Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session PO4: Laser Plasma Interactions |
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Chair: Denise Hinkel, Lawrence Livermore National Laboratory Room: Salon E |
Wednesday, October 29, 2014 2:00PM - 2:12PM |
PO4.00001: An Investigation of Two-Plasmon--Decay Localization in Spherical Implosion Experiments on OMEGA J.F. Myatt, J. Shaw, J. Zhang, A.V. Maximov, R.W. Short, W. Seka, D.H. Edgell, D.F. DuBois, D.A. Russell, H.X. Vu The localization of the two-plasmon--decay (TPD) instability to specific angular regions of the quarter-critical surface in spherical implosion experiments on OMEGA has been demonstrated through the imaging of both half- and three-halves harmonic emission.\footnote{ W. Seka \textit{et al.}, Phys. Rev. Lett. \textbf{112}, 145001 (2014).}$^,$\footnote{ D. H. Edgell \textit{et al.}, this conference.} Localization is possible because TPD is a multibeam instability and different angular locations on the quarter-critical surface are driven by beams whose incident angles and intensities vary. The degree of localization has been quantified through a series of numerical calculations that were performed with a 3-D nonlinear Zakharov model of TPD. Based on these results, estimates for localized electron plasma temperature excursions have been obtained and compared with those inferred from experiment. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, October 29, 2014 2:12PM - 2:24PM |
PO4.00002: Spatial Variation of Two-Plasmon--Decay Laser--Plasma Interactions Found in 3/2 $\omega$ Target Images D.H. Edgell, I.V. Igumenshchev, D.T. Michel, J.F. Myatt, D.H. Froula The Thomson-scattering system (TSS) on OMEGA has recorded images of 3/2$\omega $ light emitted from implosions. The 3/2$\omega $ light results from Thomson scattering of the drive beams off of electron plasma waves (EPW's) driven by the two-plasmon-decay (TPD) laser--plasma interaction at the quarter-critical surface. The images indicate that the 3/2$\omega $ emission is not uniform over the surface. The images show distinct patterns that change as the drive beam profile is varied. The fraction of laser energy converted to hot electrons has been shown to empirically scale with the TPD multibeam common-wave gain (CWG) during implosions on OMEGA.\footnote{D. T. Michel \textit{et al.}, Phys. Rev. Lett. \textbf{109}, 155007 (2012).} A hydrodynamic post-processor code calculates the CWG, including the effects of cross-beam energy exchange on the laser intensity and $k$ vectors of the EPW's driven at the quarter-critical surface. The 3/2$\omega$ light Thomson scattered off these EPW's and collected is modeled and compared to the observed images. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, October 29, 2014 2:24PM - 2:36PM |
PO4.00003: Ultraviolet Thomson Scattering from Two-Plasmon--Decay Electron Plasma Waves Driven by Multiple Laser Beams R.K. Follett, R.J. Henchen, S.X. Hu, J. Katz, D.T. Michel, J.F. Myatt, H. Wen, D.H. Froula Thomson scattering is used to probe electron plasma waves (EPW's) driven by the common-wave two-plasmon--decay (TPD) instability near the quarter-critical density. Between two and five laser beams ($\lambda_{3\omega} = 351$ nm) illuminated planar CH targets with 300-$\mu $m-diam (FWHM) laser spots with overlapped intensities $\sim 10^{15}$ W/cm$^{2}$. A 263-nm Thomson-scattering beam was used to probe densities ranging from 0.2 to 0.25 $n_{\mathrm{c}}$ while $k$ matching the TPD common wave. The Thomson-scattering spectra show two spectral peaks consistent with scattering from forward-scattered TPD common-wave EPW's and Langmuir decay of backscattered TPD waves. Broad TPD driven spectral features were observed in an alternate scattering configuration probing EPW $k$ vectors that do not lie along a TPD maximum-growth hyperbola, consistent with TPD $k$-space saturation. Experimental results are compared to \textit{ZAK3D} simulations. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, October 29, 2014 2:36PM - 2:48PM |
