Bulletin of the American Physical Society
50th Annual Meeting of the Division of Plasma Physics
Volume 53, Number 14
Monday–Friday, November 17–21, 2008; Dallas, Texas
Session CO4: Fast Ignition I |
Hide Abstracts |
Chair: Brian Albright, Los Alamos National Laboratory Room: Reunion B |
Monday, November 17, 2008 2:00PM - 2:12PM |
CO4.00001: An Assessment of the X-Ray Preheat of Fast-Ignition Cones R.P.J. Town, N. Izumi, D.S. Clark, A.J. Mackinnon, P.A. Amendt, M.H. Key, P.K. Patel, E. Storm, M. Tabak In the Fast Ignition (FI) approach to inertial confinement fusion a short-pulse high intensity laser is used to generate relativistic electrons that subsequently deposit their energy into the compressed DT fuel to initiate a propagating burn wave. A gold cone is normally inserted into the cryogenic DT capsule to allow a clear path for the ignition laser to the fuel. In the FI coupling experiments on the National Ignition Facility (NIF), the compressed fuel will be assembled using indirect drive. The cone will be subject to preheat from the hard x-rays ($>$ 2keV) generated by the interaction of the compression lasers with the high-Z hohlraum wall and the coronal plasma. The latter source could also be important for direct drive designs. This paper will assess the cone preheat, describe mitigation strategies, and review some recent designs to quantify the effect on the OMEGA laser facility. [Preview Abstract] |
Monday, November 17, 2008 2:12PM - 2:24PM |
CO4.00002: Experimental evaluation of the x-ray preheat of fast-ignition cones Nobuhiko Izumi, R.P.J. Town, M.J. May, H.F. Robey, D.S. Clark, A.J. Mackinnon, P.A. Amendt, M.H. Key, P.K. Patel, E. Storm, M. Tabak In planned fast-ignition implosions, a gold cone will be inserted into the capsule to allow a short-pulse laser to directly irradiate the compressed fuel without having to propagate through the ablated shell plasma [M. Tabak et al., Fus. Science and Technol., 49, 254 (2006)]. For the case of indirect-drive implosions, L-band line emission from the gold hohlraum wall (8$\sim $13 keV) can penetrate though the shell and heat the outer 2-6 $\mu $m of the cone, causing the gold to expand and mix with the fuel. Since mixing of high-$Z$ material with the fuel reduces the margin for achieving ignition, it is important to quantify the L-shell emission from Au hohlraums and to evaluate the effects on the Au cone. We measured the absolute x-ray flux from thin-wall (5 $\mu $m thick) gold hohlraums at the OMEGA laser facility, and we have observed the expansion of a surrogate gold surface with time-gated radiography. Results from these experiments will be discussed. [Preview Abstract] |
Monday, November 17, 2008 2:24PM - 2:36PM |
CO4.00003: Indirect drive fast ignition target design for the National Ignition Facility Daniel Clark, Peter Amendt, Max Tabak, Richard Town The approaching completion of the National Ignition Facility (NIF) in 2010 offers the prospect of large-scale Fast Ignition (FI) experiments in the 2011 time frame. Since NIF will initially be configured in an indirect drive mode, however, capitalizing on this opportunity requires the development of indirect drive FI targets. Previously [Nuc. Fusion \textbf{47} 1147 (2007)] we developed a single-shock, direct drive target design optimized for producing a minimum hot spot radius and maximal areal density as appropriate for FI. Here we describe an adaptation of this design to the indirect drive requirements of NIF. It is found that a modest peak radiation temperature of 210 eV and a reasonable pulse length ($\sim $ 30 ns) and laser energy ($\sim $ 400 kJ) can yield a highly compact fuel assembly with a reasonable areal density ($\sim $ 2.0 g/cm$^{2})$. The two-dimensional hydrodynamics of the interaction of this spherically imploding capsule with the re-entrant guide cone is also investigated. It is found that a strong axial jet, directed from the center of the stagnating fuel into the cone tip, is a recurring feature of the implosion. Mitigating the damaging effect of this jet is an important and continuing design consideration. [Preview Abstract] |
Monday, November 17, 2008 2:36PM - 2:48PM |
