Ion acceleration by stimulated-Brillouin-scattering-induced ion-acoustic turbulence*

A new source of ion-acoustic turbulence is investigated whose origin is the stimulated Brillouin scattering between two counter-propagating laser beams in inhomogeneous, flowing plasmas where the laser intensity is slightly higher than that usually encountered in inertial confinement fusion experiments, $I\sim 10^{15}\mbox{W/cm}^{2}$. Densities are $>n_{c} /4$, $ZT_{e} /T_{i} \gg 1$ and the flow scale-length is about 100$\mbox{\mu m.}$ Numerical Vlasov simulation shows that the resulting large-amplitude ion acoustic waves lead to harmonic generation which evolves into turbulence due to wave breaking. This SBS-driven turbulence generates chains of solitary waves which accelerate ions to energies that are dozens of times the energy of thermal electrons. Its ion acceleration mechanism and ion energy spectrum are described and its potential applications are discussed.