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 NO07: ICF: Laser Plasma Interactions IOn Demand
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Chair: Russell Follett, Laboratory for Laser Energetics - Rochester Room: Rooms 315-316 |
Wednesday, November 10, 2021 9:30AM - 9:42AM |
NO07.00001: Nonlinear physics of cross-beam energy transfer relevant to indirect drive ignition inertial confinement fusion experiments Lin Yin, Truong Nguyen, Guangye Chen, Luis Chacon, David Stark, Lauren Green, Brian M Haines Cross-beam energy transfer (CBET) allows crossing laser beams to exchange energy. The nonlinear physics of CBET for multi-speckled laser beams is examined using particle-in-cell simulations for a range of plasma conditions, laser intensities, and crossing angles relevant to indirect drive ignition inertial confinement fusion experiments. The growth and saturation of CBET involve complex, nonlinear ion and electron dynamics. It is found that a CBET-amplified seed beam can become unstable to forward stimulated Raman scattering (FSRS) but that FSRS is absent at low densities. Ion trapping induces nonlinear processes such as changes to the ion acoustic wave (IAW) dispersion and IAW nonlinearities (e.g., bowing and self-focusing), which, together with pump depletion and FSRS, determine the time dependent nature and level of CBET gain as the system approaches steady-state. CBET gain figures of merit and energy partitioning among laser beams, plasma waves and particles are discussed. |
Wednesday, November 10, 2021 9:42AM - 9:54AM |
NO07.00002: Inline Study of Low-Mode Asymmetry Induced by Polarized Cross-Beam Energy Transfer Interaction in Laser-Direct-Drive Spherical Implosions on OMEGA Arnaud Colaitis, Dana H Edgell, Igor Igumenshchev, David Turnbull, John P Palastro, Russell K Follett, Owen M Mannion, Christian Stoeckl, Valeri N Goncharov, Dustin H Froula Laser-direct-drive shell implosion experiments conducted on the OMEGA laser have been found to be prone to systematic flow anomalies at stagnation, which persist after elimination of perturbation sources such as target offset, vibration, stalk and ice non-uniformity. Recently, a proposed explanation for this anomaly has been the polarized Cross Beam Energy Transfer (CBET) interaction in the OMEGA beam configuration. Here we present the first polarized CBET model fully coupled to a radiative hydrodynamics code, implemented in the ASTER/IFRIIT 3D ICF code (LLE/CELIA). The inline model is used to investigate the polarized CBET interaction in two cryogenic experiments conducted at OMEGA: first in the case of a strong low mode induced by illumination imbalance, and a second which was in an optimal implosion configuration. We present simulation results with varying CBET and illumination configurations and compared to velocity and direction measurements of the DT flow obtained from neutron diagnostics. An excellent agreement with the data is found in the case that is dominated by balance and pointing error, while simulations in the second case will be finalized in the coming weeks. These results shine light on the definitive effect of polarized CBET in OMEGA implosions. |
Wednesday, November 10, 2021 9:54AM - 10:06AM |
NO07.00003: Reduction of cross beam energy transfer by speckles pattern Albertine Oudin, Arnaud Debayle, Charles D Ruyer, Didier Benisti Many experiments dedicated to Inertial Confinement Fusion and laboratory astrophysics require the use of several tens of high intensity laser beams. The crossing of these beams through the produced plasma may induce significant energy exchanges, hence modifying the laser energy deposition. This effect, known as cross beam energy transfer (CBET), is a three-wave mixing process in which an electronic wave partially scatter one beam along the direction of the second beam. |
Wednesday, November 10, 2021 10:06AM - 10:18AM |
NO07.00004: Theory and Simulation of CBET Mitigation Through Increased Laser Bandwidth Alexander Seaton, Lin Yin, Russell K Follett, Ari Le, Brian J Albright The cross-beam energy transfer (CBET) instability is currently a major obstacle to ignition in direct laser drive inertial confinement fusion (ICF). Technologies have recently been proposed that could enable a significant enhancement in the bandwidth available on fusion laser systems, and therefore improve laser coupling through mitigation of laser-plasma instabilities including CBET. In this work we present fluid and kinetic simulations of CBET driven by lasers with bandwidths in the range 2.5-10THz (exceeding the ion-acoustic wave frequency), and introduce a simple model for CBET in the presence of bandwidth. We discuss the key behaviour of the theoretical bandwidth scaling, and use it to provide an intuitive understanding of the mechanisms through which bandwidth mitigates CBET. The theory is then compared with linearized fluid simulations, performed with the LPSE code, and fully kinetic simulations performed with the VPIC particle-in-cell code. LPSE simulations exhibit good agreement with the theory due to the absence of nonlinear ion-acoustic wave dynamics. In contrast, ion-trapping induced nonlinear effects, two-ion wave decay, and stimulated Brillouin scattering cause VPIC simulations to exhibit more significant departures from linear theory. |
