Bulletin of the American Physical Society
53rd Annual Meeting of the APS Division of Plasma Physics
Volume 56, Number 16
Monday–Friday, November 14–18, 2011; Salt Lake City, Utah
Session TO8: Laser Plasma Coupling |
Hide Abstracts |
Chair: John Moody, Lawrence Livermore National Laboratory Room: Ballroom I |
Thursday, November 17, 2011 9:30AM - 9:42AM |
TO8.00001: When are driven Langmuir waves resonant? Harvey Rose We are taught that small amplitude plasma waves are associated with zeroes of the linear dielectric function, $\varepsilon _0 \left( {k,\omega } \right)$, in the complex \textit{$\omega $} plane and that, for Langmuir waves (LW) in particular, Landau damping diminishes their response to an external potential as $k\lambda _D $ increases. But finite amplitude LWs trap electrons, thus reducing Landau damping (O'Neil, Phys. Fluids \textbf{8} (1965)). Do trapping effects strengthen the response indefinitely with increase of LW amplitude or is there a $k\lambda _D $ dependent limit? One-dimensional (1D), small amplitude theory (Holloway and Dorning, Phys. Rev. \textbf{A44} (1991)) showed that thermal plasma supports traveling LWs if $k\lambda _D \mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle\sim}\vphantom{_x}}$}} $ 0.53, consistent with LW resonance, $Re\left[ {\varepsilon _0 \left( {k,\omega } \right)} \right]=0$ for real \textit{$\omega $}. Resonance is not possible for larger $k\lambda _D $. A model of 1D finite amplitude traveling LWs (Rose and Russell, Phys. Plasmas \textbf{8} (2001)) showed that increase of wave amplitude leads to a decrease of the resonant $k\lambda _D $ range, and diminished SRS gain rate (Rose and Yin, Phys Plasmas \textbf{15} (2008)). Results of 2D Vlasov simulations will be presented that manifest similar behavior: there is an amplitude limit to driven LWs, beyond which the LW response to an external potential is nonresonant. This limit decreases as $k\lambda _D $ approaches $\approx $ 0.5. [Preview Abstract] |
Thursday, November 17, 2011 9:42AM - 9:54AM |
TO8.00002: Designing STUD Pulses to control laser-plasma instabilities and adapt to changing plasma conditions Bedros Afeyan, Stefan H\"uller Designing spike trains of uneven duration and delay, or STUD pulses, for ICF targets in direct and indirect drive and for shock ignition will be explored. Taming stimulated Raman and Brillouin scattering (SRS and SBS) as well as two plasmon decay, and harnessing their hot electron generation properties for fast heating purposes at higher intensities will be explored. Theoretical statistical models capturing the essential physics of STUD pulse propagation, hot spot scrambling and SRS and SBS interaction will be presented. How to control LPI in crossing pairs of beams by staggering or interleaving their STUD pulse profiles when no interaction is desired and overlapping them when energy transfer is desirable, will be demonstrated. Technological advances required to bring about the STUD pulse program including time lenses for psec time scale modulated pulses and psec time scale resolved SRS and SBS detection lasting for nsecs and laser hot spot scrambling plasma cells will be discussed. [Preview Abstract] |
Thursday, November 17, 2011 9:54AM - 10:06AM |
TO8.00003: Collective stimulated Brillouin scatter Pavel Lushnikov, Alexander Korotkevich, Harvey Rose We develop a statistical theory of stimulated Brillouin backscatter (BSBS) of a spatially and temporally partially incoherent laser beam for laser fusion relevant plasma. We find a new collective regime of BSBS which has a much larger threshold than the classical threshold of a coherent beam in long-scale-length laser fusion plasma. We identify two contributions to BSBS convective instability increment. The first is collective with intensity threshold independent of the laser correlation time and controlled by diffraction. The second is independent of diffraction, it grows with increase of the correlation time and does not have an intensity threshold. The instability threshold is inside the typical parameter region of National Ignition Facility. We also find that the bandwidth of KrF-laser-based fusion systems would be large enough to allow additional suppression of BSBS. [Preview Abstract] |
