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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Modeling of the merging of two colliding field reversed configuration plasmoids

The field reversed configuration (FRC) is one of the candidate plasma targets for the magneto-inertial fusion, and a high temperature FRC can be formed by using the collision-merging technology. Although the merging process and mechanism of FRC are quite complicated, it is thinkable to build a simple model to investigate the macroscopic equilibrium parameters including the density, the temperature and the separatrix volume, which may play an important role in the collision-merging process of FRC. It is quite interesting that the estimates of the related results based on our simple model are in agreement with the simulation results of a two-dimensional magneto-hydrodynamic code (MFP-2D), which has being developed by our group since the last couple of years, while these results can qualitatively fit the results of C-2 experiments by Tri-alpha energy company. On the other hand, the simple model can be used to investigate how to increase the density of the merged FRC. It is found that the amplification of the density depends on the poloidal flux-increase factor and the temperature increases with the translation speed of two plasmoids.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Scaling law of electron confinement in a zero beta polywell device

Orbital theory simulation was applied to an electron trap that uses a cube shaped magnetic cusp known as a Polywell device. The purpose of this device is to create a virtual cathode in order to achieve nuclear fusion using inertial electrostatic confinement. Analytical expressions of the electron confinement time and average position within the device were obtained in terms of the current in the field coils, the dimensions of the device, and the kinetic energy of the electrons. Comparisons with numerical simulations showed good agreement over a parameter range that spanned several orders of magnitude for the current. In addition, power loss from electrons exiting the trap was estimated in order to obtain minimum power requirement to maintain a virtual cathode within the device.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Electrical design analysis and breakdown voltage test aspects of indigenously developed electrical breaks at Cryo temperatures

Electrical insulation breaks are very critical component of large-scale fusion devices employing superconducting magnets and are used to insulate electrically the coil and the cryogenic supply line (kept at ground potential). The electrical insulation of breaks consists of the composites insulations, G-10 GFRP (Glass fiber reinforced plastic), cryogenic compatible epoxy and S-glass boron free fiber in air and helium environment under vacuum. To optimize the design parameters, the detailed electrical analysis have been carried out using the electrostatic solid axi-symmetric model by COMSOL 4.1 multiphysics software for electrodes separation, electrical field strength as well as flashover phenomenon between two electrodes with composite insulator material have been analyzed at different surfaces and contours along with by varying gaps between SS electrodes. We have carried out the high voltage breakdown test (0-35) kV, insulation resistance measurement at 0-5 kV test voltage in Paschen condition of (10{sup 3} -10{sup -5}) mbar in helium gas and air environment at 300 K and 77 K experimentally on in-house developed insulation breaks. (author)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Manufactured solutions for the three-dimensional Euler equations with relevance to Inertial Confinement Fusion

We present a set of manufactured solutions for the three-dimensional (3D) Euler equations. The purpose of these solutions is to allow for code verification against true 3D flows with physical relevance, as opposed to 3D simulations of lower-dimensional problems or manufactured solutions that lack physical relevance. Of particular interest are solutions with relevance to Inertial Confinement Fusion (ICF) capsules. While ICF capsules are designed for spherical symmetry, they are hypothesized to become highly 3D at late time due to phenomena such as Rayleigh–Taylor instability, drive asymmetry, and vortex decay. ICF capsules also involve highly nonlinear coupling between the fluid dynamics and other physics, such as radiation transport and thermonuclear fusion. The manufactured solutions we present are specifically designed to test the terms and couplings in the Euler equations that are relevant to these phenomena. Example numerical results generated with a 3D Finite Element hydrodynamics code are presented, including mesh convergence studies.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Fokker–Planck kinetic modeling of suprathermal α-particles in a fusion plasma

We present an ion kinetic model describing the transport of suprathermal α-particles in inertial fusion targets. The analysis of the underlying physical model enables us to develop efficient numerical methods to simulate the creation, transport and collisional relaxation of fusion reaction products (α-particles) at a kinetic level. The model assumes spherical symmetry in configuration space and axial symmetry in velocity space around the mean flow velocity. A two-energy-scale approach leads to a self-consistent modeling of the coupling between suprathermal α-particles and the thermal bulk of the imploding plasma. This method provides an accurate numerical treatment of energy deposition and transport processes involving suprathermal particles. The numerical tools presented here are then validated against known analytical results. This enables us to investigate the potential role of ion kinetic effects on the physics of ignition and thermonuclear burn in inertial confinement fusion schemes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Effect of transverse magnetic field on laser produced plasma expansion into vacuum

