Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Plasma Physics
Volume 55, Number 15
Monday–Friday, November 8–12, 2010; Chicago, Illinois
Session CO6: Fast Ignition I |
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Chair: Brian Albright, Los Alamos National Laboratory Room: Columbus GH |
Monday, November 8, 2010 2:00PM - 2:12PM |
CO6.00001: Fast Ignition Relevant Hot Electron coupling at 1$\omega$ and 2$\omega$ D.P. Higginson, C.D. Chen, T. Ma, P.K. Patel, H. McLean, M. Key, S. Wilks, T. Bartal, H. Sawada, C. Jarrot, T. Yabuuchi, F.N. Beg, R.B. Stephens, E. Giraldez, K. Flippo, S. Gaillard, P.A. Norreys, S. Baton, F. Perez, H.-P. Schlenvoigt, G.E. Kemp, A. Krygier, R.R. Freeman, L.D. Van Woerkom 2$\omega$ lasers ($\lambda=0.5\mu$m) are expected to create favorable hot electron temperatures for fast ignition and to reduce the electron transit distance to the core due to high intensity-contrast ratios of better than $10^{-10}$. These two effects were isolated by comparing a high contrast 2$\omega$ laser (pico2000) against 1$\omega$ lasers at both low (Titan) and high contrast (Trident). Identical cone-wire targets (Au cones with Cu wires) were used to evaluate laser coupling of fast ignition relevant hot electrons into the wire. Calibrated diagnostics imaged and measured absolute K shell fluorescence from the wire. Coupling is found to increase by a factor of 2 in the high contrast case and electron temperature increased with $I\lambda^2$. Analysis was performed with hybrid PIC transport code ZUMA to infer absolute electron coupling. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and DE-AC52 07NA27344(ACE). [Preview Abstract] |
Monday, November 8, 2010 2:12PM - 2:24PM |
CO6.00002: Z Effects on Laser Energy Absorption and Fast Electron Transport in Fast Ignition ICF S. Chawla, M.S. Wei, L. Jarrott, H. Sawada, B. Westover, F.N. Beg, R.B. Stephens, K. Akli, C.D. Chen, D. Hey, H. Chen, H.S. McLean, P.K. Patel, Y. Sentoku, A. Link, V. Ovchinnikov, L. Van Woerkem, H. Friesen, R. Fedosejevs, J. Pasely, A. Morace, D. Batani, P. Koester, L. Gizzi We report on a systematic study of the Z-effects on laser energy absorption and energy coupling using multilayer solid targets consisting of interaction and transport layers made of different Z materials and fluorescent layers in planar and cone geometries. The experiment was carried out on the Titan laser (0.7 ps, 150 J, 10$^{20}$ W/cm$^{2}$ peak intensity). Results show several clear trends: i)electron flux transport systematically decreased with increasing $Z$, ii)increase in the laser intensity reduced the laser energy conversion to fast electrons in the planar geometry for high Z material and iii)in cone geometry, coupling was reduced 1.5x compared to flat targets when a 2x lower intensity was used. Detailed results will be presented. [Preview Abstract] |
Monday, November 8, 2010 2:24PM - 2:36PM |
CO6.00003: Ionization and Z Effects in Cone Wire Experiments* Brian Chrisman, Toshinori Yabuuchi, Mingsheng Wei, Tammy Ma, Farhat Beg, Yasuhiko Sentoku, Pravesh Patel, Harry McLean, Richard Stephens In cone-wire experiments, ultra-intense lasers ($>$10$^{18}$ W/cm$^{2})$ are focused at the tip of a cone with a trailing wire attached in order to characterize the cone as a hot electron source for Fast Ignition. Laser pre-pulse simulations predict preformed plasma inside the cone with which the main, ultra-intense pulse interacts. For high Z cones, ionization and Bremsstrahlung significantly alter densities and temperatures of the plasma within half a picosecond. This changes the characteristics of hot electrons generated. The PICLS Particle-in-Cell code has been used to study above-mentioned effects. The model includes laser absorption, dynamic ionization, radiative losses, and particle collisions. Results of PICLS investigations of Z dependence show the dynamics of ionization and Bremmstrahlung within the cone's preformed plasma are complex and must be included when modeling high Z cone targets. *This work performed under the auspices of the US DOE by LLNL under Contract DE-AC52-07NA27344 and DE-FG-02-05ER54834(ACE). [Preview Abstract] |
Monday, November 8, 2010 2:36PM - 2:48PM |
