Bulletin of the American Physical Society
2005 47th Annual Meeting of the Division of Plasma Physics
Monday–Friday, October 24–28, 2005; Denver, Colorado
Session GO1: Short-Pulse Laser-Matter Interactions |
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Chair: Warren Mori, University of California, Los Angeles Room: Adam's Mark Hotel Governor's Square 10 |
Tuesday, October 25, 2005 2:00PM - 2:12PM |
GO1.00001: OMEGA EP: Status and Use Planning D.D. Meyerhofer, T.C. Sangster, C. Stoeckl, S.F.B. Morse, J.H. Kelly, S.J. Loucks, R.L. McCrory The OMEGA EP Laser Facility will be completed in 2007, adjacent to the 60-beam, 30-kJ OMEGA Laser Facility at the University of Rochester. OMEGA EP will consist of four beamlines with NIF-like architecture. Each of the beams will produce 6.5 kJ in 10 ns pulses and will be directed into the OMEGA EP target chamber. Two of the beamlines will also operate as high-intensity, short-pulse lasers with 2.6 kJ each. They could be injected into either the OMEGA EP chamber or the existing OMEGA target chamber for integrated experiments. This talk will describe the OMEGA EP performance requirements, project status, and the development of the OMEGA EP Use Plan. This plan will describe the expected experiments, including resources required and opportunities for external user access. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under the Cooperative Agreement No. DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, October 25, 2005 2:12PM - 2:24PM |
GO1.00002: Hydrodynamic Simulations of Integrated Experiments Planned for OMEGA/OMEGA EP Laser Systems J.A. Delettrez, J. Myatt, P.B. Radha, C. Stoeckl, D.D. Meyerhofer Integrated fast-ignition experiments for the combined OMEGA/OMEGA EP Laser Systems have been simulated with the multidimensional hydrodynamic code \textit{DRACO}. The straight-line electron transport model includes energy loss due to collisions and to electric fields due to return currents. Simulations of an OMEGA cryogenic DT target designed to reach a 1-D fuel \textit{$\rho $R} of 500 mg/cm$^{2 }$ have been carried out in 2-D (with and without perturbations) to assess the sensitivity to energy, timing, and irradiance of the fast-ignitor (FI) beam. The neutron yields from integrated experiments are predicted to be in excess of 10$^{15}$ (compared to $\sim $10$^{14}$ for no ignitor beam) over a timing range of approximately 80 ps, using a 2.6-kJ FI beam and 50{\%} conversion into electrons. This talk will present new results of 2-D simulations that include the improvements in the transport model and the effects of target perturbations on the compressed core. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, October 25, 2005 2:24PM - 2:36PM |
GO1.00003: Measurements of Plasma Filling Inside a Fast-Ignitor Cone Target Using Streaked Optical Pyrometry C. Stoeckl, T.R. Boehly, J.A. Delettrez, J. Myatt, J.E. Miller, W. Theobald, T.C. Sangster, R.B. Stephens The cone-in-shell approach to fast ignition uses a high-density Au cone to keep the path where the ultrafast laser propagates free of plasma. The cone is inserted into the spherical shell that holds the fuel, with its tip close to the center of the target. The high pressure from the fuel close to peak compression drives a shock wave through the cone, which breaks out inside the cone and generates a plasma. The filling of the cone was studied experimentally on the OMEGA laser using a streaked optical pyrometer. No plasma was seen inside the cone before the assembled core reaches peak compression. A clear shock-breakout signal was recorded well after peak compression, with a shock temperature of the order of 10 eV. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, October 25, 2005 2:36PM - 2:48PM |
