Publications (109)45.74 Total impact
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Article: Parameter space for magnetized fuel targets in inertial confinement fusion
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ABSTRACT: A simple, zero-dimensional model describing the temporal behaviour of an imploding-shell, magnetized fuel inertial confinement fusion target is formulated. The model includes effects not normally considered in inertial confinement fusion such as magnetic back-pressure on the imploding shell, magnetic reduction of thermal conductivity, magnetic diffusion, and Ohmic heating. The model is simple enough to permit a survey of the parameter space available for magnetized fuel by computing the behaviour of thousands of targets. The survey predicts the existence of a totally new region in parameter space where significant thermonuclear fuel burn-up can occur. The new region is characterized by very low fuel densities, very low implosion velocities, and,most important, driver requirements reduced by several orders of magnitude, suggesting that "break-even" experiments may be possible with existing inertial confinement fusion drivers. The computed results are in reasonable agreement with more complete two-dimensional magnetohydrodynamic simulations.Nuclear Fusion 01/2011; 23(3):263. · 4.09 Impact Factor -
Article: Initial numerical studies of the behaviour of Z-pinch plasma under liner implosion conditions
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ABSTRACT: The principle of achieving thermonuclear temperatures by compression of a z-pinch plasma with a solid liner is demonstrated by one- and two-dimensional numerical calculations of the behaviour of the plasma under liner implosion conditions. The magnetohydrodynamic plasma model used includes radiation, thermal conduction, and resistive diffusion. The magnetohydrodynamic partial differential equations are solved by a computer code employing implicit finite-difference methods. The liner is represented by a moving, rigid wall, and the entire Eulerian finite-difference mesh linearly contracts as the liner moves inward. The effects of end losses and unstable boundary layer formation are demonstrated. The plasma is shown to behave significantly non-adiabatically, although some plasma is nearly adiabatically compressed. For an assumed initial plasma/magnetic-field configuration and an assumed liner velocity of 1 cm μs−1, plasma of 1018 cm−3 and 600 eV is heated to peak temperatures of nearly 20 keV when the plasma volume is reduced by a factor of 900.Nuclear Fusion 01/2011; 18(7):929. · 4.09 Impact Factor -
Article: Experimental investigation of thermal plasma formation from thick aluminum surfaces by pulsed multimegagauss magnetic field
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ABSTRACT: The thermal ionization of a thick metal surface by pulsed multimegagauss magnetic field has been examined experimentally. Thick 6061-alloy Al rods with initial radii (R0) from 1.00 to 0.25 mm, larger than the magnetic field skin depth, are pulsed to 1.0 MA peak current in 100 ns. Surface fields (Bs) rise at 30−80 MG/μs and reach 1.5 and 4 MG, respectively. For this range of parameters, plasma forms at a threshold level of Bs = 2.2 MG. Novel load hardware ensures that plasma formation is thermal, by Ohmic or compression heating. Surface-plasma formation is conclusively indicated through radiometry, extreme ultraviolet spectroscopy, and gated imaging. When R0 = 0.50 mm rods reach peak current, Bs = 3 MG, the surface temperature is 20 eV, and Al3+ and Al4+ spectra and surface instabilities are observed. In contrast, R0 = 1.00 mm rod surfaces [Bs(t)<2.2 MG] reach only 0.7 eV and remain extremely smooth, indicating that no plasma forms.Physics of Plasmas 10/2010; 17(10):102507-102507-11. · 2.15 Impact Factor -
Article: Numerical Simulations of Thick-Aluminum-Wire Behavior Under Megaampere-Current Drive
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ABSTRACT: A series of experiments to study the behavior of thick wires (0.5-2 mm in diameter) driven by currents of about 1 MA has recently been conducted on the Zebra facility at the University of Nevada, Reno. The objective of these experiments was to study plasma formation on the surface of conductors under the influence of megagauss magnetic fields. Laser shadowgraphy, filtered optical and extreme ultraviolet photodiodes, and extreme ultraviolet spectroscopy used in the experiments provided data on radial expansion of wires and on plasma radiation. This paper focuses on numerical simulations of these experiments. Simulations with wires having diameters up to 1.6 mm demonstrated plasma formation with temperatures above 3 eV, which is in preliminary agreement with the experiment. For 2-mm-diameter wires, although plasma can be observed in the simulations, it has substantially smaller optical thickness than in the simulations of the smaller diameter wires, and the radiation fluxes prove to be much lower. This can shed light on the experimental results where the radiation of the 2-mm wires was very weak. The simulated time dependences of the wire radii agree rather well with the experimental results obtained using laser diagnostics and visible-light imaging. The experimental data of the photodiodes also agree well with the simulated time dependence of the detected radiation.IEEE Transactions on Plasma Science 09/2010; · 1.17 Impact Factor -
