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In inertial confinement fusion double-shell designs, the inner shell experiences heating that can amplify non-uniformities and consequently enhance mixing, which degrades capsule performance. Recent OMEGA experiments study the time-dependent evolution of mix under heated and shocked conditions. In each experiment, a cylindrical Be tube was filled with a layered system of a BeCu disk and low-density CH foam. The BeCu disks were machined with a multi-mode perturbation representative of the target surface roughness present in ICF capsules. The targets were heated from one end using a hohlraum and subsequently shocked using direct-drive from the opposite end. X-ray radiography was used to quantitatively diagnose the transmission profiles of the disk/foam interface. We focus primarily on an assessment of the applicability of the radiation transport models available in the RAGE (Radiation Adaptive Grid Eulerian) hydrodynamics code. These include grey diffusion, several types of multi-group diffusion, and a new frequency-dependent source capability that addresses the NLTE nature of the laser energy deposition.

As important phenomena in plasma spray, the plasma jet perturbation by the carrier gas flow and particles loading, and their effects on particle behavior are investigated. A three-dimensional computational model was developed to describe the plasma jet coupled with the orthogonal injection of carrier gas and particles. This model considered in-flight particle physical phenomena such as accelerating, heating, melting, and evaporation. The effects of carrier gas flow rates on the characteristics of plasma jet and particle spray pattern are simulated. The simulation results compare well with experimental data, for two common particle materials, NiCrAlY and ZrO2.

High-energy-density (HED) experiments are often diagnosed using x-ray backlighting. Recently, experiments have been designed and fielded that require x-ray backlighting having large fields of view and high x-ray energies. These types of experiments will be even more prevalent on the National Ignition Facility laser. Point backlighting offers the potential to obtain higher-energy x rays using less laser energy while giving a large, uniform field of view (millimeters). We present recent results from Los Alamos National Lab, Lawrence Livermore National Lab, and the University of Rochester’s Laboratory for laser energetics obtained on the OMEGA laser at the University of Rochester on the development of such bright sources. We include discussion of the challenges and successes to date.

Experiments to study the effect of a second, counterpropagating shock on the growth of hydrodynamic instabilities in a convergent, compressible system have been performed on the Omega Laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] at the University of Rochester. Direct laser illumination of a cylindrical target launches a strong shock across hydrodynamically unstable interfaces formed between an epoxy ablator material on the outside, a buried aluminum marker layer and low-density CH foam on the inside. The Richtmyer–Meshkov instability mixes the marker into the two adjacent materials. Of particular interest is what happens when the mixing region is reshocked by using a second, coaxial central cylinder to reflect the incident shock back into the mixing region. These experiments have been extensively modeled, in two dimensions, using the hydrocodes NYM [P. D. Roberts et al., J. Phys. D 13, 1957 (1980)], PETRA [D. L. Youngs, Physica D 12, 32 (1984)], and RAGE [R. M. Baltrusaitis et al., Phys. Flui...

The development of a turbulent high-velocity, high-temperature argon plasma jet issuing into air has been computationally modeled using the computer program LAVA. LAVA is a comprehensive computational software program developed for flowing thermal plasmas in the absence of electromagnetic fields, with particular emphasis on plasma jets. The plasma is represented as a multicomponent chemically reacting ideal gas with temperature-dependent thermodynamic and transport properties. The plasma flow is governed by the complete transient, compressible Navier–Stokes equations in two-dimensions in the current simulation. Turbulence is represented by the k – e model. Neutrals, ions and electrons are considered as separate components of species of the mixture. General kinetic and equilibrium chemistry algorithms compute ionization, dissociation, recombination and other chemical reactions. Computational results and extensive comparisons with experimental data are presented. In particular the influence of inflow boundary conditions and the ability of the k – e turbulence model to describe entrainment with chemistry are examined.

The development of a high-velocity, high-temperature argon plasma jet issuing into air has been investigated. In particular the entrainment of the surrounding air, its effect on the temperature and velocity profiles and the subsequent mixing and dissociation of oxygen has been examined in detail. The total concentration of oxygen and the velocity and temperature profiles in the jet were obtained from an enthalpy probe. High-resolution Thomson scattering provided an independent measure of plasma velocity and temperature, validating enthalpy probe measurements and providing non-intrusive measurements near the nozzle exit. The concentration of atomic oxygen was obtained from 2-photon laser induced fluorescence. Molecular oxygen concentration and temperature was obtained from coherent anti-Stokes Raman spectroscopy. It was found that both the incompleteness of mixing at the molecular scale and the rate of oxygen dissociation and recombination affects jet behavior.