GO1.00004: 2D ANTHEM simulation of electron transport with B-fields in compressed cone-guided fast-ignition targets R.J. Mason Recent experiments have reported a significant increase in the neutron yield from compressed CD targets exposed to a 1.06 $\mu $m short pulse heating laser through an attached gold cone. The cone permits laser penetration through the ablation cloud to greater depths toward the target core. We have studied this scenario with the 2D implicit PIC/hybrid code ANTHEM for core densities near 1.8 x 10$^{25}$ electrons/cm$^{3}$ (200 g/cm$^{3})$ and picosecond laser intensities $\ge $ 4 x 10$^{19}$ W/cm$^{2}$. The laser deposits on the inside tip of the cone. Some hot electrons are locked on its inner surface by magnetic fields, but most stream into the core and surrounding cloud, filling them to a hot electron density beyond and up to critical. The cold return speed can become relativisitic in the cloud. The hot electron range dominates control of the core temperature, which approaches experimental values for some drag models and some geometries. Much higher temperatures can be achieved with vacuum-insulated nested cones, and heater wavelengths $\le $ 0.35 $\mu $m. [Preview Abstract] |
Tuesday, October 25, 2005 2:48PM - 3:00PM |
GO1.00005: Energy Deposition, Penetration, Blooming of Energetic Electrons in Fast Ignition and Preheat Scenarios R.D. Petrasso, C.K. Li For plasmas of arbitrary Z and density, the penetration, energy deposition, blooming, and straggling of energetic electrons are analytically modeled. Calculations spanning 25 orders of magnitude in density apply to fast ignition (n$\sim $10$^{26}$/cc), electron preheat (n$\sim $10$^{23}$/cc) and relativistic astrophysical jets (n$\sim $ 10/cc). It is shown that $\rho <$x$>$, the product of density and linear penetration, is a basic parameter and that blooming and straggling have a strong Z dependence. For fast-ignition with 1-MeV electrons in DT plasma, $\rho <$x$>$ = 0.42 g/cm$^{2 }$, $<$x$>$ = 14 $\mu $m and bloom = 5 $\mu $m; the blooming-to-penetration ratio is 0.35; in Cu (Z=29) plasma of the same electron density, the ratio is 1.1. For preheat with 100 keV electrons in DT ice, $\rho <$x$>$ = 0.007 g/cm$^{2 }$, $<$x$>$ = 280 $\mu $m, close to the 300-$\mu $m ice-layer thickness prescribed for NIF direct-drive designs. For the astrophysical jet, $\rho <$x$>$ = 0.42 g/cm$^{2 }$ and $<$x$> \quad \sim $ 10$^{4}$ light years. These calculations will be used to establish requirements for fast ignition and tolerable levels of electron preheat for ICF targets. This work was supported in part by LLE, LLNL, the U.S. DoE, the Univ. of Rochester Fusion Science Center. [Preview Abstract] |
Tuesday, October 25, 2005 3:00PM - 3:12PM |
GO1.00006: Relativistic Electron Beam Microinstabilities in the Fast-Ignition Regime R.W. Short, J. Myatt Relativistic electron beams for fast ignition can be disrupted by the growth of small-scale instabilities such as filamentation and the two-stream instability, which tend to develop faster than macroinstabilities such as kink and pinch instabilities. In this talk a comprehensive dispersion relation for these microinstabilities is presented and its consequences explored for various ranges of plasma and beam parameters. The dispersion relation includes both electrostatic and electromagnetic terms, allows arbitrary directions and complex values for the perturbation wave vector, and can incorporate fully relativistic Maxwell--Boltzman--Juttner distribution functions or approximations thereto. It can therefore be used to calculate spatial as well as temporal growth rates, to investigate both absolute and convective forms of the instabilities, and to determine the relative importance of electromagnetic (filamentation) and electrostatic (two-stream) instabilities, as well as mixed forms. The results should be useful in benchmarking and optimizing FI simulations using codes such as LSP. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under the Cooperative Agreement No. DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, October 25, 2005 3:12PM - 3:24PM |
