M. R. Douglas

Los Alamos National Laboratory, Los Alamos, California, United States

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Publications (99)80.43 Total impact

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    ABSTRACT: We report results of the experimental campaign which studied the initiation, implosion dynamics and radiation yield of tungsten wire arrays as a function of the wire number. The wire array dimensions and mass were those of interest for the Z-pinch driven ICF program. An optimization study of the X-ray emitted peak power, rise time and FWHM was effectuated by varying the wire number while keeping the total array mass constant and equal to ∼5.8 mg. The driver utilized is the ∼20 MA Z accelerator in its usual short pulse mode of 100 ns. We studied single arrays of 20 mm diameter and 1 cm height. The smaller wire number studied was 30 and the largest 600. It appears that 600 is the highest achievable wire number with present day's technology. Radial and axial diagnostics were utilized including crystal monochromatic X-ray backlighter. An optimum wire number of ∼370 was observed which is very close to the routinely utilized 300 for the ICF program in Sandia.
    Full-text · Article · Nov 2011 · Physics of Plasmas
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    ABSTRACT: In this paper, we report the results of an experimental campaign to study the initiation, implosion dynamics and radiation yield of tungsten wire arrays as a function of the wire number. An optimization study of the X-ray emitted peak power, rise time and FWHM was effectuated by varying the wire number while keeping the total array mass constant at ~5.8 mg. The driver used was the ~20 MA Z-accelerator, in its usual short pulse mode of 100 ns. We studied single arrays of diameter 20 mm and height 10 mm. The smaller wire number studied was 30 and the largest 600. It appears that 600 is the highest wire number achievable with present-day technology. Radial and axial diagnostics were used, including a crystal monochromatic X-ray backlighter. An optimum wire number of ~370 was observed, which is very close to the number (300) routinely used for the ICF program in Sandia.
    No preview · Article · May 2005 · Plasma Devices and Operations
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    ABSTRACT: We report results of the experimental campaign which studied the initiation, implosion dynamics and radiation yield of tungsten wire arrays as a function of the wire number. The wire array dimensions and mass were those of interest for the Z-pinch driven ICF program. An optimization study of the X-ray emitted peak power, rise time and FWHM was effectuated by varying the wire number while keeping the total array mass constant and equal to ~5.8 mg. The driver utilized is the ~20 MA Z accelerator in its usual short pulse mode of 100 ns. We studied single arrays of 20 mm diameter and 1 cm height. The smaller wire number studied was 30 and the largest 600. It appears that 600 is the highest achievable wire number with present day's technology. Radial and axial diagnostics were utilized including crystal monochromatic X-ray backlighter. An optimum wire number of ~370 was observed which is very close to the routinely utilized 300 for the ICF program in Sandia.
    No preview · Conference Paper · Jan 2004
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    ABSTRACT: We have just completed an experimental campaign to study the initiation, implosion dynamics, and radiation yield of tungsten wire arrays as a function of the wire number. The wire array dimensions and mass were those of interest for the z-pinch driven ICF program. An optimization study of the x-ray emitted peak power, rise time, and FWHM was effectuated by varying the wire number while keeping the total array mass constant and equal to ˜5.8mg. The driver utilized is the ˜20-MA Z accelerator in its usual short pulse mode of 100ns. We studied single arrays of 20-mm diameter and 1-cm height. The smaller wire number studied was 30 and the largest 600. It appears that 600 is the highest achievable wire number with present technology. Radial and axial diagnostics were utilized including crystal monochromatic x-ray backlighter. An optimum wire number of ˜370 was observed, which is very close to the routinely utilized 300 for the ICF program in Sandia. Experimental results will be presented and compared with numerical simulation
    No preview · Article · Oct 2003
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    ABSTRACT: Absorption spectroscopy measurements of the time-dependent heating of thin foils exposed to intense z-pinch radiation sources are presented. These measurements and their analysis provide valuable benchmarks for, and insights into, the radiative heating of matter by x-ray sources. Z-pinch radiation sources with peak powers of up to 160 TW radiatively heated thin plastic-tamped aluminum foils to temperatures approximately 60 eV. The foils were located in open slots at the boundary of z-pinch hohlraums surrounding the pinch. Time-resolved Kalpha satellite absorption spectroscopy was used to measure the evolution of the Al ionization distribution, using a geometry in which the pinch served as the backlighter. The time-dependent pinch radius and x-ray power were monitored using framing camera, x-ray diode array, and bolometer measurements. A three-dimensional view factor code, within which one-dimensional (1D) radiation-hydrodynamics calculations were performed for each surface element in the view factor grid, was used to compute the incident and reemitted radiation flux distribution throughout the hohlraum and across the foil surface. Simulated absorption spectra were then generated by postprocessing radiation-hydrodynamics results for the foil heating using a 1D collisional-radiative code. Our simulated results were found to be in good general agreement with experimental x-ray spectra, indicating that the spectral measurements are consistent with independent measurements of the pinch power. We also discuss the sensitivity of our results to the spectrum of the radiation field incident on the foil, and the role of nonlocal thermodynamic equilibrium atomic kinetics in affecting the spectra.
