Absolute instability modes due to rescattering of stimulated Raman scattering in a large nonuniform plasma

Plasma Phys. Control. Fusion

Sheng

et al. 2019

Self Cite

The development of parametric instabilities in a large scale inhomogeneous plasma with an incident laser beam composed of multiple-frequency components is studied theoretically and numerically. Firstly, theoretical analyses of the coupling between two laser beamlets with certain frequency difference δω 0 for parametric instabilities is presented. It suggests that the two beamlets will be decoupled when δω 0 is larger than certain thresholds, which are derived for stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), and two plasmon decay (TPD), respectively. In this case, the parametric instabilities for the two beamlets develop independently and can be controlled at a low level provided the laser intensity for individual beamlet is low enough. Secondly, numerical simulations of parametric instabilities with two or more beamlets (N ∼ 20) have been carried out and the above theory model is validated. Simulations confirm that the development of parametric instabilities with multiple beamlets can be controlled at a low level, provided the threshold conditions for δω 0 is satisfied, even though the total laser intensity is as high as ∼ 10 15 W/cm 2 . With such a laser beam structure of multiple frequency components (N 20) and total bandwidth of a few percentages ( 4%), the parametric instabilities can be wellcontrolled.

Section: Suppression Of Srsmentioning

confidence: 99%

Suppression of parametric instabilities in inhomogeneous plasma with multi-frequency light

Plasma Phys. Control. Fusion

Sheng

et al. 2019

Self Cite

“…By doing the Fourier analysis of equations ( 5)- (7) in the plane of ⃗ k 1 and ⃗ k 2 , one obtains the dispersion relation:…”

Section: Srs Driven By Multibeam In Homogeneous Plasmasmentioning

confidence: 99%

“…Stimulated Raman scattering (SRS) [1][2][3], the decay of a pump laser into a scattered light and an electron plasma wave, is one of the major obstacles to inertial confinement fusion (ICF) [4][5][6][7]. In ICF experiments, many laser beams are applied in order to compress and heat the fusion targets uniformly and sufficiently, either in the direct-drive or the indirectdrive scheme [6,[8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Mitigation of multibeam stimulated Raman scattering with polychromatic light

Plasma Phys. Control. Fusion

et al. 2021

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A theoretical analysis is presented for the stimulated Raman scattering (SRS) driven by multiple beams with certain frequency differences or bandwidths. The concomitant electrostatic modes are excited by the scattering lights when the pump beams share a common electron plasma wave to drive SRS. This coupling can be suppressed when the frequency difference of the two beams is three times larger than the SRS growth rate of a single beam, where the beams develop their scattering lights independently. To mitigate SRS further under the multibeam irradiation, polychromatic pumps are introduced to reduce the SRS saturation level, where the weakly coupled common modes are heavily damped in hot plasmas. The sidescattering driven by polychromatic light in inhomogeneous plasmas is significantly reduced due to the wavevector mismatch of daughter waves. Particle-in-cell simulations confirm our theoretical analysis and demonstrate that the strength of multibeam SRS and the hot electron production in inhomogeneous plasmas can be controlled at a low level by polychromatic light with a few percentage bandwidth ( ≳ 3 % ), even in the non-linear regime.

“…This is confirmed in our numerical simulation as shown in Figures 4(b) and 4(c) that the electrostatic wave and the concomitant electromagnetic wave form localized structures. The trapped light and electrostatic wave may cause the laser energy deficit in ICF related experiments [33] . The trapped waves expel the ions to form density cavity at later time t = 1950τ as seen from Figure 4(d).…”

Section: Two-dimensional Simulations For Non-eigenmode Srs In Homogenmentioning

confidence: 99%

Stimulated Raman scattering in a non-eigenmode regime

Sheng

et al. 2020

High Pow Laser Sci Eng

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Stimulated Raman scattering (SRS) in plasma in a non-eigenmode regime is studied theoretically and numerically. Different from normal SRS with the eigen electrostatic mode excited, the non-eigenmode SRS is developed at plasma density $n_{e}>0.25n_{c}$ when the laser amplitude is larger than a certain threshold. To satisfy the phase-matching conditions of frequency and wavenumber, the excited electrostatic mode has a constant frequency around half of the incident light frequency $\unicode[STIX]{x1D714}_{0}/2$ , which is no longer the eigenmode of electron plasma wave $\unicode[STIX]{x1D714}_{pe}$ . Both the scattered light and the electrostatic wave are trapped in plasma with their group velocities being zero. Super-hot electrons are produced by the non-eigen electrostatic wave. Our theoretical model is validated by particle-in-cell simulations. The SRS driven in this non-eigenmode regime is an important laser energy loss mechanism in the laser plasma interactions as long as the laser intensity is higher than $10^{15}~\text{W}/\text{cm}^{2}$ .