A comprehensive model for the simulation of the plasma spraying of functionally graded materials (FGMs) is developed based on the recently modified CFD code, LAVA-P, that incorporates a well-verified model for plasma gas flow and chemistry. The particle movement and its trajectory are described within a Lagrangian framework by considering the drag as the major driving force. Melting and evaporation of particles are considered using a recently developed model for particle–flame interaction that also accounts for the non-continuum and variable property effects of high temperature plasma on particle momentum and heat transfer. Calculations are performed for NiCrAlY (alloy) and Y 2 O 3 stabilized ZrO 2 powders with a wide range of size distribution. The influence of the power levels and flow rate of H 2 on the plasma flow field, and hence, on the particle velocity and temperature are investigated numerically. The predicted velocity and temperature fields agree well with the measurements performed under similar spraying conditions. Segregation is investigated for two powder injection configurations. The model presented here can be used successfully for FGM deposition uniformity.

Numerical modeling is used to systematically examine the effects of turbulence, injection, and particle characteristics on particle behavior during thermal plasma spraying. Using the computer program LAVA (Idaho National Engineering and Environmental Laboratory, Idaho Falls, ID), a steady-state plasma jet typical of a commercial torch at normal operating conditions is first developed. Then, assuming a single particle composition (ZrO2) and injection location, real world complexity (e.g., turbulent dispersion, particle size and density, injection velocity, and direction) is introduced “one phenomenon at a time” to distinguish and characterize its effect and enable comparisons of separate effects. A final calculation then considers all phenomena simultaneously, to enable further comparisons. Investigating each phenomenon separately provides valuable insight into particle behavior. For the typical plasma jet and injection conditions considered, particle dispersion in the injection direction is most significantly affected by (in order of decreasing importance): particle size distribution, injection velocity distribution, turbulence, and injection direction distribution or particle density distribution. Only the distribution of injection directions and turbulence affect dispersion normal to the injection direction and are of similar magnitude in this study. With regards to particle velocity and temperature, particle size is clearly the dominant effect.

A model describing the in-flight evaporation of particles injected into a high-temperature plasma jet issuing into surrounding air has been developed and incorporated into an earlier model that includes a detailed description of particle heating and melting. In addition to physical evaporation controlled by vapor diffusion and heat transfer, the evaporation due to the production of volatile oxides on the particle surface is also modeled. The effect of evaporation-induced mass transfer on heat flux to the particle surface is taken into consideration along with the effects of variable plasma properties and the modification of heat and momentum transfer due to non-continuum effects experienced under plasma conditions. Computational results on molybdenum particles in an argon–hydrogen DC plasma spray system are developed and are qualitatively compared with experimental results.

A very large area (7.5 mm(2)) laser-driven x-ray backlighter, termed the Big Area BackLighter (BABL) has been developed for the National Ignition Facility (NIF) to support high energy density experiments. The BABL provides an alternative to Pinhole-Apertured point-projection Backlighting (PABL) for a large field of view. This bypasses the challenges for PABL in the equatorial plane of the NIF target chamber where space is limited because of the unconverted laser light that threatens the diagnostic aperture, the backlighter foil, and the pinhole substrate. A transmission experiment using 132 kJ of NIF laser energy at a maximum intensity of 8.52 × 10(14) W/cm(2) illuminating the BABL demonstrated good conversion efficiency of3.5% into K-shell emission producing ~4.6 kJ of high energy x rays, while yielding high contrast images with a highly uniform background that agree well with 2D simulated spectra and spatial profiles.

