Efficient Raman Sidescatter and Hot-Electron Production in Laser-Plasma Interaction Experiments

Drake, R. P.; Turner, R. E.; Lasinski, B. F.; Estabrook, K. G.; Campbell, E. M.; Wang, C. L.; Phillion, D. W.; Williams, E. A.; Kruer, W. L.

doi:10.1103/physrevlett.53.1739

Cited by 92 publications

(37 citation statements)

References 13 publications

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“…SRS entails the decay of a laser light wave into an electron plasma wave and a scatteredlight wave at densities at or below one quarter of the critical density of the laser, while TPD is the decay of a laser light wave into two electrostatic plasma waves (plasmons) near the quartercritical density. Previous studies of SRS and TPD have examined single-beam thresholds, 9,10 quantified suprathermal electron production, 6,11,12 explored collective multibeam processes, [13][14][15][16][17][18] and investigated the spatial properties of TPD 19 and the angular distribution of the resulting hot electrons 20 -an important consideration when computing preheat. SRS imposes serious constraints on ignition designs in the indirect-drive approach to ICF because of the high single-beam intensities and large volumes of quasi-homogeneous plasma that are required when using gas-filled hohlraums.…”

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confidence: 99%

Origins and Scaling of Hot-Electron Preheat in Ignition-Scale Direct-Drive Inertial Confinement Fusion Experiments

et al. 2018

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Planar laser-plasma interaction (LPI) experiments at the National Ignition Facility (NIF) have allowed access for the first time to regimes of electron density scale length (∼500 to 700 μm), electron temperature (∼3 to 5 keV), and laser intensity (6 to 16×10^{14} W/cm^{2}) that are relevant to direct-drive inertial confinement fusion ignition. Unlike in shorter-scale-length plasmas on OMEGA, scattered-light data on the NIF show that the near-quarter-critical LPI physics is dominated by stimulated Raman scattering (SRS) rather than by two-plasmon decay (TPD). This difference in regime is explained based on absolute SRS and TPD threshold considerations. SRS sidescatter tangential to density contours and other SRS mechanisms are observed. The fraction of laser energy converted to hot electrons is ∼0.7% to 2.9%, consistent with observed levels of SRS. The intensity threshold for hot-electron production is assessed, and the use of a Si ablator slightly increases this threshold from ∼4×10^{14} to ∼6×10^{14} W/cm^{2}. These results have significant implications for mitigation of LPI hot-electron preheat in direct-drive ignition designs.

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Origins and Scaling of Hot-Electron Preheat in Ignition-Scale Direct-Drive Inertial Confinement Fusion Experiments

et al. 2018

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“…Drake et al 495 used the much larger energy available on the Novette laser (up to 4 kJ) to irradiate Au targets at 0.53-lm wavelength with focal spots of 150-to 1880-lm diameter. They integrated the angular distribution of the SRS to obtain the Raman-scattered light fraction and found that this correlated very closely over nearly three orders of magnitude with the hot-electron fraction obtained from the hard x-ray spectrum ( Fig.…”