Thursday, November 17, 2011 10:06AM - 10:18AM |
TO8.00004: SRS Reflectivity in National Ignition Campaign Targets* D.E. Hinkel, R.L. Berger, E.A. Williams, A.B. Langdon In National Ignition Campaign targets, stimulated Raman backscatter (SRS) occurs during peak power, and acts to limit laser energy coupling to the target. SRS occurs when incident laser light reflects off self-generated Langmuir waves. A detailed understanding of SRS in these targets encompasses pF3D simulations [1] that model the correct geometry, include transverse and axial gradients in the plasma conditions as derived from radiation-hydrodynamics simulations, and laser beam input that incorporates the effect of spatially non-uniform cross-beam energy transfer [2]. Simulations presented here explore reflectivity of a 30\r{ } quad in a target driven with 1.3 MJ of laser energy at peak power. Such simulations show pump depletion oscillations in the reflectivity as well as the impact of spatially non-uniform cross-beam energy transfer. The effects of a frequency shift and damping decrement (such as caused by electron trapping) on density fluctuations is also modeled [3]. The impact of such non-linearity in the presence of pump depletion oscillations will be investigated and presented. *This work was performed under the auspices of the U.S. DOE by LLNL under contract DE-AC52-07NA27344. \\[0pt] [1] R. L. Berger \textit{et al.}, PoP \textbf{5}, 4337 (1998); C. H. Still \textit{et al.}, PoP \textbf{7}, 2023 (2000)]. [2] P. A. Michel \textit{et al.,} PoP \textbf{17}, 056305 (2010). [3] H. A. Rose \textit{et al., }private communication. [Preview Abstract] |
Thursday, November 17, 2011 10:18AM - 10:30AM |
TO8.00005: Effects of Cross-Beam Transfer on the Competition between Stimulated Brillouin and Raman Scatter Richard Berger, J. Moody, P. Michel, R. Town, C. Thomas, L. Divol, D. Callahan, N. Meezan, S. Glenzer, E. Williams, D. Strozzi, J. Kline Stimulated Brillouin backcatter (SBS) measurements in NIF hohlraum targets are shown to scale with the calculated SBS gain with a threshold for significant SBS from the 30$^{\circ}$ beam for a gain of about 20 or a laser intensity of 6-7 x10$^{14}$ W/cm$^{2}$ for the simulated plasma conditions. This SBS gain threshold is consistent with previous measurements of SBS from laser beams that had polarization smoothing and SSD. The SBS measurements are interpreted as scatter from the slow ion-acoustic mode in the CH-capsule-ablator plasma. Previous experiments with similar laser intensity and plasma parameters but lower ion temperature generated SBS from the fast ion-acoustic mode. (Froula PRL \textbf{101}, 115002 (2008), Neumayer PRL \textbf{100} 105001 (2008)). We will review and interpret the dependence of SBS on gas-fill density, air condensation on the laser entrance hole, peak laser power, and cross-beam power transfer. This last process (Michel, PRL \textbf{102}, 025004 (2009)) causes the power at focus to have large scale nonuniformity that favors stimulated Raman scatter over SBS. F3D simulations will be presented with models of cross beam power transfer that affect the relative amounts of SRS and SBS. [Preview Abstract] |
Thursday, November 17, 2011 10:30AM - 10:42AM |
TO8.00006: Laser-plasma interactions and implosion symmetry in rugby hohlraums Pierre Michel, R.L. Berger, B.F. Lasinski, J.S. Ross, L. Divol, E.A. Williams, D. Meeker, B.A. Langdon, H. Park, P. Amendt Cross-beam energy transfer is studied in the context of ``rugby''-hohlraum experiments at the Omega laser facility in FY11, in preparation for future NIF experiments. The transfer acts in opposite direction between rugby and cylinder hohlraums due to the different beam pointing geometries and flow patterns. Its interaction with backscatter is also different as both happen in similar regions inside rugby hohlraums. We will analyze the effects of non-linearities and temporal beam smoothing on energy transfer using the code pF3d. Calculations will be compared to experiments at Omega; analysis of future rugby hohlraum experiments on NIF will also be presented. [Preview Abstract] |