In this article, amorphous and nanocomposite thermally deposited steel coatings have been formed by using both plasma and high-velocity oxy-fuel (HVOF) spraying techniques. This was accomplished by developing a specialized iron-based composition with a low critical cooling rate (≈104 K/s) for metallic glass formation, processing the alloy by inert gas atomization to form micron-sized amorphous spherical powders, and then spraying the classified powder to form coatings. A primarily amorphous structure was formed in the as-sprayed coatings, independent of coating thickness. After a heat treatment above the crystallization temperature (568 °C), the structure of the coatings self-assembled (i.e., devitrified) into a multiphase nanocomposite microstructure with 75 to 125 nm grains containing a distribution of 20 nm second-phase grain-boundary precipitates. Vickers microhardness testing revealed that the amorphous coatings were very hard (10.2 to 10.7 GPa), with further increases in hardness after devitrification (11.4 to 12.8 GPa). The wear characteristics of the amorphous and nanocomposite coatings were determined using both two-body pin-on-disk and three-body rubber wheel wet-slurry sand tests. The results indicate that the amorphous and nanocomposite steel coatings are candidates for a wide variety of wear-resistant applications.

An oxidation model for molybdenum particles during the plasma spray deposition process is presented. Based on a well-verified model for plasma chemistry and the heating and phase change of particles in a plasma plume, this model accounts for the oxidant diffusion around the surface of particles or splats, oxidation on the surface, as well as oxygen diffusion in molten molybdenum. Calculations are performed for a single molybdenum particle sprayed under Metco-9MB spraying conditions. The oxidation features of particles during the light are compared with those during the deposition. The result shows the dominance of oxidation of a molybdenum particle during the flight, as well as during deposition when the substrate temperature is high (above 400 °C).

Particle temperature is a fundamental parameter in the thermal spray process. The measurement of particle temperature usually relies on the measurement of the radiance of the hot, incandescent, particles in two or more wavelength or color bands. Measurement techniques can be categorized as single particle and ensemble methods. Single particle methods use high-speed pyrometry to estimate the temperature of individual particles. The mean and standard deviation of the particle temperature distribution can then be obtained from observations of sufficient numbers of individual particles. Ensemble methods observe large numbers of particles simultaneously and yield an estimated mean temperature directly, but cannot provide information on the shape or width of the particle temperature distribution. Both techniques have inherent errors, strengths, and limitations that are examined and discussed.

This paper presents a simulation and visualization system for plasma spraying of functionally graded materials (FGM). The recently modified CFD code, LAVA-P, that incorporates a well-verified model for plasma gas flow and chemistry is employed. The particle movement and its trajectory are described within a Lagrangian formulation by considering drag as the major driving force, and the particle melting, evaporation, and resolidification are considered using a recently developed model for particle-flame interaction. In addition to the noncontinuum and variable property effects associated with high-temperature plasma, the effects of particle evaporation on particle momentum and heat transfer are also taken into account. Calculations are performed for NiCrAlY and ZrO2 powders for a wide range of size distributions. The influences of power levels and flow rate of H2 on plasma flow field and, hence, on the particle velocity and temperature are investigated. The predicted velocity and temperature fields agree well with the measurements under similar spraying conditions. With the help of a special in-house built process animation and visualization algorithm, the powder injection conditions, such as the number of injectors, injector location, and injection velocity, are investigated and can be optimized to obtain coatings with a specified distribution of different species.

Electron temperature and electron density measurements were made in an atmospheric-pressure argon plasma jet by line-shape analysis of Thomson-scattered laser light. The dependence of electron temperature and electron density on the scattering angle was investigated. Measurements were made using incident laser wavelengths of 532 and 355 nm. At 532 nm, the electron-ion collision frequency exceeds the Landau damping rate for shallow scattering angles, and the electron plasma wave resonance structure in the Thomson line shape is broadened. This resulted in dramatic increase in the apparent electron temperature as a function of decreasing scattering angle. At 355 nm, collisions do not affect the Thomson line shape. In this case, an angular dependence of the measured electron temperature is not expected and was not observed. Data taken at 532 nm at larger scattering angles are consistent with the 355-nm results, and show that the electrons are not in thermodynamic equilibrium with the heavy particles.