GO1.00007: High-Density and High-\textit{$\rho $R} Fuel Assembly for Fast-Ignition Inertial Confinement Fusion R. Betti, C. Zhou Scaling relations to optimize implosion parameters for fast-ignition inertial confinement fusion are derived and used to design fast-ignition targets relevant to direct-drive inertial fusion energy (IFE). A method to assemble thermonuclear fuel at high densities, at high \textit{$\rho $R}, and with a small-size hot spot is presented. Massive cryogenic shells can be imploded with a low implosion velocity $V_{I}$ on a low adiabat \textit{$\alpha $} using the relaxation-pulse technique.\footnote{R. Betti\textit{ et al.}, Phys. Plasmas \textbf{9}, 2277 (2002).} While the low $V_{I}$ yields a small hot spot, the low \textit{$\alpha $} leads to large peak values for the density and areal density. It is shown that a 750-kJ laser can assemble fuel with $V_{I}\approx $ 1.7 $\times $ 10$^{7}$ cm/s, \textit{$\alpha $} $\approx $ 0.7, \textit{$\rho $} $\approx $ 400 g/cc, \textit{$\rho $R }$\approx $ 3 g/cm$^{2}$, and a hot-spot volume less than 10{\%} of the compressed core. If fully ignited, this fuel assembly can produce yields of $\sim $150, of interest to IFE applications. This target can also be shock-ignited with a 250-kJ laser-driven spherically convergent shock yielding a gain exceeding 120. This work has been supported by the U.S. Department of Energy under Cooperative Agreement ER54789 and DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, October 25, 2005 3:24PM - 3:36PM |
GO1.00008: Shock Fast Ignition of Thermonuclear Fuel with High Areal Density C. Zhou, R. Betti A novel method separating the assembly and ignition phases of thermonuclear fuel is presented. Massive cryogenic shells are first imploded with a low implosion velocity on a low adiabat using the relaxation laser pulse technique.\footnote{ R. Betti \textit{et al}., Phys. Plasmas \textbf{9}, 2277 (2002).} While the low implosion velocity yields a small, low-temperature hot spot, the low adiabat of the fuel leads to large peak values of the density and areal density. The assembled fuel is then ignited from the central hot spot heated by the collision of a spherically convergent shock and the return shock. The resulting thermonuclear gain can be significantly larger than in standard hot-spot ignition for equal driver energy. Shock fast ignition can be tested on the National Ignition Facility through relatively low energy implosions ranging from 130 kJ to 800 kJ, yielding gains from 60 to 110. This work has been supported by the US Department of Energy under Cooperative Agreement ER54789 and DE-FC03-92SF19460. [Preview Abstract] |
Tuesday, October 25, 2005 3:36PM - 3:48PM |
GO1.00009: Reduced Mass Targets Heated by Ultra-Intense Lasers as a Means of Creating Kilovolt Plasmas at Solid Densities Scott C. Wilks, R.I. Klein, A. Mackinnon, S.J. Moon, P.K. Patel, B.A. Remington, D. Ryutov, R. Shepherd, H. Chung, K. Fournier, G. Gregori, S. Glenzer, S. Hansen, R. Snavely, R. Town, J.M. Hill We introduce a novel target design that allows high temperature ($\sim $ 1 keV) solid density plasmas to be created using ultra-intense laser pulses. It is found that if targets composed of copper and tamped with aluminum are irradiated with $\sim $ 100 Joule, $\sim $ 10 picosecond lasers, a significant increase in temperature over standard foil targets can be achieved. Energy considerations will be used to theoretically predict achievable temperatures for a wide range of laser parameters for current and planned lasers, as well as a wide range of materials. Comparison of these predictions with recent experimental results obtained from the RAL Petawatt laser will also be presented. This work was performed under the auspice of the Department of Energy under Contract No. W-7405-Eng-48 and by the Laboratory Directed Research and Development (LDRD) Programs 04-ERD-028 and 04-ERD-023. [Preview Abstract] |
Tuesday, October 25, 2005 3:48PM - 4:00PM |
