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May 2006

Volume 13, Issue 5, Articles (05xxxx)

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back to top Inertially Confined Plasmas, Dense Plasmas, Equations of State

Simulation of the nonlinear evolution of large scale relativistic electron flow in dense plasmas

Toshikazu Matsumoto, Toshihiro Taguchi, and Kunioki Mima

Phys. Plasmas 13, 052701 (2006); http://dx.doi.org/10.1063/1.2193533 (6 pages) | Cited 5 times

Online Publication Date: 4 May 2006

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A relativistic electron beam of about 100 MA is transported through overdense plasmas in the fast ignition. The nonlinear dynamics of the relativistic electron beam in dense plasmas has been investigated using a two-dimensional fluid-particle hybrid (FPH) code [ T. Taguchi et al., Phys. Rev. Lett. 86, 5055 (2001) ] that combines a particle-in cell code with an Rational Cubic Interpolated Pseudo-Particle fluid code [ F. Xiao et al., Comput. Phys. Commun. 93, 1 (1996) ]. These simulations show that the relativistic electron beam breaks up into filaments from the Weibel instability and the filaments merge successively to larger filaments. When the relativistic electron beam diameter is large and the total current is over 100 times Alfvén limit current, many large scale filaments remain after the merging process and are confined in the initial beam diameter. It is found that the number of relativistic electron filaments decreases in proportion to t−0.9 in the fixed ion case and t−0.2 in the mobile ion case until ωpe0τ ≈ 1000, respectively. This asymptotic behavior is caused by the random motion of filaments driven by fluctuating magnetic fields.
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52.40.Mj Particle beam interactions in plasmas
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.65.Rr Particle-in-cell method
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Fi Transport properties
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Tests of the hydrodynamic equivalence of direct-drive implosions with different D2 and math mixtures

J. R. Rygg, J. A. Frenje, C. K. Li, F. H. Séguin, R. D. Petrasso, J. A. Delettrez, V. Yu Glebov, V. N. Goncharov, D. D. Meyerhofer, S. P. Regan, T. C. Sangster, and C. Stoeckl

Phys. Plasmas 13, 052702 (2006); http://dx.doi.org/10.1063/1.2192759 (10 pages) | Cited 13 times

Online Publication Date: 10 May 2006

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Direct drive implosions of targets filled with different mixtures of D2 and math gas on the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] have shown an unexpected scaling of experimental nuclear yields. At temperatures above a few electron volts, D2 and math gases are fully ionized, and hydrodynamically equivalent fuels with different ratios of D2 and math can be chosen to have the same mass density, total particle density, and equation of state. Implosions with a 50/50 mixture of D:math by atom consistently result in measured nuclear yields half of that anticipated by scaling from measured yields of implosions with pure D2 and nearly pure math. This observation is seen over a wide range of experimental configurations, including targets with a variety of shell thicknesses and fill pressures, simultaneously for two different nuclear yields (DD and Dmath), and for shock and compression yields. A number of possible mechanisms to cause the scaling are considered, but no dominant mechanism has been identified.
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52.50.Lp Plasma production and heating by shock waves and compression
28.52.Cx Fueling, heating and ignition
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Jm Ionization of plasmas
52.35.Tc Shock waves and discontinuities
28.52.Fa Materials

Addressing the problem of plasma shell formation around an exploding wire in water

A. Grinenko, S. Efimov, A. Fedotov, Ya. E. Krasik, and I. Schnitzer

Phys. Plasmas 13, 052703 (2006); http://dx.doi.org/10.1063/1.2202207 (6 pages) | Cited 7 times

Online Publication Date: 22 May 2006

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Analysis of time- and space-resolved spectrum of radiation emitted from the discharge channel generated by an underwater electrical wire explosion is reported. The purpose of this investigation was to detect a possible shunting corona discharge. During careful analysis of the emitted radiation no evidence for such discharge was found. Discharge temperature of 7 eV was estimated by quantitative analysis of the emitted spectra.
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52.80.Qj Explosions; exploding wires
52.80.Wq Discharge in liquids and solids
52.77.Fv High-pressure, high-current plasmas (plasma spray, arc welding, etc.)

Thomson-scattering measurements of high electron temperature hohlraum plasmas for laser-plasma interaction studies

D. H. Froula, J. S. Ross, L. Divol, N. Meezan, A. J. MacKinnon, R. Wallace, and S. H. Glenzer

Phys. Plasmas 13, 052704 (2006); http://dx.doi.org/10.1063/1.2203232 (8 pages) | Cited 19 times

Online Publication Date: 24 May 2006

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Accurate measurements of the plasma conditions in laser-produced high-temperature plasmas have been achieved using the recently activated 4ω Thomson-scattering diagnostic at the Omega Laser Facility, Soures et al., Laser Part. Beams 11 (1993) . These diagnostic measurements were performed in a new hohlraum target platform that will be used to study laser-plasma interaction in a strongly damped regime comparable to those occurring in indirect drive inertial confinement fusion plasmas. The Thomson-scattering spectra show the collective ion-acoustic features that fit the theory for two ion species plasmas allowing us to accurately and independently determine both the electron and ion temperatures. The electron temperature was found to range from 2 to 4 keV as the total heater beam energy deposited into the hohlraum was increased from 8 to 17 kJ. The results are compared to 2D hydrodynamic simulations using flux limited diffusion and nonlocal heat flux models. The target platform presented provides a novel test bed to investigate laser-plasma interaction physics in the strongly damped backscatter regime.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.38.Ph X-ray, γ-ray, and particle generation
52.35.Dm Sound waves
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Fi Transport properties

Hugoniot measurement of diamond under laser shock compression up to 2 TPa

H. Nagao, K. G. Nakamura, K. Kondo, N. Ozaki, K. Takamatsu, T. Ono, T. Shiota, D. Ichinose, K. A. Tanaka, K. Wakabayashi, K. Okada, M. Yoshida, M. Nakai, K. Nagai, K. Shigemori, et al.

