Auto-resonant stimulated Brillouin backscattering in supersonic flowing plasmas by fully kinetic Vlasov simulations

Abstract

The auto-resonant behavior of ion acoustic waves (IAWs) driven by stimulated Brillouin backscattering in supersonic flowing plasmas is self-consistently investigated by Vlasov simulations. Vlasov simulations show that the peak amplitude of the auto-resonant growing IAWs in the positive flow gradient is much larger than that in the negative flow gradient, which is contrary to the previous analysis (Wang et al 2018 Plasma Phys. Control. Fusion 60 025016). It is found that the IAW phase velocity remains unchanged in supersonic flowing plasmas, which significantly influences wave-particle interaction by changing the Landau damping and the coefficient of the kinetic nonlinear frequency shift in different position. As a result, the Landau damping of IAWs in the peak region in the negative case is stronger than that in the positive case, which has never been considered before. After considering its effects on particle trapping and, particularly, Landau damping of IAWs, theoretical predictions from three-wave mode equations are consistent with results by Vlasov simulations.

Suppression of auto-resonant stimulated Brillouin scattering in supersonic flowing plasmas by different forms of incident lasers*

“…The absolute growth area is determined by the resonant length L r . [9] In order to suppress the absolute growth of SBS in an inhomogenous plasma, rotation polarization and two perpendicular linear polarization with different frequencies are performed. For rotation polarization, the incident light is combined by two circle polarization lasers with different frequencies.…”

“…For rotation polarization, the incident light is combined by two circle polarization lasers with different frequencies. The linear polarization of the incident light is slowly rotating, and it can be expressed as [15] 𝐴 0 = a 0 cos(ω 0 t)[cos(Ωt) ŷ + sin(Ωt)ẑ], (9) where Ω is the frequency difference of these two circle polarization incident lasers. The growth rate of SBS in one direction is γ y,z = γ cos( Ω 2 t).…”

“…[7,8] The autoresonat behavior of IAWs driven by the SBS process in supersonic flowing plasmas is performed by using the fully kinetic Vlasov code. [9] In those work, the flow velocity decreasing in the forward direction is defined as the "negative flow gradient", and the flow velocity increasing in the forward direction is defined as the "positive flow gradient". In the simulations, the stimulated Brillouin backscattering (SBBS) reflectivity in both positive and negative flow gradients reach the level of absolute growth which will scatter the incident light greatly.…”

Influences of sinusoidal density modulation on stimulated Raman scattering in inhomogeneous plasmas

“…A fully kinetic Vlasov code 27,28 is used here to study the SRS with density modulation. The plasma density profile is shown in Fig.…”

“…And we obtain a region of modulational wavelength and amplitude that density modulation can cause the absolute SRS. Secondly, we have carried out the Vlasov simulations [27][28][29] to study the influence of density modulation at linear and nonlinear stage. At linear stage, the Vlasov simu-lations show good agreement with three-wave equations analysis.…”