Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Plasma Physics
Volume 54, Number 15
Monday–Friday, November 2–6, 2009; Atlanta, Georgia
Session JO5: Laser-plasma Coupling at Long Scale Lengths |
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Chair: Larry Suter, Lawrence Livermore National Laboratory Room: Hanover CDE |
Tuesday, November 3, 2009 2:00PM - 2:12PM |
JO5.00001: Optical backscatter measurements to study laser plasma interactions on NIF J. Moody, P. Datte, K. Krauter, E. Bond, R. Hibbard, P. Michel, B.J. MacGowan, S.H. Glenzer, L. Sutter, N. Meezan, R. London, J.L. Kline, K. Widmann, L. Divol, J. Jackson, C. Niemann, S. Vernon We describe measurements of backscattered light from NIF targets under a variety of laser conditions. These measurements will initially be used to validate the point design hohlraum and select phase plates for the ignition experiments. Backscatter measurements are made on two separate groups of 4 beams (a quad). One quad is 30 $\,^{\circ}$ from the hohlraum axis and the other at 50 $\,^{\circ}$. The backscatter measurement utilizes a full aperture backscatter system (FABS) to measure light backscattered into the final focus lens of each beam in the quad and a near backscatter imager (NBI) to measure light backscattered outside of the beam quad. Both instruments must work in conjunction to provide spectrally and temporally resolved backscattered power. We describe the measurements, analysis, and comparison with simulations. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. [Preview Abstract] |
Tuesday, November 3, 2009 2:12PM - 2:24PM |
JO5.00002: Scaling Stimulated Brillouin Scattering from OMEGA gas-filled hohlraums to NIF hohlraums with gold-boron layers Richard Berger, Laurent Divol, Dustin Froula, Siegfried Glenzer, Richard London, Nathan Meezan, Laurence Suter The long laser pulse length required to achieve ignition on the National Ignition Facility (NIF) creates long scalelength, hot, high-Z plasma inside the hohlraum from which stimulated Brillouin scatter (SBS) is predicted to be 20-40{\%}. Adding $\sim $40{\%} Boron to a thin layer of the high-Z wall reduces the predicted SBS to less than a percent. A number of experiments at the OMEGA laser facility have tested elements of the physics of SBS in gold-boron and the modeling tools. The damping rates for pure gold plasma and plasmas with various gold-boron mixtures can be duplicated with mixtures of CO$_{2}$ and hydrocarbon gasses. By combining the rad-hydro code HYDRA to compute bulk plasma parameters and the paraxial-wave-solver pF3d to compute backscatter, levels of stimulated Brillouin backscatter that agree with the measurements have been predicted in advance of the experiments. Although the SBS increases with the calculated average gain as expected, closer examination shows that, for the same gain, plasmas with very weakly damped ion acoustic waves Brillouin scatter light more strongly than plasmas with more strongly damped ion acoustic waves. We present theory and simulations to explain this behavior in the OMEGA and NIF experiments. [Preview Abstract] |
Tuesday, November 3, 2009 2:24PM - 2:36PM |
JO5.00003: Gas-Filled Targets to Study Laser Backscatter on the National Ignition Facility R.A. London, E.A. Williams, D.E. Hinkel, J.D. Moody, L.J. Suter To achieve indirect drive fusion at the National Ignition Facility (NIF), laser beams must propagate through several millimeters of high-density plasma to reach the hohlraum walls. Stimulated Brillouin and Raman backscatter could create problems with energetics and/or symmetry. Laser backscatter at NIF will be diagnosed with full aperture backscatter systems (FABS) and near backscatter imagers (NBI). Several gas-filled targets (``gas pipes'') have been designed to provide backscatter sources to commission the diagnostics. The 7-mm long gas pipes are filled with various gases, including C$_{5}$H$_{12}$ and CO$_{2}$, and are irradiated by a NIF quad with 16 kJ of energy in 2-4 ns pulses. We describe the design of the gas pipes using hydrodynamics and laser-plasma-interaction computer codes. The relationship between the design parameters (gas composition and density and laser pulse shape) and the character of the backscatter (Brillouin versus Raman and narrow versus broad angle) are discussed. Comparisons of predicted and measured backscatter distributions and levels are discussed. [Preview Abstract] |