Phys. Plasmas 13, 052705 (2006); http://dx.doi.org/10.1063/1.2205194 (5 pages) | Cited 16 times

Online Publication Date: 26 May 2006

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Hugoniot data of diamond was obtained using laser-driven shock waves in the terapascal range of 0.5–2 TPa. Strong shock waves were generated by direct irradiation of a 2.5 ns laser pulse on an Al driver plate. The shock wave velocities in diamond and Al were determined from optical measurements. Particle velocities and pressures were obtained using an impedance matching method and known Al Hugoniot. The obtained Hugoniot data of diamond does not show a marked difference from the extrapolations of the Pavlovskii Hugoniot data in the TPa range within experimental errors.
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64.30.-t Equations of state of specific substances
62.50.-p High-pressure effects in solids and liquids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
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Dynamic hohlraum radiation hydrodynamics

J. E. Bailey, G. A. Chandler, R. C. Mancini, S. A. Slutz, G. A. Rochau, M. Bump, T. J. Buris-Mog, G. Cooper, G. Dunham, I. Golovkin, J. D. Kilkenny, P. W. Lake, R. J. Leeper, R. Lemke, J. J. MacFarlane, et al.

Phys. Plasmas 13, 056301 (2006); http://dx.doi.org/10.1063/1.2177640 (9 pages) | Cited 19 times

Online Publication Date: 8 May 2006

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Z-pinch dynamic hohlraums are a promising indirect-drive inertial confinement fusion approach. Comparison of multiple experimental methods with integrated Z-pinch∕hohlraum∕capsule computer simulations builds understanding of the hohlraum interior conditions. Time-resolved x-ray images determine the motion of the radiating shock that heats the hohlraum as it propagates toward the hohlraum axis. The images also measure the radius of radiation-driven capsules as they implode. Dynamic hohlraum LASNEX [ G. Zimmerman and W. Kruer, Comments Plasma Phys. Control. Fusion 2, 85 (1975) ] simulations are found to overpredict the shock velocity by ∼ 20–40%, but simulated capsule implosion trajectories agree reasonably well with the data. Measurements of the capsule implosion core conditions using time- and space-resolved Ar tracer x-ray spectroscopy and the fusion neutron yield provide additional tests of the integrated hohlraum-implosion system understanding. The neutron yield in the highest performing CH capsule implosions is ∼ 20–30% of the yield calculated with unperturbed 2D LASNEX simulations. The emissivity-averaged electron temperature and density peak at approximately 900 eV and 4×1023 cm−3, respectively. Synthetic spectra produced by postprocessing 1D LASNEX capsule implosion simulations possess spectral features from H-like and He-like Ar that are similar in duration to the measured spectra. However, the simulation emissivity-averaged density peaks at a value that is four times lower than the experiment, while the temperature is approximately 1.6 times higher. The agreement with the capsule trajectory measurements and the ability to design capsule implosions that routinely produce implosion cores hot and dense enough to emit fusion neutrons and Ar spectra are evidence for a respectable degree of dynamic hohlraum understanding. The hohlraum shock velocity and implosion core discrepancies imply that calculations of the hohlraum radiation driving capsule implosions require further refinement.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.65.Cc Particle orbit and trajectory
52.70.La X-ray and γ-ray measurements
52.35.Tc Shock waves and discontinuities
52.50.Lp Plasma production and heating by shock waves and compression

Progress toward fabrication of graded doped beryllium and CH capsules for the National Ignition Facility

A. Nikroo, K. C. Chen, M. L. Hoppe, H. Huang, J. R. Wall, H. Xu, M. W. McElfresh, C. S. Alford, R. C. Cook, J. C. Cooley, R. Fields, R. Hackenberg, R. P. Doerner, and M. Baldwin

Phys. Plasmas 13, 056302 (2006); http://dx.doi.org/10.1063/1.2179054 (6 pages) | Cited 10 times

Online Publication Date: 8 May 2006

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Current ignition designs require graded doped beryllium or CH capsules. This paper reports on the progress toward fabricating both beryllium and CH capsules that meet the current design criteria for achieving ignition on the National Ignition Facility (NIF) [ S. Hann et al., Phys. Plasmas 12, 056316 (2005) ]. NIF scale graded copper doped beryllium capsules have been made by sputter coating, while graded germanium doped CH capsules have been made by plasma polymer deposition. The sputtering process used for fabricating graded beryllium shells was produced with a void fraction of ∼ 5%. Varying the deposition parameters can lead to several different beryllium microstructures, which have been tuned to reduce the void size and fraction to within specifications. In addition, polishing of beryllium-coated shells reduces the outer surface roughness of shells to ignition specifications. Transmission electron microscopy has been used to characterize void fraction and grain structure of beryllium coatings. The plasma polymer deposition process has produced dense, void-free graded doped CH shells that nearly meet the ignition surface finish requirements. Layer thickness and dopant concentrations have been measured by quantitative contact radiography.
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28.52.Fa Materials
28.52.Av Theory, design, and computerized simulation
52.77.Dq Plasma-based ion implantation and deposition
81.15.Cd Deposition by sputtering
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Ps Polishing, grinding, surface finishing

