Session TO6: Fast Ignition II

Chair: Christian Stoeckl, University of Rochester
Room: Rosen Centre Hotel Salon 5/6

 Thursday, November 15, 2007 9:30AM - 9:42AM TO6.00001: OMEGA EP: Status and Use Planning D.D. Meyerhofer , J.H. Kelly , S.J. Loucks , R.L. McCrory , S.F.B. Morse , C. Stoeckl The OMEGA EP Laser Facility will be completed in April 2008, 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 ultimately produce 10-ns, 6.5-kJ-energy ultraviolet pulses directed into the EP target chamber. Two of the beamlines will also operate as high-energy petawatt (HEPW) lasers, with up to 2.6 kJ each in 10-ps IR pulses. The HEPW beams can be injected into either the EP chamber or the existing OMEGA target chamber for integrated experiments. This talk will describe the project's status and progress in developing of the OMEGA EP Use Plan, including the results of the first two OMEGA EP Use Planning Workshops. 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 Cooperative Agreement DE-FC52-92SF19460. Thursday, November 15, 2007 9:42AM - 9:54AM TO6.00002: Integrated Simulation of Fast-Ignition ICF A.A. Solodov , K.S. Anderson , R. Betti , V. Gotcheva , J. Myatt , J.A. Delettrez , S. Skupsky To develop a thorough understanding of the complex physics of fast ignition, the numerical modeling of integrated fast-ignition experiments using different types of codes is required. Implosions of DT-filled cryogenic shells with a gold cone inserted to provide a plasma-free pass for an igniting pettawatt pulse need to be simulated using hydrodynamic codes. The transport of relativistic electrons from the inner cone surface to the dense fuel core must be simulated using particle and/or hybrid-PIC codes. To perform an integrated fast-ignition simulation, we have coupled the 2-D cylindrically symmetric hydrocode \textit{DRACO} and the hybrid-PIC code \textit{LSP.} \textit{LSP} is used to simulate the heating of the dense fuel by hot electrons and to generate additional source terms in the temperature equation used in \textit{DRACO}. \textit{DRACO} is a 2-D hydrocode that includes all of the necessary physics required to simulate the ignition and burn of an imploded capsule. The plasma profiles in \textit{LSP} are periodically updated according to \textit{DRACO} results. In this talk the results of an integrated fast-ignition simulation will be presented using high-density and high-\textit{$\rho$R} fuel assembly recently suggested for fast ignition. This work was supported by the U.S. Department of Energy under Cooperative Agreements DE-FC52-92SF19460 and DE-FC02-04ER54789. Thursday, November 15, 2007 9:54AM - 10:06AM TO6.00003: Direct-Drive Fuel-Assembly Simulations of Fast-Ignition Cone-in-Shell Implosions K.S. Anderson , P.W. McKenty , R. Betti , M.M. Marinak Cone-in-shell experiments are being designed for fast-ignition (FI) experiments on OMEGA EP. The basic cone-in-shell design consists of a high-density (e.g., gold) cone embedded in the capsule, with the cone tip near the center of the capsule to allow the injection of a high-intensity ignitor beam close to the compressed high-density fuel mass. The presence of the gold cone causes a deviation from a spherical implosion, leading to lower fuel densities and areal densities. Two-dimensional (2-D) hydrodynamic simulations of FI cone implosions are required both to explore the parameter space (e.g., capsule design, laser pulse shape, and pointing) and to optimize the FI fuel assembly. Furthermore, such simulations are crucial to quantify the initial conditions for integrated FI simulations including fast-electron transport. Current work on 2-D, FI cone-in-shell simulations is presented. This work was supported by the U.S. Department of Energy under Cooperative Agreements DE-FC52-92SF19460 and DE-FC02-04ER54789. Thursday, November 15, 2007 10:06AM - 10:18AM TO6.00004: Hydrodynamic Relations for Direct-Drive, Fast-Ignition Inertial Confinement Fusion Implosions C.D. Zhou , R. Betti Relations between stagnation and in-flight phases are derived both analytically and numerically for hydrodynamic variables relevant to direct-drive inertial confinement fusion implosions. Scaling laws are derived for the stagnation values of the shell density and areal density and for the hot-spot pressure, temperature, and areal density. A simple formula is also derived for the thermonuclear energy gain and in-flight aspect ratio. Implosions of cryogenic DT capsules driven by UV laser energies ranging from 25 kJ to 2 MJ are simulated with a one-dimensional hydrodynamics code to generate the implosion database used in the scaling-law derivation. These scaling laws provide guidelines for optimized fuel assembly and laser pulse design for direct-drive, fast-ignition, and conventional inertial confinement fusion. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreements DE-FC52-92SF19460 and DE-FC02-04ER54789. Thursday, November 15, 2007 10:18AM - 10:30AM TO6.00005: Control of the Fast Electron Beam Divergence for Fast Ignition Inertial Fusion P. Norreys The fast electron beam divergence in intense laser plasma interactions is a vital ingredient in determining the success of fast ignition inertial fusion- If it is too large, then the short pulse laser energy required to generate the temperatures needed for hot spark formation becomes impractical to implement on ignition scale facilities. In this talk, I will review the recent experiments performed on the Vulcan PW laser facility to investigate this question. The pulse duration was changed from 0.5 ps - 10 ps and a wide range of plasma diagnostics were fielded. An intensity dependence to the beam divergence has been identified for the first time from these measurements. Simulations show this effect is caused by Rayleigh-Taylor-like rippling of the critical density surface. I will present new ideas on how the divergence can he controlled and the fast electron transport collimated. These are supported by analytic theory and validated by hybrid Vlasov-Fokker-Planck and hybrid particle-in-cell modelling.. Thursday, November 15, 2007 10:30AM - 10:42AM TO6.00006: Kinetic and Fluid Models of the Filamentation Instability of Relativistic Electron Beams for Fast-Ignition Conditions R.W. Short , J. Myatt Filamentation of relativistic electron beams is a problem of much current interest due to its relevance to the fast-ignition approach to laser-driven fusion, in which such beams must propagate through several hundred microns of dense plasma. Several recent papers have given calculations of temporal growth rates for filamentation based on various fluid and kinetic models.\footnote{ L. Gremillet, G. Bonnaud, and F. Amiranoff, Phys. Plasmas \textbf{9}, 941 (2002).}$^{,}$\footnote{ A. Bret and C. Deutsch, Phys. Plasmas \textbf{12}, 102702 (2005).}$^{,}$\footnote{ A. Bret, L. Gremillet, and J. C. Bellido, Phys. Plasmas \textbf{14}, 032103 (2007).} However, in the fast-ignition scenario it is expected that the instability will amplify as the beam propagates into the plasma, and thus it is of interest to analyze the spatial-growth properties of filamentation. This talk will present results for spatial growth and the related phenomenon of absolute instability of filamentation, and compare fluid and kinetic models of the instability This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement DE-FC52-92SF19460. Thursday, November 15, 2007 10:42AM - 10:54AM TO6.00007: ABSTRACT WITHDRAWN Thursday, November 15, 2007 10:54AM - 11:06AM TO6.00008: Kinetic and Collisional Effects on the Linear and Non-Linear Evolution of Fast Ignition Relevant Beam Instabilities Larissa A. Cottrill , B.F. Lasinski , S.M. Lund , M. Tabak , R.P.J. Town A crucial issue surrounding the feasibility of fast ignition is the ability to efficiently couple energy from an incident short-pulse laser to a high-density, pre-compressed fuel core. Energy transfer will involve the generation and transport of a relativistic electron beam, which may be subject to a number of instabilities that act to inhibit energy transport. The initial linear and later nonlinear growth phases of these instabilities will evolve differently depending on a number of issues such as the initial beam distribution and collisional effects. Analytical calculations will be presented in the collisionless and collisional limits to demonstrate differences in instability growth in the linear growth phase for advanced distributions such as the relativistic Maxwellian and waterbag, as well as a distribution extracted from explicit PIC simulations of the laser-plasma interaction. Simulations from the LSP code will also be shown to highlight beam transport issues in the nonlinear saturated state. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract W-7405-ENG-48. Thursday, November 15, 2007 11:06AM - 11:18AM TO6.00009: Onset of Coherent Electromagnetic Structures In the REB-DT Fuel Interaction for Fast Ignition Claude Deutsch , Antoine Bret , Marie-Christine Firpo We stress the combinations of swiftly growing electromagnetic instabilities(EMI) arising in the interaction of relativistic electron beams(REB) with precompressed DT fuels of fast ignition interest for ICF.REB-target system is taken neutral in charge and current with electron distribution functions including beam and target temperatures.We also pay attention to the impact of modes growth rates(GR) of mode-mode coupling and intrabeam scattering. Collisional damping is documented at large wave numbers in terms of skin depth.A quasi-linear approach yields GR below linear ones.One of the most conspicuous output of this combined linear analysis are 3D ridges featuring the largest GR above k- space for an oblique modes propagagtion w.r.t initial beam velocity. Those modes are seen immune to any temperature induced damping. These novel patterns arise from combining Weibel,filamentation and 2-stream instabilities.They persist in the presence of smooth density gradients or strongly applied magnetic fields. In the very early propagation stage,with no current neutralization,and with strong edge density gradients,REB show a typical ringlike and regularly spiked pattern in agreement with recent experimantal and simulation results. Thursday, November 15, 2007 11:18AM - 11:30AM TO6.00010: Laser Channeling in Millimeter-Scale Underdense Plasmas of Fast Ignition G. Li , R. Yan , C. Ren , V.N. Goncharov , T.L. Wang , J. Tonge , W.B. Mori Two-dimensional particle-in-cell simulations show that laser channeling in millimeter-scale underdense plasmas is a highly nonlinear and dynamic process involving laser self-focusing and filamentation, channel expansion through ponderomotive blowout and high-Mach-number shock waves, plasma density snowplowing, laser hosing, and channel bifurcation and merging. The channeling speed is much less than the laser linear group velocity. The simulations find that the channeling time $T_{c}$ and the total required energy to reach the critical surface, $E_{c}$, scale with the laser intensity $I$ as $T_{c} \quad \sim \quad I^{-0.64}$ and $E_{c} \quad \sim \quad I^{0.36}$. The scaling shows that low-intensity channeling pulses are preferred to minimize the required pulse energy but with an estimated lower bound on the intensity of $I \quad \approx$ 4 $\times$ 10$^{18}$~W/cm$^{2}$ if the channel is to be established within 100 ps. These results will also be compared with those from smaller-scale 3-D simulations. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreements DE-FC52-92SF19460, DE-FC02-04ER54789, and DE-FG02-06ER54879. Thursday, November 15, 2007 11:30AM - 11:42AM TO6.00011: Collision of high-velocity impactor with high-density plasma as another pathway towards laser fusion ignition Hiroshi Azechi , Tatsuhiro Sakaiya , Takeshi Watari , Hiroshi Saito , Kazuto Ohtani , Kazuo Takeda , Hirokazu Hosoda , Hiroyuki Shiraga , Mitsuo Nakai , Keisuke Shigemori , Shinsuke Fujioka , Masakatsu Murakami , Atsushi Sunahara , Hideo Nagatomo , Kunioki Mima , Max Karasik , John Gardner , D.G. Colombant , J.W. Bates , Alexander Velikovich , John Sethian , Steve Obenschain , Yafim Aglitsky , Shalom Eliezer , Peter Norreys The fast ignition has a potential to have ignition with about one tenth of laser energy required for these programs. However this conventional'' fast ignition approach suffers drawback that physics understanding of hot electron generation and transport is insufficient to make quantitative prediction of the ignition. Here we employ a new approach that totally eliminates this complex problem while keeping the advantage of the compactness of the fast ignition; we accelerated a small portion of the fuel to a super-high velocity to collide with a pre-compressed main fuel. We have observed two orders-of-magnitude increase of neutron yield at the right timing of the impact collision, providing another pathway to compact and reliable fusion energy production Thursday, November 15, 2007 11:42AM - 11:54AM TO6.00012: Suprathermal pressure in low mass short-pulse laser irradiated targets M. Tabak Suprathermal pressure can be a significant parasitic loss in low mass targets illuminated by short-pulse, ultra-high intensity lasers. Recent experiments have used low mass targets as: 1) efficient sources of K$_{alpha{\rm g}{\rm g}}$ radiation for radiography applications as well as 2) clean measures of laser