Article: Linear and nonlinear development of m = 0 instability in a diffuse Bennett Z-pinch equilibrium with sheared axial flow
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ABSTRACT: The effect of sheared axial flow on the Z-pinch sausage instability has been examined with two-dimensional magnetohydrodynamic simulations. Diffuse Bennett equilibria in the presence of axial flows with parabolic and linear radial profiles have been considered, and a detailed study of the linear and nonlinear development of small perturbations from these equilibria has been performed. The consequences of both single-wavelength and random-seed perturbations were calculated. It was found that sheared flows changed the internal m = 0 mode development by reducing the linear growth rates, decreasing the saturation amplitude, and modifying the instability spectrum. High spatial frequency modes were stabilized to small amplitudes and only long wavelengths continued to grow. Full stability was obtained for supersonic plasma flows.Physics of Plasmas 07/2010; 17(7):072107-072107-10. · 2.15 Impact Factor -
Article: Sensitivity of Instability to Different Resistivity Models
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ABSTRACT: Instabilities can affect the quality of flux compression and other high-current experiments. The modeling of such experiments involves a number of numerical difficulties. One such difficulty is the selection of proper material property models. This paper investigates the effect of different electrical resistivity models on the development of the m = 0 instability in a single cylindrical conductor driven by a current typical of the Atlas generator. The nonlinear development of this magnetohydrodynamic (MHD) instability can lead to current disruption. An important challenge for modeling is to predict the maximum magnetic field on a rod surface that can be obtained prior to disruption. This problem can also be generalized to the more complicated moving liner problem. A series of 2-D MHD simulations was performed with the state-of-the-art MHRDR code to conduct a sensitivity study. Results indicate that the development and growth of m = 0 instability is sensitive to the resistivity models used. Furthermore, it was observed that models with lower values of resistivity near the metal-insulator transition produce higher growth-rate sausage instability.IEEE Transactions on Plasma Science 03/2008; · 1.17 Impact Factor -
Article: Radiation magnetohydrodynamic simulation of plasma formed on a surface by a megagauss field.
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ABSTRACT: Radiation magnetohydrodynamic modeling is used to study the plasma formed on the surface of a cylindrical metallic load, driven by megagauss magnetic field at the 1MA Zebra generator (University of Nevada, Reno). An ionized aluminum plasma is used to represent the "core-corona" behavior in which a heterogeneous Z-pinch consists of a hot low-density corona surrounding a dense low-temperature core. The radiation dynamics model included simultaneously a self-consistent treatment of both the opaque and transparent plasma regions in a corona. For the parameters of this experiment, the boundary of the opaque plasma region emits the major radiation power with Planckian black-body spectrum in the extreme ultraviolet corresponding to an equilibrium temperature of 16 eV. The radiation heat transport significantly exceeds the electron and ion kinetic heat transport in the outer layers of the opaque plasma. Electromagnetic field energy is partly radiated (13%) and partly deposited into inner corona and core regions (87%). Surface temperature estimates are sensitive to the radiation effects, but the surface motion in response to pressure and magnetic forces is not. The general results of the present investigation are applicable to the liner compression experiments at multi-MA long-pulse current accelerators such as Atlas and Shiva Star. Also the radiation magnetohydrodynamic model discussed in the paper may be useful for understanding key effects of wire array implosion dynamics.Physical Review E 03/2008; 77(3 Pt 2):036404. · 2.26 Impact Factor -
Article: The Challenge of Wall–Plasma Interaction with Pulsed Megagauss Magnetic Fields
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ABSTRACT: A method is described for choosing experimental parameters in studies of high-energy-density (HED) physics relevant to fusion energy, as well as other applications. An important HED issue for magneto-inertial fusion (MIF) is the interaction of metal pusher materials with megagauss (MG) magnetic fields during liner compression of magnetic flux and fusion fuel. The experimental approach described here is to study a stationary conductor when a pulsed current generates MG fields at the surface, instead of studying the inner surface of a moving liner. This places less demand upon the pulsed power system, and significantly improves diagnostic access. Thus the deceptively simple geometry chosen for this work is that of a z pinch composed of a metal cylinder carrying large current. Consideration of well known stability issues for