Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session TO04: ICF: Laser Plasma Interactions IIOn Demand
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Chair: Christopher Walsh, Lawrence Livermore Natl Lab Room: Rooms 304-305 |
Thursday, November 11, 2021 9:30AM - 9:42AM |
TO04.00001: Short-wavelength-and-broad-bandwidth mitigation of laser-plasma instabilities Jason W Bates, Russell K Follett, John G Shaw, Stephen P Obenschain, Robert H Lehmberg, Jason F Myatt, James L Weaver, Matthew F Wolford The U.S. Naval Research Laboratory is engaged in an ongoing research effort to demonstrate the benefits of an argon-fluoride (ArF) laser driver for inertial confinement fusion (ICF). Compared to the frequency-tripled Nd:glass lasers used in most ICF experiments today, an ArF laser provides several distinct advantages, including: 1.) a shorter wavelength (193 nm versus 351 nm); and 2.) a broader native bandwidth (5 - 10 THz versus ≤ 1 THz) — both of which help to suppress deleterious laser-plasma instabilities (LPIs). In this talk, we present numerical simulations of ICF-relevant LPIs that were performed using the LPSE code. Our numerical models incorporate multi-beam laser geometries as well as realistic plasma conditions and we compare results for ArF and Nd:glass drivers. In the case of cross-beam energy transfer, for example, we find that an ArF driver provides a 40% increase in the time-averaged, inverse-bremsstrahlung absorption in the plasma surrounding an OMEGA-scale target. Moreover, in studies of the absolute two-plasmon-decay and stimulated-Raman-scattering instabilities for both OMEGA and NIF-scale implosions, threshold intensities are found to be consistently higher using ArF laser light. This work suggests that an ArF driver would facilitate larger ablation pressures in ICF target designs, which would, in turn, permit the use of thicker- walled pellets that are more resistant to hydrodynamic instabilities. |
Thursday, November 11, 2021 9:42AM - 9:54AM |
TO04.00002: Experimental investigations on the Stimulated Raman Scattering (SRS) in a magnetized environment Simon Bolaños, Mathieu Bailly-Grandvaux, Roman Lee, Mario J Manuel, Warren B Mori, SJ Spencer, Frank S Tsung, Benjamin J Winjum, Farhat N Beg SRS plays a detrimental role in inertial confinement fusion (ICF) caused by a loss of energy and preheat of the fuel by suprathermal electrons generated through the decay of electron plasma waves (EPW). However, recent numerical work [1] has shown that SRS can be mitigated by a moderate external magnetic field. Such behavior of SRS in a pre-magnetized plasma has not been experimentally confirmed. With the development of applied magnetic fields for use in laser-plasma experiments, investigation on the effect of a magnetic field on SRS is now possible. We have introduced a new platform designed to investigate the mitigation of SRS at OMEGA-EP, which takes advantage of the MIFEDS pulse-power coil to pre-magnetize the plasma. The Sub-Aperture Backward Scatter (SABS) diagnostic was fielded to time resolve reflected light from Backward-SRS (BSRS). The first results of SABS show clear evidence of the reflected light resulting from the BSRS in the kinetic regime, kλD ~ 0.3 where k is the EPW wavenumber and λD is the Debye length. |
Thursday, November 11, 2021 9:54AM - 10:06AM |
TO04.00003: Identification and analysis of stimulated Raman side scattering in OMEGA EP experiments Jason F Myatt, Steven Hironaka, Michael J Rosenberg, Andrey Solodov, Janukan Sivajeyan, Chengzhuo Xiao, Qing Wang Recent long-scale-length spherical target experiments, performed on the OMEGA EP laser, are analyzed for stimulated Raman side-scattering (SRSS). This work has been motivated by results obtained at the National Ignition Facility (NIF), relevant to directly-driven inertial confinement fusion (ICF)1,2. These NIF experiments have shown SRSS to be an important process, possibly responsible for the observed hot electron generation. Our model, based on ray tracing, is able to explain the time-dependent scattered light spectra from the OMEGA EP experiments: It identifies SRS side-scatter and near backscatter from portions of each incident beam where the scattered electromagnetic is generated in the direction parallel to contours of constant density. These processes are shown to be the origin of the major spectral features observed in the experiment. The nature of SRSS instability (temporal versus spatial growth) is discussed. It is suggested that the OMEGA EP platform could provide a good surrogate in which to develop SRSS mitigation strategies. |