A one-dimensional time-dependent magneto-hydrodynamic ideal model is used to investigate the dynamics of initially magnetized laser produced plasma expansion into vacuum, in the context of inertial fusion. The plasma is assumed to be fully ionized and in local thermodynamic equilibrium (LTE), allowing all charged particles to have the same temperatures. Self-similar solution shows that the density, velocity, and temperature increase with the strength of the magnetic field. The transverse magnetic field causes significant changes in the plasma expansion dynamics, including the plasma confinement. The plasma velocity increasing is also observed and the temperature is found to be larger compared to temperature in un-magnetized case.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Isothermal, mass-limited rarefactions in planar and spherical geometry

Solutions are developed for isothermal, mass-limited rarefactions in which the temperature is held constant by continued heating. The case of spatially constant temperature and fixed total energy is also revisited. These solutions are useful in the context of experiments in which plasmas are continuously heated for long periods (up to tens of ns) by present-day lasers or hohlraums.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Using time-integrated K{sub {alpha}} images to study refluxing and the extent of pre-plasmas in intense laser-plasma experiment

We report the results of an experimental and numerical modeling study of the formation of time-integrated K{sub {alpha}} images by electrons excited during an intense laser-plasma interaction. We report the use of the spatial structure of time-integrated K{sub {alpha}} images to quantitatively characterize the pre-plasma profile near the critical surface and to verify the near elimination of back-surface refluxing from targets when a thick layer of a low-Z material is attached to the back. The time integrated K{sub {alpha}} images are found to be sensitive to the relative separation between the critical surface and the bulk target, permitting a single parameter exponential pre-plasma scale length to be determined by fitting to experimental results. The refluxed electrons affect different parts of the K{sub {alpha}} images in a manner that varies depending on the location of the refluxing. We use these properties to characterize refluxing also by fitting to experimental results. Experiments were performed using the Titan laser at the Lawrence Livermore National Laboratory and the simulations used a customized version of the hybrid-PIC code, LSP. We find good quantitative match between experiment and simulation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Atomic mix in directly driven inertial confinement implosions

Directly driven implosions on the Omega laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] have measured the presence of atomic mix using D+T neutron yield rates from plastic capsules with and without deuterated layers, and a nearly pure tritium fuel containing 0.7% deuterium. In 15, 19, and 24 {mu}m thick plastic shells, D+T neutron yields increased by factors of 86, 112, and 24 when the 1.2 {mu}m thick inner layer was deuterated. Based on adjusting a fully atomic mix modvfel to fit yield degradation in the un-deuterated capsule and applying it to the capsule with the deuterated layer, atomic mixing accounts for 40-75% of the yield degradation due to mix. For the first time, the time dependence of mixed mass was measured by the ratio of the yield rates from both types of capsules. As expected, the amount of mix grows throughout the D+T burn.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Wire number dependence of the implosion dynamics, stagnation, and radiation output of tungsten wire arrays at Z driver

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 Inertial Confinement Fusion (ICF) program. An optimization study of the x-ray emitted peak power, rise time, and full width at half maximum was effectuated by varying the wire number while keeping the total array mass constant and equal to {approx}5.8 mg. The driver utilized was the {approx}20-MA Z accelerator before refurbishment 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 {approx}375 was observed which was very close to the routinely utilized 300 for the ICF program in Sandia.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Opacity measurement of a gold plasma at T{sub e} = 85 eV

The opacity of a gold plasma at the temperature of 85 eV and density of 0.02 g/cm{sup 3} was measured over the energy range from 150 eV to 1200 eV. The gold sample was heated by thermal x-ray radiation generated with a foam-baffled gold cavity. The sample transmission was obtained from the backlight, absorption and self-emission spectra measured by a time-gated, spatially resolved grating spectrometer, with the backlight and absorption spectra being measured simultaneously in a single shot and the self-emission in another shot. The temperature and density of the gold absorber were determined by the hydrodynamic simulation with Multi-1D code, which was partially tested by the reemission radiative flux measurements of the heated sample. This work permits the first test of opacity models over the photon energy range that dominates the Rosseland mean opacity at the temperature of interest for the inertial confinement fusion.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Bounce-free spherical hydrodynamic implosion