CO4.00004: Hohlraum Design and Capsule Illumination Asymmetry for Fast Ignitor Darwin Ho, Max Tabak, George Zimmerman, Peter Amendt, Judy Harte In this paper, we present hohlraum design and 2-D capsule symmetry calculations for a fast ignitor in Inertial Fusion Energy applications. A hohlraum configuration with low laser incidence angle (between 10 to 20 degree) is designed using the view-factor code GERTIE. Time dependent capsule and wall albedos are obtained from 1-D LASNEX calculations. Time dependent capsule illumination asymmetry on the capsule is obtained by changing the hohlraum configuration, albedo, and capsule radius with time in the GERTIE calculations. Hohlraum configurations with two to four rings of laser illumination from two sides will be presented. The two-ring configuration has a gain of about 30, and the three and four ring configurations have gain above 40. Putting short tubes in front of the laser entrance holes can reduce the hole loss by more than 50{\%}. [Preview Abstract] |
Monday, November 17, 2008 2:48PM - 3:00PM |
CO4.00005: Direct-Drive, Fast-Ignition, Cone-in-Shell Fuel-Assembly Simulations K.S. Anderson, A.A. Solodov, R. Betti, P.W. McKenty Integrated fast-ignition (FI) cone-in-shell scaling experiments have been performed using the newly commissioned OMEGA--OMEGA EP system. Maximizing experimental yields requires achieving high areal densities within the target while, at the same time, providing a clear channel to the target for the petawatt (PW) laser by keeping the re{\-}entrant cone interior free of plasma. To accurately predict yields in these experiments requires precise characterization of the plasma conditions at peak compression. These simulations are performed using the 2-D radiation hydrodynamics code \textit{DRACO}, with fast-electron transport and heating calculated by the hybrid-PIC code \textit{LSP}. This paper reports on the current status of simulations exploring the 2-D fuel-assembly parameter space, including capsule and re-entrant cone design, and laser pointing, pulse shaping, and timing between the two laser systems. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement Nos. DE-FC52-08NA28302 and DE-FC02-04ER54789. [Preview Abstract] |
Monday, November 17, 2008 3:00PM - 3:12PM |
CO4.00006: ABSTRACT WITHDRAWN |
Monday, November 17, 2008 3:12PM - 3:24PM |
CO4.00007: Experimental Results and Numerical Predictions of Coherent Transition Radiation (CTR) for the Characterization of High-Current, Fast-Electron Beams M. Storm, J.F. Myatt, A.A. Solodov CTR imaging is a technique for analyzing the properties of high-current, relativistic electron beams created in laser--solid interactions. Al, Cu, Sn, and Au foils of thickness ranging from 5 to 100 \textit{$\mu $}m were irradiated with an intensity of $\sim $10$^{19}$ W/cm$^{2}$. Based on the measured signal, the fast-electron-beam temperature ($T_{hot})$ and divergence were estimated to be $\sim $1.4 MeV and $\sim $10.8\r{ }. Collisional effects were found to influence the estimate of $T_{hot}$ and are quantified using a Monte Carlo code. High-resolution, $\sim $1.4-\textit{$\mu $}m imaging of the rear-surface emission reveals small-scale structures $\sim $2 \textit{$\mu $}m in size, embedded in a larger ring-like structure, suggesting electron-beam filamentation and annular propagation. The interpretation of the experimental observations requires numerical calculations. Using the particle-in-cell (PIC) code \textit{OSIRIS} and the hybrid PIC \textit{LSP}, the distribution of CTR has been simulated. 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, November 17, 2008 3:24PM - 3:36PM |
CO4.00008: Three-Dimensional Effects in Laser Channeling in Fast-Ignition Targets G. Li, C. Ren, V.N. Goncharov, J. Tonge, W.B. Mori Laser channeling aims to reduce the energy loss of an ignition pulse in the millimeter-scale underdense plasma of fast-ignition targets. Currently full-scale particle-in-cell (PIC) simulations for laser channeling can be performed only in 2-D.\footnote{G. Li \textit{et al}., Phys. Rev. Lett. \textbf{100}, 125002 (2008).} Here we report results from 3-D PIC simulations with 0.1-mm-scale plasmas. These results show a larger channeling speed in 3-D than in 2-D for the same conditions. The channeling speed difference is partly due to the difference in laser self-focusing (SF) in 2-D and 3-D. We will compare the laser vector potential and spot-size evolution from the simulations to those predicted by a simple model of relativistic and ponderomotive SF. Dimensional effects on other channeling properties such as residual plasma density and temperature will also be presented. This work was supported by the U.S. Department of Energy under Cooperative Agreement Nos. DE-FC52-08NA28302, DE-FC02-04ER54789, and DE-FG02-06ER54879. [Preview Abstract] |
Monday, November 17, 2008 3:36PM - 3:48PM |
