Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Plasma Physics
Volume 64, Number 11
Monday–Friday, October 21–25, 2019; Fort Lauderdale, Florida
Session GO6: ICF: Laser-Plasma Interactions |
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Chair: David Turnbull, LLE Room: Grand D |
Tuesday, October 22, 2019 9:30AM - 9:42AM |
GO6.00001: Broadband Mitigation of Laser--Plasma Instabilities for Inertial Confinement Fusion Russell Follett, John Shaw, Dustin Froula, Cristophe Dorrer, Andrei Maximov, Andrey Solodov, John Palastro, Jason Myatt, Jason Bates, Jim Weaver Laser--plasma instabilities such as cross-beam energy transfer, stimulated Raman scattering, and two-plasmon decay present a major challenge for laser-driven inertial confinement fusion (ICF). A promising path toward mitigation of these instabilities is through the use of broadband drive lasers. The laser--plasma simulation environment (\textit{LPSE}) code is used to investigate the mitigation of these instabilities for conditions relevant to both direct- and indirect-drive ICF. The simulations indicate that lasers with \textasciitilde 1{\%} bandwidth can be used to suppress both the absolute and convective forms of the instabilities. A broadband laser based on optical parametric amplification, with sufficient energy and bandwidth to validate these predictions, is currently being developed at LLE. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. [Preview Abstract] |
Tuesday, October 22, 2019 9:42AM - 9:54AM |
GO6.00002: Fourth-Generation Laser for Ultra-Broadband Experiments---Expanding Inertial Confinement Fusion Design Space Through Mitigation of Laser$-$\textbPlasma~Instabilities Dustin Froula, R. K. Follett, C. Dorrer, J. Bromage, E. M. Hill, B. E. Kruschwitz, J. P. Palastro, D. Turnbull To demonstrate hydro-equivalent ignition in OMEGA direct-drive experiments, mitigation of cross-beam energy transfer (CBET) and hot-electron generation is likely necessary. Laser--plasma instability (LPI) modeling predicts that an ultraviolet laser with $\Delta \omega $/$\omega $~\textgreater ~1{\%} would increase the laser absorption on OMEGA implosion experiments from 55{\%} to 90{\%} by mitigating CBET while increasing the intensity threshold for hot-electron generation by a factor of 3. An LPI platform is currently being developed on OMEGA that will provide a test bed to demonstrate LPI mitigation using a novel laser FLUX (Fourth-generation Laser for Ultra-broadband eXperiments), which will produce $\Delta \omega $/$\omega $~\textgreater ~1{\%} bandwidth around 351 nm. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. [Preview Abstract] |
Tuesday, October 22, 2019 9:54AM - 10:06AM |
GO6.00003: Modeling stimulated Raman scattering with laser bandwidth and external magnetic field using Particle-in-cell method Han Wen, Benjamin Winjum, Frank Tsung, Warren Mori Stimulated Raman scattering (SRS) is of great concern in inertial confinement fusion experiments and will be an issue in the design of future ignition scale direct and indirect drive targets. Multiple schemes have been proposed to mitigate SRS, including applying temporal bandwidth and external magnetic fields. Large scale particle-in-cell (PIC) simulations have been carried out to study the bandwidth effects on SRS using the general antenna implemented in our PIC code OSIRIS. Simulation results show that although the reflectivity due to SRS decreases as the laser bandwidth increases, SRS can still occur with laser bandwidth up to 0.7{\%} of laser frequency. The simulations also show that the details of the behavior of SRS changes as the bandwidth increase. Applying external magnetic field can add additional damping to nonlinear electron plasma waves and thus SRS reflectivity is further reduced. [Preview Abstract] |
Tuesday, October 22, 2019 10:06AM - 10:18AM |
GO6.00004: Mitigating cross-beam energy transfer with optical vortices Blaine Armstrong, Robert Fedosejevs, Andrew Longman, Jason Myatt Based on recent advances, the application of laser bandwidth at the 1\% level is expected to greatly improve the prospects of direct-drive ignition on a MJ-scale facility.\footnote{R.K. Follett {\it et al.}, Phys. Rev. Lett. {\bf 120}, 135005 (2018); J.W. Bates {\it et al.}, Phys. Rev. E {\bf 97}, 061202(R) (2018)} While schemes to implement such bandwidth are being pursued, they will be both intrusive and expensive. As an alternate approach, simulation work is presented that explores the use of complex spatial (rather than temporal) laser beam conditioning on cross-beam energy transfer (CBET) with the aim of achieving similar mitigating effects. This beam conditioning might be generated by phase plates alone and therefore could be implemented on laser facilities lacking a broad bandwidth capability. Specifically, we have quantified the energy exchange occurring between crossing laser beams containing optical vortices \footnote{M. Padgett {\it et al.}, Physics Today {\bf 57}, 35 (2004)} using the {\it LPSE} code. The mitigating effects are described in terms of the exchange of orbital angular momentum (OAM) between the coupled waves, and the degree to which a difference in OAM between crossing beams can frustrate the stimulated Brillouin scattering process responsible for CBET. [Preview Abstract] |