Thursday, November 17, 2011 10:42AM - 10:54AM |
TO8.00007: Comparison of Raman Scattering Measurements and Modeling in NIF Ignition Experiments D.J. Strozzi, D.E. Hinkel, E.A. Williams, R.P.J. Town, P.A. Michel, L. Divol, R.L. Berger, J.D. Moody Recent NIF indirect-drive experiments have shown significant Raman scattering from the inner beams. NIF data has motivated improvements to rad-hydro modeling, leading to the ``high flux model'' [M. D. Rosen et al., HEDP 7, 180 (2011)]. Cross-beam energy transfer [P. A. Michel et al., Phys. Plasmas 17, 056305 (2010] in the laser entrance hole is an important tool for achieving round implosions, and is uniformly distributed across the laser spot in rad-hydro simulations (but not necessarily in experiments). We find the Raman linear gain spectra computed with these plasma conditions agree well in time-dependent peak wavelength with the measured data, especially when overlapping laser-beam intensities are used. More detailed, spatially non-uniform modeling of the cross-beam transfer has been performed [E. A. Williams, this conference]. The resulting gains better follow the time history of the measured backscatter. We shall present the impact of spatially non-uniform energy transfer on SRS gain. This metric is valid when amplification is in a linear regime, and so we shall also present an assessment of whether electron trapping in Langmuir waves can play a role in these shots. [Preview Abstract] |
Thursday, November 17, 2011 10:54AM - 11:06AM |
TO8.00008: NIF hohlraum plasma characteristics inferred from optical backscatter measurements J.D. Moody, J. Ralph, P. Michel, L. Divol, S.H. Glenzer, N. Meezan, D. Callahan, O. Jones, N. Izumi, H. Robey, R. London, R.L. Berger, B.J. MacGowan, E. Bond, E.A. Williams, D. Hinkel, D. Strozzi, J.L. Kline, K. Widmann, R.K. Kirkwood Measurements of optical backscattered SRS and SBS light from NIF hohlraum targets are used with hydrodynamic modeling to develop a consistent experimental understanding of the hohlraum plasma. Measurements are made of the temporally resolved spectra, power, and near field light distribution for a range of plasma conditions using a FABS (full aperture backscatter system) and an NBI (near backscatter imager). The measurements are combined with simulations to develop an overall model for backscatter origin locations, SRS and SBS interaction, hohlraum energetics, and the evolution of the hohlraum plasma in time. We will describe the backscatter measurements and the modeling used to infer plasma characteristics in the hohlraum targets. [Preview Abstract] |
Thursday, November 17, 2011 11:06AM - 11:18AM |
TO8.00009: Scaling of the Time Dependent Stimulated Raman Scattering (SRS) with Incident Power in Ignition Target R.K. Kirkwood, J. Moody, D. Hinkel, P. Michel, L. Divol, D. Callahan, J. Kay, N. Meezan, E. Williams, S. Glenzer, L. Suter, O. Landen, B. MacGowan, Y. Lin, J. Kline, H. Rose, B. Albright SRS saturates at a level that allows $>$ 85{\%} energy coupling to targets in the National Ignition Campaign (NIC) with up to 1.3 MJ incident. When energy is increased from 1.0 to 1.3 MJ in hohlraums with Symcap capsules the SRS energy reflectivity changes little. But in early and late time periods, for which the plasma conditions are significantly different, the power reflectivity (R) is also different and a nearly linear increase of R with incident power is seen at late time. These data are compared with VPIC and Hydra simulations and models of the power transfer between the beams that predict the SRS R [1,2]. Simulations over a 0.07 x 0.5 mm region of the late time profile that is expected to have rapid SRS growth show R rising rapidly and becoming nearly independent of intensity under NIC conditions. Simulations over a wider 0.5 x 0.5 mm region of the profile show R increasing nearly linearly with intensity as less active regions of the plasma are also driven into saturation. Multi-beam SRS experiments at Omega with similar normalized plasma conditions will also be described. \\[4pt] [1] R. K. Kirkwood et al, Phys. Plasmas, 18, 056311 (2011) \\[0pt] [2] L. Yin, et al Phys. Plasmas, 15, 013109 (2008), and invited. [Preview Abstract] |