PO4.00004: Absolute and Convective Two-Plasmon Decay Driven by Multiple Laser Beams R.W. Short, J.F. Myatt, J. Zhang, W. Seka Analysis of two-plasmon decay (TPD) driven by multiple laser beams indicates that the linear phase of the instability is dominated by an absolute instability that most strongly drives plasma waves with small wave numbers; this is consistent with Zakharov simulations.\footnote{J. Zhang \textit{et al}., this conference.} Two types of absolute mode are found in the small-$k$ region, with the dominant mode depending on the relative angles between the beams. Thresholds decrease with increasing angle of incidence. Although the analysis presented here is linear, observations indicate that the absolute mode persists well into the nonlinear regime.\footnote{W. Seka \textit{et al.}, Phys. Rev. Lett. \textbf{112}, 145001 (2014).} Representative results for the absolute TPD threshold as a function of beam geometry and polarization will be presented, and the consequences for direct-drive experiments 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, October 29, 2014 2:48PM - 3:00PM |
PO4.00005: Particle-in-Cell Modeling of Laser--Plasma Interactions in Three Dimensions H. Wen, A.V. Maximov, R. Yan, J. Li, C. Ren, J.F. Myatt In the direct-drive method of inertial confinement fusion, the laser--plasma interactions (LPI's) near quarter-critical density are very important for laser absorption and fast-electron generation.\footnote{J. F. Myatt \textit{et al}., Phys. Plasmas \textbf{20}, 052705 (2013).} Three-dimensional simulations with the particle-in-cell (PIC) code \textit{OSIRIS} have allowed us to study different parametric instabilities including two-plasmon decay, stimulated Raman scattering, and stimulated Brillouin scattering. These instabilities may coexist and interact in the region near quarter-critical density. The spectra of forward-going and backward-going scattered light and fast electrons in two-dimensional and three-dimensional PIC simulations have been studied. Characteristics of LPI driven by a plane-wave laser and by an incoherent laser beam are compared. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, October 29, 2014 3:00PM - 3:12PM |
PO4.00006: Self-Consistent Calculation of Half-Harmonics Emission Generated by the Two-Plasmon--Decay Instability J. Zhang, J.F. Myatt, A.V. Maximov, R.W. Short, D.F. DuBois, D.A. Russell, H.X. Vu Half-harmonics emission can be used as an effective diagnostic tool\footnote{ W. Seka \textit{et al.}, Phys. Fluids \textbf{28}, 2570 (1985).} for the two-plasmon--decay (TPD) instability.\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).} However, interpretation of the half-harmonics spectrum is difficult because of its complicated generation mechanism. We have developed a code that can calculate half-harmonics emission self-consistently with the TPD instability. The results would be useful to interpret experimental data and help design 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, October 29, 2014 3:12PM - 3:24PM |
PO4.00007: Two-plasmon decay instabilities in a plasma with ion density fluctuations Jun Li, Chuang Ren, Rui Yan Previous study found that the two-plasmon decay (TPD) modes in the low density region were important to hot electron generation in direct-drive inertial confinement fusion [R. Yan et al, Phys.Rev.Lett 108, 175002 (2012)]. These modes were linked to ion density fluctuations and formed the first stage for electron acceleration due to their low phase velocities. Here we investigate the excitation mechanism of these modes by studying linear growth of TPD instabilities in a plasma with ion density modulations under parameters relevant to OMEGA experiments using LTS [R. Yan et al, Phys.Plasmas 17, 052701 (2010)] fluid simulations. It is found that when a sinusoidal static ion density modulation is added to the linear plasma density profile, the otherwise convective TPD modes become absolute with a growth rate depending on the modulation amplitude and wave number. 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. An analytical theory is also developed to understand these results. 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, October 29, 2014 3:24PM - 3:36PM |
