title: Saturation of backward stimulated scattering of a laser beam in the kinetic regime.
abstract: Stimulated Raman (SRS) and Brillouin scattering (SBS) are examined in the kinetic regime using particle-in-cell simulations. Wave front bowing of electron-plasma waves (ion-acoustic waves) from trapped particle nonlinear frequency shift is observed in the SRS (SBS) regime for the first time. Self-focusing from trapped particle modulational instability (TPMI) is shown to occur in 2D and 3D SRS simulations. The key physics of SRS saturation is identified as a combination of wave front bowing, TPMI, and self-focusing: Bowing marks the beginning of SRS saturation and self-focusing terminates SRS. Ion-acoustic wave bowing also contributes to SBS saturation. Velocity diffusion by transverse modes and rapid loss of hot electrons in regions of small transverse extent formed from self-focusing dissipate wave energy and increase Landau damping, despite trapping that reduces Landau damping initially.
authors.affiliation: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: L
authors.initials: L
authors.lastname: Yin
authors.forename: B J
authors.initials: BJ
authors.lastname: Albright
authors.forename: K J
authors.initials: KJ
authors.lastname: Bowers
authors.forename: W
authors.initials: W
authors.lastname: Daughton
authors.forename: H A
authors.initials: HA
authors.lastname: Rose