Wednesday, November 10, 2021 10:18AM - 10:30AM |
NO07.00005: Cross-Beam Energy Transfer Saturation by Ion Trapping-Induced Detuning Khanh Linh Nguyen, Lin Yin, Brian J Albright, Aaron M Hansen, Dustin H Froula, David Turnbull, Russell K Follett, John P Palastro The performance of direct-drive inertial confinement fusion implosions relies critically on the coupling of laser energy to the target plasma. Cross-beam energy transfer (CBET), the resonant exchange of energy between intersecting laser beams mediated by ponderomotively driven ion-acoustic waves (IAW's), inhibits this coupling by scattering light into unwanted directions. The variety of beam intersection angles and varying plasma conditions in an implosion results in IAW's with a range of phase velocities. Here we show that CBET saturates through a resonance detuning that depends on the IAW phase velocity and that arises from trapping-induced modifications to the ion distribution function. For smaller phase velocities, the modifications to the distribution function can rapidly thermalize, leading to a blue shift in the resonant frequency. For larger phase velocities, the modifications can persist, leading to a redshift in the resonant frequency. Ultimately, these results may reveal pathways toward CBET mitigation and inform reduced models for radiation-hydrodynamics codes to improve their predictive capability. |
Wednesday, November 10, 2021 10:30AM - 10:42AM |
NO07.00006: A model to investigate the hydrodynamic interplay between magnetic fields and Cross Beam Energy Transfer. Philip Moloney, Jeremy P Chittenden, Christopher A Walsh Magnetising an ICF capsule prior to illumination provides a promising potential route to achieving ignition through reduced electron thermal conduction losses during the capsule stagnation. Recent experiments at the National Ignition Facility aim to demonstrate increased ion temperatures and neutron yields by pre-magnetisation in an indirect drive configuration. Further NIF experiments are also proposed using a magnetised Polar Direct Drive (PDD) configuration. The inherently asymmetric illumination in PDD means that Cross Beam Energy Transfer (CBET) can dramatically redistribute the absorbed energy. While the effect of CBET on PDD configurations has been investigated, the inclusion of magnetic fields can significantly alter the hydrodynamics of the implosion and there is limited capability in current numerical models to include both effects. To this end, we have developed an inline ray-based CBET model for the radiative-MHD code CHIMERA. The model is based on a plane-wave, steady-state formulation and has been shown to provide good agreement with test data from a complete, wave-based solver (LPSE). We plan to conduct multi-dimensional simulations of magnetised PDD implosions to investigate the hydrodynamic interplay between CBET and magnetic fields. |
Wednesday, November 10, 2021 10:42AM - 10:54AM |
NO07.00007: Stimulated Brillouin Scattering from hot, multiple-species plasma with interspecies collisions Richard L Berger, Thomas D Chapman, William Arrighi, Andris M Dimits, Joseph E Ralph, Jeffrey W Banks, Stephan Brunner The reduction of laser energy deposition in Inertial Confinement Fusion from stimulated Brillouin backscattering (SBS) is a major concern that constrains the design space. One promising design option is the use of multiple ion species which can increase the Ion Acoustic wave (IAW) damping rate and thereby lower the amplification rate significantly provided nonlinear trapping of the ions in the IAW can be suppressed.1 In previous work on mixtures of high-Z and low-Z ions, we have shown with Vlasov simulations2 of externally driven IAWs that trapping of the light ions, which reduces the damping, can be decreased by collisional scattering of the light ions from the heavy ions. Here, we use the Vlasov code LOKI,3 to simulate SBS self-consistently where the ponderomotively driven IAWs accelerate and trap the light ions near the IAW phase velocity. Inclusion of interspecies and self-collisions leads to large reductions of SBS compared to a single species high-Z plasma or a multi-species, collisionless high-Z plasma. |