Thursday, November 11, 2021 10:06AM - 10:18AM Not Participating |
TO04.00004: Suppression of inflationary stimulated Raman scattering (SRS) by bandwidth on Nd:glass, KrF, and ArF laser systems. SJ Spencer, Tony Arber Stimulated Raman Scattering (SRS) is a parametric instability of concern to inertial confinement fusion (ICF) schemes; since it scatters light away from the target, and accelerates hot electrons towards the cold fuel. In directly-driven ICF schemes we are concerned with the convective growth of SRS; which can have very large gain in the ICF corona, leading to pump-depletion of the laser ahead of the quarter critical density surface. Guzdar et al. [1991] showed that random phase modulated bandwidth has no net effect on the gain of convective SRS. Wen et al. [2021] showed that the threshold for inflationary convective SRS can be increased by sinusoidal frequency-modulated bandwidth. |
Thursday, November 11, 2021 10:18AM - 10:30AM |
TO04.00005: 2D PIC simulations of backward and forward stimulated Raman side-scattering in direct-drive ignition-scale plasmas Qing Wang, Chengzhuo Xiao, Wojciech Rozmus, Jason F Myatt The experimental observation of stimulated Raman side-scattering (SRSS) in planar-target experiments at the National Ignition Facility (NIF) renews research and interest of SRSS. Side scatter requires scattered light propagating perpendicularly to the density gradient. Therefore, for oblique incidence, the propagation direction of side-scattered light is either backward or forward with respect to the incident beam. Here, the competition between backward SRSS and forward SRSS are investigated in direct-drive ignition-scale plasmas where laser intensity is ∼ 1014 W/cm2, densities range from 0.15 nc to 0.2 nc, electron temperature is 4 keV, and the density scale-length is 800 μm. Linear analysis shows that both BSRSS and FSRSS are absolute (temporally growing) at higher densities (ne>0.17nc), and, at lower densities (ne<0.15nc) , BSRSS becomes convective with a large gain, but FSRSS is still absolute for conditions relevant to direct drive. 2D PIC simulations show that BSRSS and FSRSS coexist at both higher densities and lower densities, and backward side-scattered light is stronger than forward side-scattered light in the nonlinear stage. The effects of pump depletion on the growth rate of FSRSS and kinetic enhancement and saturation of BSRSS are presented. |
Thursday, November 11, 2021 10:30AM - 10:42AM |
TO04.00006: Mitigation of Inflationary Stimulated Raman Scattering with Laser Bandwidth Han Wen, Russell K Follett, Andrei V Maximov, John P Palastro Kinetic inflation exacerbates the threat of the stimulated Raman scattering (SRS) instability to inertial confinement fusion. Continued growth of the instability requires phase matching between the incident light wave and the decay products, a scattered light wave, and an electron plasma wave (EPW). In principle, a density inhomogeneity can disrupt the phase matching by changing the frequency of the EPW along the gradient. In reality, electron trapping in the EPW produces a frequency shift that can compensate this change. This autoresonance, or kinetic inflation, can substantially enhance the SRS reflectivity. Here we demonstrate that laser bandwidth can mitigate inflationary SRS and limit the reflectivity to non-inflationary levels by rapidly moving the location of exact phase matching. While the instantaneous reflectivity depends on the local chirp of the incident light, the inflationary SRS threshold depends on the bandwidth format, for example random or smoothing by spectral dispersion. This leads to distinct scaling laws which can help guide SRS mitigation efforts. |
Thursday, November 11, 2021 10:42AM - 10:54AM |
TO04.00007: Parameter scan of stimulated Raman scattering in magnetic fields Benjamin J Winjum, Roman Lee, SJ Spencer, Simon Bolanos, Frank S Tsung, Warren B Mori Stimulated Raman scattering (SRS) can be mitigated in the kinetic regime (kλD > ~0.3) by weak magnetic fields (ωc/ωp << 1) due to the damping of electron plasma waves (EPWs) propagating perpendicular to the magnetic fields. However, we have also found that magnetic fields can interfere with the nonlinear frequency shift of SRS-driven EPWs, and for SRS that is dominated by the dynamics of this frequency shift, magnetic fields can thereby indirectly enhance the frequency resonance between the light and plasma waves involved in SRS. Furthermore, in some parameter regimes, the SRS waves can themselves be unstable (e.g. the backscattered light wave can decay via rescatter and the backscattered EPW can decay via LDI), and for finite-width waves in multi-dimensions, the damping and transverse evolution of SRS EPWs depends sensitively on wave-particle interactions that can be impacted by magnetic fields. We show particle-in-cell simulations that illustrate how magnetic fields impact SRS and EPWs across a wide range of laser and plasma parameters. |
