Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session NO5: Laser Plasma Interactions II |
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Chair: Amanda Davis, University of Rochester Room: 200 |
Wednesday, November 18, 2015 9:30AM - 9:42AM |
NO5.00001: Mitigation of Two-Plasmon Decay in Direct-Drive Implosions Using Multilayer Targets D.H. Froula, V.N. Goncharov, R.K. Follett, R.J. Henchen, B. Yaakobi, D.H. Edgell, A.A. Solodov, J.F. Myatt, J.G. Shaw, C. Stoeckl, M.J. Bonino, T.C. Sangster Mitigation of cross-beam energy transfer in direct-drive implosions may increase the hot-electron preheat above acceptable levels for ignition. To study preheat mitigation concepts on OMEGA, a thin layer (0.6 $\mu $m) of Si in the target ablator is being considered to increase the electron temperature at the quarter-critical surface. A beryllium inner layer (6 $\mu $m thick) is used to increase the hydrodynamic efficiency and an outer layer of CH-doped Si (4 $\mu $m thick) reduces the laser imprint. Spatially resolved Thomson-scattering measurements show a 15{\%} increase in the electron temperature at the quarter-critical surface and the time-resolved hot electrons are reduced by a factor of 8 compared with a standard CH target. The shell trajectory in the multilayer targets is significantly faster than the CH target, resulting in a factor-of-3 increase in the neutron yield. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 18, 2015 9:42AM - 9:54AM |
NO5.00002: A Numerical Model for Two-Plasmon--Decay Hot-Electron Production and Mitigation in Direct-Drive Implosions J.F. Myatt, J.G. Shaw, A.A. Solodov, A.V. Maximov, R.W. Short, W. Seka, R.K. Follett, D.H. Edgell, D.H. Froula, V.N. Goncharov Hot-electron preheat, caused by laser--plasma instabilities, can impair the performance of inertial confinement fusion implosions. It is therefore imperative to understand processes that can generate hot electrons and to design mitigation strategies should preheat be found to be excessive at the ignition scale (laser--plasma interactions do not follow hydrodynamic scaling). For this purpose, a new 3-D model [laser-plasma simulation environment (\textit{LPSE})] has been constructed that computes hot-electron generation in direct-drive plasmas based on the assumption that two-plasmon decay is the dominant, hot-electron--producing instability.\footnote{ B. Yaakobi \textit{et al}., Phys. Plasmas \textbf{19}, 012704 (2012); D. H. Froula \textit{et al}., Phys. Rev. Lett. \textbf{108}, 165003 (2012).} It uses an established model of TPD-driven turbulence\footnote{ D. F. DuBois \textit{et al}., Phys. Rev. Lett. \textbf{74}, 3983 (1995); D. A. Russell and D. F. DuBois, Phys. Rev. Lett. \textbf{86}, 428 (2001).} together with a new GPU based hybrid particle method of hot-electron production. The time-dependent hot-electron power, total energy, and energy spectrum are computed and compared with data from recent OMEGA implosion experiments that have sought to mitigate TPD by the use of multilayered (mid-$Z)$ ablators. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 18, 2015 9:54AM - 10:06AM |
NO5.00003: Modeling Hot-Electron Measurements in Multibeam Two-Plasmon--Decay Experiments R.K. Follett, D.H. Edgell, R.J. Henchen, S.X. Hu, J. Katz, D.T. Michel, J.F. Myatt, J.G. Shaw, A.A. Solodov, B. Yaakobi, D.H. Froula Many-beam laser facilities introduce laser--plasma interactions where multiple beams can couple to common daughter waves. Recent theory, modeling, and experiments have suggested that multiple laser beams can drive the two-plasmon--decay (TPD) instability through common electron plasma waves. Experiments and modeling suggest that these waves lead to turbulence and the acceleration of electrons to high energies. Experiments on OMEGA used ultraviolet Thomson scattering to observe TPD-driven electron plasma waves and hard x-ray detectors to infer the corresponding hot-electron production. The experiments were modeled in 3-D using a hybrid code (\textit{LPSE}) that combines a pseudospectral wave solver for calculating the bulk fluid behavior with a particle tracker for calculating nonlinear Landau damping. Detailed comparison of both the hot-electron generation and the turbulent electron plasma wave spectrum are in excellent agreement with the experimental measurements. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 18, 2015 10:06AM - 10:18AM |