GO1.00010: WITHDRAWN--Kilo-Volt Heating in Very High Energy Density Experiments with Short-Pulse Laser Irradiation of Solids Richard Snavely Ultra-intense lasers are capable of extreme energy densities. Experiments are performed to study various mechanisms of intense laser heating at the 100 TW to 1 PW levels. Heating via Wiebel instabilities, Ohmic return currents and refluxing electron electrostatic confinement by Debye sheath potentials, are studied with the technique of laser irradiated reduced mass targets. Experiments were performed at .5-10 ps and at 100 J and 400 J levels using the TAW and Petawatt beams of the Vulcan laser facility at Rutherford Appleton Laboratory. Evidence for enhanced energy density in both planar micro targets and cone-fiber configurations is presented. New diagnostics were developed: two-color XUV/soft x-ray imaging of Planck radiation, and a dual channel Highly Oriented Pyrolytic Graphite (HOPG) spectrometer in addition to the Bragg crystal imaging of Cu-K$_{\alpha }$. Preliminary estimates indicate enhanced heating of 100 eV to kilo-Volt temperatures in high-density Cu masses. In addition, 10 um diameter cone-fiber data shows good relativistic electron transport to 1 mm lengths. Issues regarding surface versus bulk heating will be discussed. This work was performed as part of a United Kingdom university collaboration funded by the Council for the Central Laboratory of the Research Councils (CCLRC). [Preview Abstract] |
Tuesday, October 25, 2005 4:00PM - 4:12PM |
GO1.00011: Numerical modeling of laser isochoric heating of hot dense matter Yasuhiko Sentoku, Andreas Kemp, Mike Bakeman, Radu Presura, Thomas Cowan Ultra-intense short-pulse lasers are important tools for creating short-lived high energy plasmas, however to date, it has not been possible to create several hundred eV solid density matter because of the rapid transport of the laser-generated hot electrons throughout the target volume. We proposed a new way to isochorically heat matter at solid density to extreme temperatures by magnetic confinement of laser- generated hot electrons for several picoseconds by application of a multi-MG external field. In advance of an experiment at the Nevada Terawatt Facility (NTF), using a 100 TW- class laser, which will be synchronized to a 1MA Z-pinch machine, we have performed theoretical studies using a collisional particle-in-cell codes PICLS, which is optimized for a study of isochoric heating of solid density plasmas. One of the critical issues of the PIC simulation of the the laser isochoric heating is significant numerical heating, which makes difficult to simulate 100 eV solid density plasmas over picoseconds by PIC. In this talk, we introduce a couple of numerical techniques to extend the grid size with suppressing the numerical heating and also the full relativistic collision model to simulate the isochoric heating by ultra-intense lasers. This work was supported by DOE/NNSA-UNR grant DE-FC52-01NV14050. [Preview Abstract] |
Tuesday, October 25, 2005 4:12PM - 4:24PM |
GO1.00012: Probing the disassembly of ultrafast laser heated gold using frequency domain interferometry. Tommy Ao, Yuan Ping, Klaus Widmann, Dwight Price, Al Ellis, Andrew Ng, Edward Lee Ultrafast laser heating of a solid offers a unique approach to examine the behavior of non-equilibrium high energy density states. Initially, the electrons are optically excited while the ions in the lattice remain cold. This is followed by electron-electron and electron-phonon relaxation. Recently, experiments were performed in which ultrathin freestanding, gold foils were heated by a femtosecond pump laser to a strongly overdriven regime with energy densities reaching 20 MJ/kg. Interestingly, femtosecond laser reflectivity and transmission measurements on the heated sample revealed a quasi-steady-state behavior before the onset of hydrodynamic expansion. This led to the conjecture of the existence of a metastable, disordered state prior to the disassembly of the solid. To further examine the dynamics of ultrafast laser heated solids, frequency domain interferometry (FDI) was used to provide an independent observation. The highly sensitive change in the phase shift of the FDI probe clearly showed evidence of the quasi-steady-state behavior. The new experiment also yielded a detailed measurement of the time scale of such a quasi-steady-state phase that may help elucidate the process of electron-phonon coupling and disassembly in a strongly overdriven regime. [Preview Abstract] |
Tuesday, October 25, 2005 4:24PM - 4:36PM |