to suprathermal electron coupling efficiency because electron transport should be less important when the hot electrons fill the target. Recent experiments have shown apparent coupling efficiency at variance with previous experiments and significantly reduced for the thinnest targets. We use the multigroup electron diffusion package in Lasnex to model these experiments. We first model the two-temperature expansion of a collisionless plasma and obtain good agreement with recent calculations of Mora. We then introduce a simple post-processor model for Kalpha$_{{\rm g}{\rm g}}$ radiation into collisional, radiative calculations. A significant fraction of the incident energy is directly coupled to the hydrodynamic expansion of the slabs. This accounts for some of the discrepancies with earlier experiments, but still leaves some open questions. Thursday, November 15, 2007 11:54AM - 12:06PM TO6.00013: Recent energy transport experiments on the VULCAN Petawatt laser Kate Lancaster VULCAN Petawatt experiments have been performed to investigate aspects of energy transport in solid targets. A range of targets were used to study the transport in insulating (SiO$_{2})$ and conducting (Al) materials of similar Z, and low Z materials. Thick SiO$_{2,}$ Al, and CH targets with copper coated on the rear surface were designed to yield information about energy transport in larger targets of different material properties. Data were obtained from x-ray and optical imaging systems. Unusual patterns in the expansion profiles were observed consistently for the Al case compared with the other target materials. Buried Nickel layers were sandwiched between the thin (2-5$\mu$m) target materials (Al, SiO$_{2}$,CH) to enable measurement of the Ni Lyman Alpha thermal emission using a spherical crystal imaging system. Data were also obtained from the other x-ray and optical imaging systems. Modeling using hybrid, radiation hydrodynamic, and atomic codes is presented to assist interpretation of the data. Thursday, November 15, 2007 12:06PM - 12:18PM TO6.00014: Quenching mode of efficient heating in entrant cone laser interactions. H. Nakamura , B. Chrisman , Y. Sentoku , M. Borghesi , J. Fuchs , K. Kondo , M. Nakatsutsumi , M. Tampo , K.A. Tanaka , T. Tanimoto , T. Yabuuchi , R. Kodama We measured hot electron spectra in ultra intense laser interaction with an entrant cone target attached by fine wire on the tip. Fast heating of the wire with the electron was investigated when the laser pulse was focused into the cone changing the pointing of the laser from the tip center to the side wall. Higher slope components appeared on the high energy tail of the hot electron energy spectra for the illumination on the side wall. In contrast, pointing of the laser on the tip relatively increased the lower energy component of the electrons as compared with that for the illumination on the side wall, resulting in well heating of the wire by more than 1keV. The experiments indicate the importance of the pointing of the laser into cone geometry for fast heating of high density imploded plasmas. Thursday, November 15, 2007 12:18PM - 12:30PM TO6.00015: Integrated LSP Modeling of Fast-electron Production and Transport in a Wire Target Mingsheng Wei , John Pasley , Farhat Beg , Richard Stephens , Dale Welch Integrated simulations using the implicit PIC code LSP$^{\# }$ have been performed to study the production of relativistic electrons from ultra-intense (I $\sim$ 7 x 10$^{19}$ W/cm$^{2})$ sub-picosecond laser solid interactions including a preformed plasma and the transport of such beam in a thin (50 $\mu$m in diameter), 100's $\mu$m long wire target. Our 3D simulations show that greater than 40{\%} of laser energy is transferred to fast electrons whose energy spectrum can be fitted to a two-temperature Maxwellian distribution. The fast electrons have a typical propagation length of about 100 $\mu$m inside the wire target. A very small fraction of the fast electrons is confined in the wire target surface by strong electric and magnetic fields and these electrons have a much longer range. The simulation results agree well with recent Titan wire experiments [1], as well as with other collisional PIC modeling. \newline [1] F. N. Beg, Invited talk, 9th International Fast Ignition Workshop, Cambridge, MA, Nov. 3-5, 2006; J. Pasley et al., to be submitted to Phys. of Plasmas. $^{\# }$LSP is a software product of ATK Mission Research.