Computational modeling is used to systematically examine many of the sources of statistical variance in particle parameters during thermal plasma spraying. Using the computer program LAVA, a steady-state plasma jet typical of a commercial torch at normal operating conditions, is first developed. Then, assuming a single particle composition(ZrO2) and injection location, real world complexity (e.g., turbulent dispersion, particle size and density, injection velocity, and direction) is introduced ``one phenomenon at a time” to distinguish and characterize its effect and enable comparisons of separate effects. Calculations are also performed wherein all phenomena are considered simultaneously to enable further comparisons. Both nonswirling and swirling plasma flow fields are considered. Investigating each phenomenon separately provides valuable insight into particle behavior. For the typical plasma jet and injection conditions considered, particle dispersion in the injection direction is mostsignificantly affected by (in order of decreasing importance): particle size distribution, injection velocity distribution, turbulence, and injection direction distribution or particle density distribution. Only the distribution of injection directions and turbulence affect dispersion normal to the injection direction and are of similar magnitude in this study. With regards to particle velocity and temperature, particle size is clearly the dominant effect.

A comprehensive model is developed to study the heating, melting, evaporation, and resolidification of powder particles in plasma flames. The well-established LAVA code for plasma flame simulation is used to predict the plasma gas field under given power plasma flame simulation is used to predict the plasma gas field under given power conditions, and provide inputs to the particle model. The particle is assumed to be a spherical and one-dimensional heat conduction equation with phase change within the particle is solved numerically using an appropriate coordinate transformation and finite difference method. Melting, vaporization, and resolidification interfaces are tracked and the particle vaporization is accounted for by the mass diffusion of vapor through the boundary layer around the particle. The effect of mass transfer on convective heat transfer is also included. Calculations have been carried out for a single particle injected into an Ar-H{sub 2} plasma jet. Zirconia and nickel are selected as solid particles because of their widespread industrial applications as well as significant differences in their thermal properties. Numerical results show strong nonisothermal effect of heating, especially for materials with low thermal conductivity, such as zirconia. The model also predicts strong evaporation of the material at high temperatures.

The Richtmyer-Meshkov instability creates or seeds hydrodynamic instabilities that will mix cold shell material into the hot DT fuel in an ignition capsule and may prevent ignition. Characteristic of this process is multiple shocks crossing converging interfaces. To mimic this situation, strong converging shocks were created, passed over an unstable interface, reflected by an inner cylinder, and then reshocked the interface. Analysis of the mix width at the unstable surface shows no additional growth, within experimental uncertainty, due to an initially perturbed surface and no dependence on reshock strength.

A 2-D Eulerian code with a turbulent mix model was used for the first time to model a set of plastic (CH) ablator capsules with 15 μm thick CH shells. Our simulations of these capsules do a reasonable job of matching the implosion radius versus time, self-emitting core radius, and have an experiment/simulation yield ratio that is about 0.24.

Characterization of high power plasma devices and processes requires the direct measurement of heavy particle temperature, electron temperature, electron number density, plasma velocity, and composition. Traditional diagnostic techniques, such as emission spectroscopy, which rely on the assumption of local thermodynamic equilibrium are questionable at best for high velocity flow fields. Because of nonequilibrium and demixing effects, direct measurements which do not rely on assumptions of local thermodynamic equilibrium or composition are necessary.

A program to investigate the mixing of a marker layer in a convergent cylindrical geometry has been carried out on the Omega laser facility. The principal diagnostic for these experiments was the Los Alamos National Laboratory (Los Alamos, NM) QXI framing camera. The results obtained displayed an unphysical pattern, partly attributed to nonlinear gain effects. We propose a method to compensate for these effects, which relies only on shot data and so can be used retrospectively on previously obtained data. Modifications carried out on the camera to minimize the effect are described and the results are compared with compensated data from previous runs. We also present results which evaluate the state of gain effects in the camera during each experimental shot day.

Radiography of driven targets using point projection backlighting often requires extensive baffling to mitigate background x rays and physical damage due to target debris. One solution to this problem is a camera configuration that places the nosecone very close to the target such that extraneous light is excluded; however debris and blast damage becomes an issue. A successful close-in (

Mix is an important issue in High Energy Density Laboratory Plasmas (HEDLP), specifically Inertial Confinement Fusion (ICF) implosions. In ICF, shock waves traverse fuel capsule defects and material interfaces, and due to hydrodynamic instabilities transitioning into turbulence, these shocks can initiate mix between shell and fuel, degrading yield. To this end, a series of laser-driven mix experiments has been designed for the OMEGA and NIF laser facilities to investigate the turbulent mixing of materials proceeded by reshock and shear, which initiates Richtmyer-Meshkov and\or Kelvin-Helmholtz instabilities on a tracer layer. The experiments are designed to understand if the Besnard-Harlow-Rauenzahn (BHR) mix model that has been implemented in LANL's RAGE hydrodynamics code has coefficients that are properly determined for an HEDLP environment.