NO5.00004: Recent Advances in the Modeling of the Transport of Two-Plasmon--Decay Electrons in the 1-D Hydrodynamic Code \textit{LILAC} J.A. Delettrez, J.F. Myatt, B. Yaakobi The modeling of the fast-electron transport in the 1-D hydrodynamic code \textit{LILAC} was modified because of the addition of cross-beam-energy-transfer (CBET) in implosion simulations.\footnote{C. J. Randall, J. R. Albritton, and J. J. Thomson, Phys. Fluids \textbf{24}, 1474 (1981).} Using the old fast-electron with source model CBET results in a shift of the peak of the hard x-ray (HXR) production from the end of the laser pulse, as observed in experiments, to earlier in the pulse. This is caused by a drop in the laser intensity of the quarter-critical surface from CBET interaction at lower densities. Data from simulations with the laser plasma simulation environment (LPSE) code\footnote{J. F. Myatt \textit{et al}., ``A Numerical Model for Two-Plasmon--Decay Hot-Electron Production and Mitigation in Direct-Drive Implosions,'' this conference.} will be used to modify the source algorithm in \textit{LILAC}. In addition, the transport model in \textit{LILAC} has been modified to include deviations from the straight-line algorithm and non-specular reflection at the sheath to take into account the scattering from collisions and magnetic fields in the corona. Simulation results will be compared with HXR emissions from both room-temperature plastic and cryogenic target experiments. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 18, 2015 10:18AM - 10:30AM |
NO5.00005: Experiments on the scaling of growth and saturation of two-plasmon decay with plasma conditions J.R. Fein, J.P. Holloway, D.H. Edgell, D.H. Froula, D. Haberberger, P.A. Keiter, J.F. Myatt, M.R. Trantham, R.P. Drake In inertial confinement fusion (ICF), multiple overlapping lasers interact with under-dense plasma to drive the two-plasmon decay (TPD) instability. The resulting plasma waves can produce hot electrons that preheat the ICF capsule fuel and reduce compression efficiency. Preliminary experiments have demonstrated that TPD can be controlled through varying electron density scale-length and temperature by increasing plasma Z.\footnote{Hu, S.X., et al. POP, 20(3), (2013).} Additionally, simulations have indicated that TPD may saturate by nonlinear processes that depend on plasma Z through the ion-acoustic wave damping rate.\footnote{Myatt, J.F., et al., POP, 20(5), (2013).} We have performed experiments on OMEGA EP to thoroughly study the dependence of TPD on plasma conditions, through varying target material over a wide range of Z. Hot electron energy is observed to decrease as plasma Z increases, in a manner that is consistent with the shortening electron density scale-lengths that were measured. Finally, we present a scaling of total hot electron energy with the TPD linear gain parameter to identify whether the instability has nonlinearly saturated. [Preview Abstract] |
Wednesday, November 18, 2015 10:30AM - 10:42AM |
NO5.00006: Planar Two-Plasmon--Decay Experiments at Polar-Direct-Drive Ignition-Relevant Scale Lengths at the National Ignition Facility M.J. Rosenberg, A.A. Solodov, W. Seka, J.F. Myatt, S.P. Regan, M. Hohenberger, R. Epstein, T.J.B. Collins, D.P. Turnbull, J.E. Ralph, M.A. Barrios, J.D. Moody Results from the first experiments at the National Ignition Facility (NIF) to probe two-plasmon$-$decay (TPD) hot-electron production at scale lengths relevant to polar-direct-drive (PDD) ignition are reported. The irradiation on one side of a planar CH foil generated a plasma at the quarter-critical surface with a predicted density gradient scale length of $L_{\mbox{n}} \sim 600\mu m,$ a measured electron temperature of $T_{e} \sim 3.5$ to 4.0 keV, an overlapped laser intensity of $I\sim 6\times 10^{14}$ W/cm$^{2}$, and a predicted TPD threshold parameter of $\eta \sim 4.