CO6.00004: Bremsstrahlung measurements for fast electron characterization at OMEGA EP Hiroshi Sawada, Pravesh Patel, Cliff Chen, Harry McLean, Mike Key, Toshinori Yabuuchi, Farhat Beg, Kramer Akli, Richard Stephens, Wolfgang Theobald, Philip Nison, Christian Stoeckl Fast electrons in 1-3 MeV energy range are required for efficient core heating in Fast Ignition concept. An experiment to infer the fast electron spectrum from the bremsstrahlung x rays has been performed at the OMEGA EP using two pulse lengths, 1 ps at 150 J and 10 ps at 1000 J. The EP beam with the intensity of $\sim $ 5$\times $10$^{18}$ W/cm$^{2}$ was focused normal onto a planar Al target with a buried Cu layer. The bremsstrahlung x-ray emission was measured with a stack of image plates and differential filtering at the front and rear sides. The Cu K$\alpha $ from the tracer layer was measured using an absolutely calibrated HOPG crystal spectrometer. Preliminary results show that the measured laser-to-electron conversion efficiency and energy spectrum are similar at 1 and 10 ps shots. A detailed data analysis and consequences on FI will be presented. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and DE-FG-02-05ER54834 (ACE). [Preview Abstract] |
Monday, November 8, 2010 2:48PM - 3:00PM |
CO6.00005: Bremsstrahlung and KA Measurements of Laser to Hot Electron Coupling in Fast Ignition Conical Geometries Cliff Chen, F.N. Beg, J.R. Davies, L. Divol, R. Fedosjevs, R.R. Freeman, H. Friesen, A.J. Kemp, M.H. Key, K. Li, A. Link, H. McLean, A. Morace, V. Ovchinnikov, P.K. Patel, Y. Ping, H. Sawada, A. Sorokovikova, R. Stephens, M. Streeter, L. Van Woerkom, D. Wertepny, B. Westover, S.C. Wilks The laser coupling efficiency into forward going relativistic electrons was studied on the Titan laser (1054 nm, 150 J, 0.7 p.s., 10$^{20}$ W/cm$^2$) at LLNL in a conical geometry using two separate techniques: an array of absolutely calibrated Bremsstrahlung spectrometers (differential sensitivity up to 700 keV) measuring emission from an Al cone-multilayer foil target, and a spherical Bragg crystal imager to image the Cu KA emission from the 1-D electron transport along an Al cone-Cu wire target. The electron transport and x-ray emission is modeled with the hybrid-PIC code LSP. [Preview Abstract] |
Monday, November 8, 2010 3:00PM - 3:12PM |
CO6.00006: Fast Ignition Modeling with Realistic Electron Source D.J. Strozzi, M. Tabak, A.J. Kemp, L. Divol, D.P. Grote, M.H. Key, D.R. Welch, B.I. Cohen, R.P.J. Town We perform electron-beam transport simulations with the LSP code [D. R. Welch et al., Phys. Plasmas 13, 063105 (2006)] to determine the ignition requirements for cone-guided fast ignition. We run LSP as a direct-implicit PIC code, with a fluid treatment of the dense background. We use idealized plasma conditions for dense ($\sim$ 300 g/cm$^3$) DT fuel with a carbon or other low- to mid-Z cone. We do not include a laser, but excite an electron beam in the cone with a distribution based on explicit-PIC calculations with the PSC code of the short-pulse laser-plasma interaction. These simulations show the electron source has a two-temperature energy spectrum, and a relatively large angular divergence. This second fact pushes us toward ignition hot spots whose radial width exceeds their lateral depth, and larger beam energies. In particular, the role of short-pulse laser characteristics (e.g. wavelength), beam radius, magnetic-field focusing by resistivity tailoring, and cone-fuel standoff distance are explored. We are generalizing these burn-free calculations to include fusion reactions. [Preview Abstract] |
Monday, November 8, 2010 3:12PM - 3:24PM |
CO6.00007: Simulation Study of Pre-Plasma Effects on Core Heating in FIREX-I Tomoyuki Johzaki, Hideo Nagatomo, Atsushi Sunahara, H.-B. Cai, Hitoshi Sakagami, Kunioki Mima, Hiroyuki Shiraga, Hiroshi Azechi In ILE, Osaka University, using a 4-beam bundled new ultra-intense laser LFEX, the FIREX project has been started. About 30-fold enhancement in neutron yields was achieved by the heating laser irradiation at the first integrated experiments where the LFEX laser was operated with one-beam and low-energy mode. This enhancement is quite smaller than that in the previous experiments using PW laser ($\sim $1000-fold enhancement). One reason for the low neutron yields is existence of relatively high-level pre-pulse. The pre-pulse generates the long-scale pre-formed plasma, which results in leading the fast electron generation point away from the core and in generating very energetic fast electrons not contributing the core heating. As the results of 2D PIC simulations, we showed the reduction of core heating efficiency due to the pre-plasma. The double cone effects for the case with pre-plasma are also discussed. In addition, we proposed use of thin foil, which is located at the entrance of the cone as absorber of pre-pulse, to reduce the pre-pulse level. We also discuss the thin foil effects. [Preview Abstract] |