Measurements of velocity, temperature, entrained air, and Ar/He concentration profiles in a subsonic thermal plasma jet were obtained using an enthalpy probe and mass spectrometer combination. The rapid entrainment of air into the jet results in rapidly decreasing velocities and temperatures. A significant diffusive separation of the premixed Ar/He feed gases is observed in the large temperature gradients present. Predictions are obtained from a comprehensive computational model of the thermal plasma jet. The 2-D axisymmetric model includes self-consistent effective binary and ambipolar diffusion and uses a κ—e turbulence model.

The velocity, temperature, entrained air fraction, and Ar/He concentration profiles were measured in a subsonic thermal plasma jet using an enthalpy probe and mass spectrometer. Through interaction with the surrounding atmosphere, air is quickly entrained into the jet, resulting in rapidly decreasing velocities and temperatures. Due to the difference in ionization potential, a significant diffusive separation or demixing of Ar and He is also observed in the large temperature gradients present. Near the exit of the torch, in the jet center, the relative He concentration is enhanced by approximately 50% over that of the premixed feed gases. Demixing occurs primarily in the discharge region and torch nozzle. As jet mixing progresses in the downstream direction, the Ar to He ratio approaches the initial input ratio.

Enthalpy probe measurements in compressible argon/helium thermal plasma jets are compared with results from high spectral resolution laser light scattering. In the laser scattering measurement the plasma temperature and velocity are determined directly from high‐resolution line‐shape analysis of light scattered by the plasma. The technique yields an unambiguous determination of gas or kinetic temperature without the assumption of local thermodynamic equilibrium. Velocity is determined directly from the measured Doppler shift. The enthalpy probe is a combination stagnation probe and flowing calorimeter. Gas temperatures and velocities are calculated from measured values using both frozen flow and equilibrium flow assumptions for the stagnation process. Over the Mach number range examined, the assumption of isentropic, frozen composition stagnation best matches the laser results. In the jet periphery a significant streamline displacement is caused by the presence of the probe. The displacement, which is a f...

To better understand the plasma spray coating process, an experimental study of the interaction between a subsonic thermal plasma jet and injected nickel- aluminum particles was performed. The velocity, temperature, and composition of the argon/helium gas flow field was mapped using an enthalpy probe/mass spectrometer system. The sprayed particle flow field was examined by simultaneously measuring the size, velocity, and temperature of individual particles. Particle and gas temperatures were compared at the nominal substrate stand- off distance and axially along the median particle trajectory. Temperature and velocity differences between the particle and the gas surrounding it are shown to vary substantially depending on the trajectory of the particles. On the median trajectory, the average particle is transferring heat and momentum back to the plasma by the time it reaches the substrate. Because the exchange of heat and momentum is highly dependent on the particle residence time in the core of the plasma, the condition of particles at the substrate can be optimized by controlling the particle trajectory through the plasma.

Gas-temperature and velocity profiles at the exit plane of a thermal argon plasma torch have been determined directly from a high-resolution Doppler-shifted line-shape analysis of laser light scattered by the plasma. Peak temperature and velocity values observed were 13 350 K\ifmmode\pm\else\textpm\fi{}7% and 1100 m ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$\ifmmode\pm\else\textpm\fi{}3%. Velocities as low as 45 m ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$\ifmmode\pm\else\textpm\fi{}45% were measured in the fringe of the jet. An injection-seeded pulsed neodymium-doped yttrium aluminum garnet laser was used as the laser source and the scattered laser light was analyzed with a scanning tandem Fabry-P\'erot interferometer. Temperature data obtained from laser scattering are compared with values obtained from emission spectroscopy and show a severe departure from local thermodynamic equilibrium (LTE) in the outer regions of the jet. Gas temperatures were observed to increase as the torch operating current increased from 300 to 500 A, but remained constant as the operating current increased to 900 A. However, electron temperatures and densities continued to increase with operating current. This suggests that increasing the electrical power drives the plasma away from LTE. Measured temperature and velocity profiles were found to be nearly parabolic.