$ The hard x-ray spectrum and the K$_{\alpha }$ emission from a buried Mo layer were measured to infer the hot-electron temperature and the fraction of total laser energy converted to TPD hot electrons. Optical emission at $\omega $/2 correlated with the time-dependent hard x-ray signal confirms that TPD is responsible for the hot-electron generation. The effect of laser beam angle of incidence on TPD hot-electron generation was assessed, and the data show that the beam angle of incidence did not have a strong effect. These results will be used to benchmark simulations of TPD hot-electron production at conditions relevant to PDD ignition-scale implosions. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 18, 2015 10:42AM - 10:54AM |
NO5.00007: Modeling of Two-Plasmon--Decay Experiments at Polar-Direct-Drive Ignition-Relevant Plasma Conditions at the National Ignition Facility A.A. Solodov, M.J. Rosenberg, J.F. Myatt, R. Epstein, S.P. Regan, W. Seka, J.G. Shaw, M. Hohenberger, J.D. Moody, J.E. Ralph, D.P. Turnbull The two-plasmon--decay (TPD) instability can be detrimental for direct-drive inertial confinement fusion because of target preheat by high-energy electrons generated by TPD. The radiation--hydrodynamic code \textit{DRACO} has been used to design planar target experiments that generate plasma and interaction conditions relevant to ignition polar-direct-drive (PDD) designs. The use of planar targets allows TPD to be decoupled from cross-beam energy transfer, which reduces the laser absorption in current National Ignition Facility (NIF) PDD implosion experiments. The laser--plasma interaction code \textit{LPSE} has been used to investigate TPD using the predicted plasma profiles and laser irradiation geometry in three dimensions. The energetic electrons generated by \textit{LPSE } are propagated into the planar target using the Monte Carlo transport code \textit{EGSnrc.} This enables a direct comparison between the simulated and experimentally observed Mo K$_{\alpha }$ fluorescence and hard x-ray bremsstrahlung. The plasma profiles have been post-processed for stimulated Raman and Brillouin backscatter gains. Comparisons of these results with recent experiments at the NIF and the implications for ignition-scale PDD experiments will be presented. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 18, 2015 10:54AM - 11:06AM |
NO5.00008: Application and Analysis of the Isoelectronic Line Ratio Temperature Diagnostic in a Planar Ablating-Plasma Experiment at the National Ignition Facility R. Epstein, M.J. Rosenberg, A.A. Solodov, J.F. Myatt, S.P. Regan, W. Seka, M. Hohenberger, M.A. Barrios, J.D. Moody The Mn/Co isoelectronic emission-line ratio from a microdot source in planar CH foil targets was measured to infer the electron temperature ($T_{\mathrm{e}})$ in the ablating plasma during two-plasmon--decay experiments at the National Ignition Facility (NIF). We examine the systematic uncertainty in the $T_{\mathrm{e}}$ estimate based on the temperature and density sensitivities of the line ratio in conjunction with plausible density constraints, and its contribution to the total $T_{\mathrm{e}}$ estimate uncertainty. The potential advantages of alternative microdot elements (e.g., Ti/Cr and Sc/V) are considered. The microdot mass was selected to provide ample line strength while minimizing the effect of self-absorption on the line emission, which is of particular concern, given the narrow linewidths of mid-$Z$ emitters at subcritical electron densities. Atomic line-formation theory and detailed atomic-radiative simulations show that the straight forward interpretation of the isoelectronic ratio solely in terms of its temperature independence remains valid with lines of moderate optical thickness (up to $\sim 10$) at line center. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 18, 2015 11:06AM - 11:18AM |