Tuesday, October 22, 2019 10:18AM - 10:30AM |
GO6.00005: Cross-Beam Energy Transfer Experiments at High Ion-Acoustic Wave Amplitudes Aaron Hansen, David Turnbull, Avram Milder, Joseph Katz, Russell Follett, John Palastro, Dustin Froula The tunable OMEGA port 9 (TOP9) laser on OMEGA was used to perform cross-beam energy transfer (CBET) experiments in a gas-jet plasma where it interacted with one or five other 351-nm UV beams to study the limitations of linear CBET modeling. The TOP9 laser is a wavelength-tunable UV beam which enables CBET experiments in a stationary plasma. The frequency of the TOP9 beam was set so that the beat frequency generated with other UV pump beams was resonant with the ion-acoustic wave frequency of the gas-jet plasma. By changing the intensity of the TOP9 probe beam, the amplitude of the resonantly excited ion-acoustic waves was scaled from low amplitudes (dn/n \textless 0.7{\%}) to high amplitudes (dn/n \textgreater 2.5{\%}), where ion-wave saturation mechanisms were expected to limit the amount of energy transfer in the interaction. [Preview Abstract] |
Tuesday, October 22, 2019 10:30AM - 10:42AM |
GO6.00006: Beam amplification to high fluence in a plasma optic Patrick Poole, Robert Kirkwood, Thomas Chapman, Scott Wilks, Pierre Michel, Laurent Divol, Nathaniel Fisch, Peter Norreys, Wojciech Rozmus, Brent Blue New intense laser applications and experiments require increases in pulse energy, power, and intensity beyond the limitations of conventional solid-state media. Plasma optics are a promising solution due to their increased resiliency to damage but require characterization in the linear and nonlinear response regimes. The plasma amplifier project at NIF has demonstrated the combination of up to 21 frequency shifted beams via Cross-Beam Energy Transfer, achieving 10x amplification of a seed beam up to nearly 8 kJ in a 1 ns pulse. The full capability of such an optic is being explored, most recently by investigating amplification in a high fluence regime using a small spot seed beam (continuous phase plate removed). This resulted in a greater fluence in the amplified seed than the combined fluence of all (large area) pump beams. A good quality amplified mode was obtained despite initial speckled structure confirming predicted plasma optic behavior from simulation and models. This demonstration suggests a path to a future small-scale amplifier design that does not require superior pump beam quality. Further experimental details and supporting simulation results will also be discussed. [Preview Abstract] |
Tuesday, October 22, 2019 10:42AM - 10:54AM |
GO6.00007: Measurements of Arbitrary Distribution Functions Using Angularly Resolved Thomson Scattering A.L. Milder, J. Katz, R. Boni, J.P. Palastro, D.H. Froula The basis of many phenomena in laser-produced plasmas is contingent upon the understanding of the underlying electron distribution function. The sensitivity of Thomson scattering to electron distribution function has been shown numerically 1 and has been used experimentally to identify non-Maxwellian electron distribution functions driven by thermal transport, 2 inverse bremsstrahlung heating, and ionization. 3 A new angularly resolved Thomson-scattering diagnostic has been invented to measure electron distribution functions with arbitrary shape. The relationship between scattering angle and the resonant thermal plasma wave probed by Thomson scattering results in scattering features that vary with angle in correspondence to the shape of the electron distribution over several orders of magnitude. A numerical forward fit to the complete angularly resolved Thomson-scattered spectra provides a measurement of the electron distribution function without predicting which physical processes will contribute to its shape. \\ $[1]$ A. L. Milder et al., Phys. Plasmas 26, 022711 (2019). \\ $[2]$ R. J. Henchen et al., Phys. Rev. Lett. 121, 125001 (2018). \\ $[3]$ A. L. Milder et al., “Evolution of the electron distribution function in the presence of inverse bremsstrahlung heating and collisional ionization” to be submitted to Physical Review Letters. [Preview Abstract] |
Tuesday, October 22, 2019 10:54AM - 11:06AM |