Thursday, November 11, 2021 10:54AM - 11:06AM |
TO04.00008: Stimulated Raman backscatter in the kinetic regime of lasers with orbital angular momentum Sarah E Chase, Benjamin J Winjum, Frank S Tsung, Kyle G Miller, Warren B Mori, Denise E Hinkel In the field of the nonlinear optics of plasmas, stimulated Raman scattering (SRS) has been actively studied because this process is deleterious to inertial confinement fusion. While SRS has been studied extensively for plane waves and single and multiple speckled beams, there has been little work on SRS of a laser with orbital angular momentum (OAM.) SRS of a laser with OAM introduces an additional matching condition for the angular momentum index, l, in addition to the frequency and wavenumber matching conditions. Therefore, a given laser can scatter into a number of different modes with different angular momentum and create plasma waves with OAM. The OAM of the plasma wave can affect its nonlinear damping rate and therefore the growth of backscattered SRS-driven light waves. Lasers and plasma waves with OAM can only be studied in 3D geometry. We present preliminary results of SRS of lasers with OAM using the Quasi-3D OSIRIS particle-in-cell code and the fluid code pF3D. Simulations results of driven plasma waves with OAM will also be presented. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, by DE-NA0003842, and by DE-SC0019010. |
Thursday, November 11, 2021 11:06AM - 11:18AM |
TO04.00009: A Local-Field Approach to Understanding Multibeam Laser–Plasma Instabilities Russell K Follett, Dustin H Froula, Andrei V Maximov, Andrey Solodov, Han Wen, Jason F Myatt, Jason W Bates, John P Palastro Laser–plasma instabilities such as stimulated Raman scattering and two-plasmon decay present a major challenge for laser-driven inertial confinement fusion. Predicting the severity of these instabilities requires a model that captures the complex, 3-D interaction of multiple laser beams, including effects such as speckle, polarization, and bandwidth. Analytic approaches typically employ the frequency and wave-vector matching condition for multiple laser beams to drive a shared daughter wave while neglecting the local field structure that results from the interference between many overlapping beams. Three-dimensional simulations, on the other hand, capture the full interaction dynamics and field structure but can obscure the underlying physical processes. Here we introduce an intermediate approach that uses a simplified model of the local field structure to study the impact of multibeam interactions on absolute instabilities. |
Thursday, November 11, 2021 11:18AM - 11:30AM |
TO04.00010: Hot electron scaling from PIC simulations of two-plasmon decay instability Shihui Cao, Dhrumir P Patel, Riccardo Betti, Chuang Ren, Michael J Rosenberg A series of 2D in-plane Particle-In-Cell simulations has been carried out to study the scaling of hot-electron fraction from two-plasmon decay (TPD) instability at conditions relevant to OMEGA-scale experiments. Scaling laws obtained give good prediction of the simulations. Using this scaling and laser-plasma conditions from LILAC simulations, we calculate whole-pulse hot-electron fractions and convert them into hard x-ray signals for validation and prediction. Results show that the simulation scaling ’predicts’ a much higher hot-electron fraction than the experiments. Plans to address missing physics in these simulations, including laser speckles, laser pump depletion under 0.21nc, and cogeneration from TPD and Stimulated Raman Side Scattering, will also be discussed. |
Thursday, November 11, 2021 11:30AM - 11:42AM |
