Effective suppression of parametric instabilities with decoupled broadband lasers in plasma

TL;DR

This paper proposes a novel method using broadband laser beamlets to suppress parametric instabilities like SRS and SBS in plasma, potentially improving inertial confinement fusion efficiency.

Contribution

It introduces a decoupled broadband laser strategy that effectively suppresses SRS and SBS by exploiting frequency differences among beamlets, supported by theoretical analysis and particle-in-cell simulations.

Findings

SRS can be nearly completely suppressed with broadband lasers at 10^15 W/cm^2.

Decoupling of beamlets depends on their energy and frequency spacing.

SBS suppression occurs simultaneously with SRS when using broadband lasers.

Abstract

A theoretical analysis for the stimulated Raman scattering (SRS) instability driven by two laser beams with certain frequency difference is presented. It is found that strong coupling and enhanced SRS take place only when the unstable regions corresponding respectively to the two beams are overlapped in the wavenumber space. Hence a threshold of the beam frequency difference for their decoupling is found as a function of their intensity and plasma density. Based upon this, a strategy to suppress the SRS instability with decoupled broadband lasers (DBLs) is proposed. A DBL can be composed of tens or even hundreds of beamlets, where the beamlets are distributed uniformly in a broad spectrum range such as over 10\% of the central frequency. Decoupling among the beamlets is found due to the limited beamlet energy and suitable frequency difference between neighboring beamlets. Particle-in-cell simulations demonstrate that SRS can be almost completely suppressed with DBLs at the laser intensity $\sim10^{15}$ W/cm$^2$. Moreover, stimulated Brillouin scattering (SBS) will be suppressed simultaneously with DBLs as long as SRS is suppressed. DBLs can be attractive for driving inertial confined fusion.