Growth rate and gain of stimulated Brillouin scattering considering nonlinear Landau damping due to particle trapping

Abstract

Growth rate and gain of SBS considering the reduced Landau damping due to particle trapping has been proposed to predict the growth and average level of SBS reflectivity. Due to particle trapping, the reduced Landau damping has been taken used of to calculate the gain of SBS, which will make the simulation data of SBS average reflectivity be consistent to the Tang model better. This work will solve the pending questions in laser-plasma interaction and have wide applications in parametric instabilities. PACS numbers: 52.38.Bv, 52.35.Fp, 52.35.Mw, 52.35.Sb Backward stimulated Brillouin scattering (SBS) is a three-wave interaction process where an incident electromagnetic wave (EMW) decays into a backscattered EMW and a forward propagating ion-acoustic wave (IAW), which will lead to a great energy loss of the incident laser and is detrimental in inertial confinement fusion (ICF) [1][2][3]. In the indirect-drive ICF [2,3] or the hybrid-drive ignition [1,[4][5][6], CH was chosen as the standard ablator material for ICF ignition capsules due to its low atomic number, high density, and a host of manufacturing considerations. Thus, the inside of hohlraum will be filled with low-Z plasmas, such as H or CH plasmas from the initial filled material or from the ablated material off the capsule.It is one of the key issues for the success of laser fusion to control backward SBS. Many mechanisms for the saturation of SBS have been proposed, including increasing linear Landau damping by kinetic ion heating [7,8], frequency detuning due to particle trapping [9], coupling with higher harmonics [10,11], the creation of cavitons in plasmas [12][13][14] and so on. One of the pending questions in laser-plasma interaction is the discrepancy between the theoretically predicted reflectivity and the experimentally observed reflectivity.[15] SBS reflectivity is directly proportional to the IAW amplitude, and SBS driven IAW behaves in a nonlinear way, such as particle trapping and harmonic generation. Particle trapping may produce a non-Maxwellian distribution, reducing Landau damping of IAW [16] and potentially eliminating the higher IAW damping of the multi-ion species plasmas. Therefore, it is not applicable to predicting SBS reflectivity in experiment by the traditional linear growth rate and gain of SBS taking use of only the linear Landau damping, where the particle trapping is not considered and the Maxwell distribution is assumed. On the other * cao lihua@iapcm.ac.cn † zheng chunyang@iapcm.ac.cn hand, harmonic generation will dissipate the energy of fundamental IAW mode to harmonics, which will induce an efficient damping to decrease the growth rate of SBS.[17, 18] However, when the harmonic amplitude is large, the pump depletion will be obvious, thus the SBS will be saturated mainly due to pump depletion. In this Rapid Communication, we report the first demonstration that the growth rate and gain of SBS considering the nonlinear Landau damping of IAW due to particle trapping will be consistent to the simulation results better. Th...

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