Nonlinear kinetic estimate of Raman reflectivity in a hohlraum plasma with a radiation hydrodynamics code.

In this Letter, we introduce an inline model for stimulated Raman scattering (SRS), which runs on our radiation hydrodynamics code troll. This model accounts for nonlinear kinetic effects and for the SRS feedback on the plasma hydrodynamics. We dubbed it PIEM because it is a fully "PredIctivE Model," because no free parameter is to be adjusted a posteriori in order to match the experimental results. PIEM predictions are compared against experimental measurements performed at the Ligne d'Intégration Laser. From these comparisons, we discuss the PIEM ability to correctly catch the impact of nonlinear kinetic effects on SRS.

Reduction of Cross-Beam Energy Transfer by a Speckle Pattern.

In this Letter, we show that cross-beam energy transfer (CBET), ubiquitous in inertial confinement fusion (ICF) experiments, may be strongly modified by the speckle pattern of the beams. This is demonstrated by the means of two-dimensional particle in cell simulations, supported by a linear model. In particular, we show that, although they would be the same in a plane wave model, the exchange rates of energy may be significantly different whether there is a plasma flow, or a wavelength shift, especially when the waves are weakly damped. When the crossed laser beams have different frequencies, the energy exchange rate is substantially reduced compared with the predictions of the plane wave model, widely used in the hydrodynamic codes that model and interpret ICF experiments. Such effects can partly explain the disagreement of the CBET predictions compared with experimental results.

Experimental Evidence of Backward Raman Scattering Driven Cooperatively by Two Picosecond Laser Pulses Propagating Side by Side.

This Letter investigates experimentally the backward stimulated Raman scattering (SRS) of two copropagating, 1-µm wavelength, 1.5-ps duration laser pulses focused side by side, but not simultaneously, in a preformed underdense plasma. When the two lasers do not interact, one of the pulses (so-called strong) yields a large SRS reflectivity, while the other weak pulse is essentially ineffective as regards SRS. By contrast, the weak pulse shows significant SRS activity if it is launched in the plasma slightly after the strong one, and for time delays as large as about 15 ps. For crossed polarizations and a lateral distance of 80-90 µm, the time delay has to be larger than 3-4 ps for the weak pulse to be active, while it has just to be positive when the polarizations are parallel. The experimental results are discussed with the help of large-scale particle-in-cell simulations.

Publisher's Note: Experimental investigation of stimulated Raman and Brillouin scattering instabilities driven by two successive collinear picosecond laser pulses [Phys. Rev. E 93, 043209 (2016)].

This corrects the article DOI: 10.1103/PhysRevE.93.043209.

Experimental investigation of stimulated Raman and Brillouin scattering instabilities driven by two successive collinear picosecond laser pulses.

Backward stimulated Raman and Brillouin scattering (SRS and SBS) are experimentally investigated by using two successive 1-µm, 1.5-ps FWHM laser pulses. The collinear pulses, separated by 3 or 6 ps and of moderate laser intensities (∼2×10^{16}Wcm^{-2}), are fired into a preionized He plasma of density ∼2.5-6×10^{19}cm^{-3}. The electron plasma waves and ion acoustic waves, respectively driven by SRS and SBS, are analyzed through space- and time-resolved Thomson scattering. Depending on the laser and plasma parameters, we observe the effect of the first pulse on the time-resolved SRS and SBS signals of the second pulse. The measurements are found to qualitatively agree with the results of a large-scale particle-in-cell simulation.

Exact relativistic kinetic theory of the full unstable spectrum of an electron-beam-plasma system with Maxwell-Jüttner distribution functions.

Following a recent Letter by Bret [Phys. Rev. Lett. 100, 205008 (2008)], we present a detailed report of the entire unstable k spectrum of a relativistic collisionless beam-plasma system within a fully kinetic framework. In contrast to a number of previously published studies, our linear analysis makes use of smooth momentum distribution functions of the Maxwell-Jüttner form. The three competing classes of instabilities, namely, two-stream, filamentation, and oblique modes, are dealt with in a unified manner, no approximation being made regarding the beam-plasma densities, temperatures, and drift energies. We investigate the hierarchy between the competing modes, paying particular attention to the relatively poorly known quasielectrostatic oblique modes in the regime where they govern the system. The properties of the fastest growing oblique modes are examined in terms of the system parameters and compared to those of the dominant two-stream and filamentation modes.

Experimental evidence of predominantly transverse electron plasma waves driven by stimulated Raman scattering of picosecond laser pulses.

We report on highly time- and space-resolved measurements of the evolution of electron plasma waves driven by stimulated Raman scattering of a picosecond, single laser speckle propagating through a preformed underdense plasma. Two-dimensional Thomson scatter spectra indicate that the dominant waves have significant transverse components. These results are supported by particle-in-cell simulations which pinpoint the dominant role of the wave front bowing and of secondary nonlinear electrostatic instabilities in the evolution of the plasma waves.

Exact relativistic kinetic theory of an electron-beam-plasma system: hierarchy of the competing modes in the system-parameter space.

The stability analysis of an electron-beam-plasma system is of critical relevance in many areas of physics. Surprisingly, decades of extensive investigation have not yet resulted in a realistic unified picture of the multidimensional unstable spectrum within a fully relativistic and kinetic framework. All attempts made so far in this direction were indeed restricted to simplistic distribution functions and/or did not aim at a complete mapping of the beam-plasma parameter space. The present Letter comprehensively tackles this problem by implementing an exact linear model. Three kinds of modes compete in the linear phase, which can be classified according to the direction of their wave number with respect to the beam. We determine their respective domain of preponderance in a three-dimensional parameter space and support our results with multidimensional particle-in-cell simulations.