the z pinch shows that for given peak current and rise time from a particular power supply, there is a minimum radius and thus maximum B field that can be created without disruption of the conductor before peak current. The reasons are reviewed why MG levels of magnetic field, as required for MIF, result in high temperatures and plasma formation at the surface of the metal in response to Ohmic heating. The distinction is noted between the liner regime obtained with cylindrical rods, which have a skin depth small compared to the conductor radius, and the exploding thin-wire regime, which has skin depth larger than the wire radius. A means of diagnostic development is described using a small facility (DPM15) built at the University of Nevada, Reno. It is argued that surface plasma temperature measurements in the 10-eV range are feasible based on the intensity of visible light emission.Journal of Fusion Energy 01/2008; 27(4):235-240. · 0.52 Impact Factor -
Conference Proceeding: Numerical modeling of plasma formation with megagauss magnetic fields
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ABSTRACT: Recently a set of experiments was conducted on thick 1-mm diameter wires (rods) on the Zebra (1MA) machine at the University of Nevada, Reno. The goal of the experiments was to investigate plasma creation on the surface in the presence of megagauss magnetic field. Laser backlighting, photo detectors, and a gated image intensifier were used to measure radial expansion and surface luminosity. A unique type of rod with a machined hourglass shape to eliminate electrode connections was investigated to avoid influence of plasma formed in the vicinity of the usual electrode connections. Reasonably good agreement is found between numerical modeling of radius expansion in time and experimental results obtained from laser diagnostics (shadowgraphs) and intensifier images. Initial efforts are also presented on comparisons between data and a variety of numerical codes used to model this deceptively simple configuration.Pulsed Power Conference, 2007 16th IEEE International; 07/2007 -
Conference Proceeding: Analytic model for wall-heating in pulsed-power driven systems
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ABSTRACT: Pulsed-power experiments can drive very high surface current densities in metallic conductors in time scales on the order of microseconds. The character of magnetic diffusion guarantees that field and current distributions will vary rapidly on these time-scales. We have found an analytic procedure for calculating these distributions in the material, even for time-varying surface conditions. This procedure has been compared with resolved one-dimensional MHD computations, both in the absence of material heating and with the inclusion of this effect. Results are presented.Pulsed Power Conference, 2007 16th IEEE International; 07/2007 -
Conference Proceeding: MHD instabilities in non-equilibrium Z-pinch driven by a multi-megaampere current
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ABSTRACT: Magnetohydrodynamic (MHD) instabilities play a critical role in a number of pulsed power experiments in which multi-megaampere currents melt solid conductor surfaces and turn them into hot plasmas in a matter of microseconds or less. Complex motions that these plasmas exhibit lead to the development and growth of violent MHD instabilities that have the potential of disrupting the currents flowing through the conducting material or of introducing conductor material into locations where such material is not desired. The accelerated boundary of a non-equilibrium Z-pinch driven by a multi-megaampere current exhibits both curvature-driven m=0 (sausage) and Rayleigh-Taylor instabilities. The interplay between these instabilities and the effect it may have on the dynamics of the z-pinch is studied through a number of 2-D magnetohydrodynamic simulations performed with the state-of-the-art MHD code MHRDR. In result of the numerical simulations we have found that even though the magneto RT instability may have been developed during the discharge, the dominant instability for the current non-equilibrium Z pinch is m=0 instability. We have estimated that for the most of the discharge it grows exponentially with a constant growth rate, suggesting that the predictions of the ideal MHD theory can be applied to study the instability development of non-ideal, non-equilibrium Z pinches without any significant error.Pulsed Power Conference, 2007 16th IEEE International; 07/2007 -
Conference Proceeding: Wall Heating and Impurity Mixing Considerations During Magnetic Compression Experiments
