Transition from convective to absolute Raman instability via the longitudinal relativistic effect by using Vlasov-Maxwell simulations

Abstract

The longitudinal relativistic effect on stimulated Raman backscattering (SRBS) is investigated by using one-dimensional (1D) Vlasov-Maxwell simulations. Using a short backscattered light seed pulse with a very small amplitude, the linear gain spectra of SRBS in the strongly convective regime is presented by combining the relativistic and non-relativistic 1D Vlasov-Maxwell simulations, which is in agreement with the steady-state linear theory. More interestingly, by considering transition from convective to absolute instability due to electron trapping, we successfully predict the critical duration of the seed which can just trigger the kinetic inflation of the excited SRBS after the seed leaves the simulation box. The critical duration in the relativistic case is much shorter than that in the nonrelativistic case, which indicates that the kinetic inflation more easily occurs in the relativistic case than in the nonrelativistic case. In the weakly convective regime, the transition from convective to absolute instability for SRBS can directly occur in the linear regime due to the longitudinal relativistic modification. For the same pump, our simulations first demonstrate that the SRBS excited by a short and small seed pulse is a convective instability in the nonrelativistic case but becomes an absolute instability due to the decrease of the linear Landau damping from the longitudinal relativistic modification in the relativistic case. In more detail, the growth rate of the backscattered light is also in excellent agreement with theoretical prediction.

Stimulated Brillouin scattering of backward stimulated Raman scattering

“…A one dimension (1D) relativistic Vlasov-Maxwell code 47,48 is taken used of to verify the SBS of BSRS. Since H plasmas is common in ICF hohlraum, it is taken as a typical example in our simulation.…”

Suprathermal electrons from the anti-Stokes Langmuir decay instability cascade

“…A one-dimensional relativistic kinetic Vlasov-Maxwell code [41][42][43][44][45] was used to simulate the electron cascade acceleration by the backward-SRS and the forward-SRS-induced Langmuir waves. Since the backward-SRS and the forward-SRS-induced Langmuir waves propagate in the direction of the incident laser propagation, a one-dimensional simulation is sufficient to study the effects of both processes.…”

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

“…In inhomogeneous plasmas, the three-wave interaction equations involves a nonlinear kinetic frequency shift in the forms as follows: [8,18]…”