Shock-timing experiments using double-pulse laser irradiation

T. R. Boehly, E. Vianello, J. E. Miller, R. S. Craxton, T. J. B. Collins, V. N. Goncharov, I. V. Igumenshchev, D. D. Meyerhofer, D. G. Hicks, P. M. Celliers, and G. W. Collins

Phys. Plasmas 13, 056303 (2006); http://dx.doi.org/10.1063/1.2179057 (7 pages) | Cited 14 times

Online Publication Date: 8 May 2006

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The timing of multiple shock waves is crucial to the performance of inertial confinement fusion ignition targets. Presented are measurements of velocities and optical self-emission from shock waves in polystyrene targets driven by two 90-ps pulses separated by 1.5–2 ns. These pulses drive two shock waves that coalesce in the target, and the resultant velocity histories, coalescence times, and transit times are unambiguously observed in both velocity interferometry and self-emission data. These results are in good agreement with one-dimensional hydrodynamics code predictions.
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52.50.Lp Plasma production and heating by shock waves and compression
52.35.Tc Shock waves and discontinuities
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Fi Transport properties
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.58.Qv Electrostatic and high-frequency confinement

Late-time radiography of beryllium ignition-target ablators in long-pulse gas-filled hohlraums

J. A. Cobble, T. E. Tierney, N. M. Hoffman, B. G. DeVolder, and D. C. Swift

Phys. Plasmas 13, 056304 (2006); http://dx.doi.org/10.1063/1.2181567 (7 pages) | Cited 7 times

Online Publication Date: 8 May 2006

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A multiple-laboratory campaign is underway to qualify beryllium as a fusion capsule ablator for the National Ignition Facility [Moses and Wuest, Fusion Sci. Technol. 43, 420 (2003)] . Although beryllium has many advantages over other ablator materials, individual crystals of beryllium have anisotropic properties, e.g., sound speed, elastic constants, and thermal expansion coefficients, which may seed hydrodynamic instabilities during the implosion phase of ignition experiments. Experiments based on modeling have begun at the OMEGA laser [Boehly, McCrory, Verdon et al., Fusion Eng. Design 44, 35 (1999)] to create a test bed for measuring instability growth rates with face-on radiography of perturbed beryllium samples with the goal of establishing a specification for microstructure in beryllium used as an ablator. The specification would include the size and distribution of sizes of grains and voids and the impurity content. The experimental platform is a 4 kJ laser-heated (for ∼ 6 ns) hohlraum that is well modeled for radiation temperature and for shock pressure and breakout timing through the driven beryllium sample. A 1 atm methane gas fill has been used to maintain a clear line of sight through the hohlraum for radiography with acceptable plasma backscatter losses. The peak radiation temperature is 145 eV; the pressure early in the laser pulse is 1 Mbar for over 1 ns. Radiographs of sinusoidally perturbed copper-doped (0.9% by atom) beryllium samples have been obtained more than 10 ns after drive initiation. With the current laser drive, a growth factor approaching ten has been measured for initial 2.5 μm perturbations with on-axis radiography.
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28.52.Lf Components and instrumentation
52.70.La X-ray and γ-ray measurements
28.52.Cx Fueling, heating and ignition
28.52.Fa Materials
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.57.Fg Implosion symmetry and hydrodynamic instability (Rayleigh-Taylor, Richtmyer-Meshkov, imprint, etc.)

Developing a commercial production process for 500 000 targets per day: A key challenge for inertial fusion energy

D. T. Goodin, N. B. Alexander, G. E. Besenbruch, A. S. Bozek, L. C. Brown, L. C. Carlson, G. W. Flint, P. Goodman, J. D. Kilkenny, W. Maksaereekul, B. W. McQuillan, A. Nikroo, R. R. Paguio, R. W. Petzoldt, R. Raffray, et al.

Phys. Plasmas 13, 056305 (2006); http://dx.doi.org/10.1063/1.2177129 (4 pages) | Cited 2 times

Online Publication Date: 11 May 2006

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As is true for current-day commercial power plants, a reliable and economic fuel supply is essential for the viability of future Inertial Fusion Energy (IFE) [Energy From Inertial Fusion, edited by W. J. Hogan (International Atomic Energy Agency, Vienna, 1995)] power plants. While IFE power plants will utilize deuterium-tritium (DT) bred in-house as the fusion fuel, the “target” is the vehicle by which the fuel is delivered to the reaction chamber. Thus the cost of the target becomes a critical issue in regard to fuel cost. Typically six targets per second, or about 500 000/day are required for a nominal 1000 MW(e) power plant. The electricity value within a typical target is about $3, allocating 10% for fuel cost gives only 30 cents per target as-delivered to the chamber center. Complicating this economic goal, the target supply has many significant technical challenges—fabricating the precision fuel-containing capsule, filling it with DT, cooling it to cryogenic temperatures, layering the DT into a uniform layer, characterizing the finished product, accelerating it to high velocity for injection into the chamber, and tracking the target to steer the driver beams to meet it with micron-precision at the chamber center.
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28.52.Fa Materials
28.52.Av Theory, design, and computerized simulation
52.57.Bc Target design and fabrication
28.52.Cx Fueling, heating and ignition

