Trapping, Landau damping, and Self-focusing of Multiple-ion Acoustic Waves with Interspecies Collisions

The reduction of laser energy deposition in Inertial Confinement Fusion resulting from stimulated Brillouin backscattering (SBS) is a significant constraint on hohlraum and capsule design. One promising option is the use of multiple ion species. Provided nonlinear trapping of the ions in the Ion Acoustic wave (IAW) can be suppressed,[i] multiple ion species increase the IAW damping rate and thereby lower the amplification rate significantly compared to single species materials. In previous work on mixtures of high-Z and low-Z ions, we showed with Vlasov simulations[ii] that light ion trapping, which reduces the damping, can be decreased by collisional scattering of the light ions from the heavy ions. By varying the IAW wave amplitude, we obtain a scaling for the reduction of the damping rate with respect to the wave amplitude and collision strength. The dynamic energy partition among the species and field is discussed. In addition, using 2D LOKI simulations, we find that collisions can suppress IAW self-focusing.

[i] R. Berger, Phys. Plasmas 26, 012709 (2019)

[ii] R. Berger, et al, 62 Annual Meeting of the DPP, November 11, 2020