Thursday, November 17, 2011 11:18AM - 11:30AM |
TO8.00010: Energetics and Symmetry Measurements from Shorter Wider Gold Hohlraums J.E. Ralph, S.N. Dixit, T. Doeppner, S.H. Glenzer, D.A. Callahan, O.S. Jones, N.B. Meezan, J. Milovich, R.P.J. Town, M.J. Edwards, D. Eder, D. Farley, S. Glenn, D.H. Kalantar, K. Widmann, O.L. Landen, T. Ma, B.J. MacGowan, A. MacKinnon, P.A. Michel, J.D. Moody, M.B. Schnieder, L.J. Suter, J.L. Kline, G.A. Kyrala We report on the experimental results of implosions of symmetry capsules (symcaps) on the National Ignition Facility (NIF) using a new geometry gold Hohlraum. The symcap capsules (CH shells) used in the NIF are designed as surrogates for layered fuel target capsules (containing cryogenic Tritium Hydrogen Deuterium or Deuterium Tritium) with a lower neutron yield from fusion reactions allowing for an extensive suite of diagnostics to be fielded without the risk of radiation damage. Experiments intended to produce symmetric implosions of symcaps were conducted with the full 192 beams and used a laser drive pulse with a total energy of 1.3 MJ. A discussion of measured performance of the helium filled Hohlraum with respect to x-ray Hohlraum emission, x-ray drive and laser plasma interactions will be discussed. This work performed by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Thursday, November 17, 2011 11:30AM - 11:42AM |
TO8.00011: ABSTRACT WITHDRAWN |
Thursday, November 17, 2011 11:42AM - 11:54AM |
TO8.00012: The impact of the Hall effect on the dynamics of radial foils Pierre Gourdain, John Greenly, David Hammer, Bruce Kusse, Charles Seyler Radial foils can generate high energy density plasmas with Mbar pressures on the COBRA generator. However, this experimental setup exhibits peculiar behaviors which the magnetohydrodynamics (MHD) model falls short to describe. Anode-cathode asymmetries are one clear example of non-MHD effects. The break in symmetry observed experimentally can be understood if one includes the Hall term in the Ohm's law. Under the condition of sufficiently low density in which relevant scales are of the order of the ion inertial length, the Hall term will be on the order of the \textbf{u} x \textbf{B} induction term. However any large electric field will generate a polarization current which, through the \textbf{J }x \textbf{B} force, will generate a flow in the direction of the electric field, even in regions of larger plasma densities. This additional non-MHD flow affects noticeably the plasma density, temperature and velocity in foil experiments. This research focuses on experimental results to highlight anode cathode asymmetries, showing the importance of the Hall term on plasma dynamics and the underlying instabilities that it can trigger. We will supplement experimental observations with numerical modeling using the three dimensional code PERSEUS. [Preview Abstract] |
Thursday, November 17, 2011 11:54AM - 12:06PM |
TO8.00013: Kelvin-Helmholtz instability in magnetized plasma flows Sandra Stein, David Martinez, Showera Haque, Leela O'Brien, Matthew Tooth, Radu Presura Sheared flows are found in many systems in the universe. These sheared flows are generally Kelvin-Helmholtz unstable. In many instances the presence of a magnetic field can influence the evolution of this instability, which depending on the field strength and orientation, has either a stabilizing or destabilizing effect. Experiments to gain insight into the underlying physics were performed at the Nevada Terawatt Facility. These experiments utilized the Zebra pulsed power generator to implode wire arrays with a planar symmetry, onto a center foil. The wires have an angular offset to where the wires' connection was closer to the foil at the cathode than at the anode. This produced an axial plasma flow with a transverse velocity gradient similar to that found in conical wire arrays with a center wire. The time evolution and the morphology of the characteristic Kelvin-Helmholtz vortices were investigated with laser diagnostics. [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