Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session BO4: Fast/Shock Ignition Computation/Theory |
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Chair: Kenneth Anderson, University of Rochester Room: 551AB |
Monday, October 29, 2012 9:30AM - 9:42AM |
BO4.00001: Shock ignition: gain curves and energy-wavelength scaling Stefano Atzeni, Alberto Marocchino, Angelo Schiavi In shock ignition, separation of the stages of fuel compression and hot spot creation introduces some degree of design flexibility. A lower implosion velocity can be compensated for by a more intense ignition pulse. Flexibility increases with target (and driver) size and allows for a compromise between energy gain and risk reduction. Having designed a reference ignition target, we have developed an analytical model for (up)-scaling targets, and for estimating target gain, as a function of laser energy and parameters related to hydro- and plasma-instabilities. Detailed 1D simulations confirm the model and generate gain curves, while 2D simulations show how different design options affect robustness to asymmetries caused by laser nonuniformities and target mis-positioning. The previous results apply to UV ($\lambda = 0.35~\mu$m) laser light. We also show that our scaling model can be used in the design of targets driven by green laser ($\lambda = 0.53~\mu$m). 1D simulations show that gain in the range 100 -- 200 can be obtained for total green light laser energy in the range 1.5 -- 3 MJ, while operating in the same laser-plasma regime as the UV-driven targets. [Preview Abstract] |
Monday, October 29, 2012 9:42AM - 9:54AM |
BO4.00002: Analysis of Fast Electrons in Shock-Ignition Implosions on OMEGA R. Nora, W. Theobald, R. Betti, J.A. Delettrez, M. Lafon We present an analysis on the effects of fast electrons in shock-ignition inertial confinement implosions on OMEGA. In direct-drive configuration, electrons in the corona can be accelerated to tens of keV's via laser--plasma instabilities, such as two-plasmon decay and stimulated Raman scattering. These moderately hot electrons have the potential to quench ignition if directed into the target and their energy is deposited into the cold fuel, resulting in a significantly higher adiabat. Alternatively, in shock-ignition implosions these hot electrons can strengthen the ignitor shock if their energy is below $\sim $100 keV.\footnote{ R. Betti\textit{ et al.}, J. Phys., Conf. Ser. \textbf{112}, 022024 (2008).} We present experimental hard x-ray data that indicates $\sim $40-keV Maxwellian electrons are generated with a conversion efficiency of 5{\%} to 15{\%}, as well as correlations between the hard x-ray signal and several important implosion parameters. \textit{LILAC} simulations with the inclusion of hot electrons are shown to agree with the experimental results. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Monday, October 29, 2012 9:54AM - 10:06AM |
BO4.00003: Integrated hybrid-PIC modeling of fast ignition Frederico Fiuza, Ricardo Fonseca, Luis Silva, Warren Mori The integrated modeling of fast ignition of ICF targets is important to understand the electron source requirements and the optimal laser/target configuration for ignition. We have used the hybrid-PIC algorithm of OSIRIS [F. Fiuza et al., PPCF 53, 074004 (2011)] to model fast ignition in a self-consistent way at realistic densities, spatial and temporal scales. We will present a detailed analysis of the laser absorption and the fast electron source characterization for different laser and target parameters in 2D and 3D. Integrated electron transport and energy deposition calculations for realistic ignition laser parameters (100 kJ, multi-ps) will be shown and used to identify the electron source requirements for ignition. The control of the electron energy distribution and divergence by using of an external magnetic structure and/or multiple radially incident short pulses will be discussed, showing the possibility of achieving conditions consistent with ignition. [Preview Abstract] |
Monday, October 29, 2012 10:06AM - 10:18AM |
BO4.00004: Burning DT Plasmas with Ultrafast Soft X-Ray Pulses S.X. Hu, V.N. Goncharov, S. Skupsky Fast ignition with narrowband, coherent ultrafast soft x-ray pulses\footnote{S. X. Hu, V. N. Goncharov, and S. Skupsky, ``Burning Plasmas with Ultrashort Soft-X-Ray Flashing,'' to be published in Physics of Plasmas.