Detailed diagnosis of a double-shell collision under realistic implosion conditions

G. A. Kyrala, M. A. Gunderson, N. D. Delamater, D. A. Haynes, D. C. Wilson, J. A. Guzik, and K. A. Klare

Phys. Plasmas 13, 056306 (2006); http://dx.doi.org/10.1063/1.2179047 (7 pages) | Cited 2 times

Online Publication Date: 11 May 2006

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Double-shell implosions provide a noncryogenic path to inertial confinement fusion. In the double-shell target, the energy is absorbed in an outer shell that is accelerated inward and collides with an inner shell that implodes against the deuterium fuel. Symmetric collision of the shells requires that the shells be illuminated and built symmetrically. In reality, the targets are complicated and the construction is not symmetric, due to the seam that our current assembly method requires. Using the Omega laser [ R. T. Boehly et al., Opt. Comm. 133, 495 (1997) ], an illumination strategy was designed that uses 40 beams in an offset geometry, leaving 20 beams to perform radiography from two different directions. This places a significant nonsymmetric illumination challenge that may not exist in final targets shot on the National Ignition Facility. This paper presents a measurement of the time history of a collision of two shells in a double-shell capsule, briefly reviews the illumination geometry, gives the results of the measurements of the trajectory and symmetry of the outer and inner shells, shows the effect of a seam on the inner shell implosion, and compares the results with calculations. The measurement of such a collision in a spherical geometry is of great interest to the study of double-shell implosions as well as code validation.
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28.52.Lf Components and instrumentation
52.70.La X-ray and γ-ray measurements
52.50.Lp Plasma production and heating by shock waves and compression
28.52.Cx Fueling, heating and ignition
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.57.Kk Fast ignition of compressed fusion fuels

Using laser entrance hole shields to increase coupling efficiency in indirect drive ignition targets for the National Ignition Facility

D. A. Callahan, P. A. Amendt, E. L. Dewald, S. W. Haan, D. E. Hinkel, N. Izurni, O. S. Jones, O. L. Landen, J. D. Lindl, S. M. Pollaine, L. J. Suter, M. Tabak, and R. E. Turner

Phys. Plasmas 13, 056307 (2006); http://dx.doi.org/10.1063/1.2196287 (6 pages) | Cited 15 times

Online Publication Date: 11 May 2006

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Coupling efficiency, the ratio of the capsule absorbed energy to the driver energy, is a key parameter in ignition target designs. The hohlraum originally proposed for the National Ignition Facility (NIF) [ G. H. Miller, E. I. Moses, and C. R. Wuest, Nucl. Fusion 44, S228 (2004) ] coupled ∼ 11% of the absorbed laser energy to the capsule as x rays. Described here is a second generation of the hohlraum target which has a higher coupling efficiency, ∼ 16%. Because the ignition capsule’s ability to withstand three-dimensional effects increases rapidly with absorbed energy, the additional energy can significantly increase the likelihood of ignition. The new target includes laser entrance hole (LEH) shields as a principal method for increasing coupling efficiency while controlling symmetry in indirect-drive inertial confinement fusion. The LEH shields are high Z disks placed inside the hohlraum on the symmetry axis to block the capsule’s view of the relatively cold LEHs. The LEH shields can reduce the amount of laser energy required to drive a target to a given temperature via two mechanisms: (1) keeping the temperature high near the capsule pole by putting a barrier between the capsule and the pole; (2) because the capsule pole does not have a view of the cold LEHs, good symmetry requires a shorter hohlraum with less wall area. Current integrated simulations of this class of target couple 140 kJ of x rays to a capsule out of 865 kJ of absorbed laser energy and produce ∼ 10 MJ of yield. In the current designs, which continue to be optimized, the addition of the LEH shields saves ∼ 95 kJ of energy (about 10%) over hohlraums without LEH shields.
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28.52.Fa Materials
52.57.Bc Target design and fabrication
28.52.Cx Fueling, heating and ignition
28.52.Av Theory, design, and computerized simulation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)

A global simulation for laser-driven MeV electrons in 50-μm-diameter fast ignition targets

C. Ren, M. Tzoufras, J. Tonge, W. B. Mori, F. S. Tsung, M. Fiore, R. A. Fonseca, L. O. Silva, J.-C. Adam, and A. Heron

Phys. Plasmas 13, 056308 (2006); http://dx.doi.org/10.1063/1.2173617 (7 pages) | Cited 11 times

