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A dust storm consisting of carbon grains accelerated to speeds of up to ~3 km/s has been launched by a plasma jet produced in a coaxial gun. Diamond and graphite powders with grain radii of 0.5-30 [micro]m have been used. A distinctive feature of this plasma accelerator is that it can use different types of gases and can operate with microparticles having a large range of sizes. Deuterium gas and carbon dust are chosen to be compatible with fusion plasmas as a diagnostic tool. The operating voltages of the coaxial gun are between 5 and 10 kV, and the maximum measured discharge current is 250 kA. High-speed imaging of the plasma jet accelerated by the J x B force, and exiting the gun at 34 km/s, shows a good collimation of the flow for about 1.5 m before it diverges inside a large vacuum tank. Index Terms--Coaxial plasma gun, dust particles, hypervelocity, plasma drag, plasma flow.

Magnetized target fusion (MTF) is a means to compress plasmas to fusion conditions that uses magnetic fields to greatly reduce electron thermal conduction, thereby greatly reducing compression power density requirements. The compression is achieved by imploding the boundary, a metal shell. This effort pursues formation of the field-reversed configuration (FRC) type of magnetized plasma, and implosion of the metal shell by means of magnetic pressure from a high current flowing through the shell. We reported previously on experiments demonstrating that we can use magnetic pressure from high current capacitor discharges to implode long cylindrical metal shells (liners) with size, symmetry, implosion velocity, and overall performance suitable for compression of FRCs. We also presented considerations of using deformable liner-electrode contacts of Z-pinch geometry liners or theta pinch-driven liners, in order to have axial access to inject FRCs and to have axial diagnostic access. Since then, we have experimentally implemented the Z-pinch discharge driven deformable liner-electrode contact, obtained full axial coverage radiography of such a liner implosion, and obtained 2 112 dimensional MHD simulations for a variety of profiled thickness long cylindrical liners. The radiographic results indicate that at least 16 times radial compression of the inner surface of a 0.11-cm-thick AI liner was achieved, with a symmetric implosion, free of instability growth in the plane of the symmetry axis. We have also made progress in combining 21/2-D MHD simulations of FRC formation with imploding liner compression of FRCs. These indicate that capture of the injected FRC by the imploding liner can be achieved with suitable relative timing of the FRC formation and liner implosion discharges. Index Terms--Field-reversed configuration, liner implosion, magnetized plasma compression, magnetized target fusion.

Field reversed theta pinch technology is employed with programmed cusp fields at the theta coil ends to form high-density field-reversed configuration (FRC) plasmas. The well-formed FRC plasmas have volume-averaged density of 2 - 4 X [10.sup.22] [m.sup.-3], total temperature ([T.sub.e] + [T.sub.i]) of 300-500 eV, and plasma lifetime between 10-20 [micro]s in 50-70 mtorr of deuterium static gas fill. The achieved FRC parameters are very close to the desired target plasma requirements for magnetized target fusion. Index Terms--Field-reversed configuration, fusion reactors, magnetized target fusion, plasma confinement, plasma generation, plasma measurements, plasma pinch, plasmas.

Two applications of microparticles (micron-size particles) for laboratory plasma diagnosis are discussed. The first application is about injecting hypervelocity microparticles [(HDI) for hypervelocity dust injection] for internal magnetic field measurement in high-temperature plasmas. Since the concept of HDI has already been examined in details in our previous works, the primary focus here is to compare different schemes of microparticle acceleration. A new design of HDI based on plasma-dynamic accelerator is described to inject multiple microparticles to velocities around 10 km/s simultaneously. The other application is about using microparticles to measure plasma flow [(mPTV) for microparticle tracer velocimetry]. Directions of plasma flow at multiple locations can be measured simultaneously using mPTV because ion drag dominates over other forces inside laboratory plasmas of order [10.sup.19] [m.sup.-3] in density and a few electron volts in temperature. In addition to complex interactions between a microparticle with plasma, the magnitude of plasma flow may not be obtained directly from the microparticle velocity because of the time it takes for each microparticle to relax to local plasma velocity. In summary, microparticles are naturally small objects in all three dimensions and can, therefore, become useful diagnostics for laboratory plasmas with minimal perturbation. Index Terms--Hypervelocity, internal magnetic field measurement, ion flow measurement, microparticle, plasma flow measurement, plasma gun.