NO5.00009: Absolute Two-Plasmon Decay and Stimulated Raman Scattering in Direct-Drive Irradiation Geometries R.W. Short, A.V. Maximov, J.F. Myatt, W. Seka, J. Zhang Absolute stimulated Raman scattering (SRS) and two-plasmon decay (TPD) are analyzed and found to have comparable thresholds for recent OMEGA experiments, so that both may play a role in generating the half-harmonic emission observed in these experiments.\footnote{W. Seka \textit{et al}., Phys. Rev. Lett. \textbf{112}, 145001 (2014).} The scaling of the two instabilities with plasma parameters and irradiation and polarization geometries are analyzed and shown to be quite different. Longer scale lengths and higher temperatures favor SRS over TPD, while more-oblique angles of incidence favor TPD. Consequently, for multibeam irradiation, different beams may contribute preferentially to different instabilities. Examples relevant to recent experiments will be discussed. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 18, 2015 11:18AM - 11:30AM |
NO5.00010: Competition between convective stimulated Raman scattering and convective two-plasmon decay in hybrid-drive regime Chengzhuo Xiao, Zhanjun Liu, Chunyang Zheng, Xiantu He Hybrid-drive method for inertial confinement fusion (ICF), which combines direct-drive ICF and indirect-drive ICF, has a higher laser intensity and large density scale length than conventional indirect-drive ICF. The thresholds for convective stimulated Raman scattering (SRS) and convective two-plasmon decay (TPD) near the quarter-critical density are derived. The parameter space lies beyond or just near the thresholds, which may trigger strong interactions between convective SRS and TPD. Two dimensional particle-in-cell (PIC) simulations have been performed to demonstrate the interactions. We have also studied the temperature effects which may cause the frequency mismatch in the linear stage and strongly suppress TPD. [Preview Abstract] |
Wednesday, November 18, 2015 11:30AM - 11:42AM |
NO5.00011: Laser-plasma instabilities under density fluctuations C. Ren, J. Li, R. Yan In the corona of an ICF target, laser-plasma instabilities can drive significant plasma density fluctuations. Using fluid simulations with parameters relevant to both conventional direct drive scheme and shock ignition, we show that convective stimulated Raman scattering (SRS) and two-plasmon decay (TPD) modes in the low density region can turn into absolute ones and grow beyond the convective limit under static ion density fluctuations. The TPD modes can form the first stage for hot electron generation due to their low phase velocities. The maximum absolute growth rate is $\sim$70\% of the corresponding homogeneous TPD growth rate, much higher than the convective growth rate without the ion density modulation. This may explain why in Particle-in-Cell simulations these modes were only found in the nonlinear stage when ion density fluctuations were present. [Preview Abstract] |
Wednesday, November 18, 2015 11:42AM - 11:54AM |
NO5.00012: Effects of Laser--Plasma Instabilities on Hydro Evolution in Direct-Drive Inertial Confinement Fusion J. Li, S.X. Hu, C. Ren Laser--plasma instabilities and hydro evolution of coronal plasmas in an OMEGA EP long-scale-length experiment with planar targets are studied with particle-in-cell (PIC) and hydrodynamics simulations. Plasma and laser conditions are first obtained in a \textit{DRACO} simulation with only inverse-bremsstrahlung absorption. Using these conditions, an \textit{OSIRIS} simulation is performed to study laser absorption and hot-electron generation caused by laser--plasma instabilities near the quarter-critical region. The obtained PIC information has subsequently been coupled to another \textit{DRACO} simulation to examine how the laser--plasma instabilities affect the overall hydrodynamics. The results show that the more-realistic laser absorption can increase the electron temperature but only slightly changes the density scale length in the corona. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944, DE-FC02-04ER54789 (Fusion Science Center), and DE-SC0012316. [Preview Abstract] |