PO4.00008: Boosting the performance of Brillouin amplification via reduction of parasitic Raman scattering and filamentation R. Trines, R. Bingham, P.A. Norreys, E.P. Alves, R.A. Fonseca, L.O. Silva, K.A. Humphrey, F. Fiuza, R.A. Cairns Brillouin amplification of laser pulses in plasma is a promising scheme to produce picosecond pulses of petawatt power, as it is more robust than Raman amplification. However, parasitic instabilities spoil the quality of the amplified pulse: Raman backscattering affects the contrast ratio, filamentation ruins the pulse envelope and Raman forward scattering spoils the pulse's coherence and causes the amplification to saturate. Through analytic theory and simulations, we have identified a novel parameter window where the performance of Brillouin amplification is maximized and the highest pulse powers are reached while the deleterious influence of parasitic instabilities is strongly reduced. The respective merits of using plasma densities either above or below the quarter-critical density will be discussed. [Preview Abstract] |
Wednesday, October 29, 2014 3:36PM - 3:48PM |
PO4.00009: Laser-Plasma Instabilities by Avoiding the Strong Ion Landau Damping Limit: The Central Role of Statistical, Ultrafast, Nonlinear Optical Laser Techniques (SUNOL) Bedros Afeyan, Stefan H\"uller, David Montgomery, John Moody, Dustin Froula, James Hammer, Oggie Jones, Peter Amendt In mid-Z and high-Z plasmas, it is possible to control crossed bean energy transfer (CBET) and subsequently occurring single or multiple beam instabilities such as Stimulated Raman Scattering (SRS) by novel means. These new techniques are inoperative when the ion acoustic waves are in their strong damping limit, such as occurs in low Z plasmas with comparable electron and ion temperatures. For mid-Z plasmas, such as Z $=$ 10, and near the Mach 1 surface, the strong coupling regime (SCR) can be exploited for LPI mitigation. While at higher Z values, it is thermal filamentation in conjunction with nonlocal heat transport that are useful to exploit. In both these settings, the strategy is to induce laser hot spot intensity dependent, and thus spatially dependent, frequency shifts to the ion acoustic waves in the transient response of wave-wave interactions. The latter is achieved by the on-off nature of spike trains of uneven duration and delay, STUD pulses. The least taxing use of STUD pulses is to modulate the beams at the 10 ps time scale and to choose which crossing beams are overlapping in time and which are not. [Preview Abstract] |
Wednesday, October 29, 2014 3:48PM - 4:00PM |
PO4.00010: Laser plasma interaction in rugby-shaped hohlraums P.-E. Masson-Laborde, F. Philippe, V. Tassin, M.-C. Monteil, P. Gauthier, A. Casner, S. Depierreux, P. Seytor, D. Teychenne, P. Loiseau, P. Freymerie Rugby shaped-hohlraum has proven to give high performance compared to a classical similar-diameter cylinder hohlraum. Due to this performance, this hohlraum has been chosen as baseline ignition target for the Laser MegaJoule (LMJ). Many experiments have therefore been performed during the last years on the Omega laser facility in order to study in details the rugby hohlraum. In this talk, we will discuss the interpretation of these experiments from the point of view of the laser plasma instability problem. Experimental comparisons have been done between rugby, cylinder and elliptical shape rugby hohlraums and we will discuss how the geometry differences will affect the evolution of laser plasma instabilities (LPI). The efficiency of laser smoothing techniques on these instabilities will also be discussed as well as gas filling effect. The experimental results will be compared with FCI2 hydroradiative calculations and linear postprocessing with Piranah. Experimental Raman and Brillouin spectrum, from which we can infer the location of the parametric instabilities, will be compared to simulated ones, and will give the possibility to compare LPI between the different hohlraum geometries. [Preview Abstract] |
Wednesday, October 29, 2014 4:00PM - 4:12PM |
PO4.00011: Multibeam Laser--Plasma Interactions Lead to Localized Interaction Regions W. Seka, W. Theobald, J.F. Myatt, R.W. Short, R.E. Bahr, R. Nora, R. Betti Spherical high-intensity laser--plasma interaction experiments on OMEGA with and without smoothing by spectral dispersion show evidence of stimulated Brillouin and Raman scattering and two-plasmon decay in the corona at or below $n_{\mathrm{c}}$/4. The multibeam nature of the interaction and its symmetry requirements automatically lead to localized interaction regions that may influence energy deposition and drive uniformity. The localized nature of these processes manifests itself in scattered-light images and spectra in various wavelength regimes. We will present experimental evidence for these processes supported by hydrodynamic and laser--plasma interaction simulations. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944 and the Office of Fusion Energy Sciences Number DE-FG02-04ER54786. [Preview Abstract] |
