A two-dimensional laser-sustained plasma model, which is based on the laminar, Navier-Stokes equations for the flow and geometric ray tracing for the laser beam, has been evaluated and compared with existing experimental results for a wide range of forced convective argon flows. The influence of gas inlet velocity, gas pressure, laser power, and focusing geometry on the structure of the plasma was examined. The model agreed well with the existing experimental data in both global structure and detailed temperature distribution, particularly for static pressures greater than 2 atm. It was found that the diffusion approximation for the optically thick portion of the thermal radiation was not adequate for low-pressure (less than 2 atm) plasmas and that the radiationinduced thermal conductivity had to be adjusted in order to obtain agreement between the model calculations and experimental results. The present model calculations were also compared with a recently published semitwo-dimensional model and the results indicate that the existing one-dimensional and semi-two-dimensional models do not provide adequate solutions for the laser-sustained plasma. Nomenclature c p = specific heat at constant pressure, J/kg-K h = specific enthalpy, J/kg / = laser intensity, W/m 2 k = intrinsic thermal conductivity, W/m-K & eff = effective thermal conductivity, W/m-K rad = radiation-induced thermal conductivity, W/m-K <7rad -radiation heat loss, J/m 3 -s r = radius, m s = distance along the laser ray, m u -axial velocity, m/s v = radial velocity, m/s x = axial distance, m y -radial distance, m a.= absorption coefficient at 10.6 />tm wavelength, 1/m ju = viscosity, kg/m-s p = density, kg/m 3

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In this experimental investigation, stable and axisymmetric laser-sustained plasmas were produced in flowing argon. Energy was provided by the focused beam from a carbon dioxide laser; two different focusing geometries were used. Spatial distributions of absolute radiance from the plasmas, in a narrow-wavelength band, were measured. The assumption of axial symmetry, along with the assumption of local thermodynamic equilibrium, was used to deduce the radial profiles of temperature in the plasmas. From this and a geometric raytrace, the detailed spatial distribution of power absorption was calculated, as well as the radiation lost from the plasmas. In addition to the focusing geometry, the flow velocity, pressure, and incident laser power were systematically varied in the experiments. The quantitative results indicate clearly that a perceptive analysis of such laser-sustained plasmas must take into consideration the two-dimensionality of both the flowfield and the laser energy distribution in the focused beam.

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High Energy Density Physics (HEDP) applications require high line charge density ion beams. An efficient method to obtain this type of beams is to extract a long pulse, high current beam from a gun at high energy, and let the beam pass through a decelerating field to compress it. The low energy beam-bunch is loaded into a solenoid and matched to a Brillouin flow. The Brillouin equilibrium is independent of the energy if the relationship between the beam size (a), solenoid magnetic field strength (B) and line charge density is such that (Ba)^2 is proportional to the line charge density. Thus it is possible to accelerate a matched beam at constant line charge density. An experiment, NDCX-1c is being designed to test the feasibility of this type of injectors, where we will extract a 1 microsecond, 100 mA, potassium beam at 160 keV, decelerate it to 55 keV (density ~0.2 μC/m), and load it into a 2.5 T solenoid where it will be accelerated to 100-150 keV (head to tail) at constant line charge density. The head-to-tail velocity tilt can be used to increase bunch compression and to control longitudinal beam expansion. We will present the physics design and numerical simulations of the proposed experiment.