Tuesday, November 3, 2009 2:36PM - 2:48PM |
JO5.00004: Laser-plasma interaction analyses of National Ignition Campaign energetics experiments D.E. Hinkel, C.H. Still, A.B. Langdon, E.A. Williams The National Ignition Campaign is beginning a series of energetic experiments[1,2] at the National Ignition Facility (NIF), to be performed in the summer and fall of 2009. These experiments will test our understanding of, and our ability to, simulate laser-plasma interactions under NIF-like conditions. To this end, we will perform pF3D[3] simulations of beam propagation of energetics campaign targets. Reflectivity levels and spectra, images of the scattered light angular distribution, and hot electron estimates will be presented and compared to experimental results. Modification of the energy deposition by laser-plasma interactions, and the impact on symmetry, will also be presented. 1. S. H. Glenzer et al., this meeting. 2. N. B. Meezan et al., this meeting. 3. R. L. Berger, C. H. Still, E. A. Williams, and A. B Langdon, Phys. Plasmas 5, 4337 (1998); C. H. Still, R. L. Berger, A. B. Langdon, D. E. Hinkel, L. J. Suter, and E. A. Williams, Phys. Plasmas 7, 2023 (2000). [Preview Abstract] |
Tuesday, November 3, 2009 2:48PM - 3:00PM |
JO5.00005: Modeling laser-plasma interactions in NIF vacuum hohlraums E.A. Williams, D.E. Hinkel, C.H. Still, A.B. Langdon, R.E. Olson, J. Kline In preparation for the NIF ignition campaign, a series of experiments are underway firing 96 and 192 beams of the NIF laser into empty gold hohlraums. The primary purpose of these experiments is to qualify the DANTE filtered x-ray diode radiation temerature diagnostic. We plan to have backscatter diagnostics available, giving us an opportunity to test our LPI modeling on the NIF scale. In addition to scaling with energy, we test the use of a gold-boron coating on the hohlraum wall to reduce SBS via increased ion Landau damping of the ion-acoustic waves. We use Lasnex to simulate the hydrodynamic evolution of the hohlraum plasma. Steady state gains were computed using our diagnostic NEWLIP. These were used to suggest appropriate backscatter simulations to be performed with pF3D, a massivel parallel code that couples paraxial light propagation with fluid models of the stimulated plasma ansd ion waves evolving on a background plasma. We describe the results of these simulations, pre- and post-shot, and compare them with experimental results. [Preview Abstract] |
Tuesday, November 3, 2009 3:00PM - 3:12PM |
JO5.00006: Light Amplification by Seeded Stimulated Raman Scattering of a Crossing Beam and Its Saturation as is Relevant to Ignition Experiments R.K. Kirkwood, Y. Ping, S.C. Wilks, N. Meezan, P. Michel, E.A. Williams, D. Clark, L.J. Suter, O.L. Landen, N.J. Fisch, E.O. Valeo, V. Malkin, J. Wurtele, T.L. Wang, S.F. Martins, C. Joshi Experiments with Janus laser seed the SRS of a 1ns 1054 nm beam with a frequency shifted 3.5 ps pulse, in a plasma in which the resonant density and temperature exist over a $<\sim $ 2mm interaction length. The hot ($< \quad \sim $ 240 eV), low density (n/nc = 0.01), plasma created in the experiments produces a low gain spatial rate, similar to what is experienced by the outgoing SRS scatter which is generated in the interior of indirect drive ignition targets when it subsequently interacts with multiple incoming beams. The experiments show that even with a 1 x 10$^{14}$ W/cm$^2$ pump intensity, gains of greater than 20x can occur under these conditions. The observed amplification is seen to reduce as seed energy increases, consistent with the scattering waves being saturated by electron kinetic effects that operate on the 3.5 ps time scale, (ie; electron trapping), and scaling like 1D PIC simulations. These results benchmark models used to design USP plasma amplifiers, and indirect drive ignition targets. This Work was performed under the auspices of the U.S. DOE by Lawrence Livermore Lab under contract No. DE-AC52- A27344, LLNL-ABS-405480. [Preview Abstract] |
Tuesday, November 3, 2009 3:12PM - 3:24PM |
JO5.00007: Laser Plasma Instability (LPI) Driven Light Scattering Measurements with 44 beam-lines of Nike KrF Laser$^*$ J. Oh, J.L. Weaver, D.M. Kehne, L.S. Phillips, S.P. Obenschain, V. Serlin, E.A. McLean, R.H. Lehmberg, C.K. Manka With short wavelength (248 $nm$), large bandwidth ($\sim1$ $THz$), and ISI beam smoothing, Nike KrF laser provides unique opportunities of LPI research for direct-drive inertial confinement fusion. Previous experiments at intensities $(10^{15}\sim10^{16} W/cm^2)$ exceeded two-plasmon decay (TPD) instability threshold using 12 beam-lines of Nike laser.$^{a,b}$ For further experiments to study LPI excitation in bigger plasma volumes, 44 Nike main beams have been used to produce plasmas with total laser energies up to 1 kJ of $\sim$350 psec FWHM pulses. This talk will present results of the recent LPI experiment focusing on light emission data in spectral ranges relevant to the Raman (SRS) and TPD instabilities. The primary diagnostics were time-resolved spectrometers with an absolute-intensity-calibrated photodiode array in $(0.4\sim0.8)\omega_0$ and a streak camera near $0.5\omega_0$. Blackbody temperature and expansion speed measurements of the plasmas were also made. The experiment was conducted at laser intensities of $(1\sim4)\times10^{15}$ $W/cm^{2}$ on solid planar CH targets. $^a$ J. L. Weaver, et al, NO4.14, APS DPP (2008) $^b$ J. Oh, et al, NO4.15, APS DPP (2008) * Work supported by DoE/NNSA and performed at Naval Research Laboratory. [Preview Abstract] |
Tuesday, November 3, 2009 3:24PM - 3:36PM |
JO5.00008: Updated LPI Thresholds for the Nike Laser* J.L. Weaver, J. Oh, B. Afeyan, L. Phillips, J. Seely, D. Kehne, C. Brown, S.P. Obenschain, V. Serlin, A.J. Schmitt, U. Feldman, G. Holland, C. Manka, R.H. Lehmberg, E. McLean Advanced implosion designs for direct drive inertial confinement fusion use high laser intensities (10$^{15}$-10$^{16}$ W/cm$^{2})$ to achieve gain (g$>$100) with a reduction in total laser energy (E$<$1 MJ). Krypton-fluoride lasers such as the Nike laser at NRL are an attractive choice due to their combination of short wavelength (248 nm), large bandwidth (1-2 THz), and beam smoothing by induced spatial incoherence but the potential threat from laser-plasma instabilities (LPI) needs to be assessed. The 2008 LPI campaign at Nike yielded threshold intensities above 10$^{15}$ W/cm$^{2 }$for the two-plasmon instability, a value higher than reported for 351 nm glass lasers. The experiments used a planar geometry, solid polystyrene targets, and a subset of beams (E$<$200 J) with a reduced focal spot (d$<$125 $\mu $m). The 2009 campaign extended the shot parameters to higher laser energies (E$<$1 kJ) and larger spot sizes (d$<$300 $\mu $m). Spectrally-resolved and time-resolved measurements of x-rays and emission near $^{1}$/$_{2}\omega _{o}$ and $^{3}$/$_{2}\omega _{o}$ harmonics of the laser wavelength show threshold intensities consistent with the 2008 results. *Work supported by DoE/NNSA [Preview Abstract] |
Tuesday, November 3, 2009 3:36PM - 3:48PM |