Monday, November 8, 2010 3:24PM - 3:36PM |
CO6.00008: Simultaneous Investigation of Hot-electron Transport and Preplasma Formation in Cone-wire Targets H. Friesen, H.F. Tiedje, S. Singh, Y.Y. Tsui, R. Fedosejevs, T. Ma, D. Hey, Y. Ping, C.D. Chen, A. MacPhee, M.H. Key, H.S. McLean, P. Patel, A. Mackinnon, J. Pasley, K.U. Akli, R. Stephens, A. Link, D.W. Schumacher, R.R. Freeman, L.D. Van Woerkom, B. Westover, M.S. Wei, F.N. Beg The generation and transport of MeV electrons is essential to the realization of Fast Ignition fusion. An important factor in determining the hot electron source is the preplasma distribution that is inevitably formed even in high-contrast short-pulse laser systems. A larger preplasma moves the critical surface further from the region where heating is required, and has a significant effect on the electron source and transport. In this paper we present analysis of results where bremstrahhlung emission from the preplasma region was imaged simultaneously with k-alpha emission from a copper tracer in cone-wire targets using a grazing-incidence x-Kirkpatrick-Baez x-ray microscope. The predicted scalings from simulations and theory will be compared with experimental results to determine unique characteristics of how the hot electron source and transport are affected by the presence of the wire as well as preplasma. [Preview Abstract] |
Monday, November 8, 2010 3:36PM - 3:48PM |
CO6.00009: Controlling the Divergence of Laser-Generated Fast Electrons Through Resistivity Gradients in Fast-Ignition Targets A.A. Solodov, R. Betti, K.S. Anderson, J.F. Myatt, W. Theobald, C. Stoeckl The divergence of laser-generated fast electrons is a crucial parameter that determines the incident petawatt laser energy in fast-ignition targets. Experiments and particle-in-cell (PIC) simulations predict a large divergence of laser-generated fast electrons, underlining the importance of finding regimes in which electron divergence can be controlled. This paper investigates the recently suggested scheme of controlling the fast-electron divergence using a resistivity mismatch in structured targets, in the regime of realistic ignition-relevant laser energies and intensities. This analysis applies to ignition-relevant energies of the fast-electron beam, different from most studies and proof-of-principle experiments performed so far for low-energy laser pulses and room-temperature targets. Hybrid-PIC simulations using the code \textit{LSP} are performed for cone-in-shell fast-ignition targets with cones comprised of different material layers. The effects of wires attached to the cone tip to guide hot electrons to the dense core are also investigated. This work was supported by the U.S. Department of Energy under Cooperative Agreement Nos. DE-FC02-04ER54789 and DE-FC52-08NA28302. [Preview Abstract] |
Monday, November 8, 2010 3:48PM - 4:00PM |
CO6.00010: Dynamics of relativistic laser-plasma interaction: filamentation, ponderomotive steepening and hole boring Y. Ping, A. Kemp, C. Chen, D. Hey, P. Patel, H. McLean, M. Key, S. Wilks, L. Divol, E. Kemp, A. Link, L. Woerkom, R. Freeman, D. Turnbull, S. Chawla, B. Westover, C. Jarrot, H. Sawada, F. Beg, K. Akli, R. Stephens We performed time-resolved measurements of the wavelength shift of specularly reflected light from flat targets at fast-ignition relevant intensities with subpicosecond time resolution. A large red shift was observed at beginning of the laser pulse, indicating the onset of filamentation. The plasma density profile is modified consequently due to ponderomotive pressure and the effect on the hot electron energy spectrum will be discussed. Comparison with 2D PIC simulations and the dependence on preplasma scale length, laser intensity and pulse duration will also be presented. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Monday, November 8, 2010 4:00PM - 4:12PM |
CO6.00011: Interaction of intense laser pulses with plasma gradients at fast-ignition scales Andreas Kemp, Laurent Divol Fast ignition depends on the efficient conversion from picosecond-scale intense laser pulses into MeV electrons to heat the compressed core of an inertial confinement fusion target. We study the interaction of multi-picosecond, intense laser pulses with plasma density gradients, using full-scale particle-in-cell simulations. We find that, in contrast to the diffraction-limited sub-ps laser pulses used in experiments today, the long-energetic-large-spot pulses relevant to fast ignition create over a few picoseconds a plasma profile and a hot electron spectrum that are nearly independent of the initial conditions. We discuss scaling properties with laser intensity, spot size and plasma scale length. [Preview Abstract] |