    No preview · Article · Nov 2002 · Physical Review E
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    ABSTRACT: Dynamic hohlraum experiments have been fielded on the Z accelerator at Sandia National Laboratories that demonstrate their usefulness as a radiation source for high energy density physics applications [1]. In these experiments, radiation is generated via the impact of a high wire number tungsten array onto a solid cylindrical foam target. As the tungsten/foam interface collapses, some fraction of the radiation is trapped inside the imploding hohlraum, eventually exiting through an axial hole centered on the stagnation axis. The radiation source produced by this method has a measured temperature drive of 215 (+/-10)eV and a total radiated energy of 40 (+/-8)kJ for a 2.4-mm exit hole. Radiation magnetohydrodynamic simulations have been carried out to characterize this source and the results have been compared with experimental data. Most of these simulations have focused in detail on the wire array implosion dynamics up to the foam surface and intial impact with the foam. Although some quantitative and qualitative agreement has been seen between simulation and experiment, there are still many questions surrounding the evolution of the tungsten/foam interface, the radiation propagation in the foam, and the radiation properties at the exit hole, where electrode effects may be important. Here we present preliminary calculations further investigating these issues. 1.Sanford et al., in press, Aug 2002, Phys. Plasmas.
    No preview · Article · Nov 2002
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    ABSTRACT: Three hohlraum concepts are being pursued at Sandia National Laboratories (SNL) to investigate the possibility of using pulsed power driven magnetic implosions (Z pinches) to drive targets capable of fusion yields in the range 200-1000 MJ. This research is being conducted on SNL's Z facility, which is capable of driving peak currents of 20 MA in various Z pinch load configurations that produce implosion velocities as high as 7.5 × 107cm/s, X ray energies of 1-2 MJ and X ray powers of 100-250 TW. The first concept, denoted dynamic hohlraum, has achieved a temperature of 180 ± 14 eV in a configuration suitable for driving capsules. In addition, this concept has also achieved a temperature of 230 ± 18 eV in an arrangement suitable for driving an external hohlraum. The second concept, denoted static walled hohlraum, has achieved temperatures of ~80-100 eV. Experimental investigation of the third concept, denoted Z pinch driven hohlraum, has recently begun. The article discusses each of these hohlraum concepts and provides an overview of the experiments that have been conducted on these systems to date.
    Full-text · Article · May 2002 · Nuclear Fusion
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    ABSTRACT: We have performed realistic two-dimensional (2-D) r-θ resistive MHD simulations of high-current aluminum wire array initiation and implosion. These show only a moderate differentiation of wire plasma into a warm dense core and a hot diffuse corona. Wire plasmas in 28-wire array simulations implode without forming a shell; those in 56-wire simulations first merge but then separate. As both implode, thread-like plasmas settle into valleys formed across the field lines by the thread mass. Thus, shell formation does not smooth the initial wire asymmetry, because the r-θ Rayleigh-Taylor instability amplifies it. This argues against shell-formation as the primary explanation for the observed effect of increased wire number on radiation power. We have also performed three-dimensional (3-D) ideal MHD simulations that continue those 2-D simulations; they start with a fully consistent MHD state. These simulations, perturbed between the 2-D and 3-D phases, show that azimuthally uncorrelated 3-D perturbations-appropriate for wires-grow more slowly than fully azimuthally correlated 2-D r-z perturbations. Further, the uncorrelated perturbation growth rate is smaller for 56 wires than for the 28, as the magnetic field couples more plasma threads over the same distance. These 3-D effects may explain the observed radiation power improvement with increased wire number.