TO04.00011: Measurement of hot-electron-driven fast ions in polar-direct drive exploding pusher implosions at the NIF Maria Gatu Johnson, Patrick J Adrian, Johan A Frenje, Tim M Johnson, Neel Kabadi, Brandon G Lahmann, Richard Petrasso, Warren J Garbett, Stephen Craxton, Matthias Hohenberger, Heather D Whitley, Charles B Yeamans, Alex B Zylstra When hot electrons, generated through laser-plasma interactions (LPI) such as two-plasmon decay (TPD) or stimulated raman scattering (SRS), are accelerated away from a directly driven inertial confinement fusion implosion, the resulting charge gap can lead to acceleration of ions on the capsule surface to MeV energies. In this talk, we will show the first measurements of such MeV protons from polar direct drive exploding pusher (PDXP) implosions on the NIF. Correcting for blowby due to the large NIF laser spots to calculate an effective intensity on capsule, the maximum proton energies generated through this mechanism at NIF are higher than previously observed at OMEGA, but lower than predicted from TPD common wave theory. We explore if this observation is consistent with SRS being the dominant hot-electron generating mechanism on NIF and TPD on OMEGA. In addition, strong energy modulations have been observed in broad spectra of ions born in the NIF PDXP implosions, and we discuss if this could also be related to LPI effects. |
Thursday, November 11, 2021 11:42AM - 11:54AM |
TO04.00012: Absorption of Laser Light by Coupling to Incoherent Plasma Waves at Quarter-Critical Density Andrei V Maximov, David Turnbull, Russell K Follett, Dana H Edgell, John G Shaw, Han Wen, Dustin H Froula, John P Palastro Inertial confinement fusion (ICF) relies critically on the absorption of laser light in high-density plasma. Laser–plasma instabilities, such as two-plasmon decay (TPD), can interfere with this absorption by scattering or prematurely depleting the laser light at lower plasma densities. Here we identify a novel mechanism for laser absorption that occurs as laser light passes through quarter-critical density and interacts with a pre-existing, incoherent ensemble of TPD-driven plasma waves. The interaction, mediated by a newly scattered, but stable, plasma wave, produces an imaginary refractive index proportional to the energy density of the incoherent plasma waves. This additional absorption occurs independent of the intensity and can modify the interplay of TPD, cross-beam energy transfer, and irradiation uniformity in direct-drive ICF implosions. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. |
Thursday, November 11, 2021 11:54AM - 12:06PM |
TO04.00013: Kinetic Simulations of Stimulated Whistler Scattering in Magnetized Plasma Ryan Lau, David J Strozzi, Yuan Shi We present simulations of stimulated whistler scattering using the one-dimensional kinetic |
Thursday, November 11, 2021 12:06PM - 12:18PM Not Participating |
TO04.00014: Hot Electron and Shock Breakout Characterization in Shock Ignition Relevant Experiments Anthony Raymond, Christine M Krauland, Shu Zhang, Kazuki Matsuo, Joohwan Kim, Eric N Hahn, Farhat N Beg Shock ignition is an alternative inertial confinement fusion scheme, which uses a strong convergent shock generated by a ∼1016 W/cm2 spike laser pulse to ignite a pre-compressed fusion capsule. Understanding nonlinear laser-plasma instabilities and hot electron generation is critical for SI and has been studied extensively by the authors. We have recently conducted a series of experiments on the OMEGA EP and OMEGA-60 laser facilities exploring a variety of regimes relevant to shock ignition, with experimental parameters informed by radiation hydrodynamic simulations. To verify modeling of the plasma conditions with and without a high intensity UV beam interaction, the 4ω probe beam was utilized for Thomson scattering on OMEGA 60 at variable focal standoff from the initial target surface between 300 – 1100 μm, corresponding to plasma densities between ncrit to ncrit/10. Derived results will be presented and compared to expectations from FLASH simulations. In addition, simultaneously collected shock breakout measurements are presented using VISAR and SOP diagnostic techniques and are additionally compared to expectations. Such validations of simulation results will aid to inform future experiments conducted in this regime. |
Thursday, November 11, 2021 12:18PM - 12:30PM |
TO04.00015: Impact Of Stimulated Raman Scattering on ICF in Density Rippled Magnetized Plasma Oriza Kamboj, Ashish Yadav, Devki N Gupta, John Pasley, Niti Kant In inertial confinement fusion, the development of stimulated Raman scattering is observed in the presence of an azimuthal magnetic field and a density rippling plasma. The Gaussian laser beam traveling through a density rippled plasma is amplified by forward Raman scattering in the presence of an azimuthal magnetic field, resulting in two radially localized electromagnetic sideband waves and a lower hybrid wave. The nonlocal effect generated by the azimuthal magnetic field decreases the nonlocal contact area. As a result, the growth rate in the presence of density rippling magnetized plasma limits the probability of plasma pre-heating in ICF. |
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