CO4.00009: Recent Progress on Ion-Driven Fast Ignition Juan C. Fernandez, B.J. Albright, K.A. Flippo, D.C. Gautier, B.M. Hegelich, M.J. Schmitt, R.C. Shah, L. Yin, J.J. Honrubia, M. Temporal We report on the encouraging progress from research on fusion fast ignition (FI) initiated by laser-driven ion beams. Compared to electrons, FI based on a beam of quasi-monoenergetic ions (protons or heavier ions) has the advantage of a more localized energy deposition, which minimizes the required total beam energy. High-current, laser-driven ion beams are very promising for this purpose, and because of their ultra-low transverse emittance, these beams can be focused to the required dimension, $\sim $ tens of microns. Because they are created in ps timescales, these beams can deliver the power required to ignite the compressed D-T fuel, $\sim $ 10 kJ / 50 ps. Our recent integrated calculations of ion-based FI include high fusion gain targets and a proof of principle experiment, which indicate the progress is feasible. The scientific issues and progress in the generation of the required laser-driven ion beams are summarized. [Preview Abstract] |
Monday, November 17, 2008 3:48PM - 4:00PM |
CO4.00010: A Comparison of Ponderomotive Scaling to Hot Electron Slope Temperatures inferred from Bremsstrahlung Measurements in Short-pulse Laser Experiments C.D. Chen, D. Hey, M.H. Key, K.U. Akli, F.N. Beg, H. Chen, R.R. Freeman, A. Link, A.J. Mackinnon, A.G. MacPhee, P.K. Patel, M. Porkolab, R.B. Stephens, L.D. Van Woerkom The hot electron slope temperature is an important component in estimating the coupling of the electrons produced in the laser-plasma interaction region to the compressed core. Bremsstrahlung measurements were made from thick-foil targets irradiated with the TITAN laser (1054 nm, 150 J, 0.7 ps, 10$^{20}$ W/cm$^{2})$ at LLNL. A Hard X-Ray Bremsstrahlung Spectrometer comprised of filtered image plates was used to measure the x-ray spectrum with discrimination up to 500 keV. The electron slope temperatures were inferred from the x-ray measurements using the Monte Carlo code ITS 3.0. The inferred spectra are compared to synthetic distributions calculated from ponderomotive scaling and images of the laser focal spot using an equivalent plane imager. Resistive transport effects on the x-ray spectrum have also been studied with the hybrid-PIC code LSP and results will be discussed. [Preview Abstract] |
Monday, November 17, 2008 4:00PM - 4:12PM |
CO4.00011: The hot electron temperature and laser light absorption in fast ignition Malcolm Haines, Mingsheng Wei, Farhat Beg, Richard Stephens Experimental data [F. N. Beg et al, Phys. Plasmas 4, 447 (1997)] indicates that for intense short pulse laser-solid interactions at intensities up to 5$\times $10$^{18}$ Wcm$^{-2}$, the hot electron temperature scales as (I$\lambda ^{2})^{1/3}$. A series of analytic models based on conservation laws is presented here. The first and simplest model finds this scaling with the appropriate constant assuming 100{\%} energy absorption from the laser beam to fast electrons. The second and more accurate, fully relativistic model includes momentum conservation and a more general formula is found that essentially agrees closely with the first, the scaling being much lower than ponderomotive scaling. The reason for this is to be found in examining the electron forward displacement compared to the collisionless skin-depth. The effect of reflected and back-scattered light in the third model indicates that at high intensity ( $>$10$^{19}$ Wcm$^{-2})$ the absorption of laser light approaches 80 to 90{\%}. [Preview Abstract] |
Monday, November 17, 2008 4:12PM - 4:24PM |
CO4.00012: Progress of the Fast Ignition REalization EXperiment (FIREX) Project H. Azechi, K. Mima, S. Fujioka, H. Homma, T. Jitsuno, T. Johzaki, J. Kawanaka, M. Koga, N. Miyanaga, H. Nagatomo, K. Nagai, M. Nakai, H. Nishimura, T. Norimatsu, N. Sarukura, K. Shigemori, H. Shiraga, R. Kodama, H. Habara, K.A. Tanaka, A. Iwamoto, O. Motojima, T. Ozaki, H. Sakagami, T. Taguchi Fast ignition has a potential to achieve ignition and burn with about one tenth of laser energy required for ongoing NIF and LMJ programs. With the fast ignition, the fuel compression and heating are separated, with ignition initiated by a short very high power laser pulse incident on the already compressed fuel. The fast heating of a compressed core, together with the scalability to high-density compression, provided the scientific basis of the Fast Ignition Realization EXperiment (FIREX) project. The goal of its first phase (FIREX-I) is to demonstrate ignition temperature of 5-10 keV, followed by the second phase (FIREX-II) to demonstrate ignition and burn. Coupled with the achievement of central ignition, the research focus would converge onto an international laser fusion test reactor that can deliver net electric power. [Preview Abstract] |