    No preview · Article · May 2002 · IEEE Transactions on Plasma Science
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    ABSTRACT: Experiments performed on the 8-MA Saturn accelerator to investigate the effects of interwire gap spacing on long-implosion-time Z pinches have resulted in the observation of a regime of optimal wire number. The experiments varied the wire number of 40 and 32 mm diam arrays, resulting in interwire gaps from 3.9 to 0.36 mm, with fixed mass and length. aluminum K-shell powers up to 3.4 TW were measured, with long, slow rising, lower power x-ray pulses for interwire gaps greater than 2.2 mm and less than 0.7 mm, and short, fast rising, higher power pulses for interwire gaps in the range 0.7-2.2 mm.
    No preview · Article · Mar 2002 · Physical Review Letters
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    ABSTRACT: Summary form only given, as follows. We are pursuing a systematic experimental investigation of the effect of the tungsten interwire gap spacing (IWG) on initiation, implosion dynamics and quality of the 100-ns fast wire array z-pinch. The wire array dimensions and mass are those of interest for the z-pinch driven ICF program. Namely, the diameter is 20mm, the height 10mm, and the mass -5.8mg. Up to now, wire arrays containing 50, 120, 194, 300, and 500 wires have been imploded. We are currently continuing the experiments with 30, 90, and 300 wire arrays. Most of the Z accelerator radial line of sight diagnostics were fielded, including XRD's, PCD's, bolometers, calorimeters, spectrometers, and X-ray imaging time resolved pinhole cameras. In the new experiments axial diagnostics will be added. The X-ray radiated energy and power increase with wire number while the rise time and FWHM decrease. Analysis of the X-ray images suggests that the wires in the 50 wire array remain discreet and visible (not merged) until at least 20ns before pinch time while with 120 and higher wire number, wires appear merged at pinch times. Experimental results will be presented, analyzed and compared with numerical simulations.
    No preview · Conference Paper · Feb 2002
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    ABSTRACT: In order to estimate the radiated power that can be expected from the next-generation z-pinch driver such as ZR at 28 MA, current-scaling experiments have been conducted on the 18-MA driver Z. We report on the current scaling of single 40-mm diameter tungsten 240-wire arrays with a fixed 110-ns implosion time. The wire diameter is decreased in proportion to the load current. The load current is reduced by reducing the charge voltage on the Marx banks. On one shot firing only 3 of the 4 levels of the Z machine further reduced the load current. The radiated energy scales as the current squared as expected but the radiated power scales as the current to the 3.5 power due to increased pinch instability at lower current. As the current is reduced the rise-time of the x-ray pulse increases and at the lowest current value of 10.4 MA a shoulder appears on the leading edge of the x-ray pulse. We will report on experiments in February 2002 which will attempt to image the pinch along the axis to determine the nature of the reduced stability at lower currents.
    No preview · Conference Paper · Feb 2002
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    ABSTRACT: Summary form only given, as follows. In the years since the 20 MA Z accelerator has come online, many experiments have been performed to study the radiation emitted from wire array Z-pinches. Several K-shell sources have been studied in recent years at Z, including aluminum, titanium, stainless steel, nickel, and copper. Observations from these experiments show that low wire number (interwire gaps >0.7 mm) nested arrays produce higher powers with narrower pulsewidths and faster risetimes than single wire arrays. They also produce smaller diameter pinches with improved axial uniformity, and higher plasma temperatures and densities. Theory suggests that this improvement could result from the mitigation of the Rayleigh-Taylor instability, and reduced asymmetry development due to current switch between arrays. Spectral analyses indicate that the radiation output in the K-shell is limited due to low densities and low mass fractions, however. To investigate one method for increasing the density on-axis, low Z foam targets have been used at the center of nested wire arrays. The foams could lead to additional improvements in the stagnation and implosion stability. TPX foams with densities of 10 - 30 mg/cm3 and diameters of 2.0-2.8 mm were mounted at the center of 50 mm diameter nested nickel-clad titanium wire arrays. This nested wire array configuration has been fielded numerous times with no target and therefore provides excellent comparative data. The presence of the foam target resulted in an enhancement of the total radiated power from 120 TW (no foam) to 160 TW (30 mg/cm3). The Kshell power increased from 8 TW to 11 TW. These improvements likely result from decreases in pulsewidth that were observed; the K-shell FWHM decreased from 7ns (no foam) to 4 ns (30 mg/cm). The risetimes were relatively constant. In general, the pulsewidth decreased, and the power increased, with increased foam density. The radiated yields remained similar to the loads with no foam, however. In this paper, the results of the foam target experiments will be presented and compared to nested and single aff ay experiments without targets.
