the plasma radius were obtained from both microwave interferometry and optical streak photography. To measure the energy distribution of the ions which escape through the mirror loss cones, an electrostatic ion energy analyzer was developed. The theoretical effort in support of the experimental program dealt with the solution of the rate equations and Fokker-Planck equations which describe the confined plasmas in the Laser Initiated Target Experiment (LITE). The rate equation analysis of the plasma heating and evolution to steady state with neutral injection using the LITE parameters indicates that a 0.5 Ampere current of 10-keV neutrals with intensity 5 mA/cm/sup 2/ at the target will balance the Coulomb decay and charge exchange losses with the neutral background and will susiain a plasma of density)10/sup 12/ cm/sup -3/. In addition, self-consistent Fokker -- Planck calculations (now including the effects of charge exchange with the background neutrals) were performed to give the time evolution of the particle energies, density, and plasma potential. The design of the neutral beam line for the charge exchange heating and neutral injection experiments was completed. To accommodate the energetic neutral flux while maintaining the necessary high vacuum conditions, a self-consistent calculation, including recycling of the neutral flux from the walls, has shown the need for an enlarged experiment chamber to provide more effective pumping. The criteria on which the designs of the experiment chamber and the neutral beam line are based, are discussed. (auth

High-betabeta capture and mirror confinement of laser-produced plasmas. Semiannual report, August 1, 1973--January 31, 1974

Experimental studies aimed at improving the reproducibility of the dense, laser produced plasmas were performed. Efforts in this area were concerned with the positioning of the target particle more accurately in the laser focal region and with preventing the premature displacement of the particle from the focal region. To address this latter problem, the single beam laser system of the previous experiments was modified to permit the simultaneous irradiation of the lithium hydride pellet by two opposed laser beams. In addition, the diagnostic capabilities of the present experiment were augmented so that more detailed measurements of the plasma lifetime, density, and energy can be made. A 4 mm microwave interferometer was installed to follow the plasma decay from higher densities. The measured density decay histories were analyzed to give estimates of the plasma lifetime and energy. Independent measures of the time dependence of the plasma radius were obtained from both microwave interferometry and optical streak photography. To measure the energy distribution of the ions which escape through the mirror loss cones, an electrostatic ion energy analyzer was developed. The theoretical effort in support of the experimental program dealt with the solution of the rate equations and Fokker-Planck equations which describe the confined plasmas in the Laser Initiated Target Experiment (LITE). The rate equation analysis of the plasma heating and evolution to steady state with neutral injection using the LITE parameters indicates that a 0.5 Ampere current of 10-keV neutrals with intensity 5 mA/cm/sup 2/ at the target will balance the Coulomb decay and charge exchange losses with the neutral background and will susiain a plasma of density)10/sup 12/ cm/sup -3/. In addition, self-consistent Fokker -- Planck calculations (now including the effects of charge exchange with the background neutrals) were performed to give the time evolution of the particle energies, density, and plasma potential. The design of the neutral beam line for the charge exchange heating and neutral injection experiments was completed. To accommodate the energetic neutral flux while maintaining the necessary high vacuum conditions, a self-consistent calculation, including recycling of the neutral flux from the walls, has shown the need for an enlarged experiment chamber to provide more effective pumping. The criteria on which the designs of the experiment chamber and the neutral beam line are based, are discussed. (auth

High beta capture and mirror confinement of laser produced plasmas. Final report

The LITE fusion plasma research program at UTRC has been investigating the stabilization and confinement physics of a mirror plasma created by energetic neutral beam heating of a confined target plasma. During the period covered by this report work has been concentrated on the investigation of hot ion losses in a warm target plasma, development of a cryocondensation pump for the LITE beam line neutralizer, theoretical studies of ECRH modification of the ambipolar potential in mirror plasmas, and analysis of the effects of localized cold plasma on DCLC stabilization. The results of these investigations are summarized below and detailed in four papers which comprise the body of this report. Measurements of the lifetime of hot ions in a mirror confined warm plasma have been carried out by observations of the hot ion buildup time obtained with energetic neutral beam injection. A cryocondensation pump of novel design has been constructed and incorporated in the neutralizer chamber of the LITE neutral beam line. Calculations have been carried out to evaluate the sizes and shapes of ambipolar potential modification produced by electron cyclotron resonance heated electrons and to determine the spatial distribution and densities of cold ions trapped in the potential wells. The effects of the spatial distribution of the cold ions on their effectiveness for stabilizing the drift cyclotron loss cone instability has been studied numerically using the formulation of Pearlstein in which the dispersion relation for the DCLC mode is solved for finite-size plasmas containing hot and cold components