Large-scale kinetic simulations of colliding plasmas within a hohlraum of indirect-drive inertial confinement fusion.

The National Ignition Facility has recently achieved successful burning plasma and ignition using the inertial confinement fusion (ICF) approach. However, there are still many fundamental physics phenomena that are not well understood, including the kinetic processes in the hohlraum. Shan et al. [Phys. Rev. Lett. 120, 195001 (2018)0031-900710.1103/PhysRevLett.120.195001] utilized the energy spectra of neutrons to investigate the kinetic colliding plasma in a hohlraum of indirect drive ICF. However, due to the typical large spatial-temporal scales, this experiment could not be well simulated by using available codes at that time. Utilizing our advanced high-order implicit PIC code, LAPINS, we were able to successfully reproduce the experiment on a large scale of both spatial and temporal dimensions, in which the original computational scale was increased by approximately seven to eight orders of magnitude. Not only is the validity of the explanation of the experiment confirmed by our simulations, i.e., the abnormally large width of neutron spectra comes from beam-target nuclear fusions, but also a different physical insight into the source of energetic deuterium ions is provided. The acceleration of deuterium ions can be categorized into two components: one is propelled by a sheath electric field created by the charge separation at the onset, while the other is a result of the reflection of the potential of the shock wave. The robustness of the acceleration mechanism is analyzed with varying initial conditions, e.g., temperatures, drifting velocity, and ion components. This paper might serve as a reference for benchmark simulations of upcoming simulation codes and may be relevant for future research on mixtures and entropy increments at plasma interfaces.

Kinetic investigations of nonlinear electrostatic excitations in quantum plasmas.

For plasmas in an extremely high-density state, like stellar cores or compressed fuel in inertial fusion facilities, their behavior turns out to be quite different when compared with those plasmas in interstellar space or magnetic confinement devices. To figure out those differences and uncover the kinetic physics in electrostatic excitations, a quantum kinetic code solving Wigner-Poisson equations has been developed. Basic plasmon decay, Landau damping, and two-stream instability of extremely high-density plasmas are investigated by using our newly developed code. Numerical simulations show that in the linear region, the dispersion relations of intrinsic modes can be significantly affected by quantum effects, and such simulation results can be well described by the existing analytical theory. Especially in the nonlinear region, since the space-time scale of collective modes of plasmas is comparable to the electron de Broglie wavelength, their couplings produce some new physics: the energy exchange between the electron and the collective mode results in an abnormal oscillation that does not exist in classical plasmas.

Kinetic studies of exchange-correlation effect on the collective excitations of warm dense plasmas.

The exchange-correlation of electrons, as a fundamental effect in quantum mechanics, plays an important role in the collective motions of electrons in warm dense matter. We derive the quantum kinetic equations based on the time-dependent Kohn-Sham equation. By using a temperature-dependent functional for the exchange correlation, the excitations of electrostatic waves are analyzed under the adiabatic local density approximation (ALDA). We find that the influences of the exchange-correlation effect on the group velocity of electrostatic waves can be as high as 10% when both the density and temperature are low. Moreover, we also compare the results obtained by using ALDA-based kinetic theory, exchange kinetic theory, and quantum hydrodynamics, and discuss the differences among them.

Kinetic study of quantum two-stream instability by Wigner approach.

Classical plasma are typically of low density and/or high temperature. Two of its basic properties are Landau damping and two-stream instabilities. When increasing the plasma density, quantum effects appear and beam-plasma interactions show behavior different from the classical cases. We revisit Landau damping and two-stream instabilities under conditions when quantum hydrodynamic and quantum kinetic theory can be applied, the latter accounting for wave-particle interactions. We find that the instability growth rate behaves as pure two-stream instability without Landau damping when the countering stream velocity exceeds a certain threshold, which differs from the classical case.