JO5.00009: Two-Plasmon Decay: Simulations and Experiments on the NIKE Laser System Lee Phillips, J.L. Weaver, J. Oh, A.J. Schmitt, S. Obenschain, D. Colombant NIKE is a Krf laser system at the Naval Research Laboratory used to explore hydrodynamic stability, equation of state, and other issues arising in the research toward inertial fusion energy. The relatively small KrF wavelength, according to widely used theories, raises the threshold of most parametric instabilities. We report on simulations performed using the FAST3d radiation hydrocode to design TPD experiments. By post-processing the results of the simulations we have designed experiments that have explored the use of simple threshold formulas (from developing theories) and help establish the soundness of our simulational approach. Turning to the targets proposed for ICF energy research, we have found that among the designs for the proposed Fusion Test Facility (Obenschain et al., Phys. Plasmas 13 056320 (2006)), are some that are below LPI thresholds. We have also studied high-gain KrF shock ignition designs and found that they are below LPI thresholds for most of the implosion, becoming susceptible to TPD only late in the pulse. [Preview Abstract] |
Tuesday, November 3, 2009 3:48PM - 4:00PM |
JO5.00010: Mitigation of Fast-Electron Production by the Two-Plasmon-Decay Instability in Directly Driven Targets. W. Seka, D.H. Edgell, J.F. Myatt, A.V. Maximov, R.W. Short, R.S. Craxton, D. Russell, D.F. DuBois, H.X. Vu Under certain conditions the fast-electron production caused by the two-plasmon-decay (TPD) instability can be mitigated through modulation of the laser pulse shape. This mitigation can be enhanced when combined with a target that contains a high-$Z$ material. Planar- and spherical-target experiments on OMEGA that show this mitigation are diagnosed using hard x-ray diagnostics and Thomson scattering for the TPD plasma waves. The results of these experiments will be presented. 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] |
Tuesday, November 3, 2009 4:00PM - 4:12PM |
JO5.00011: Growth and Saturation of Two-Plasmon-Decay Instability Driven by Crossing Laser Beams in OMEGA Plasmas A.V. Maximov, J.F. Myatt, R.W. Short, W. Seka, C. Stoeckl, J.A. Delettrez Under the conditions of direct-drive inertial confinement fusion experiments on the OMEGA Laser System, the threshold of two-plasmon-decay (TPD) instability is typically exceeded, and the TPD instability can generate fast electrons that are important for target implosions.\footnote{ C. Stoeckl \textit{et al.}, Phys. Rev. Lett. \textbf{90}, 235002 (2003).}$^{,}$\footnote{W. Seka \textit{et al.}, Phys. Plasmas \textbf{16}, 052701 (2009).} The characteristic feature of OMEGA experiments and of experiments at the National Ignition Facility is that the laser--plasma interaction is driven by multiple crossing laser beams that are randomized in space because of distributed phase plates, and randomized in time because of smoothing by spectral dispersion. The thresholds and growth rates of TPD instability are calculated and compared with the results of the three-wave TPD model.\footnote{ A. Simon \textit{et al.}, Phys. Fluids \textbf{26}, 3107 (1983).} The saturation of TPD instability is found to be caused by low-frequency ion-acoustic perturbations driven by the laser beams and also by the ponderomotive force of plasma waves, including the Langmuir decay instability. 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] |
Tuesday, November 3, 2009 4:12PM - 4:24PM |
JO5.00012: Anisotropy and Angular Dependence of Two-Plasmon Decay Driven by Multiple Overlapping Laser Beams in Direct-Drive Geometry R.W. Short Experimental observations of half-harmonic and hard x-ray emission on OMEGA have shown that two-plasmon-decay (TPD) signals depend on the collective rather than the single-beam intensity.\footnote{ C. Stoeckl \textit{et al.}, Phys. Rev. Lett. \textbf{90}, 235002 (2003).} Previous theoretical work has shown that if one of the plasmon wave vectors is aligned along the density gradient and the axis of symmetry of several laser beams, the beams act in concert and result in the same growth as would be obtained for a single beam at the combined intensity.