GO6.00008: Experimental Evidence for Reduced Stimulated Brillouin Backscatter in hohlraums when using a Ta2O5 liner. Joseph Ralph, Pierre Michel, Andreas Kemp, Brian MacGowan, Nuno Lemos, Nathan Meezan, Richard Berger, Richard Berger, Tom Chapman, Mikhail Belyaev, Lauren Divol, Oggie Jones High levels of Stimulated Brillouin Backscatter (SBS) from experiments on the National Ignition Facility remain a significant damage risk for optics. Light from SBS near the 351 nm laser wavelength can propagate backward through the final optics assembly and result in damage. As a result, new experiments on the NIF must ramp up in power and energy over several shots slowing the development of new designs. Mitigation of SBS may be achieved by designing targets with materials that damp the growth of ion acoustic waves. Theory and simulations show that the light oxygen species, in Ta2O5, damps the Ta and/or Au ion acoustic waves effectively, resulting in decreased backscatter. We performed a series of four experiments in which the interior of a gold hohlraum was lined with a 1.1 micron Ta2O5 liner or left unlined and measured the effect on SBS, implosion symmetry, hohlraum hydrodynamics, and hohlraum performance. Measurements show that lining the gold hohlraum interior with Ta2O5 reduces the SBS by 5x in the outer 50 deg. beamlines. Images of the wall bubble show that the Ta2O5 liner expands roughly 10{\%} faster resulting in a more oblate implosion. Legendre mode P2/P0 decreases from -29{\%} to -49{\%} when using the liner. Experimental results will be presented and compared with simulations. [Preview Abstract] |
Tuesday, October 22, 2019 11:06AM - 11:18AM |
GO6.00009: Energy Coupling and LPI Dependencies in MagLIF Pre-Heat Matthias Geissel, Adam J. Harvey-Thompson, David E. Bliss, Jeffrey R. Fein, Benjamin R. Galloway, Matthew R. Gomez, Christopher Jennings, Mark W. Kimmel, Kyle Peterson, Patrick Rambo, Jens Schwarz, Jonathon E. Shores, Ian C. Smith, Shane Speas, Matthew R. Weis, John L. Porter The Magnetized Liner Inertial Fusion (MagLIF) program at Sandia National Laboratories is pursues magneto-inertial fusion concept on the Z-Accelerator. It involves pre-heating the deuterium fuel with the Z-Beamlet laser. In order to optimize pre-heat, dedicated laser-plasma studies at the Pecos target chamber are performed to develop an ideal laser configuration. Besides the general goal of increasing coupled energy, the experiments put a specific focus on losses from laser plasma instabilities (LPI). We present insights from varying fill density, fill gas (deuterium vs.~helium), and laser pulse shape. For the latter, we show the results of varying the gap between pre-pulse that evaporates the window of the laser-entrance-hole(LEH)and the main pulse that heats the fuel. [Preview Abstract] |
Tuesday, October 22, 2019 11:18AM - 11:30AM |
GO6.00010: Capturing speckle-scale beam-bending in ray-tracing schemes for nanosecond-class RPP-beam propagation modeling Charles Ruyer, Arnaud Debayle, Michel Casanova, Pascal Loiseau, Paul-Edouard Masson-Laborde In the context of inertial confinement fusion (ICF), laser-plasma interaction (LPI) refers mainly to the study of ponderomotively driven phenomena that affects the laser propagation and the subsequent laser energy deposition. Due to the multi-millimeters extent and the nanoseconds duration of ICF experiments, the full numerical resolution of the LPI requires strong simplifications. In particular, the complex speckle dynamics of a random phase plate (RPP) laser beams is neglected. Hence, aiming at improving our realistic modeling of laser beams, we will show that the advection of ponderomotive-induced density fluctuations by a flow may result in the significant deflection of the laser pulse. This phenomenon, often called beam-bending [Hinkel et. al., Phys. Rev. Lett. 1996], can be modeled in the kinetic framework [Drake et. al., Phys. Fluids 1974; Vu, Phys. Plasmas 1997]. The validation of the analytical deflection angle with PIC simulations pinpoints the importance of kinetic damping of the acoustic perturbations. The speckle-scale beam-bending physics will then be included in ray tracing schemes, often used to model RPP-beam in hydrodynamic codes. A successful comparison between the resulting ray tracing and PIC simulations of RPP-beam propagation validates our modeling. [Preview Abstract] |
Tuesday, October 22, 2019 11:30AM - 11:42AM |
GO6.00011: Absorption and Scattered-Light Asymmetry in OMEGA Implosions Dana Edgell, Joseph Katz, Dustin Froula Hydrodynamics codes predict that the laser absorption and unabsorbed light distribution over the spherical surface should be very uniform, with an rms deviation of at most a few percent when the effects of energy redistribution caused by cross-beam energy transfer (CBET) are included. Measurements show much larger variations of the order of tens of percent in the unabsorbed light distributed over the target chamber surface in three independent diagnostics: scatteredlight calorimeters, the CBET beamlets diagnostic, and the TOP9 transmittedbeam diagnostic. The variation is larger than can be reasonably accounted for by beam imbalance. The possibility of a CBET polarization effect being the source of the asymmetry will be examined. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. [Preview Abstract] |