Wednesday, November 18, 2015 11:54AM - 12:06PM |
NO5.00013: Self-Consistent Calculation of Half-Harmonic Emission with an Electromagnetic Zakharov Model J. Zhang, J.F. Myatt, A.V. Maximov, R.W. Short, D.F. DuBois, D.A. Russell, H.X. Vu Half-harmonic emission has been regarded as a signal of two-plasmon decay or stimulated Raman scattering (SRS). Experimental observations at the Omega Laser Facility show both blue and red shifts of half-harmonic light. The red shift might be a powerful diagnostic tool to measure electron temperature near quarter-critical density.\footnote{W. Seka \textit{et al}., Phys. Fluids \textbf{28}, 2570 (1985); W. Seka \textit{et al}., Phys. Rev. Lett. \textbf{112}, 145001 (2014).} However, the interpretation of the half-harmonics spectrum is difficult because of its complicated generation mechanism. To resolve this problem, a self-consistent electromagnetic Zakharov code that is able to calculate half harmonics emission has been developed, including all the possible generation mechanisms such as absolute SRS, Thomson down-scattering, linear mode conversion, and nonlinear mode conversion.\footnote{D. F. DuBois, D. A. Russell, and H. A. Rose, Phys. Rev. Lett. \textbf{74}, 3983 (1995); D.~A. Russell and D. F. DuBois, Phys. Rev. Lett. \textbf{86}, 428 (2001).} This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 18, 2015 12:06PM - 12:18PM |
NO5.00014: Three-Dimensional Modeling of Laser--Plasma Interactions Near the Quarter-Critical Density in Plasmas H. Wen, A.V. Maximov, R. Yan, C. Ren, J. Li, J.F. Myatt Three dimensional particle-in-cell simulations have been performed in the plasma region near quarter-critical density for the parameters typical for direct-drive inertial confinement fusion experiments.\footnote{J. F. Myatt \textit{et al}., Phys. Plasmas \textbf{21}, 055501 (2014).} The laser--plasma instabilities of two-plasmon decay (TPD), stimulated Raman scattering (SRS), and stimulated Brillouin scattering have been identified in the time evolution of different electric- and magnetic-field components. A good agreement between the simulation results and the theories of TPD and SRS\footnote{A. Simon \textit{et al}., Phys. Fluids \textbf{26}, 3107 (1983); J. F. Drake and Y. C. Lee, Phys. Rev. Lett. \textbf{31}, 1197 (1973); H. Wen \textit{et al}., Phys. Plasmas \textbf{22}, 052704 (2015).} has been observed. In the nonlinear saturation regime, the field intensities and the fast-electron distributions are compared for plane-wave and speckled laser beams. The effects of collisions are studied. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 18, 2015 12:18PM - 12:30PM |
NO5.00015: Fokker Planck and Krook theory for energetic electron deposition in laser fusion Wallace Manheimer, Denis Colombant We have developed a Fokker Planck and Krook model to calculate the transport and deposition of energetic electrons, produced for instance by the two plasmon decay instability at the quarter critical surface of a laser produced plasma [1]. In steady state, the Fokker Planck equation reduces to a single universal equation in energy and space, an equation which whose asymptotic solution we calculate. The Krook theory also gives rise to an analytic expression solution. From each, one can calculate the spatially dependent heating of the interior plasma, which can be implemented at each time step in a fluid simulation. The equation is equally valid in planar and spherical geometry, and it depends on only a single parameter, the charge state Z. Hence one can solve for a universal solution, valid for each Z. the two approaches will be compared and discussed. We look to cooperate with anyone having a more advanced simulation capability, Direct Simulation Monte Carlo or Fokker Planck, who is willing to test our results.\\[4pt] [1] B. Yaakobi et al, Phys. Plasmas 19, 012704, 2012. [Preview Abstract] |
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