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ABSTRACT: We present an analytic treatment of the transport of magnetic field into a metallic material, when the surface field is changing in time. This has many applications in the area of high-current pulsed power. We focus on one of these in this paper, magnetized target fusion (MTF), a simple, potentially inexpensive method of creating burning fusion conditions through fast compression of dense, warm magnetized plasma. Magnetization of the plasma electrons, needed to inhibit thermal transport losses, means that compression, on the order of 10 microseconds (10<sup>-5</sup> seconds), results in large magnetic field compression. Current density, J, proportional to the field gradient in the walls, is also found analytically. Heating in the wall is also a function of etaJ<sup>2</sup>, and so can also be evaluated with these solutions. MTF studies proposed to be conducted at the ATLAS pulsed-power facility (23 MJ, 30 MA, 240 kV), must explicitly determine energy dissipation in the wall. Vaporization, or possibly even melting, of metallic wall material could lead to mixing of such high-Z material with the hot hydrogen plasma. The ensuing radiation losses and plasma cooling would be catastrophic to any MTF scheme.Magagauss Magnetic Field Generation and Related Topics, 2006 IEEE International Conference on; 12/2006 -
Conference Proceeding: The Challenge of Wall-Plasma Interaction with Pulsed MG Fields Parallel to the Wall
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ABSTRACT: Experiments suitable for a variety of pulsed power facilities are being developed to study plasma formation and stability on the surface of typical liner materials in the megagauss (MG) regime. Understanding the plasma properties near the surface is likely to be critical for the design of Magnetized Target Fusion experiments, where the plasma density in the region near the wall can play an important role in setting the transport from hot fuel to the cold boundary. From the perspective of diagnostic access and simplicity, the surface of a stationary conductor with large enough current to generate MG surface field offers advantages compared with studying the surface of a moving liner. This paper reports on recent experiments at UNR that have generated magnetic fields in the range of about 0.2 to 3 MG, which confirm the viability of future experiments planned at Atlas and/or Shiva Star. Diagnostics reported here involve electrical measurements, streak camera photography, and surface luminosity. Additional diagnostic measurements and numerical modeling will be reported in the future.Megagauss magnetic field generation and related topics, 2006 ieee international conference on; 12/2006 -
Conference Proceeding: Modeling of Plasma Formation and Evolution on the Surface of Ohmically Heated Conductors
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ABSTRACT: The surface response to MG fields is important for eventual Magnetized Target Fusion (MTF) experiments " . Recent radiation-hydro numerical simulations in a planar geometry by Garanin et al. show how plasma can be generated through thermal processes on a metal surface. Experiments to study metal plasma formation and stability on the surface of typical liner materials in the MG regime are underway at the University of Nevada at Reno (UNR). Additional experiments on larger facilities such as Atlas and Shiva Star are also planned. We present here our initial modeling of the surface response of aluminum cylindrical conductors, assuming experimentally relevant current rise-times, which determine the ratio of current skin depth relative to conductor radius. Important effects include plasma formation, radiation transport, and the unstable m=0 mode driven by curvature of the magnetic field that holds the surface plasma against the metal. The sensitivity of results to various equation-of-state and resistivity models is also discussed.Megagauss magnetic field generation and related topics, 2006 ieee international conference on; 12/2006 -
Conference Proceeding: Sensitivity of M=0 Growth to EOS and Other Material Properties
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ABSTRACT: Instabilities can affect the quality of flux compression and other high current experiments. The modeling of such experiments involves a number of numerical difficulties. One such difficulty is the selection of proper material property models. This work investigates the effect of different EOS and other material property models on the development of the m=0 instability on a single cylindrical conductor driven by a current typical of the Atlas generator. The nonlinear development of this magnetohydrodynamic instability can lead to current disruption. An important challenge for modeling is to predict the maximum magnetic field on the rod surface that can be obtained prior to disruption. This problem can also be generalized to the more complicated moving liner problem. A series of 2-D magnetohydrodynamic simulations are performed with the state-of-the-art MHRDR code to conduct a sensitivity study.Magagauss Magnetic Field Generation and Related Topics, 2006 IEEE International Conference on; 12/2006 -
Article: Stability analysis and numerical simulation of a hard-core diffuse z pinch during compression with Atlas facility liner parameters