Online Publication Date: 15 May 2006

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The results from 2.5-dimensional particle-in-cell simulations for the interaction of a picosecond-long ignition laser pulse with a plasma pellet of 50-μm diameter and 40 critical density are presented. The high-density pellet is surrounded by an underdense corona and is isolated by a vacuum region from the simulation box boundary. The laser pulse is shown to filament and create density channels on the laser-plasma interface. The density channels increase the laser absorption efficiency and help generate an energetic electron distribution with a large angular spread. The combined distribution of the forward-going energetic electrons and the induced return electrons is marginally unstable to the current filament instability. The ions play an important role in neutralizing the space charges induced by the temperature disparity between different electron groups. No global coalescing of the current filaments resulted from the instability is observed, consistent with the observed large angular spread of the energetic electrons.
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52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.38.Hb Self-focussing, channeling, and filamentation in plasmas
52.38.Ph X-ray, γ-ray, and particle generation
52.65.Rr Particle-in-cell method
52.80.Hc Glow; corona
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

High-energy Kα radiography using high-intensity, short-pulse lasers

H.-S. Park, D. M. Chambers, H.-K. Chung, R. J. Clarke, R. Eagleton, E. Giraldez, T. Goldsack, R. Heathcote, N. Izumi, M. H. Key, J. A. King, J. A. Koch, O. L. Landen, A. Nikroo, P. K. Patel, et al.

Phys. Plasmas 13, 056309 (2006); http://dx.doi.org/10.1063/1.2178775 (10 pages) | Cited 71 times

Online Publication Date: 15 May 2006

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The characteristics of 22–40 keV Kα x-ray sources are measured. These high-energy sources are produced by 100 TW and petawatt high-intensity lasers and will be used to develop and implement workable radiography solutions to probe high-Z and dense materials for the high-energy density experiments. The measurements show that the Kα source size from a simple foil target is larger than 60 μm, too large for most radiography applications. The total Kα yield is independent of target thicknesses, verifying that refluxing plays a major role in photon generation. Smaller radiating volumes emit brighter Kα radiation. One-dimensional radiography experiments using small-edge-on foils resolved 10 μm features with high contrast. Experiments were performed to test a variety of small volume two-dimensional point sources such as cones, wires, and embedded wires, measured photon yields, and compared the measurements with predictions from hybrid-particle-in-cell simulations. In addition to high-energy, high-resolution backlighters, future experiments will also need imaging detectors and diagnostic tools that are workable in the high-energy range. An initial look at some of these detector issues is also presented.
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52.70.La X-ray and γ-ray measurements
52.38.Ph X-ray, γ-ray, and particle generation
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

On the control of filamentation of intense laser beams propagating in underdense plasma

E. A. Williams

Phys. Plasmas 13, 056310 (2006); http://dx.doi.org/10.1063/1.2179051 (7 pages) | Cited 4 times

Online Publication Date: 15 May 2006

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In indirect drive inertial confinement fusion ignition designs, the laser energy is delivered into the hohlraum through the laser entrance holes (LEHs), which are sized as small as practicable to minimize x-ray radiation losses. On the other hand, deleterious laser plasma processes, such as filamentation and stimulated backscatter, typically increase with laser intensity. Ideally, therefore, the laser spot shape should be a close fit to the LEH, with uniform (envelope) intensity in the spot and minimal energy at larger radii spilling onto the LEH material. This keeps the laser intensity as low as possible, consistent with the area of the LEH aperture and the power requirements of the design. This can be achieved (at least for apertures significantly larger than the laser’s aberrated focal spot) by the use of custom-designed phase plates. However, outfitting the 192–beam National Ignition Facility [ J. A. Paisner, E. M. Campbell, and W. J. Hogan, Fusion Tech. 26, 755 1994) ] laser with multiple sets of phase plates optimized for a variety of different LEH aperture sizes is an expensive proposition. It is thus important to assess the impact on laser-plasma interaction processes of using phase plates with a smaller than optimum focal spot (or even no phase plates at all!) and then defocusing the beam to expand it to fill the LEH and lower its intensity. Significant effects are found from changes in the characteristic sizes of the laser speckle, from the lack of uniformity of the laser envelope out of the focal plane and on the efficacy of additional polarization smoothing and/or smoothing by spectral dispersion (SSD). These effects are quantified with analytic estimates and simulations using PF3D, our laser-plasma interaction code.
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52.38.Hb Self-focussing, channeling, and filamentation in plasmas
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.57.Kk Fast ignition of compressed fusion fuels

Polar-direct-drive simulations and experiments

J. A. Marozas, F. J. Marshall, R. S. Craxton, I. V. Igumenshchev, S. Skupsky, M. J. Bonino, T. J. B. Collins, R. Epstein, V. Yu. Glebov, D. Jacobs-Perkins, J. P. Knauer, R. L. McCrory, P. W. McKenty, D. D. Meyerhofer, S. G. Noyes, et al.

Phys. Plasmas 13, 056311 (2006); http://dx.doi.org/10.1063/1.2184949 (8 pages) | Cited 20 times