Tuesday, October 22, 2019 11:42AM - 11:54AM |
GO6.00012: Effect of Multibeam Two-Plasmon--Decay Instability on Cross-Beam Energy Transfer in Plasmas A. V. Maximov, D. Turnbull, J. G. Shaw, R. K. Follett, J. P. Palastro In the plasmas of direct-drive inertial confinement fusion (ICF), the region near quarter of the critical density is of particular importance for laser--plasma interactions (LPI's). In this region the LPI instabilities of absolute two-plasmon decay (TPD) and cross-beam energy transfer (CBET) can develop together for the experimental conditions of the OMEGA Laser System. The interplay between these instabilities determines the balance between scattering and absorption of light and the generation of plasma waves that accelerate electrons into the core of the ICF target. Two-dimensional simulations of LPI including TPD and CBET in OMEGA-scale ICF plasmas have been performed with the laser-plasma simulation environment (\textit{LPSE}).\footnote{ J. F. Myatt \textit{et al.}, Phys. Plasmas \textbf{24}, 056308 (2017).} \textit{LPSE} results show that multibeam TPD can modify CBET through redistribution of laser power and through low-frequency, ion-acoustic density perturbations shared by TPD and CBET. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. [Preview Abstract] |
Tuesday, October 22, 2019 11:54AM - 12:06PM |
GO6.00013: Reduction of hot electron generation from laser plasma instabilities using circularly-polarized lasers Shihui Cao, Chuang Ren, Rui Yan, Han Wen, Jun Li Understanding laser-plasma instabilities (LPI) is critical to the success of inertial confinement fusion (ICF). The interaction of two plasmon decay (TPD) and side stimulated Raman scattering (SSRS) was studied using 3-D particle-in-cell simulations under ICF-relevant conditions for linearly and circularly polarized lasers. In the linear stage, theoretical growth rates agreed well with the simulation results. SSRS took place under $n_e = 0.235n_c$ and TPD dominated near the quarter-critical density surface. In the nonlinear stage, SSRS reduced TPD through pump depletion. Hot electrons were found to be first accelerated by the SSRS plasma waves and then by TPD plasma waves, different from the TPD-only staged-acceleration in the 2-D simulations. This reduced the hot-electron flux. Compared to the linearly polarized case with the same laser intensity, both SSRS and TPD were reduced due to the lower laser amplitude in the circularly-polarized case. As a result, a 30 percent decrease in hot electron flux was observed. [Preview Abstract] |
(Author Not Attending)
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GO6.00014: \textbf{A model of hot electron generation in a plasma wave with increasing phase velocity} Chuang Ren, Wenda Liu Preheating from hot electrons generated in laser-plasma instabilities (LPI) is a major concern in direct-drive inertial confinement fusion. Plasma waves in LPI generally have increasing phase velocities as they propagate toward higher density. We developed a model of hot electron generation in a plasma wave of given amplitude, width, and phase velocity gradient. The resultant closed-form analytical expression of hot electron flux was benchmarked with numerical solutions and particle-in-cell simulations. It provides a first step to develop a theory for LPI hot electron generation that can be used in hydro codes. [Preview Abstract] |
Tuesday, October 22, 2019 12:18PM - 12:30PM |
GO6.00015: Effects of an external magnetic field on the generation of stimulated Raman scattering Adam Higginson, Chris McGuffey, Mario Manuel, Mathieu Bailly-Grandvaux, Krish Bhutwala, Joe Strehlow, Ben Winjum, Roman Lee, Frank Tsung, Scott Andrews, Felice Albert, Nuno Lemos, Mingsheng Wei, Warren Mori, Farhat Beg The damping of electron plasma waves propagating in an external magnetic field (B-field) is of fundamental interest for inertial confinement fusion (ICF). Laser plasma instabilities (LPIs) in the low-Z region of an imploding fuel capsule act to transfer laser energy to the background plasma, and a development of our understanding of the fundamental processes involved with LPIs, and techniques to control them, is crucial for the success of ICF. Stimulated Raman scattering (SRS) is particularly detrimental, accounting for the bulk of energy losses on ignition-scale experiments, and remains a fundamental impediment to ICF. We present simulation results showing that the presence of a modest (B $=$ 10 T) B-field around an underdense plasma results in a reduction of SRS reflectivity by up to 50{\%}. We also provide highlights of the first experimental measurements to-date of SRS in the presence of an external B-field, for an underdense Nitrogen target and range of laser intensities relevant to ICF. [Preview Abstract] |
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