    No preview · Article · Jan 2002
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    ABSTRACT: The standard 20-mm tungsten wire array configuration that is currently used on the Z accelerator is a design that was developed to optimize radiated power based on height and mass only. Over the years, a number of experiments have been conducted which indicate that wire array power should also be optimized based on wire number. In particular, experimental results show that higher number wire arrays provide increasingly higher powers for broadband emissions. A number of effects may together influence this observed trend and focus on the wire initiation/pre-acceleration evolution. In particular, the ability to initiate the wires themselves, the amount of plasma precursor produced, and the global magnetic field structure, are all dependent to some degree on the wire number. To this end, a recent experimental campaign was carried out to investigate the effect of wire number on a 20-mm diameter, 10-mm high tungsten wire array, keeping the array mass at 5.8 mg. Wire numbers ranged from 50 to 500 wires, corresponding to wire diameters between 8.8 mum and 27 mum, and interwire gap spacings of 1.23 mm down to 0.12 mm. Numerical simulations investigating the role of wire number for this configuration are in progress and will be presented along with a summary of the experimental results.
    No preview · Article · Oct 2001
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    ABSTRACT: A systematic experimental investigation of the effect of the tungsten interwire gap spacing (IWG) on initiation, implosion dynamics and quality of the 100-ns fast wire array z-pinch has been conducted. The wire array dimensions and mass are those of interest for the z-pinch driven ICF program. Namely, the diameter is 20mm, the height 10mm, and the mass 5.8mg. Up to now, wire arrays containing 50, 120, 194, 300, and 500 wires have been imploded. Most of the Z accelerator radial line of sight diagnostics were fielded, including XRD's, PCD's, bolometers, calorimeters, spectrometers, and x-ray imaging time resolved pinhole cameras. The x-ray radiated energy and power increases with wire number while the rise time and FWHM decreases. Preliminary analysis of the x-ray images suggests that the wires in the 50 wire array remain discreet and visible (not merged) until pinch time while with 120 and higher wire number, wire appear merged. Experimental results will be presented and analyzed and compared with numerical simulations. * Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94-AL85000.
    No preview · Article · Oct 2001
  • M.R.  DOUGLAS  · J.S.  DE GROOT  · R.B.  SPIELMAN 
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    ABSTRACT: The magneto-Rayleigh–Taylor (MRT) instability limits the performance of dynamic z pinches. This instability develops at the plasma-vacuum/field interface, growing in amplitude throughout the implosion, thereby reducing the peak plasma velocity and spatial uniformity at stagnation. MRT instabilities are believed to play a dominant role in the case of high wire number arrays, gas puffs and foils. In this article, the MRT instability is discussed in terms of initial seeding, linear and nonlinear growth, experimental evidence, radiation magnetohydrodynamic simulations, and mitigating schemes. A number of experimental results are presented, where the mitigating schemes have been realized. In general, the problem is inherently three dimensional, but two-dimensional simulations together with theory and experiment enhance our physical understanding and provide insight into future load design.
