Electron kinetic effects in the nonlinear evolution of a driven ion-acoustic wave

Kinetic model and Vlasov simulation verification of two-ion decay instability

A kinetic theory is developed to describe the longitudinal decay of two-ion decay (TID): The pump ion-acoustic wave (IAW) decays into two daughter IAWs with a longer wavelength. The instability growth rate and threshold are given by the theory. Both the simulations of full kinetic Vlasov and hybrid Vlasov (kinetic ions and Boltzmann electrons) are employed to verify the theory and have a high quantitative agreement with the theory for 8≤ZT_{e}/T_{i}≤15, where Z is the ion charge number and T_{i}(T_{e}) is the ion (electron) temperature. The kinetic model developed here solves a long-standing problem that the simple fluid theory underestimates growth rate by a factor of 2∼3. Also, a reasonable explanation is given to the typical characteristics of TID that the dependence curves of subharmonic growth rate γ and wave number k.

Longitudinal and Transverse Instability of Ion Acoustic Waves

Ion acoustic waves are found to be susceptible to at least two distinct decay processes. Which process dominates depends on the parameters. In the cases examined, the decay channel where daughter modes propagate parallel to the mother mode is found to dominate at larger amplitudes, while the decay channel where the daughter modes propagate at angles to the mother mode dominates at smaller amplitudes. Both decay processes may occur simultaneously and with onset thresholds below those suggested by fluid theory, resulting in the eventual multidimensional collapse of the mother mode to a turbulent state.

Kinetic theory and Vlasov simulation of nonlinear ion-acoustic waves in multi-ion species plasmas

The theory of damping and nonlinear frequency shifts from particles resonant with ion-acoustic waves (IAWs) is presented for multi-ion species plasma and compared to driven wave Vlasov simulations. Two distinct IAW modes may be supported in multi-ion species plasmas, broadly classified as fast and slow by their phase velocity relative to the constituent ion thermal velocities. In current fusion-relevant long pulse experiments, the ion to electron temperature ratio, T(i)/T(e), is expected to reach a level such that the least damped and thus more readily driven mode is the slow mode, with both linear and nonlinear properties that are shown to differ significantly from the fast mode. The lighter ion species of the slow mode is found to make no significant contribution to the IAW frequency shift despite typically being the dominant contributor to the Landau damping.

Three-dimensional modeling of stimulated Brillouin scattering in ignition-scale experiments

The first three-dimensional simulations of a high power 0.351 mum laser beam propagating through a high temperature hohlraum plasma are reported. We show that 3D fluid-based modeling of stimulated Brillouin scattering, including linear kinetic corrections, reproduces quantitatively the experimental measurements, provided it is coupled to detailed hydrodynamics simulation and a realistic description of the laser beam from its millimeter-size envelope down to the micron scale speckles. These simulations accurately predict the strong reduction of stimulated Brillouin scattering measured when polarization smoothing is used.