\footnote{ R. W. Short, Bull. Am. Phys. Soc. \textbf{53}, 245 (2008).} In this talk this analysis will be extended to plasmon wave vectors that deviate from the beam axis of symmetry or from the density gradient. The dependence of the integrated spatial growth of the instability on the angle of deviation will be determined. In a direct-drive spherical configuration this dependence determines the anisotropy of the resulting hot-electron distribution, so it is important in modeling the preheat of the core by TPD-generated hot electrons.\footnote{ J. A. Delettrez \textit{et al.}, Bull. Am. Phys. Soc. \textbf{53}, 248 (2008).} 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] |
Tuesday, November 3, 2009 4:24PM - 4:36PM |
JO5.00013: Extended Zakharov Modeling of Preheat Caused by the Two-Plasmon Decay Instability in Direct-Drive ICF Plasmas. J.F. Myatt, J.A. Delettrez, W. Seka, D.H. Edgell, A.V. Maximov, R.W. Short, D.F. DuBois, D.A. Russell, H.X. Vu The results of two-dimensional extended Zakharov calculations\footnote{ D. F. DuBois, D. A. Russell, and H. A. Rose, Phys. Rev. Lett. \textbf{74}, 3983 (1995).} of saturated two-plasmon-decay spectra and absorption will be presented in inhomogeneous long-scale-length plasma---the plasma parameters motivated by OMEGA-scale designs. Estimates of hot-electron production and preheat are obtained from the Zakharov calculations using a ``test particle'' approach and a \textit{LILAC} model for target hydrodynamic evolution.\footnote{ J. Delettrez \textit{et al.}, Phys. Rev. A \textbf{36}, 3926 (1987).} 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] |
Tuesday, November 3, 2009 4:36PM - 4:48PM |
JO5.00014: Cross-Beam Energy Transport in Direct-Drive-Implosion Experiments D.H. Edgell, W. Seka, J.A. Delettrez, R.S. Craxton, V.N. Goncharov, I.V. Igumenshchev, J.F. Myatt, A.V. Maximov, R.W. Short, T.C. Sangster, R.E. Bahr Time-resolved scattered-light spectroscopy from spherical-target implosions on OMEGA provides information about the time-dependent absorbed power and the spectral shift of the scattered light. Modeled spectra reproduce the major features in the observed spectral shifts but not the absolute magnitudes of the predicted spectral shifts and the total scattered light, suggesting that modeling overpredicts absorption (typically a difference of 10{\%} to 15{\%} of the total time-integrated laser-pulse power). Cross-beam energy transfer appears to explain the discrepancy and its effect on the absorbed power, scattered-light spectra, and bang-time and is examined for a series of implosions with varying intensity. 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] |
Tuesday, November 3, 2009 4:48PM - 5:00PM |
JO5.00015: Modeling Crossed-Beam Energy Transfer in Implosion Experiments on OMEGA I.V. Igumenshchev, D.H. Edgell, V.N. Goncharov, J.A. Delettrez, A.V. Maximov, J.F. Myatt, W. Seka, A. Shvydky Scattered-light measurements in direct-drive-implosion experiments on the OMEGA Laser System indicate enhanced light scattering in comparison with radiative-hydrodynamic simulations that include inverse bremsstrahlung as the primary absorption mechanism of the laser light. Beam-to-beam energy transfer caused by stimulated Brillouin scattering (SBS) is likely responsible for the reduction in absorbed energy at the end of drive pulses in OMEGA implosions. We have developed a simplified model for crossed-beam energy transfer that accounts for the propagation and coupling of multiple laser beams and associated plasma waves in spherically symmetric plasmas. This model has been implemented in the radiative-hydrodynamic code \textit{LILAC}, demonstrating effects of SBS in implosion experiments on OMEGA. 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] |
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