} has been investigated for cryogenic deuterium--tritium (DT) plasma conditions achieved on the OMEGA Laser System. In contrast to using hard x-rays (\textit{h$\nu $} = 3 to 6 keV) proposed in the original x-ray fast-ignition proposal, we find that soft x-ray sources with \textit{h$\nu $} $\approx $ 500-eV photons can be more suitable for igniting the dense DT plasmas. Two-dimensional radiation--hydrodynamics simulations have identified the breakeven conditions for realizing such a ``hybrid'' ignition scheme (direct-drive compression with soft x-ray heating) with 50-\textit{$\mu $}m-offset targets: an $\sim $10-ps soft x-ray pulse (\textit{h$\nu $} $\approx $ 500 eV) with a total energy of 500 to 1000 J to be focused into a 10-\textit{$\mu $}m spot size. A variety of x-ray pulse parameters have also been investigated for optimization. It is noted that an order of magnitude increase in neutron yield has been predicted even with x-ray energy as low as $\sim $50 J. Scaling this idea to a 1-MJ large-scale NIF target, a gain above $\sim $30 can be reached with the same soft x-ray pulse at 1.65-kJ energy. Even though such energetic x-ray sources do not currently exist, we hope that the proposed ignition scheme may stimulate efforts on generating powerful soft x-ray sources in future. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Monday, October 29, 2012 10:18AM - 10:30AM |
BO4.00005: Heating of the imploded plasma by fast ions in the fast ignition scheme Atsushi Sunahara, Tomoyuki Johzaki, Hitoshi Sakagami, Hideo Nagatomo, Shinsuke Fujioka, Yasunobu Arikawa, Youichi Sakawa, Hiroyuki Shiraga, Kunioki Mima, Hiroshi Azechi In the fast ignition scheme of laser fusion, the laser-accelerated particles~are used to heat the imploded plasma core. We have been tying to increase the~energy coupling from heating laser~to the plasma core by generating MeV fast~electrons with improved high-contrast of the heating laser,~usage of magnetic field,~and optimization of cone shape. For further improving the~energy coupling, we are trying to use~laser-accelerated ion for heating plasma~in addition to the~heating by fast electrons. When CD plasma is directly~irradiated by the ultra-intense laser,~C and D ions can be~accelerated~as well as~electrons. Based on the~hole-boring~model by S. C. Wilks PRL 69 (1992) 1383, ion can be accelerated up to MeV kinetic energy by ultra intense laser, and its conversion efficiency~from the laser to fast ions~can be estimated to be order of 1{\%}.~This ion acceleration~is confirmed by~PIC simulation with the FIREX~condition, Sakagami et al., Nuclear fusion 49 (2009) 075026. In this paper, we show the concept and numerical analysis of ion acceleration and its energy deposition to the plasma.~ [Preview Abstract] |
Monday, October 29, 2012 10:30AM - 10:42AM |
BO4.00006: Instabilities for a relativistic electron beam interacting with a laser-irradiated plasma Hrachya B. Nersisyan, Claude Deutsch The effects of a radiation field(RF) on the unstable modes developed in a relativistic beam-plasma interaction are investigated assuming a RF frequency $>$ electron plasma frequency. These unstable modes are parametrically coupled to each other due to the RF and show up as a mix between 2-stream and parametric instabilities. The dispersion equations are derived by linearization of kinetic equations for a beam-plasma system as well as by the Maxwell equations [1]. We present a comparison of our analytical and numerical results obtained for nonzero RF with those for vanishing RF. Assuming that the drift velocity Ub is parallel to the wave vector k of the excitations, two specific transverse and parallel configurations of the polarization vector E0 of the RF w.r.t k are considered. In both geometries, resonant and nonresonant couplings between different modes are likely to occur. Largest growth rates are expected at transverse configuration when E0 is perpendicular to k. The spectrum of unstable modes in the Omega-k plane is split into two distinct domains at long and short wavelenths, where unstable modes are sensitive to beam or RF parameters, respectively.\\[4pt] [1] H.B. Nersisyan and C. Deutsch, Phys. Rev. E85, 056414 (2012) [Preview Abstract] |
Monday, October 29, 2012 10:42AM - 10:54AM |
BO4.00007: Particle-In-Cell modeling of Fast Ignition experiments on the Titan Laser Anthony Link, K.U. Akli, F. Beg, C.D. Chen, J.R. Davies, R.R. Freeman, G.E. Kemp, K. Li, H.S. McLean, A. Morace, P.K. Patel, D.W. Schumacher, A.V. Sorokovikova, R. Stephens, M.J.V Streeter, D. Wertepny, B. Westhover We report on particle-in-cell-modeling (PIC) of fast ignition experiments conducted on the Titan laser. The Titan laser was used to irradiate multilayer planar targets at intensities greater than 10$^{20}$ Wcm$^{-2}$ to diagnose the laser to electron coupling, electron beam divergence, and energy spectrum of the hot electrons at relativistic intensities. Hot electron beam properties were inferred through buried fluors, escaping electrons and bremsstrahlung measurements. The PIC simulations of the experiment were conducted in two stages: a high resolution laser plasma interaction (LPI) simulation using measured on shot laser parameters but with a subscale target; and a lower resolution transport simulation containing the full scale multilayer target. The transport simulation utilized the electron source based on the output of the LPI simulation and included necessary models to simulate the experimental diagnostics. Comparison of the predicted electron source properties and the experimental data will be presented. [Preview Abstract] |