GO1.00013: Preplasma Expansion Measurements by Observing Prepulse-Induced Proton Energy Distribution in Ultrahigh-Intensity-Laser and Solid-Target Interactions Teh Lin, Takeshi Matsuoka, Anatoly Maksimchuk, Donald Umstadter Different preplasma conditions in laser-plasma interactions affect the plasma density profile and change the plasma heating mechanism and efficiency. However, to measure its effect involves complicated experimental setups. We used a novel and easy-manipulated method to measure the preplasma, which is produced by the prepulse of the ultrahigh intensity laser and solid targets. By introducing prepulse delays (1.5ps$\sim $600ps) and intensities (0$\sim $10{\%}), different maximum proton energies at target normal direction will be generated from the laser-plasma interactions. A peaked distribution of the maximum proton energy with respect to the prepulse delays is observed, and with different prepulse delays, different widths of the peaks suggest the preplasma expansion behavior. Furthermore, a clear correspondence of preplasma expansion scale and proton acceleration efficiency is derived to explore the optimal preplasma scale length to provide higher maximum proton energy. This experiment was conducted with the frequency doubled laser pulses from the T$^{3}$ laser system at the Center for Ultrafast Optical Science of the University Michigan. The pulse energy is up to 1 J, a pulse duration of 400 fs, the wavelength is 0.53 $\mu $m and the maximum intensity is 10$^{19}$ W/cm$^{2}$. The prepulses are introduced by inserting a Michelson interferometer in the laser chain. [Preview Abstract] |
Tuesday, October 25, 2005 4:36PM - 4:48PM |
GO1.00014: Anomalous Transmission of High Contrast Relativistically Intense Short Laser Pulses through Thin Metal Foils T. Matsuoka, A. Maksimchuk, T. Lin, O.V. Batishchev, A.A Batishcheva, V. Yu. Bychenkov The frequency doubled laser pulses from the T$^{3}$ laser system at the Center for Ultrafast Optical Science of the University Michigan (with energy up to 1 J, a pulse duration of 400 fs, the wavelength is 0.53 $\mu $m and the maximum intensity is 10$^{19}$ W/cm$^{2})$ has been used for the measurement of the light transmitted through thin metal targets. The intensity contrast ratio of the laser pulses was better than 10$^{-9}$ which is low enough to suggest the interaction with solid density plasma. We observed the transmittance of the laser pulse through the aluminum foil with thickness up to 4 $\mu $m and found that this radiation is polarized and centered at 0.53 $\mu $m. We found that for 0.8 $\mu $m thick foils the transmission was anomalously high ($\sim $10$^{-4})$ and can't be explained by the skin effect for relativistic pulse. The performed adaptive grid PIC simulations show good agreement between the calculated transmission coefficient and the experimental transmittance. Energetic electrons produced by the interaction are responsible for the anomalous transmission. [Preview Abstract] |
Tuesday, October 25, 2005 4:48PM - 5:00PM |
GO1.00015: Influences of target size on hot electron number and emission image Toshinori Yabuuchi, Ryosuke Kodama, Ken Adumi, Motonobu Tampo, Shinya Awano, Hideaki Habara, Kiminori Kondo, Kazuo Tanaka, Kunioki Mima The number of electrons accelerated by ultra-intense laser-solid interactions could be as high as $10^{13}$. Therefore, intense electric fields and magnetic fields are generated around the electron cloud. The electrons are influenced by these fields especially at the rear side of the solid target. The electric field is caused by the charge separation between the target (positive charge) and the electron cloud (negative charge). We assume that the magnitude of the electric field depends on the charge density. If the diffusion speed of the positive charge in the target is fast enough, the charge density on the target surface could be varied depending on target material, size and shape. In this study, we keep target material and shape, but change only the target size. The detected electron number and emission image changed with the target size. These dependences can be explained by the formation of the electric fields. [Preview Abstract] |
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