Gas temperature and velocity profiles in argon thermal plasmas, measured by an enthalpy probe and high spectral resolution laser light scattering, are compared. In the laser scattering measurement the plasma temperature and velocity are determined directly from high‐resolution Doppler‐shifted line‐shape analysis of light scattered by the plasma. The technique yields an unambiguous determination of gas or kinetic temperature without the assumption of local thermodynamic equilibrium. Velocity is determined directly from the measured Doppler shift. The enthalpy probe is a combination Pitot tube and flowing calorimeter. The assumption of thermodynamic equilibrium is required to obtain velocity and temperature from measured enthalpy and stagnation pressure. Peak temperature and velocity values observed were ∼13 000 K and 1300 m s−1. The results from both the intrusive enthalpy probe and nonintrusive laser light scattering technique compare favorably. The limitations of both techniques are discussed.

The enthalpy or calorimetric probe is a water‐cooled stagnation/sampling probe for studying the temperature, velocity, and composition of hot‐gas flow fields. In order to derive the thermodynamic properties of complex flow fields such as plasma arc jets or high‐velocity oxygen fuel jets, the specie concentration must be known accurately. To this end a differentially pumped quadrapole mass spectrometer has been integrated with a fully automated enthalpy probe system. An inexpensive modular probe is described along with the system and its theory of operation. Calibration and error are also discussed. Typical results are presented for the system operating in an argon/helium plasma arc jet in atmospheric pressure air. The maximum temperature measured is 13434 K on the center line of the jet, 5 mm from the exit, with a corresponding velocity of 1295 m/s. The utility in integrating the mass spectrometer to the enthalpy probe system is not only an accurate measurement of the gas mixture components for obtaining ...

Measurements of particle size, velocity, and relative mass flux were made on a spray field produced by aspirating liquid tin into 350 °C argon flowing through a venturi nozzlevia a small orifice in the throat of the nozzle. Details of the aspiration and droplet formation process were observed through windows in the nozzle. The spatial distribution of droplet size, velocity, and relative number density was measured at a location 10 mm from the nozzle exit. Due to the presence of separated flow in the nozzle, changes in nozzle inlet pressure did not significantly effect resulting droplet size and velocity. This suggests that good aerodynamic nozzle design is required if spray characteristics are to be controlled by nozzle flow.

The achievable beam quality resulting from heavy charged particle pumping of transverse flow, gas laser amplifiers is presented. The charged particles are generated by nuclear reactions in either B4C or UO2 coated on plates parallel to the lasant flow. The character of the laser medium aberration resulting from the nonuniform energy deposition and fluid dynamic effects is discussed as well as the effects on the far‐field beam quality of the amplifier. Pumping from plates parallel to the flow produces a medium aberration which is dominated by a cylindrical focus perpendicular to the flow, and a tilt in the flow direction. Beam qualities of better than 2 times diffraction limited (TDL) are obtained with a B4C fueled 1‐m‐long amplifier pumped at an average power deposition of 100 W/cm3 with an inlet 0.1‐MPa helium flow at 100 m/s. Amplifiers using UO2 fuel coatings to pump argon under the same flow conditions with fission fragments have similar qualitative laser medium aberrations but with larger magnitude, ...

An indirectly-driven shock tube experiment fielded on the National Ignition Facility (NIF) was used to create a high-energy-density hydrodynamics platform at unprecedented scale. Scaling up a shear-induced mixing experiment previously fielded at OMEGA, the NIF shear platform drives 130 μm/ns shocks into a CH foam-filled shock tube (∼ 60 mg/cc) with interior dimensions of 1.5 mm diameter and 5 mm length. The pulse-shaping capabilities of the NIF are used to extend the drive for >10 ns, and the large interior tube volumes are used to isolate physics-altering edge effects from the region of interest. The scaling of the experiment to the NIF allows for considerable improvement in maximum driving time of hydrodynamics, in fidelity of physics under examination, and in diagnostic clarity. Details of the experimental platform and post-shot simulations used in the analysis of the platform-qualifying data are presented. Hydrodynamic scaling is used to compare shear data from OMEGA with that from NIF, suggesting a possible change in the dimensionality of the instability at late times from one platform to the other.