We describe a program to demonstrate the scientific basis of magnetized target fusion (MTF). MTF is a potentially low-cost path to fusion which is intermediate in plasma regime between magnetic (MFE) and inertial fusion energy (IFE). MTF involves the compression of a magnetized target plasma and pressure times volume (PdV) heating to fusion relevant conditions inside a converging flux conserving boundary. We have chosen to demonstrate MTF by using a field-reversed configuration (FRC) as our magnetized target plasma and an imploding metal liner for compression. These choices take advantage of significant past scientific and technical accomplishments in MFE and defense programs research and should yield substantial plasma performance (n[tau] > [10.sup.13] s-[cm.sup.-3] T > 5 keV) using an available pulsed-power implosion facility at modest cost. We have recently shown the density, temperature, and lifetime of this FRC to be within a factor of 2-3 of that required for use as a suitable target plasma for MTF compression for a fusion demonstration. Index Terms--Field-reversed configuration, fusion energy, magnetized target fusion (MTF).

The design and test results of a crowbar switch developed for the formation of long-lifetime field-reversed configurations are presented. These research efforts are being pursued at the FRX-L facility at Los Alamos National Laboratory using the 'Colt' capacitor bank (a 36 [micro]F Shiva Star bank module capable of storing up to 250 kJ) and at the Air Force Research Laboratory using the 'Formation' capacitor bank (consisting of three parallel banks identical to Colt). The crowbar switch design includes four Maxwell rail-gap switches mounted on a cable header that transitions from the capacitor bank bus plates to 48 RG 17/14 coaxial cables. For the testing performed at AFRL, a dummy load was set up to simulate the magnetic field coils of the actual experiment. Tests thus far have demonstrated the crowbarring of peak currents up to 1.25 MA. Breakdown within the cable header due to the initial high voltage applied from the bank has been successfully suppressed by the cable feed-through design, proper placement of Mylar sheets around the switch for insulation, and replacement of air in the header with S[F.sub.6]. Timing for the triggering of the crowbar is somewhat critical, as inductance in the switch increases when the switch is triggered with lower voltages across the switch rails. At the higher bank charge voltages, the charge-flow ratings on the rail-gap switches are exceeded; however, other than requiring that the rail electrodes in the switches be cleaned more frequently, no detrimental effects have been observed from the excessive charge flow. Index Terms--Cable feedthroughs, crowbar switches, pulsed power, rail-gap switches, field-reversed configurations.

This paper summarizes preliminary experimental and theoretical research that was directed toward the study of quasi-steady-state power flow in a large, unoptimized, multimegawatt coaxial plasma thruster. The paper addresses large coaxial thruster operation and includes evaluation and interpretation of the experimental results with a view to the development of efficient, steady-state, megawatt-class magnetoplasmadynamic (MPD) thrusters. Experimental studies utilized the Coaxial Thruster Experiment (CTX) facility at the Los Alamos National Laboratory. The unoptimized thruster, 1 m in length with inner and outer tungsten-coated electrode diameters of 0.37 and 0.56 m, respectively, was operated over a range of peak power levels (nominally 10-40 MW) in order to ascertain high-power performance scaling. In addition to pure self-field operation, an unoptimized applied magnetic field configuration, with adjustable flux densities, was used to form a rudimentary, annular magnetic nozzle. In this initial research, an accurate power balance was precluded due to the lack of spatial resolution of power deposition on the electrodes. However, the data, together with a calorimetric IR data reduction algorithm, did quantify energy flux deposition on electrode surfaces and provided a qualitative picture of global power flow and thruster performance. Highlights of this study include the observations that the measured longitudinal flow velocity of the propellant was in essential agreement with the prediction of self-field nozzle theory, achieving Alfvenic flow velocities of approximately equal to 10 to the fifth power m/s. Furthermore, radiative emission was a negligible power loss mechanism (

The design and first successful demonstration of an imploding solid liner with height to diameter ratio, radial convergence, and uniformity suitable for compressing a field reversed configuration is discussed. Radiographs indicated a very symmetric implosion with no instability growth, with ~13x radial compression of the inner liner surface prior to impacting a central measurement unit. The implosion kinetic energy was 1.5 megajoules, 34% of the capacitor stored energy of 4.4 megajoules. Index Terms--Capacitor bank, field reversed configuration, FRC, implosion, magnetized target fusion, megamp, MTF, radiography, solid liner.

Fast-framing imaging of visible radiation from magnetically confined plasmas has lately become a useful tool for both machine operation and physics studies. Using an intensified, commercial Kodak Ektapro imaging system, the effects of a plasma disruption were observed in the Tokamak Fusion Test Reactor (TFTR). The high-energy 'runaway' electrons created soon after the disruption collide with the plasma facing components damaging this surface and producing a shower of debris that traverses the toroidal vessel and 'falls' over the inner bumper limiter. Index Terms - Digital systems, magnetic confinement, optical imaging, plasmas, tokamaks.