In inertial confinement fusion (ICF), superhot electrons, which are usually generated by stimulated Raman scattering (SRS), two-plasmon-decay (TPD) and their secondary processes, may preheat the fuel which may result in fail of ignition. In this paper, the competition process among several secondary processes of SRS is revealed, and the laser intensity is found to be the key parameter that determines the dominated process. This study provides guidance for suppressing the generation of hot electrons, as well as explaining the source of abnormal superhot electrons.
The detailed analysis of these secondary processes and the reasons for the change in the dominated process are published in High Power Laser Science and Engineering, vol. 11, Issue 6 (K. Q. Pan, Z. C. Li, L. Guo, T. Gong, S. W. Li, D. Yang, C. Y. Zheng, B. H. Zhang, X. T. He. Competition among the two-plasmon decay of backscattered light, filamentation of the electron-plasma wave and side stimulated Raman scattering[J]. High Power Laser Science and Engineering, 2023, 11(6): 06000e76).
Graphic description: Snapshots of the EPWs in two dimensional wavenumber space. (a) and (b) are results for the case with the laser intensity <1015 W/cm2 at t=500T0 and t=2500T0, respectively. (c) and (d) are results for the case with the laser intensity >1015 W/cm2 at t=500T0 and t=2500T0, respectively. Here, t is the simulation time and T0 is the laser cycle.
With the help of particle-in-cell (PIC) simulations, the competition among the TPD of backscattered light ofSRS, filamentation of the electron-plasma wave (EPW) and forward side SRS in a plasma with the density near tenth of the critical density (the maximum cut-off plasma density for laser propagation) is investigated in this paper. The simulation results showed that the scattered light of SRS will excite TPD when the laser intensity is <1015 W/cm2. Although the excitation of TPD will suppress SRS, the risk of generation of superhot electrons with energy near 100 keV will be raised. However, when the laser intensity is >1015 W/cm2, the EPW of SRS will excite filamentation instability which will induce side SRS but inhibit TPD, thus the generation of near 100 keV superhot electrons is mitigated. The paper discussed how to distinguish these secondary instabilities in detail and also analyzed how these instabilities compete with each other.
Since preheat of superhot electron is a big obstacle for successful ignition, we need to suppress the generation of superhot electrons. This work provides a guidance for the suppression of superhot electron generation, as well as provide an idea to explain where these abnormal superhot electrons come from.