Strongly shocked cylindrically convergent implosions were conducted on the OMEGA laser. The directly driven targets consist of a low-density foam core and an embedded aluminum shell covered by an epoxy ablator. The outer surface of the aluminum shell has imposed single-mode perturbations with wave numbers k = 0.25, 0.7, 1.05, and 2.5 (rad/μm) and initial amplitudes η0 /λ = 0.04, 0.11, 0.33, and 0.4. In our convergent geometry, perturbation growth without evidence of saturation, for η/λ as large as 4.5 is observed for k 1 growth rate scaling with wavenumber breaks down and transition to turbulence is suggested.

A three-dimensional computational model has been developed to describe the compressible, multi-component, turbulent, reacting plasma jet coupled with the orthogonal injection of carrier gas and particles. This model has been applied to plasma spray process that includes physical phenomena such as heating, melting, accelerating, and evaporation of in-flight particles. The entrained particles, NiCrAlY and ZrO2 , are discretely treated in a Lagrangian coordinate and stochastically generated by sampling from the probability distributions of the particle size and its velocity at the injection nozzle. In this study, special attention has been directed to the effects of carrier gas injection on the characteristics of plasma jet. The computational results show that the injection of carrier gas from the orthogonal injector above the plasma jet introduce the 3-D phenomena of plasma gas flow. The plasma jet is defected and the thermo-fluid flow near the injector is locally deformed.Copyright © 2003 by ASME

A comprehensive model describing the melting and oxidation of in-flight particles during plasma spray has been presented which includes the models for heat, momentum and mass transfer of carrier gas, and particle heating, acceleration and evaporation. The effect of evaporation-induced mass transfer on heat flux to the particle surface has been taken into consideration along with the effect of oxidation-induced evaporation due to the production of volatile oxides on the particle surface, and effects of variable plasma properties and non-continuum effects under plasma conditions. Computational results on molybdenum and zirconium particles in an argon-hydrogen DC plasma spray system have been obtained and discussed. The temperature and melting formation of particles with different sizes along their trajectories are depicted as well as other particle parameters such as velocity, evaporation rate and oxide content, which manifests that the behavior of particles are diverse due to particle size distribution in the spray coating operation. The effects of gun power on the heating, acceleration, melting, evaporation and oxidation of particles have also been discussed.

We report on the novel integration of streaked radiography into a counter-flowing High Energy Density (HED) shear environment that continually measures a growing mix layer of Al separating two low-density CH foams. Measurements of the mix width allow us to validate compressible turbulence models and with streaked imaging, make this possible with a minimal number of experiments on large laser facilities. In this paper, we describe how the HED counter-flowing shear layer is created and diagnosed with streaked radiography. We then compare the streaked data to previous two-dimensional, single frame radiography and radiation hydrodynamic simulations of the experiment with inline compressible turbulent mix models.

Thermal spray processing of functionally graded materials requires that the spray patterns of different particle types coincide at impact and that each particle type arrives with the appropriate temperature and degree of melting. Measurements of particle velocity, temperature, and size along with spray pattern characteristics have been obtained for co-injected NiCrAlY and zirconia powder. The plasma and particle flow fields were also simulated with a pseudo 3-D model using the LAVA computer code. The model assumes that the gas flow is axisymmetric while the particles are treated in a fully 3-D manner. A stochastic discrete-particle model that includes turbulent dispersion dictates particle behavior. The simulation produced reasonably accurate velocities and particle trajectories, although, particle temperature is consistently over predicted. Comparisons between the calculated and measured velocity and temperature statistical distributions and calculated molten fractions are discussed.

The counterpropagating shear experiment has previously demonstrated the ability to create regions of shock-driven shear, balanced symmetrically in pressure, and experiencing minimal net drift. This allows for the creation of a high-Mach-number high-energy-density shear environment. New data from the counterpropagating shear campaign is presented, and both hydrocode modeling and theoretical analysis in the context of a Reynolds-averaged-Navier-Stokes model suggest turbulent dissipation of energy from the supersonic flow bounding the layer is a significant driver in its expansion. A theoretical minimum shear flow Mach number threshold is suggested for substantial thermal-turbulence coupling.