Monday, November 17, 2008 4:24PM - 4:36PM |
CO4.00013: Core Heating Simulations for Cone-Guiding Fast Ignition Tomoyuki Johzaki, Yasuhiko Sentoku, Hitoshi Sakagami, Hideo Nagatomo, Atsushi Sunahara, Kunioki Mima In the cone-guiding fast ignition, an imploded core is heated by fast electrons generated at the cone inner surface. In FIREX-I, our goal is the demonstration of efficient core heating (Ti $\sim $ 5keV) using a newly developed 10kJ LFEX laser. When irradiating such an intense laser, the bulk electron temperature in the cone tip becomes very high and Au atoms are highly ionized. We evaluated those effects by 1D the PIC and Fokker-Planck simulations. It was found that in the Au cone case, the rapid density steepening of the interaction surface and the strong scattering by highly ionized Au ions occur, which reduce the conversion efficiency of heating laser to fast electrons. In addition, the fast electron beam quality deteriorates due to the collisional and resistive drags and scattering by the Au ions. We proposed a CH as an alternative of cone tip material to reduce the collisional defects. We found a twice higher rise in temperature of a compressed core with the CH cone tip. We will also discuss multi-dimensional effects. [Preview Abstract] |
Monday, November 17, 2008 4:36PM - 4:48PM |
CO4.00014: Expansion of Cone Inner Surface Irradiated by Low intensity Pre-Pulse of Main Heating Laser in Fast-Ignition Atsushi Sunahara, Tomoyuki Johzaki, Hideo Nagatomo, Kunioki Mima We investigated the plasma expansion of the inner surface of the cone used for the fast-ignition scheme (FIS) of the inertial confinement fusion (ICF) by two-dimensional simulation code (Star-2D) with laser-ray tracing. The most intense and short pulse lasers used for the core heating in FIS have a low intensity pre-pulse of several 100ps duration before the main pulse irradiation. The typical contrast of pre-pulse and main pulse ranges from 10$^{-5}$ to 10$^{-9}$. In low contrast cases, the pre-pulse intensity could lead to 10$^{13}$ to 10$^{14}$W/cm$^{2}$ which is high enough to ablate the inner surface of the cone wall made of gold. The profile of this pre-formed plasma on the inner surface of cone has significant effects on interaction between the main high intensity laser pulse and the surface of the cone, and the resulted energetic electron spectrum may change depending on the plasma gradient scale length [1]. We show our simulation results with the various intensity and duration of pre-pulse and discuss their effects on the energetic electron production and core heating REFERENCE [1] T. Johzaki et al., ``Holistic Simulation for FIREX Project withFI3'', Laser Part. Beams. Volume 25, Issue 04, Dec 2007, pp 621-629. [Preview Abstract] |
Monday, November 17, 2008 4:48PM - 5:00PM |
CO4.00015: Electron Generation and Transport as a Function of Preplasma in Cone-Attached Targets T. Ma, M.H. Key, D. Hey, S. LePape, A.J. Mackinnon, A.G. MacPhee, P.K. Patel, K. Akli, R.B. Stephens, T. Bartal, S. Chawla, D. Higginson, J.A. King, M.S. Wei, B. Westover, T. Yabuuchi, F.N. Beg, C.D. Chen, R.R. Freeman, E. Kemp, V. Ovchinnikov, L. Van Woerkom, C. Stoeckl, W. Theobald, Y.Y. Tsui The underlying physics of laser energy deposition and transport in cone-guided fast ignition is very complex. It has been shown recently that preplasma can significantly affect the generation and transport of electrons in cone targets.\footnote{S. D. Baton, et al., Phys. Plasmas \textbf{15}, 042706 (2008).}$^{,}$\footnote{L. Van Woerkom, et al., Phys. Plasmas \textbf{15}, 056304 (2008).} In integrated FI, prepulse energies of the order of 1 J are expected. Experiments have been performed at the Titan laser (10$^{20}$ W/cm$^{2})$ at LLNL in which prepulse levels were artificially induced at levels of up to 1 J using the long pulse beam into cone-wire targets. By simultaneously using Cu K$\alpha$ imaging, single photon counting cameras, and HOPG crystal spectroscopy, absolute information of spatially resolved K$\alpha$ radiation could give yields of hot electrons and their transport scalelengths as a function of preplasma. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700