In a bounce-free spherical hydrodynamic implosion, the post-stagnation hot core plasma does not expand against the imploding flow. Such an implosion scheme has the advantage of improving the dwell time of the burning fuel, resulting in a higher fusion burn-up fraction. The existence of bounce-free spherical implosions is demonstrated by explicitly constructing a family of self-similar solutions to the spherically symmetric ideal hydrodynamic equations. When applied to a specific example of plasma liner driven magneto-inertial fusion, the bounce-free solution is found to produce at least a factor of four improvement in dwell time and fusion energy gain.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Using high-intensity laser-generated energetic protons to radiograph directly driven implosions

The recent development of petawatt-class lasers with kilojoule-picosecond pulses, such as OMEGA EP [L. Waxer et al., Opt. Photonics News 16, 30 (2005)], provides a new diagnostic capability to study inertial-confinement-fusion (ICF) and high-energy-density (HED) plasmas. Specifically, petawatt OMEGA EP pulses have been used to backlight OMEGA implosions with energetic proton beams generated through the target normal sheath acceleration (TNSA) mechanism. This allows time-resolved studies of the mass distribution and electromagnetic field structures in ICF and HED plasmas. This principle has been previously demonstrated using Vulcan to backlight six-beam implosions [A. J. Mackinnon et al., Phys. Rev. Lett. 97, 045001 (2006)]. The TNSA proton backlighter offers better spatial and temporal resolution but poorer spatial uniformity and energy resolution than previous D{sup 3}He fusion-based techniques [C. Li et al., Rev. Sci. Instrum. 77, 10E725 (2006)]. A target and the experimental design technique to mitigate potential problems in using TNSA backlighting to study full-energy implosions is discussed. The first proton radiographs of 60-beam spherical OMEGA implosions using the techniques discussed in this paper are presented. Sample radiographs and suggestions for troubleshooting failed radiography shots using TNSA backlighting are given, and future applications of this technique at OMEGA and the NIF are discussed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Development of the large neutron imaging system for inertial confinement fusion experiments

Inertial confinement fusion (ICF) requires a high resolution ({approx}10 {mu}m) neutron imaging system to observe deuterium and tritium (DT) core implosion asymmetries. A new large (150 mm entrance diameter: scaled for Laser MegaJoule [P. A. Holstein, F. Chaland, C. Charpin, J. M. Dufour, H. Dumont, J. Giorla, L. Hallo, S. Laffite, G. Malinie, Y. Saillard, G. Schurtz, M. Vandenboomgaerde, and F. Wagon, Laser and Particle Beams 17, 403 (1999)]) neutron imaging detector has been developed for such ICF experiments. The detector has been fully characterized using a linear accelerator and a {sup 60}Co {gamma}-ray source. A penumbral aperture was used to observe DT-gas-filled target implosions performed on the OMEGA laser facility. [T. R. Boehly, D. L. Brown, R. S. Craxton, R. L. Keck, J. P. Knauer, J. H. Kelly, T. J. Kessler, S. A. Kumpan, S. J. Loucks, S. A. Letzring, F. J. Marshall, R. L. McCrory, S. F. B. Morse, W. Seka, J. M. Soures, and C. P. Verdon, Opt. Commun. 133, 495 (1997)] Neutron core images of 14 MeV with a resolution of 15 {mu}m were obtained and are compared to x-ray images of comparable resolution.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Hot-spot mix in ignition-scale implosions on the NIF

Ignition of an inertial confinement fusion (ICF) target depends on the formation of a central hot spot with sufficient temperature and areal density. Radiative and conductive losses from the hot spot can be enhanced by hydrodynamic instabilities. The concentric spherical layers of current National Ignition Facility (NIF) ignition targets consist of a plastic ablator surrounding a thin shell of cryogenic thermonuclear fuel (i.e., hydrogen isotopes), with fuel vapor filling the interior volume [S. W. Haan et al., Phys. Plasmas 18, 051001 (2011)]. The Rev. 5 ablator is doped with Ge to minimize preheat of the ablator closest to the DT ice caused by Au M-band emission from the hohlraum x-ray drive [D. S. Clark et al., Phys. Plasmas 17, 052703 (2010)]. Richtmyer-Meshkov and Rayleigh-Taylor hydrodynamic instabilities seeded by high-mode () ablator-surface perturbations can cause Ge-doped ablator to mix into the interior of the shell at the end of the acceleration phase [B. A. Hammel et al., Phys. Plasmas 18, 056310 (2011)]. As the shell decelerates, it compresses the fuel vapor, forming a hot spot. K-shell line emission from the ionized Ge that has penetrated into the hot spot provides an experimental signature of hot-spot mix. The Ge emission from tritium-hydrogen-deuterium (THD) and deuterium-tritium (DT) cryogenic targets and gas-filled plastic-shell capsules, which replace the THD layer with a mass-equivalent CH layer, was examined. The inferred amount of hot-spot-mix mass, estimated from the Ge K-shell line brightness using a detailed atomic physics code [J. J. MacFarlane et al., High Energy Density Phys. 3, 181 (2006)], is typically below the 75-ng allowance for hot-spot mix [S. W. Haan et al., Phys. Plasmas 18, 051001 (2011)]. Predictions of a simple mix model, based on linear growth of the measured surface-mass modulations, are consistent with the experimental results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Investigating inertial confinement fusion target fuel conditions through x-ray spectroscopy