Monday, November 8, 2010 4:12PM - 4:24PM |
CO6.00012: Fast ignition studies with an improved transport model implemented in a 2D radiation hydrodynamic code Philippe Nicolai, Jean-Luc Feugeas, Cyril Regan, Jerome Breil, Arnaud Debayle, Bruno Dubroca, Ludovic Hallo, Javier Honrubia, Marina Olazabal, Joao Santos, Benjamen Vauzour, Vladimir Tikhonchuk A two dimensional (2D) radiation hydrodynamic code is a powerful tool to study the relativistic electron or energetic ion transport in the frame work of the Inertial Confinement Fusion (ICF). However, it needs to be complemented with a sufficiently precise and robust model of electron transport. The radiation hydrodynamic code CHIC [1] has been combined with a new efficient fast electron transport model, M1 [2]. We use this tool to address several issues related to recent studies of the fast ignition scheme. Experiment related to the energetic particle transport through a warm dense matter and recent direct drive fast ignition target designs will be presented in this talk and the energy deposition and plasma heating effects induced by energetic particle beam will be discussed. \\[4pt] [1] Breil et al, J.Co.Ph. 224, 785 (2007) \\[0pt] [2] Dubroca et al, to be published in Eu.J.Ph.D [Preview Abstract] |
Monday, November 8, 2010 4:24PM - 4:36PM |
CO6.00013: A self consistent model for relativistic electron transport in a resistive plasma Damon Swatton, Matthew Hunt, Stephen Hughes, David Chapman In this paper we develop a model for describing the early time transport of hot electrons in a resistive plasma to investigate the onset of hot electron field inhibition in laser-plasma experiments. We consider a 1D plasma into which a monoenergetic, relativistic beam of electrons is injected. The beam is represented by a collisionless fluid, so that the momentum conservation and continuity equations apply, and the electric field is calculated from Ampere's law. We find that the plasma supplies a return current that rapidly neutralises the inward flux, and that the electric field becomes a constant behind the beam front. We show that these findings agree well with Monte Carlo electron transport codes. We consider our model to be an improvement on other analytical models because: (i) it does not assume a vanishing net current density; (ii) the system is closed via Maxwell's equations rather than by assuming a Boltzmann distribution for the hot electrons; and (iii) it does not predict the infinite electron speeds characteristic of diffusion models. It also offers a future method for considering a temperature dependent resistivity, or the two-dimensional problem where magnetic fields are important. [Preview Abstract] |
Monday, November 8, 2010 4:36PM - 4:48PM |
CO6.00014: A new tool for efficient full density scale modeling of fast ignition Frederico Fiuza, Michael Marti, Ricardo Fonseca, Jonathan Davies, Luis Silva, John Tonge, Joshua May, Warren Mori Fast ignition modeling presents a grand challenge due to the different spatial and temporal scales involved and the need to accurately model relativistic laser absorption and inward and return current patterns across collisionless and collisional regions. Recently, Cohen et al. proposed a novel framework for fast ignition simulations that merges accurate collisional PIC models between regions where only the field solver is reduced in the collisional region. This framework has been integrated into OSIRIS, which together with higher order particle shapes and dynamic load balancing is allowing the first simulations of fast ignition targets over full density and time scales. We will demonstrate how OSIRIS can be used to perform the first time full-scale one-to-one modeling of fast ignition, where the critical issues of laser absorption, electron beam divergence, and energy deposition with the compressed core will be addressed in a fully self-consistent manner. We also show how this new tool can be applied to other high-energy density problems, like ion acceleration in laser-solid interactions and shock ignition. [Preview Abstract] |
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