Plasma Physics (physics.plasm-ph)

Abstract: Colliding of two high Mach-number quantum degenerate plasmas is one of the most essential components in the double-cone ignition (DCI) inertial confinement fusion scheme, in which two highly compressed plasma jets from the cone-tips collide along with rapid conversion from the colliding kinetic energies to the internal energy of a stagnated isochoric plasma. Due to the effects of high densities and high Mach-numbers of the colliding plasma jets, quantum degeneracy and kinetic physics might play important roles and challenge the predictions of traditional hydrodynamic models. In this work, the colliding process of two high Mach number quantum degenerate Deuterium-plasma jets with sizable scale ($\sim 1000\ \si{\mu m}$, $\sim 300\ \si{ps}$, $\sim 100\ \si{g/cc}$, $\sim 300\ \si{km/s}$) were investigated with first-principle kinetic simulations and theoretical analyses. In order to achieve high-density compression, the colliding kinetic pressure should be significantly higher than the pressure raised by the quantum degeneracy. This means high colliding Mach numbers are required. However, when the Mach number is further increased, we surprisingly found a decreasing trend of density compression, due to kinetic effects. It is therefore suggested that there is theoretically optimal colliding velocity to achieve the highest density compression. Our results would provide valuable suggestions for the base-line design of the DCI experiments and also might be of relevance in some violent astrophysical processes, such as the merger of two white dwarfs.

Abstract: In this paper, we present the theoretical formalism describing the collective ion dynamics of the nonideal Coulomb classical one-component plasmas on the basis of the self-consistent relaxation theory. The theory is adapted to account for correlations between the frequency relaxation parameters that characterize the three- and four-particle dynamics and the parameters associated with the two-particle dynamics. The dynamic structure factor spectra and dispersion characteristics calculated for a wide range of wave numbers are in agreement with the molecular dynamics simulation data and the results obtained with the theory of the frequency moments. The proposed formalism reproduces all the features inherent to the Coulomb one-component plasmas and requires only knowledge of the coupling parameter and the information about the structure.

Abstract: Electron acoustic waves (EAWs), as well as electron-acoustic solitary structures, play a crucial role in thermalization and acceleration of electron populations in Earth's magnetosphere. These waves are often observed in association with whistler-mode waves, but the detailed mechanism of EAW and whistler wave coupling is not yet revealed. We investigate the excitation mechanism of EAWs and their potential relation to whistler waves using particle-in-cell simulations. Whistler waves are first excited by electrons with a temperature anisotropy perpendicular to the background magnetic field. Electrons trapped by these whistler waves through nonlinear Landau resonance form localized field-aligned beams, which subsequently excite EAWs. By comparing the growth rate of EAWs and the phase mixing rate of trapped electron beams, we obtain the critical condition for EAW excitation, which is consistent with our simulation results across a wide region in parameter space. These results are expected to be useful in the interpretation of concurrent observations of whistler-mode waves and nonlinear solitary structures, and may also have important implications for investigation of cross-scale energy transfer in the near-Earth space environment.