Wednesday, October 29, 2014 4:12PM - 4:24PM |
PO4.00012: Cross-Beam Energy Transfer Driven by Incoherent Laser Beams with Colors A.V. Maximov, J.F. Myatt, R.W. Short, I.V. Igumenshchev, W. Seka Recently, the effect of cross-beam energy transfer (CBET) has become one of the most important challenges for the effective coupling of laser energy to the target in inertial confinement fusion (ICF) (see, e.g., Ref. 1). CBET is based on the process of stimulated Brillouin scattering (SBS) driven by multiple crossing laser beams in the regime of moderate SBS amplification gains, and is consequently sensitive to the frequency characteristics of the laser beams driving the ICF targets: smoothing by spectral dispersion or frequency shifts between the beams (colors). Different from reduced ray-type models used in large-scale hydrodynamic simulations with CBET,\footnote{ I. V. Igumenshchev \textit{et al}., Phys. Plasmas \textbf{19}, 056314 (2012). } we have developed a laser--plasma interaction (LPI)-type model of CBET that is capable of capturing the effects of laser speckles and the non-paraxial propagation of multiple laser beams.\footnote{ A. V. Maximov \textit{et al}., Phys. Plasmas \textbf{11} 2994 (2004).} The LPI-type CBET model has been applied to the interaction between incoherent laser beams with different colors and the differences from the ray-type CBET model have been shown. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, October 29, 2014 4:24PM - 4:36PM |
PO4.00013: Manipulation of the polarization of intense laser beams via optical wave mixing in plasmas Pierre Michel, Laurent Divol, David Turnbull, John Moody When intense laser beams overlap in plasmas, the refractive index modulation created by the beat wave via the ponderomotive force can lead to optical wave mixing phenomena reminiscent of those used in crystals and photorefractive materials. Using a vector analysis, we present a full analytical description of the modification of the polarization state of laser beams crossing at arbitrary angles in a plasma. We show that plasmas can be used to provide full control of the polarization state of a laser beam, and give simple analytical estimates and practical considerations for the design of novel photonics devices such as plasma polarizers and plasma waveplates. [Preview Abstract] |
Wednesday, October 29, 2014 4:36PM - 4:48PM |
PO4.00014: The numerical study of Stimulated Raman and Brillouin Scattering in multiple laser beams Chunyang Zheng, Liang Hao Two dimensional simulations of multi-beam laser-plasma interactions have been performed in the 2D particle-in-cell (PIC) code. The Raman or Brillouin amplification and competition between them in the presence of strong cross beam energy transfer are discussed. We observe that the total backward scattering level can be significantly enhanced or reduced by varying the wavelength separations among the interaction beams. The effects of particle trapping and side scattering which are responsible for the nonlinear saturation of SRS or SBS are also analyzed. [Preview Abstract] |
Wednesday, October 29, 2014 4:48PM - 5:00PM |
PO4.00015: Saturation of stimulated Brillouin scattering by ion acoustic wave bowing and breakup Lin Yin, Brian Albright, David Montgomery, Ben Bergen, Kevin Bowers In laser-driven fusion and high-energy-density physics experiments, two crossing laser beams can transfer energy between one another via stimulated Brillouin scattering (SBS) involving the two laser beams and an ion acoustic wave (IAW). Obtaining a physics-based understanding of the nonlinear saturation of cross-beam energy transfer is important to low-mode asymmetry control in ICF implosions. In this work, nonlinear saturation of SBS in speckled laser beams is examined in the kinetic regime using 2D and 3D particle-in-cell simulations. Rapid SBS saturation is found to be caused by IAW bowing from trapped particle nonlinear frequency shift and IAW break up in the direction transverse to the laser. Both processes can lead to rapid loss of trapped ions in regions of small transverse extent during IAW bowing and breakup and dissipation of wave energy. [Preview Abstract] |
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