The transition from thermally driven to ponderomotively driven stimulated Brillouin scattering and filamentation of light in plasma

Abstract

The dispersion properties of ion acoustic waves and their nonlinear coupling to light waves through ponderomotive and thermal forces are sensitive to the strength of electron-ion collisions.Here, we consider the growth rate of stimulated Brillouin scattering when the driven acoustic wave frequency and wavelength span the range of small to large compared to electron-ion collision frequency and mean free path respectively. We find in all cases the thermal contributions to the SBS growth rate are insignificant if the ion acoustic wave frequency is greater than the electron-ion collision frequency and the wavelength is much shorter than the electron-ion mean free path. On the other hand, the purely growing filamentation instability remains thermally driven for shorter wavelengths than SBS even when the growth rate is larger than the acoustic frequency.

High-power laser delocalization in plasmas leading to long-range beam merging

“…1(d). Such spreading, already witnessed in experiments using smoothed beams composed of many individual beamlets [28], is observed in simulations to originate from a combination of stimulated Brillouin forward scattering (SBFS) and filamentation [24,28,29,30,31] triggered at high-power. Indeed, ionization induced refraction [32] is not likely to occur in our experimental conditions as the same spreading was observed when pre-ionizing the He gas by an auxiliary beam.…”

How much laser power can propagate through fusion plasma?

“…λ e is related to the standard e − i mean free path, λ ei , by λ e = (λ ei /3)(2Z * /πφ) 1/2 . The basic ion acoustic wave parameters, ν ia and c s , are regarded as given by kinetic theory [27,28,29] which, e.g., takes into account the effect of compressional heating on sound wave propagation. For comparison with experiment in this paper, however, collisionless theory is used for evaluation of acoustic wave parameters.…”

“…The basic ion acoustic wave parameters, ν ia and c s , are regarded as given by kinetic theory [27,28,29] which, e.g., takes into account the effect of compressional heating on sound wave…”

“…Berger for attracting our attention to Refs. [27,28] and pointing out that seed for CFSBS provided by the fluctuating speckles is much larger than thermal. We thank W. Rozmus for pointing out the limitation of Epperlein's model…”

Forward scattering and filamentation of a spatially smoothed laser pulse in the hydrodynamic and kinetic frameworks

“…III B and III C). Note that, for the parameters explored in this study, the non-local correction remains non negligible and therefore essential to obtain realistic predictions [41,42].…”