Online Publication Date: 15 May 2006

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Polar direct drive (PDD) [S. Skupsky et al., Phys. Plasmas 11, 2763 (2004)] will allow direct-drive ignition experiments on the National Ignition Facility (NIF) [J. Paisner et al., Laser Focus World 30, 75 (1994)] as it is configured for x-ray drive. Optimal drive uniformity is obtained via a combination of beam repointing, pulse shapes, spot shapes, and∕or target design. This article describes progress in the development of standard and “Saturn” [R. S. Craxton and D. W. Jacobs-Perkins, Phys. Rev. Lett. 94, 0952002 (2005)] PDD target designs. Initial evaluation of experiments on the OMEGA Laser System [T. R. Boehly et al., Rev. Sci. Instrum. 66, 508 (1995)] and simulations were carried out with the two-dimensional hydrodynamics code SAGE [R. S. Craxton et al., Phys. Plasmas 12, 056304 (2005)] . This article adds to this body of work by including fusion particle production and transport as well as radiation transport within the two-dimensional DRACO [P. B. Radha et al., Phys. Plasmas 12, 032702 (2005)] hydrodynamics simulations used to model experiments. Forty OMEGA beams arranged in six rings to emulate the NIF x-ray-drive configuration are used to perform direct-drive implosions of CH shells filled with D2 gas. Target performance was diagnosed with framed x-ray backlighting and by the measured fusion yield. Saturn target experiments have resulted in ∼ 75% of the yield from energy-equivalent, symmetrically irradiated implosions. The results of the two-dimensional PDD simulations performed with DRACO are in good agreement with experimental x-ray radiographs. DRACO is being used to further optimize standard PDD designs. In addition, DRACO simulations of NIF-scale PDD designs show ignition with a gain of 20 and the development of a 40 μm radius, 10 keV region with a neutron-averaged ρr of 1270 mg/cm2 near stagnation.
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28.52.Cx Fueling, heating and ignition
28.52.Av Theory, design, and computerized simulation
28.52.Fa Materials
28.52.Lf Components and instrumentation
52.57.Bc Target design and fabrication
52.50.Lp Plasma production and heating by shock waves and compression

Rayleigh-Taylor growth measurements of three-dimensional modulations in a nonlinear regime

V. A. Smalyuk, O. Sadot, R. Betti, V. N. Goncharov, J. A. Delettrez, D. D. Meyerhofer, S. P. Regan, T. C. Sangster, and D. Shvarts

Phys. Plasmas 13, 056312 (2006); http://dx.doi.org/10.1063/1.2174826 (7 pages) | Cited 10 times

Online Publication Date: 17 May 2006

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An understanding of the nonlinear evolution of Rayleigh-Taylor (RT) instability is essential in inertial confinement fusion and astrophysics. The nonlinear RT growth of three–dimensional (3-D) broadband nonuniformities was measured near saturation levels using x-ray radiography in planar foils accelerated by laser light. The initial 3-D target modulations were seeded by laser nonuniformities and subsequently amplified by the RT instability. The measured modulation Fourier spectra and nonlinear growth velocities are in excellent agreement with those predicted by Haan's model [ S. Haan, Phys. Rev. A 39, 5812 (1989) ]. These spectra and growth velocities are insensitive to initial conditions. In a real-space analysis, the bubble merger was quantified by a self-similar evolution of bubble size distributions, in agreement with the Alon–Oron–Shvarts theoretical predictions [ D. Oron et al. Phys. Plasmas 8, 2883 (2001) ].
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.70.La X-ray and γ-ray measurements
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)

Measurement and modeling of the implosion of wire arrays with seeded instabilities

Brent Jones, Christopher J. Garasi, David J. Ampleford, Christopher Deeney, Thomas A. Mehlhorn, Simon N. Bland, Sergey V. Lebedev, Jeremy P. Chittenden, Simon C. Bott, James B. A. Palmer, Gareth N. Hall, and Jack Rapley

Phys. Plasmas 13, 056313 (2006); http://dx.doi.org/10.1063/1.2174833 (7 pages) | Cited 10 times

Online Publication Date: 17 May 2006

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In order to study wire array Z-pinch instabilities, perturbations have been seeded by etching 15 μm diameter aluminum wires to introduce 20% modulations in radius with a controlled axial wavelength. These perturbations seed additional imploding structures that are studied experimentally on the 1 MA, 250 ns MAGPIE generator [ S. V. Lebedev et al., Plasma Phys. Control. Fusion 47, A91 (2005) ] and with three-dimensional magnetohydrodynamic calculations using the ALEGRA-HEDP [ A. C. Robinson and C. J. Garasi, Comput. Phys. Commun. 164, 408 (2004) ] and GORGON [ J. P. Chittenden et al., Plasma Phys. Control. Fusion 46, B457 (2004) ] codes. Simulations indicate that current path nonuniformity at discontinuities in the wire radius result in perturbation-induced magnetic bubble formation. Imploding bubbles originating from discontinuities are observed experimentally, and their collision on axis determines the start of the main x-ray pulse rise. These mechanisms likely govern dynamics of standard wire array Z pinches, and tailoring the profile of imploding mass may allow x-ray pulse shaping for inertial confinement fusion applications.
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52.59.Qy Wire array Z-pinches
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.80.Qj Explosions; exploding wires
52.65.Kj Magnetohydrodynamic and fluid equation

Energy deposition of MeV electrons in compressed targets of fast-ignition inertial confinement fusion

C. K. Li and R. D. Petrasso

Phys. Plasmas 13, 056314 (2006); http://dx.doi.org/10.1063/1.2178780 (6 pages) | Cited 16 times