Monday, October 29, 2012 10:54AM - 11:06AM |
BO4.00008: Entire-target, Particle-In-Cell Modeling of Ultra-Intense Laser Experiments with Cone-Coupled Wire Targets Chris Orban, Kramer Akli, Robert Mitchell, Vladimir Ovchinnikov, Douglass Schumacher, Richard Freeman, Milad Fatenejad, Donald Lamb Ultra-intense laser-matter interactions with cone-wire target geometries have been extensively studied both experimentally and theoretically. We present some of the most physically-motivated Particle-In-Cell (PIC) simulations of these experiments to date using the LSP code. These simulations allow us to self-consistently model, everywhere and and over long (15 ps) timescales, the laser-generated E \& B fields and sheath fields that arise on entire mm-scale cone-wire targets. Using FLASH radiative-hydrodynamic simulations of the pre-pulse interaction with the target, these PIC simulations illuminate key trends in total Cu $K\alpha$ fluence in recent experiments performed at the Titan laser without any free parameters. The match between our simulations and the observed $K\alpha$ trends is qualitatively good and we discuss the implications of our results which indicate a critical role played by refluxing through the cone walls. [Preview Abstract] |
Monday, October 29, 2012 11:06AM - 11:18AM |
BO4.00009: The effects of pre-plasma scale length and laser intensity on hot electron divergence V.M. Ovchinnikov, D.W. Schumacher, M. McMahon, R.R. Freeman We report on a numerical study of the effects of pre-plasma scale length and laser intensity on the hot electron divergence angle using full-scale 2D3V LSP PIC simulations including a self-consistent laser-plasma interaction (LPI) and photoionization. Our simulations show that the fast electron ($\ge $1 MeV) divergence angle increases almost linearly with the pre-plasma scale length for a fixed laser intensity while the laser intensity has little effect on the divergence angle in the range between 10$^{18}$ and 10$^{21}$~W/cm$^{2}$ for a fixed pre-plasma scale length. [Preview Abstract] |
Monday, October 29, 2012 11:18AM - 11:30AM |
BO4.00010: Integrated Fast Ignition Target Design at LLNL Pravesh Patel, Claudio Bellei, Cliff Chen, Bruce Cohen, Laurent Divol, Andreas Kemp, David Larson, Tony Link, Frederic Perez, Yuan Ping, Hank Shay, David Strozzi, Mike Key, Max Tabak, Hiroshi Sawada, Brad Westover We report on progress in the design of a high gain fast ignition (FI) target using an integrated suite of codes capable of simulating all aspects of an FI implosion. Integrated hohlraum and capsule simulations are performed with the radiation-hydrodynamics code, HYDRA. The ultrashort-pulse laser-plasma interaction and fast electron generation is simulated with an explicit particle-in-cell (PIC) code. The subsequent transport of the electrons through the imploding plasma and their heating of the dense core is modeled with a hybrid-PIC electron transport code coupled to the HYDRA code. The PIC calculations predict an over-energetic and divergent electron source that results in low energy coupling to the compressed core and reduced gain. We describe techniques to improve energy coupling and gain through the use of both azimuthal and axial magnetic fields generated through gradients in material resistivity and magnetic compression of initially imposed seed fields. Integrated calculations are used to design and optimize these schemes, assess overall target performance, and determine the ignition energy requirements for achieving high fusion gain. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Monday, October 29, 2012 11:30AM - 11:42AM |
BO4.00011: Simulation study on electron beam guiding by magnetic fields for fast ignition core heating Tomoyuki Johzaki, Atsushi Sunahara, Shinsuke Fujioka, Hideo Nagatomo, Javier Honrubia, Hiroyuki Shiraga, Hitoshi Sakagami, Kunioki Mima In core heating of cone-guiding fast ignition, the control of fast electron beam having large divergence at the generation is one of the most critical issues. There are some ideas for beam guiding with magnetic fields, $i.e.$ self-generated pinching field from $\eta (\nabla \times j_f )$, the field from resistivity gradient $(\nabla \eta )\times j_f $ and externally applied fields in the beam direction. We have proposed ``Tongari (pointed) tip cone'' for beam guiding due to the resistive fields [1]. In the present paper, to enhance the heating efficiency, we evaluate the dependence of the guiding performance on the tip shape with simulations and then optimize the tip shape. As for the external field, we have successfully generated kT --class magnetic field using capacitor-coil target irradiated by GEKKO-XII laser. We also discuss the core heating performance when such high magnetic fields are applied in addition to the resistive fields. [Preview Abstract] |
Monday, October 29, 2012 11:42AM - 11:54AM |