An Eulerian code with a turbulent mix model is used to model a set of plastic (CH) ablator capsules with and without equatorial grooves. The “perfect” capsule results were used to calibrate simulations of capsules with equatorial grooves of different depths that provided information on increasingly perturbed implosions. Simulations with a turbulence model were able to calculate the same yield over mix (YOM) ratio (experiment/mix simulation) of 0.2 to 0.3 for thin (8-μm thick) and thick shell (15-μm thick) capsules with no grooves and thin capsules with shallow grooves. When the capsules have deep grooves, the YOM ratio increases to greater than unity, probably because the deformed shocks focus too strongly on the symmetry axis in our two-dimensional simulations. This is supported by a comparison of simulated and experimental x-ray images.

Line-shape analysis of the electron feature of Thomson-scattered laser light has been used to directly determine electron-temperature and electron-density profiles of an atmospheric-pressure argon plasma jet. Measured center line values of the electron temperature are in excess of 20 000 K at the torch exit, and remain essentially constant with increasing axial distance even though the plasma is recombining. These results are shown to be inconsistent with Saha equilibrium and classical electron-ion momentum transfer theory.

The distribution of Al2O3 particle size, velocity and temperature was mapped over the flow field of a 31.5 kW plasma torch. The effects of varying the powder loading were studied. The powder feed rate was varied between.45 and 2.05 kg/hr independent of the carrier gas flow rate. The particle flow field was non-symmetric due to the method of particle injection. The data indicate that powder feed rate does not significantly affect either the temperature or velocity of the particles, for typical plasma spray conditions, and that the assumption of a dilute particle flow field is valid.

The concentration and temperature of air entrained into an argon plasma jet has been measured using coherent anti-Stokes Raman spectroscopy (CARS). The flow field is characterized by a short region of well behaved laminar flow near the nozzle exit followed by an abrupt transition to turbulence. Once the transition to turbulence occurs, air is rapidly entrained into the jet core. The location of the transition region is thought to be driven by the rapid cooling of the jet and the resulting increase in Reynolds number. 8 refs., 6 figs.

Initial experiments were performed at the OMEGA laser [J. Soures et al., Phys. Plasmas 3, 2108 (1996)] to investigate the physics associated with inertial confinement fusion capsule fill tubes and holes. These experiments were performed in planar geometry and examined the hydrodynamics of a 6.7:1 aspect ratio fill-hole. X-ray radiographs at 310eV show a jet has formed due to the interaction between the temperature drive and the beryllium (Be) washer.

Accurate predictive hydrodynamics codes increase the efficiency with which ignition will be achieved at the National Ignition Facility (NIF) [J. W. Hogan et al., J. Nucl. Fus. 41, 567 (2001)]. By validating these codes against well-diagnosed experiments, additional confidence in their predictive capability is attained. This work presents comparisons between the predictive simulations of the Los Alamos hydrocode RAGE [R. M. Baltrusaitus et al., Phys. Fluids 8, 2471 (1996)] and data obtained from cylindrical defect-driven mix experiments conducted on the OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] laser. The results show that RAGE accurately captures much of the bulk hydrodynamics of the experiments. However, persistent discrepancies with respect to the small-scale fluid flows remain.

The technique of reconstructive tomography (RT) is a powerful method of obtaining local, spatially resolved volumetric emission coefficients from line integral data. The applicability of this technique as a diagnostic for nonuniform sources is studied using simulated data with and without noise. The major advantage of RT techniques is that they may be applied, without restriction, to highly asymmetric data as well as symmetric data. When applied to symmetric data, the technique appears to be less susceptible to noise than Abel inversion techniques. Also examined is a method of accounting for self-absorption under certain circumstances.

Two coincidence techniques for simultaneously obtaining particle size and temperature in a plasma torch are described. The absolute magnitude of scattered laser light is used to determine particle size while particle temperature is determined using a two-colour pyrometer technique. Typical results on alumina particles injected into a 7 kW plasma torch are presented.