Online Publication Date: 17 May 2006

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Energy deposition of MeV electrons in dense plasmas, important for fast ignition in inertial confinement fusion, is modeled analytically. It is shown that classical stopping and scattering dominate electron transport and energy deposition when the electrons reach the dense plasmas in the cores of compressed targets, while “anomalous” stopping associated with self-generated fields and micro-instabilities (suggested by previous simulations) might initially play an important role in the lower-density plasmas outside the dense core. For MeV electrons in precompressed deuterium-tritium fast-ignition targets, the initial penetration results in approximately uniform energy deposition but the latter stages of penetration involve mutual couplings of energy loss, straggling, and blooming that lead to enhanced, nonuniform energy deposition. This model can be used for quantitatively assessing ignition requirements for fast ignition.
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52.57.Kk Fast ignition of compressed fusion fuels
52.40.Mj Particle beam interactions in plasmas
52.50.Lp Plasma production and heating by shock waves and compression
52.25.Fi Transport properties
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
28.52.Cx Fueling, heating and ignition

First hohlraum drive studies on the National Ignition Facility

E. L. Dewald, O. L. Landen, L. J. Suter, J. Schein, J. Holder, K. Campbell, S. H. Glenzer, J. W. McDonald, C. Niemann, A. J. Mackinnon, M. S. Schneider, C. Haynam, D. Hinkel, and B. A. Hammel

Phys. Plasmas 13, 056315 (2006); http://dx.doi.org/10.1063/1.2178783 (8 pages) | Cited 12 times

Online Publication Date: 17 May 2006

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The first hohlraum experiments on the National Ignition Facility (NIF) [ G. H. Miller, E. I. Moses, and C. R. Wuest, Nucl. Fusion 44, 228 (2004) ] using the first four laser beams have activated the indirect-drive experimental capabilities and tested radiation temperature limits imposed by hohlraum plasma filling. Vacuum hohlraums have been irradiated with laser powers up to 9  TW, 1 to 9 ns long square pulses and energies of up to 17 kJ to study the hohlraum radiation temperature scaling with the laser power and hohlraum size, and to make contact with hohlraum experiments performed previously at other laser facilities. Furthermore, for a variety of hohlraum sizes and pulse lengths, the measured x-ray flux shows signatures of plasma filling that coincide with hard x-ray emission from plasma streaming out of the hohlraum. These observations agree with hydrodynamic simulations and with analytical modeling that includes hydrodynamic and coronal radiative losses. The modeling predicts radiation temperature limits on full NIF (1.8 MJ) that are significantly greater than required for ignition hohlraums.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.38.Ph X-ray, γ-ray, and particle generation
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.59.Px Hard X-ray sources
52.70.La X-ray and γ-ray measurements

Forming cryogenic targets for direct-drive experiments

D. R. Harding, D. D. Meyerhofer, S. J. Loucks, L. D. Lund, R. Janezic, L. M. Elasky, T. H. Hinterman, D. H. Edgell, W. Seka, M. D. Wittman, R. Q. Gram, D. Jacobs-Perkins, R. Early, T. Duffy, and M. J. Bonino

Phys. Plasmas 13, 056316 (2006); http://dx.doi.org/10.1063/1.2192468 (10 pages) | Cited 11 times

Online Publication Date: 17 May 2006

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More than 100 spherical deuterium ice layers have been formed to make cryogenic targets for direct-drive ICF implosion experiments on OMEGA. These ice layers have an inner surface roughness that ranges from 1.3 to 6μm root-mean-square (rms), with the best layers having a value less than 2 μm rms. These surface roughness values are averaged two-dimensional roughness measurements that cover the entire surface and includes all of the Fourier cosine modes. The ice thickness variation within the layer is predominately in the low spectral modes (mode 5 and lower) and is caused by the support used to hold the target. Changing the design of this support to minimize the thermal effect is constrained by the necessity of having a dynamically stable target for the implosion. We have demonstrated that it is possible to form crystalline ice layers that are facet-free and transparent by slowing the solidification rate of the liquid. Faster freezing rates form layers comprised of polycrystalline ice with a greater roughness (1 to 2 μm greater). Cooling an ice layer 0.5 K below the triple point temperature does not affect the roughness of the layer. Cooling the layer a further 1 K to achieve the desired internal gas pressure sometimes induces additional ice roughness; this roughness is manifest over low- to mid-spectral modes. Removing the thermal shrouds from around the target causes the ice to melt and the internal gas pressure to increase. Using the behavior of a cryogenic deuterium target as a reference, calculations of the response of the more interesting National Ignition Facility-scale deuterium and tritium targets show that exposing the target for 0.8 s to ambient radiation will cause ∼ 10% of the ice to melt and partially slump whereas the gas pressure will increase by 15%.
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28.52.Fa Materials
28.52.Cx Fueling, heating and ignition
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.57.Bc Target design and fabrication
52.50.Lp Plasma production and heating by shock waves and compression
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Inertial confinement fusion neutron images

L. Disdier, A. Rouyer, I. Lantuéjoul, O. Landoas, J. L. Bourgade, T. C. Sangster, V. Yu. Glebov, and R. A. Lerche

Phys. Plasmas 13, 056317 (2006); http://dx.doi.org/10.1063/1.2174828 (6 pages) | Cited 25 times

