Sanqiu Liu

Fluid modeling of radical species generation mechanism in dense methane-air mixture streamer discharge

Atmospheric dielectric barrier discharge (DBD) was found to be promising in the context of plasma chemistry, plasma medicine, and plasma-assisted combustion. In this paper, we present a detailed fluid modeling study of abundant radical species produced by a positive streamer in atmospheric dense methane-air DBD. A two-dimensional axisymmetric fluid model is constructed, in which 82 plasma chemical reactions and 30 different species are considered. Spatial and temporal density distributions of dominant radicals and ions are presented. We lay our emphasis on the effect of varying relative permittivity (er = 2, 4.5, and 9) on the streamer dynamics in the plasma column, such as electric field behavior, production, and destruction pathways of dominant radical species. We find that higher relative permittivity promotes propagation of electric field and formation of conduction channel in the plasma column. The streamer discharge is sustained by the direct electron-impact ionization of methane molecule. Furthermo...

Plasmon turbulence spectra with the filamentation patterns in a laser plasma

The instantaneous spectra of the transverse, Langmuir, and ion-sound plasmons near the critical surface in a laser-plasma are numerically obtained from the complete Zakharov equations under the condition of the nonstatic limit. They are used to discuss the filamentation process in the strong Langmuir turbulence. From the turbulence spectra, the energy flux flow from small k space to large k space can be identified. The higher incident laser intensity associated with a quicker filamentation process can also be identified.

Dispersion relation of longitudinal oscillation in relativistic plasmas with nonextensive distribution

The theory and application of nonextensive statistical mechanics (NESM) have underwent rapid development since the nonextensive entropy is put forward in 1988; its tentacles are almost throughout all areas of physics and has been a huge success. The nonextensive distribution function, however, as a basic part of NESM theory and application foundation, suffers a controversy: two different mathematical definitions of nonextensive distributions. Here, we show that the one dimensional nonextensive distribution function has the form of [ 1 + ( 1 − q ) x 2 ] 1 q − 1. We are starting from the nonextensive entropy, derive the nonextensive distribution function adopting the Maxwellian method, and prove the correctness of the form, and illustrate the physical meaning of the nonextensive parameter q as the fractal dimension when the Euclidean dimension is one. Furthermore, we derive the three-dimensional distribution function and the relativistic nonextensive distribution function, which perfect the theory of NESM and lay a solid application foundation of the NESM. We use the relativistic nonextensive distribution function to investigate the dispersion relations of relativistic longitudinal oscillation in nonextensive plasma and obtain the analytical expression of long wave dispersion relations under the ultra-relativistic case and the complete numerical dispersion curves. These results under an extensive limit reproduce Maxwellian statistical results. The proposed theory provides a method to measure the dimension of a plasma system, which may greatly promote our understanding for complex nonlinear plasma systems and thus, promote the understanding and solving of nonlinear problems such as turbulence, chaos, and soliton. This work also is the application foundation of nonextensive statistical mechanics to high energy physics such as relativistic plasma, M-theory, and so on in physical and mathematical aspects.

The influence of polarization and charge gradient forces on the dust sheath formation

The influence of the polarization and charge gradient forces on the dust sheath formation using a fluid model is investigated. The corresponding new Bohm criterion for the dust sheath formation is obtained. By analyzing the Sagdeev potential numerically, it is found that the polarization and charge gradient forces have opposite effects on the Sagdeev potential and the critical Mach number, i.e., the polarization effect enlarges the width and depth of the Sagdeev potential, while the charge gradient effect narrows the width and depth of the Sagdeev potential. Furthermore, the critical Mach number decreases with the increase in polarization parameter RP and increases with the increase in charge gradient parameter RCG. Finally, regardless of whether the polarization effect or the charge gradient effect is considered, the depth and width of the potential well increase with the increase in the Mach number, while the critical Mach number decreases with the increase in the ratio of ion and electron density ρ.The influence of the polarization and charge gradient forces on the dust sheath formation using a fluid model is investigated. The corresponding new Bohm criterion for the dust sheath formation is obtained. By analyzing the Sagdeev potential numerically, it is found that the polarization and charge gradient forces have opposite effects on the Sagdeev potential and the critical Mach number, i.e., the polarization effect enlarges the width and depth of the Sagdeev potential, while the charge gradient effect narrows the width and depth of the Sagdeev potential. Furthermore, the critical Mach number decreases with the increase in polarization parameter RP and increases with the increase in charge gradient parameter RCG. Finally, regardless of whether the polarization effect or the charge gradient effect is considered, the depth and width of the potential well increase with the increase in the Mach number, while the critical Mach number decreases with the increase in the ratio of ion and electron density ρ.

The effect of methane gas flow rate on the streamer propagation in an atmospheric-pressure methane-air plasma jet

In this paper, a two-dimensional axisymmetric fluid model is applied to investigate the streamer discharge characteristics in an atmospheric pressure methane-air plasma jet as a function of methane flow velocities (2.5 m/s and 20 m/s, respectively). Although the streamer ignition and propagation in the dielectric tube are not sensitive to the methane gas flow velocity, the concentration field of methane and air in the mixing layer established by a balance between convective methane flow and back-diffusion of air ambient is crucial for streamer propagation in the gap. As the methane flow velocity is 2.5 m/s, the structure of the streamer head transits from ring-shape into solid disk-shape, while the streamer head always maintains a donut-shaped pattern at high flow velocity of 20 m/s until it impinges on the substrate. At lower gas velocity, the back-diffusion of ambient air into the methane jet is even more pronounced, which causes a larger space charge density at the streamer head, and thus the local ele...

Dust lattice waves in Debye binary dust chain

The dust lattice waves in a one-dimensional Debye binary dust chain consisting of two distinct dust particle species with different charges and masses are investigated. It is found that there are two branches for both longitudinal and transverse modes, namely the optical mode of high frequency and the acoustic mode of low frequency, which will be merged into one ordinary longitudinal (transverse) mode of single dust chain. The influence of the parameters, i.e., the dimensionless lattice parameter α, the mass ratio σ, and the charge ratio e of the two particles, on the dispersion relation of longitudinal and transverse waves is discussed. Furthermore, the branching and the merging of longitudinal and transverse waves are discussed in detail.

Turbulent cascade in a two-ion plasma

It is shown that small but finite-amplitude drift wave turbulence in a two-ion-species plasma can be modeled by a Hasegawa-Mima equation. The mode cascade process and resulting turbulent spectrum are investigated. The spectrum is found to be similar to that of a two-component plasma, but the space and time scales of the turbulent cascade process can be quite different since they are rescaled by the presence of the second ion species.