Inertial confinement fusion (ICF) targets are designed to produce hot, dense fuel in a neutron-producing core that is surrounded by a shell of compressing material. The x-rays emitted from ICF plasmas can be analyzed to reveal details of the temperatures, densities, gradients, velocities, and mix characteristics of ICF targets. Such diagnostics are critical to understand the target performance and to improve the predictive power of simulation codes.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Inertial confinement fusion implosions with imposed magnetic field compression using the OMEGA Laser

Experiments applying laser-driven magnetic-flux compression to inertial confinement fusion (ICF) targets to enhance the implosion performance are described. Spherical plastic (CH) targets filled with 10 atm of deuterium gas were imploded by the OMEGA Laser, compare Phys. Plasmas 18, 056703 or Phys. Plasmas 18, 056309. Before being imploded, the targets were immersed in an 80-kG magnetic seed field. Upon laser irradiation, the high implosion velocities and ionization of the target fill trapped the magnetic field inside the capsule, and it was amplified to tens of megagauss through flux compression. At such strong magnetic fields, the hot spot inside the spherical target was strongly magnetized, reducing the heat losses through electron confinement. The experimentally observed ion temperature was enhanced by 15%, and the neutron yield was increased by 30%, compared to nonmagnetized implosions [P. Y. Chang et al., Phys. Rev. Lett. 107, 035006 (2011)]. This represents the first experimental verification of performance enhancement resulting from embedding a strong magnetic field into an ICF capsule. Experimental data for the fuel-assembly performance and magnetic field are compared to numerical results from combining the 1-D hydrodynamics code LILAC with a 2-D magnetohydrodynamics postprocessor.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

D-T gamma-to-neutron branching ratio determined from inertial confinement fusion plasmas

A new deuterium-tritium (D-T) fusion gamma-to-neutron branching ratio [{sup 3}H(d,{gamma}){sup 5}He/{sup 3}H(d,n){sup 4}He] value of (4.2 {+-} 2.0) Multiplication-Sign 10{sup -5} was recently reported by this group [Y. Kim et al. Phys. Rev. C (submitted)]. This measurement, conducted at the OMEGA laser facility located at the University of Rochester, was made for the first time using inertial confinement fusion (ICF) plasmas. Neutron-induced backgrounds are significantly reduced in these experiments as compared to traditional beam-target accelerator-based experiments due to the short pulse nature of ICF implosions and the use of gas Cherenkov {gamma}-ray detectors with fast temporal responses and inherent energy thresholds. It is expected that this ICF-based measurement will help resolve the large and long-standing inconsistencies in previously reported accelerator-based values, which vary by a factor of approximately 30. The reported value at ICF conditions was determined by averaging the results of two methods: (1) a direct measurement of ICF D-T {gamma}-ray and neutron emissions using absolutely calibrated detectors and (2) a separate cross-calibration against the better known D-{sup 3}He gamma-to-proton branching ratio [{sup 3}He(d, {gamma}){sup 5}Li/{sup 3}He(d,p){sup 4}He]. Here we include a detailed explanation of these results, and introduce as a corroborative method an in-situ{gamma}-ray detector calibration using neutron-induced {gamma}-rays. Also, by extending the established techniques to two additional series of implosions with significantly different ion temperatures, we test the branching ratio dependence on ion temperature. The data show a D-T branching ratio is nearly constant over the temperature range 2-9 keV. These studies motivate further investigation into the {sup 5}He and {sup 5}Li systems resulting from D-T and D-{sup 3}He fusion, respectively, and result in improved ICF {gamma}-ray reaction history diagnosis at the National Ignition Facility.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