    No preview · Article · Sep 2001 · Laser and Particle Beams
  • C.  DEENEY  · C.A.  COVERDALE  · M.R.  DOUGLAS 
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    ABSTRACT: In the past few years, long-implosion-time (150 ns to 200 ns) z pinches have made significant progress in terms of their ability to make kilovolt X rays or to produce high-power subkilovolt emissions. These advances are enabling the community to utilize lower-cost pulsed power designs for high current X-ray facilities. The advances will be reviewed in historical context in this paper, plus some new physics regimes and understanding resulting from this work will be highlighted.
    No preview · Article · Jun 2001 · Laser and Particle Beams
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    ABSTRACT: The authors have constructed a quasi-analytic model of the dynamic hohlraum. Solutions only require a numerical root solve, which can be done very quickly. Results of the model are compared to both experiments and full numerical simulations with good agreement. The computational simplicity of the model allows one to find the behavior of the hohlraum temperature as a function the various parameters of the system and thus find optimum parameters as a function of the driving current. The model is used to investigate the benefits of ablative standoff and axial convergence.
    Full-text · Article · May 2001 · Physics of Plasmas
  • T.J. Nash · M.R. Douglas
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    ABSTRACT: The magnetic implosion of a high-Z quasi-spherical shell filled with DT fuel by the 20-MA Z accelerator can heat the fuel to near-ignition temperature. The attainable implosion velocity on Z for an 8 mm diameter quasi-spherical shell, 13-cm/5s, is fast enough that thermal losses from the fuel to the shell are small. The fuel is initially heated by an ion acoustic wave to 200-eV after a convergence of 4. Thereafter the implosion is adiabatic and the temperature increases as the square of the convergence. To reach the ignition temperature of 5-keV an additional convergence of 5 is required. The implosion dynamics of the quasi-spherical implosion is modeled with the 2-D radiation hydrodynamic code LASNEX. LASNEX shows the main instability in the implosion to be surface mass flow from the higher latitudes to the equator that limits the convergence to 20. The LASNEX simulation shows an 8-mm diameter quasi-spherical tungsten shell weighing 20 mg on Z driving 6-atmospheres of DT fuel nearly to ignition at 3.5-keV with a convergence of 20. Simulations with MACH2 that determine the limits of convergence due to the Rayleigh-Taylor instability will be presented. Results of the simulations with LASNEX and proposals for experimental measurements will be presented
    No preview · Conference Paper · Feb 2001
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    ABSTRACT: Summary form only given, as follows. The advent of nested wire arrays has enabled far higher quality and high power Z-pinch implosions but questions have been raised on the exact mechanisms by which nested arrays improve the implosion dynamics. In a series of experiments on the Saturn generator, we have imploded high and low wire number nested arrays. By using either pure aluminum (Al 1100) or Al:Mg alloy (Al 5056) in the inner or outer arrays, we can perform tracer spectroscopy. Tracer spectroscopy has been an important diagnostic in laser-plasma interactions and there have been some very successful applications to Z-pinches including coated wires or doped gas puffs by Sze, et al.(2000). In these recent nested array experiments, we show that the wire number does effect the degree of mixing that occurs between the inner and outer. Analyses indicate that for low-wire number case (28 onto 14 wires) the mass of the outer forms the hot emitting region on the stagnated pinch. This is contrary to results from gas puffs. We present the comparison of the low- and high-wire number arrays
    No preview · Article · Jan 2001 · Electroencephalography and Clinical Neurophysiology/Electromyography and Motor Control
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    ABSTRACT: Summary form only given. Magnetized target fusion (MTF) relies on magnetic field suppression of thermal transport to achieve fusion conditions at relatively low driver power. One method proposed for MTF uses an imploding liner which starts at solid density to compress a hot magnetized plasma. Analytic methods and one and two dimensional magnetohydrodynamic simulations are being used to study this plasma liner compression approach. Plasma from the liner walls represents a contaminant that can increase radiation losses and lower plasma temperatures below desired values. As part of this effort are we are investigating the generation and evolution of such plasmas. Energy input to the liner from thermal conduction and joule heating from both the magnetized plasma and the driving magnetic field are under study to determine their contributions to the production of contaminant and the interaction of these plasmas with the hot fusion plasma. Results from these ongoing calculations will be presented
    No preview · Article · Jan 2001 · Electroencephalography and Clinical Neurophysiology/Electromyography and Motor Control