Online Publication Date: 24 May 2006

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At the OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] , 14-MeV neutron images are acquired with a 20‐μm resolution and a large signal-to-noise ratio (SNR) using penumbral and ring apertures. The two aperture types produce coded images of the source that are unfolded using a similar autocorrelation method. The techniques provide comparable images for various deuterium-tritium filled target implosions, with glass and plastic (CH) shells. SNR analysis reveals that the annular (ring) technique will achieve a good image quality at the 10‐μm resolution level with the planned upgrade of our novel detector. The detector is an array of 85‐μm‐diam capillary tubes filled with a liquid scintillator. Its resolution is limited to 650 μm by the track length of the elastically scattered recoil protons. Replacing the hydrogen in the scintillator with deuterium improves detector spatial resolution to 325 μm, and makes high source resolution achievable. The readout design provides an efficient light collection of the scintillation photons by relaying the image through a fiber optic taper. Improved efficiency produces images with better SNR. Also, the increased detector sensitivity allows single event recording of 2.45-MeV neutron interactions. For the first time ever, we show neutron images of deuterium filled, warm, and cryogenic target implosions.
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52.70.Nc Particle measurements
52.57.Kk Fast ignition of compressed fusion fuels
52.50.Lp Plasma production and heating by shock waves and compression
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
28.52.Cx Fueling, heating and ignition

Compact single and nested tungsten-wire-array dynamics at 14–19 MA and applications to inertial confinement fusion

M. E. Cuneo, D. B. Sinars, E. M. Waisman, D. E. Bliss, W. A. Stygar, R. A. Vesey, R. W. Lemke, I. C. Smith, P. K. Rambo, J. L. Porter, G. A. Chandler, T. J. Nash, M. G. Mazarakis, R. G. Adams, E. P. Yu, et al.

Phys. Plasmas 13, 056318 (2006); http://dx.doi.org/10.1063/1.2177140 (18 pages) | Cited 37 times

Online Publication Date: 24 May 2006

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Wire-array z pinches show promise as a high-power, efficient, reproducible, and low-cost x-ray source for high-yield indirect-drive inertial confinement fusion. Recently, rapid progress has been made in our understanding of the implosion dynamics of compact (20-mm-diam), high-current (11–19 MA), single and nested wire arrays. As at lower currents (1–3 MA), a single wire array (and both the outer and inner array of a nested system), show a variety of effects that arise from the initially discrete nature of the wires: a long wire ablation phase for 50%-80% of the current pulse width, an axial modulation of the ablation rate prior to array motion, a larger ablation rate for larger diameter wires, trailing mass, and trailing current. Compact nested wire arrays operate in current-transfer or transparent mode because the inner wires remain discrete during the outer array implosion, even for interwire gaps in the outer and inner arrays as small as 0.21 mm. These array physics insights have led to nested arrays that produce radiation pulse shapes required for three-shock low-adiabat compression of high-yield inertial confinement fusion capsules.
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52.50.Lp Plasma production and heating by shock waves and compression
52.59.Qy Wire array Z-pinches
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Fi Transport properties
52.35.Tc Shock waves and discontinuities

Gas-filled hohlraum experiments at the National Ignition Facility

Juan C. Fernández, S. R. Goldman, J. L. Kline, E. S. Dodd, C. Gautier, G. P. Grim, B. M. Hegelich, D. S. Montgomery, N. E. Lanier, H. Rose, D. W. Schmidt, J. B. Workman, D. G. Braun, E. L. Dewald, O. L. Landen, et al.

Phys. Plasmas 13, 056319 (2006); http://dx.doi.org/10.1063/1.2183907 (9 pages) | Cited 6 times

Online Publication Date: 24 May 2006

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Experiments done at the National Ignition Facility laser [ J. A. Paisner, E. M. Campbell, and W. Hogan, Fusion Technol. 26, 755 (1994) ] using gas-filled hohlraums demonstrate a key ignition design feature, i.e., using plasma pressure from a gas fill to tamp the hohlraum-wall expansion for the duration of the laser pulse. Moreover, our understanding of hohlraum energetics and the ability to predict the hohlraum soft-x-ray drive has been validated in ignition-relevant conditions. Finally, the laser reflectivity from stimulated Raman scattering in the fill plasma, a key threat to hohlraum performance, is shown to be suppressed by choosing a design with a sufficiently high ratio of electron temperature to density.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
28.52.Cx Fueling, heating and ignition
28.52.Av Theory, design, and computerized simulation
52.40.Hf Plasma-material interactions; boundary layer effects
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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Pathway to a lower cost high repetition rate ignition facility

S. P. Obenschain, D. G. Colombant, A. J. Schmitt, J. D. Sethian, and M. W. McGeoch

Phys. Plasmas 13, 056320 (2006); http://dx.doi.org/10.1063/1.2198796 (11 pages) | Cited 16 times

Online Publication Date: 26 May 2006

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An approach to a high-repetition ignition facility based on direct drive with the krypton-fluoride laser is presented. The objective is development of a “Fusion Test Facility” that has sufficient fusion power to be useful as a development test bed for power plant materials and components. Calculations with modern pellet designs indicate that laser energies well below a megajoule may be sufficient. A smaller driver would result in an overall smaller, less complex and lower cost facility. While this facility might appear to have most direct utility to inertial fusion energy, the high flux of neutrons would also be able to address important issues concerning materials and components for other approaches to fusion energy. The physics and technological basis for the Fusion Test Facility are presented along with a discussion of its applications.
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28.52.Av Theory, design, and computerized simulation
28.52.Cx Fueling, heating and ignition
28.52.Fa Materials
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