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ABSTRACT: In the 'metal liner' approach to magnetized target fusion (MTF), a preheated magnetized plasma target is compressed to thermonuclear temperature and high density by externally driving the implosion of a flux conserving metal enclosure, or liner, which contains the plasma target. As in inertial confinement fusion, the principal fusion fuel heating mechanism is pdV work by the imploding enclosure, called a pusher in ICF. One possible MTF target, the hard-core diffuse z pinch, has been studied in MAGO experiments at VNIIEF and is one possible target being considered for experiments on the Atlas pulsed power facility. Numerical MHD simulations show two intriguing and helpful features of the diffuse z pinch with respect to compressional heating. First, in two-dimensional simulations the m = 0 interchange modes, arising from an unstable pressure profile, result in turbulent motions and self-organization into a stable pressure profile. The turbulence also gives rise to convective thermal transport, but the level of turbulence saturates at a finite level, and simulations show substantial heating during liner compression despite the turbulence. The second helpful feature is that pressure profile evolution during compression tends towards improved stability rather than instability when analysed according to the Kadomtsev criteria. A liner experiment is planned for Atlas to study compression of magnetic flux without plasma, as a first step. The Atlas geometry is compatible with a diffuse z pinch, and simulations of possible future experiments show that kiloelectronvolt temperatures and useful neutron production for diagnostic purposes should be possible if a suitable plasma injector is added to the Atlas facility.Nuclear Fusion 08/2005; 45(9):1148. · 4.09 Impact Factor -
Conference Proceeding: A Series of Joint VNIIEF/LANL Explosive Magnetic Experiments RHSR-0,1,2 on Radiographic Study of Perturbations Growth at a Copper Liner Boundary with Polyethylene or Water
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ABSTRACT: In the three joint VNIIEF/LANL experiments RHSR-0,1,2 with a disk EMG and a three-layer liner system (Al-dielectric-Cu) a method of radial radiography was used to study growth of perturbations amplitude at the boundary between copper layer and polyethylene (in experiments RHSR-0,1) and water (in experiment RHSR-2); the growth occurs during the evolution of the Raleigh-Taylor instability of this boundary.Pulsed Power Conference, 2005 IEEE; 07/2005 -
Conference Proceeding: Explosive Magnetic Device with a Three-Layered Liner for Radiographic Study of Dynamic Strength of Materials
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ABSTRACT: This paper presents the construction-technology schematic of the device comprising the helical and disk EMGs with a three-layered cylindrical liner (Al-dielectric-Cu) designed for experiments RHSR-0,1,2 at the current of 33-35 MA. Polyethylene or water was used as a dielectric layer. The experiments tested successfully the idea to study the dynamic strength of materials by X-raying the growth of amplitude of axisymmetric sinusoidal perturbations machined initially on the outer surface of the examined inner layer of the liner.Pulsed Power Conference, 2005 IEEE; 07/2005 -
Article: Self-organization observed in numerical simulations of a hard-core diffuse Z pinch
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ABSTRACT: A hard-core Z-pinch plasma (metal conductor on axis) with an unstable pressure profile can rearrange itself through m = 0 interchange motions to produce a stable pressure profile. In this paper the self-organization process is demonstrated in numerical simulations of an experimental plasma formation process, using a two-dimensional compressible two-fluid magnetohydrodynamic code. The stabilization process results in m = 0 turbulence, which has a level of kinetic energy that is saturated typically at a few percent of the plasma thermal energy. Using idealized initial conditions for simulations with an axial sinusoidal density perturbation, it is possible to observe in detail the development of instability and then turbulence. At first a coherent Rayleigh–Taylor type motion grows exponentially, with localized isentropic heating and cooling associated with the motion. Then the bubble and spike structure breaks up and incoherent m = 0 turbulence develops.Physics of Plasmas 04/2005; 12(4):042312-042312-9. · 2.15 Impact Factor -
Article: Results of a 100-megaampere liner implosion experiment
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ABSTRACT: A very high-current liner implosion experiment was conducted, using an explosive magnetic-compression generator (EMG) to deliver a peak current of 102 ± 3 MA, to implode a 4.0-mm-thick aluminum liner. Analysis of experimental data showed that the inner surface of the liner had attained a velocity of between 6.8-8.4 km/s, consistent with detailed numerical calculations. Both calculations and data were consistent with a final liner state that was still substantially solid at target impact time and had a total kinetic energy of over 20 MJ.IEEE Transactions on Plasma Science 11/2004; · 1.17 Impact Factor
Top co-authors
Top Journals
Institutions
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2011
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Lawrence Livermore National Laboratory
Livermore, CA, USA
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2004–2010
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University of Nevada, Reno
- Department of Physics
Reno, NV, USA
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1989–2003
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Los Alamos National Laboratory
- Plasma Physics Group
Los Alamos, NM, USA
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