Wednesday, November 10, 2021 10:54AM - 11:06AM |
NO07.00008: Amplification of beams with orbital angular momentum to ultra-high intensity by Brillouin scattering Qingsong Feng, Ramy Aboushelbaya, Marko W Mayr, Ben T Spiers, Robert W Paddock, Iustin Ouatu, Robin Timmis, Robin Wang, Peter A Norreys To date high-order harmonics in the extreme ultra-violet with orbital angular momentum (OAM) have been observed in laser-atom interactions, operating at a moderate intensity. Recently, the use of a plasma as the optical medium has been shown to be strong candidate as a potential route towards the production of OAM light with relativistic intensities and ultra-high peak and average power laser pulses. Plasmas also allow for greater flexibility in the level of OAM in the output laser beam than other more conventional techniques. |
Wednesday, November 10, 2021 11:06AM - 11:18AM |
NO07.00009: Forward Brillouin scattering of a spatially and temporally smoothed laser pulse in ICF conditions Charles Ruyer, A. Debayle, Pascal P Loiseau, Paul-Edouard Masson-Laborde, M. Casanova
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Wednesday, November 10, 2021 11:18AM - 11:30AM |
NO07.00010: Ray-based scattering approach to modeling the filamentation instability in speckled laser beams Eugene Kur, Thomas D Chapman, Denise E Hinkel, Mordecai D Rosen, George Zimmerman, Pierre A Michel In laser fusion experiments such as those conducted at the National Ignition Facility (NIF), small-scale intensity fluctuations (speckles) in the laser beams result from the use of random phase plates to shape the beams' far-field focal spot. These speckles are often above the critical power threshold for self-focusing and so trigger the filamentation instability, which can cause increased beam spreading and result in less power delivered to the target. Traditional ray-tracing codes do not model the speckle structure in the laser beam and therefore neglect any effects due to filamentation. We present a novel model of filamentation based on ray scattering that can be incorporated into traditional ray-tracing codes to account for filamentation-induced spreading. We describe how to incorporate additional effects, such as polarization smoothing and smoothing by spectral dispersion (SSD), into the model. We validate the model by comparing its predictions to those of paraxial wave solvers and show how the model can be used to inform hohlraum simulations. |
Wednesday, November 10, 2021 11:30AM - 11:42AM |
NO07.00011: Investigations of Nonlinear Polarization Transfer Between Obliquely Intersecting Beams Holger Schmitz, Raoul M Trines, Robert Bingham, Eugene Kur, Pierre A Michel, Jonathan S Wurtele Electromagnetic waves propagating through a plasma can interact nonlinearly through a variety of different mechanisms. The excitation of a plasma beat wave (ions or electrons) can create a refractive index modulation that changes the dispersion of the interacting beams. Alternatively, high-intensity beams can enter the regime where relativistic nonlinearities influence the propagation dynamics. In recent studies [Kur E., et al. "Nonlinear polarization transfer and control of two laser beams overlapping in a uniform nonlinear medium", Opt. Express 29, 1162-1174 (2021)], it was proposed that two beams propagating along the same axis can exchange their polarization state due to nonlinear interaction. Here we present a numerical analysis of two laser beams intersecting in a nonlinear medium at varying angles. Polarisation transfer is observed as predicted by analytical theory for a range of angles. For small angles, it is found that filamentation of the interacting beams becomes important. Analytical estimates of the filamentation threshold are presented and good agreement is found with the simulation data. |
Wednesday, November 10, 2021 11:42AM - 11:54AM |