Section: Stimulated Raman Scattering (Srs)mentioning

confidence: 99%

Direct-drive inertial confinement fusion: A review

et al. 2015

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The direct-drive, laser-based approach to inertial confinement fusion (ICF) is reviewed from its inception following the demonstration of the first laser to its implementation on the present generation of high-power lasers. The review focuses on the evolution of scientific understanding gained from target-physics experiments in many areas, identifying problems that were demonstrated and the solutions implemented. The review starts with the basic understanding of laser–plasma interactions that was obtained before the declassification of laser-induced compression in the early 1970s and continues with the compression experiments using infrared lasers in the late 1970s that produced thermonuclear neutrons. The problem of suprathermal electrons and the target preheat that they caused, associated with the infrared laser wavelength, led to lasers being built after 1980 to operate at shorter wavelengths, especially 0.35 μm—the third harmonic of the Nd:glass laser—and 0.248 μm (the KrF gas laser). The main physics areas relevant to direct drive are reviewed. The primary absorption mechanism at short wavelengths is classical inverse bremsstrahlung. Nonuniformities imprinted on the target by laser irradiation have been addressed by the development of a number of beam-smoothing techniques and imprint-mitigation strategies. The effects of hydrodynamic instabilities are mitigated by a combination of imprint reduction and target designs that minimize the instability growth rates. Several coronal plasma physics processes are reviewed. The two-plasmon–decay instability, stimulated Brillouin scattering (together with cross-beam energy transfer), and (possibly) stimulated Raman scattering are identified as potential concerns, placing constraints on the laser intensities used in target designs, while other processes (self-focusing and filamentation, the parametric decay instability, and magnetic fields), once considered important, are now of lesser concern for mainline direct-drive target concepts. Filamentation is largely suppressed by beam smoothing. Thermal transport modeling, important to the interpretation of experiments and to target design, has been found to be nonlocal in nature. Advances in shock timing and equation-of-state measurements relevant to direct-drive ICF are reported. Room-temperature implosions have provided an increased understanding of the importance of stability and uniformity. The evolution of cryogenic implosion capabilities, leading to an extensive series carried out on the 60-beam OMEGA laser [Boehly et al., Opt. Commun. 133, 495 (1997)], is reviewed together with major advances in cryogenic target formation. A polar-drive concept has been developed that will enable direct-drive–ignition experiments to be performed on the National Ignition Facility [Haynam et al., Appl. Opt. 46(16), 3276 (2007)]. The advantages offered by the alternative approaches of fast ignition and shock ignition and the issues associated with these concepts are described. The lessons learned from target-physics and implosion experiments are taken into account in ignition and high-gain target designs for laser wavelengths of 1/3 μm and 1/4 μm. Substantial advances in direct-drive inertial fusion reactor concepts are reviewed. Overall, the progress in scientific understanding over the past five decades has been enormous, to the point that inertial fusion energy using direct drive shows significant promise as a future environmentally attractive energy source.

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“…Another is due to the decay of an EPW into an ion acoustic wave ͑IAW͒ and daughter EPWs as a result of modulational instability of EPWs. [3][4][5] Both have been observed in the damping of the EPW excited by Raman backscattering instability ͑which is a slow-phase-velocity wave͒, [6][7][8] and the latter have been observed in the collinear laser-beat-wave ͑which is a fast-phase-velocity wave͒. 9,10 The damping of a self-modulated laser wakefield was attributed to electron beam loading by Tzeng et al 11 in studies using a particle-in-cell simulation that assumes immobile ions.…”

Section: Introductionmentioning

confidence: 99%

Excitation and damping of a self-modulated laser wakefield

et al. 2000

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, "Excitation and damping of a self-modulated laser wakefield" (2000). Spatially, temporally, and angularly resolved collinear collective Thomson scattering was used to diagnose the excitation and damping of a relativistic-phase-velocity self-modulated laser wakefield. The excitation of the electron plasma wave was observed to be driven by Raman-type instabilities. The damping is believed to originate from both electron beam loading and modulational instability. The collective Thomson scattering of a probe pulse from the ion acoustic waves, resulting from modulational instability, allows us to measure the temporal evolution of the plasma temperature. The latter was found to be consistent with the damping of the electron plasma wave.

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Efficient Raman Sidescatter and Hot-Electron Production in Laser-Plasma Interaction Experiments

Cited by 92 publications

References 13 publications

Origins and Scaling of Hot-Electron Preheat in Ignition-Scale Direct-Drive Inertial Confinement Fusion Experiments

Origins and Scaling of Hot-Electron Preheat in Ignition-Scale Direct-Drive Inertial Confinement Fusion Experiments

Direct-drive inertial confinement fusion: A review

Excitation and damping of a self-modulated laser wakefield

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