BO4.00012: Hybrid-PIC Simulations of Shock Formation in Laser-Irradiated Plasmas Adam Tableman, M. Tzoufras, F. Fiuza, F. Tsung, R.A. Fonseca, W.B. Mori Shock generation by hot electron beams (with corresponding energy fluxes ranging from 1e14 W/cm$^2$ to 1e16 W/cm$^2$ impinging on high density targets (1e15 1/cm$^3$) is investigated using the hybrid-PIC version of OSIRIS. The hybrid-PIC code uses a fluid model to follow electron transport at high densities. In these simulations an electron cathode is used as a proxy for hot electrons generated in under-dense regions by laser-plasma interactions. This approach enables control over the composition and energy distribution of the hot electrons entering the high density region, which, in turn, allows the direct study of hot electron energy deposition and the corresponding shock structure. Results on hot electron flux caused by laser energy absorbed in under-dense plasma regions will also be discussed. Understanding how to harness the hot electrons to enhance shock formation will aid in designing Shock Ignition ICF targets with improved yield. Work Supported by the DOE under a Fusion Science Center through a University of Rochester subcontract No. 415025- G and under DE-FG52-09NA29552. [Preview Abstract] |
Monday, October 29, 2012 11:54AM - 12:06PM |
BO4.00013: Interaction of intense multi-picosecond laser pulses with matter for HEDP Andreas Kemp, Laurent Divol, Frederic Perez, Bruce Cohen We present new results on kinetic modeling of Petawatt laser pulses relevant to fast-ignition inertial confinement fusion and related experiments. First, fully resolved simulations of relativistic electron beams at reduced scale provide guidance on numerical requirements and mitigation strategies with respect to instabilities that occur near the laser-plasma interaction region. In a second step, full-scale 2D and 3D simulations are used to characterize the multi-picosecond evolution of the laser energy conversion into hot electrons, i.e., conversion efficiency as well as angular- and energy distribution; the impact of return currents on the laser-plasma interaction; and the effect of self-generated electric and magnetic fields on the onset of electron transport near the laser interaction region. We will report applications to current experiments at LLNL's Titan laser and to a Fast-Ignition point design. [Preview Abstract] |
Monday, October 29, 2012 12:06PM - 12:18PM |
BO4.00014: Exploiting Resistive Guiding for Fast Ignition Alex Robinson Devising methods and schemes for controlling fast electron transport remains a major challenge in Fast Ignition research. Realistic estimates of the fast electron divergence angle require this control in order to ensure that the fast electron to hot spot coupling efficiency does not reach excessively low values. Resistivity gradients in the target will lead to strong magnetic field growth (via $\nabla\eta \times {\bf j}$) which can be exploited for the purposes of controlling the fast electron propagation (Robinson and Sherlock, PoP (2007)). There are a number of possible schemes which might be considered. Here we will report on numerical simulations that we have carried out on both simple configurations such as parabolic reflectors, and complex arrangements (Robinson, Key and Tabak, PRL (2012)). Substantial improvements to the fast electron to hot spot coupling efficiency have been found even for realistic fast electron divergence angles. [Preview Abstract] |
Monday, October 29, 2012 12:18PM - 12:30PM |
BO4.00015: Simulations of Cone-in-Shell Targets for Integrated Fast-Ignition Experiments on OMEGA A.A. Solodov, W. Theobald, K.S. Anderson, A. Shvydky, R. Betti, J.F. Myatt, C. Stoeckl, R.B. Stephens Integrated cone-in-shell fast-ignition experiments on OMEGA will benefit from improved performance of the OMEGA EP laser, including higher contrast, higher energy, and a smaller focus. A new target design has been developed with a 60-$\mu$m-thick, low-$Z$ aluminum cone tip. A very thin ($\sim $2-$\mu$m) gold layer inside the cone tip is used to shield the radiation. Hydrodynamic \textit{DRACO} simulations predict that this design is more resilient against shock than the previous gold-only design and the cone-tip breakout is delayed by about 100 ps. \textit{DRACO} simulations are confirmed by the recent 8-keV flash radiography and shock-breakout measurements on OMEGA. Simulations of core heating by fast electrons generated by the OMEGA EP pulse using the hybrid particle-in-cell code \textit{LSP} integrated with \textit{DRACO} are performed. The electrical resistivity mismatch between the aluminum tip and the surrounding plastic plasma is shown to collimate fast electrons into the assembled fuel. Energy deposition of fast electrons in the compressed core is investigated. Core heating and neutron yield are computed. This work was supported by the U.S. Department of Energy under Cooperative Agreement Nos. DE-FC52-08NA28302 and DE-FC02-04ER54789. [Preview Abstract] |
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