NO07.00012: Development of Lasers with Broad Bandwidth for LPI mitigation at NRL James L Weaver, David M Kehne, Matthew F Wolford, Matthew Myers, Malcolm McGeoch, Jason W Bates, Jaechul Oh, Stephen P Obenschain, Andrew J Schmitt, Robert H Lehmberg Research at the Naval Research Laboratory pursues advanced lasers that can mitigate laser-plasma instabilities (LPI) in applications such as inertial confinement fusion. This presentation will discuss two main components of the current program: stimulated Rotational Raman scattering (SRRS) and Argon-Fluorine (ArF) excimer lasers. Stimulated rotational Raman scattering (SRRS) has been demonstrated on the Nike laser facility [Weaver, Applied Optics, 2017] as a path with potential application at existing laser facilities. Through a combination of high intensity propagation and control of the laser spectrum in the low-energy stages of the laser, the output spectrum of Nike has been broadened due to SRRS from an intrinsic 1 THz bandwidth to ~5 THz. This amount of bandwidth has been shown to be effective for mitigation of slow-growth instabilities, such as cross-beam energy transport (CBET) [Bates, High Energy Density Physics, 2020]. Target experiments using this capability are being planned. The development of Argon-Fluorine lasers [Wolford, High Energy Density Physics, 2020] is a more recent addition to the NRL program. This advanced system looks particularly useful for LPI mitigation due its short wavelength (193 nm) and potential for bandwidths approaching ~10 THz. The development effort at NRL's Electra laser facility has reached record output energies for an ArF system and has begun to evaluate the characteristics of the output spectrum for different modes of operation. |
Wednesday, November 10, 2021 11:54AM - 12:06PM |
NO07.00013: Impact of Bandwidth on the Electron Distribution Functions of Laser-Produced Plasmas Nathaniel Shaffer, Andrei V Maximov, Mark Sherlock, Valeri N Goncharov The nonlinear absorption of laser light by an underdense plasma and associated development of non-Maxwellian distribution functions is a classic problem in plasma kinetics. To date, theory and simulations of this basic process have focused on the case of monochromatic laser light. However, ultra-broadband laser drivers are being developed that are capable of fractional bandwidths as high as 1.5% at 3ω. Using Vlasov–Fokker–Planck simulations, we reconsider the problem of nonlinear inverse bremsstrahlung absorption, taking into account non-negligible laser bandwidth. Special attention is paid to evolution on the slow beat wave time scale that is absent in the monochromatic case. |
Wednesday, November 10, 2021 12:06PM - 12:18PM |
NO07.00014: Revisiting laser optical smoothing in weakly-damped plasmas: from spectral dispersion to spectral distribution Adrien Fusaro, Gilles Riazuelo, Pascal P Loiseau, Rodolphe Collin, Denis D Penninckx Optical smoothing techniques are widely used in large high-power laser facilities designed for inertial confinement fusion research in order to improve the laser-energy deposition. However, those techniques are not sufficient and may produce deleterious effects in the laser chain, leading to the need of new laser smoothing schemes such, as those using large bandwidth laser, like the StarDriver laser [D. Eimerl et al. , J. Fusion Energy 33, 2014]. In order to reduce the unwanted conversion of frequency modulation into intensity modulation, it has been shown [M. Duluc et al. , Phys. Rev. Applied 12, 2019] that it is possible to divide by two the spectral width and distribute it on sub-beams, while maintaining smoothing performance for the reduction of the Stimulated Brillouin Scattering (SBS). We revisit optical smoothing by pursuing the spectral distribution along several colors. We reduce the total spectrum bandwidth by dividing the total spectrum in k segments distributed in k sub-beams. We succeed in decreasing the spectral bandwidth up to a monochromatic spectrum leading to the same SBS level. We also show that this configuration allows obtaining a more homogeneous spectrum leading to an even better beam smoothing. |
Wednesday, November 10, 2021 12:18PM - 12:30PM |
NO07.00015: Unified theory of absolute sidescattering in inhomogeneous plasma Chengzhuo Xiao, Jason F Myatt, Qing Wang A unified theory of absolute stimulated Raman and Brillouin sidescattering in inhomogeneous plasma is presented. The linearized coupling equations are transformed into a Schroedinger equation in k space and are solved through an eigenvalue problem. The threshold, growth rate, and scattering geometry are obtained for the pump laser with an arbitrary incidence angle relative to the density gradient. Numerical solutions of the k-space coupling equations show good agreement between the theoretical and numerical results. Previous threshold calculations of absolute Brillouin sidescattering [C.S. Liu et al., Phys. Fluids 17, 1211 (1974)] are corrected, and the relationship between forward and backward sidescattering is analysed. This theory, and the determination of regions of absolute instabiliy, is applied to experiments relevant to direct drive inertial confinement fusion. The possibility of observing such instabilities is discussed. |
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