Time-varying Plasma Sheath Research Articles

Propagation Properties of Terahertz Waves in a Time-Varying Dusty Plasma Slab Using FDTD

The complex dielectric permittivity of a dusty plasma, which contains an inhomogeneous electron density, charging response factor, and dust charging frequency caused by dust particles, is given to simulate the time-varying dusty plasma sheath. The recurrence field and current equations for terahertz (THz) wave propagation in the plasma are deduced and discretized using the auxiliary differential equation finite-difference time-domain (ADE-FDTD) method. The reflection, transmission, and absorption coefficients of a time-varying dusty plasma slab are calculated by using the ADE-FDTD method. The numerical results indicate that the reflection coefficients of the slab are easily affected by the rise time of the electron density. Besides, the absorption coefficients increase with the decrease in the rise time and working frequency as well as with the increase in the densities of electrons and dust particles. It is shown that THz waves may have potential applications in radio communications with a spacecraft at its re-entry into the atmosphere.

CHANNEL CHARACTERIZATION AND FINITE-STATE MARKOV CHANNEL MODELING FOR TIME-VARYING PLASMA SHEATH SURROUNDING HYPERSONIC VEHICLES

Efiects on the communication signals caused by the time-varying plasma sheath surrounding hypersonic vehicles are investigated. Using computational ∞uid dynamics (CFD) technique, Demetriades's plasma turbulence model and flnite-difierence time-domain (FDTD) algorithm, amplitude variation and phase ∞uctuation induced by plasma electron density turbulence are obtained, and their statistical properties are analyzed and characterized. Furthermore, a flnite-state Markov channel (FSMC) model is proposed, to represent the dynamical efiects on electromagnetic wave propagation through plasma sheath. With high accuracy and greatly reduced complexity, the FMSC model could be very useful to develop novel communication techniques for alleviating the radio blackout problem.

Research on electromagnetic scattering characteristics of reentry vehicles and blackout forecast model

Vehicles flying at high velocity within the atmosphere become enveloped in a time-varying plasma sheath. This paper adopts a more efficient and stable modified advection upstream splitting method by introducing the pressure-based weight functions (AUSMPW+) to solve the Navier–Stokes equations, calculating aircraft periphery flow field based on Dunn-Kang 11-component air chemical model and obtaining the flow field parameter of different flight speeds. According to the simulation flow field parameter, it applies physical optics method to calculate electromagnetic scattering section of blunt-nosed cone aircraft. Moreover, according to plasma critical frequency of different wave bands, it puts forward a blackout prediction model. The calculation result indicates that when the aircraft has a high-speed flight, with the rising speed of the aircraft, electron density of plasma sheath will increase continuously. Influenced by it, aircraft radar cross section shows a decreasing trend. When electron density inside plasma sheath around aircraft exceeds critical plasma densities of the corresponding communication frequency, it will result in “blackout.” This model predicts the blackout of S, C, and X wave bands of spacecraft reentry. The result perfectly corresponds to the experimental data. The results obtained in this paper are significant to the guidance technology and communication technique for hypersonic vehicle.

The dust direct current self-bias potential in a time varying plasma sheath

We introduce an important physical effect, namely, the response of the dust particle charge to an oscillating electric field in a plasma sheath. The ac field may lower the average dust potential well below the corresponding floating potential Uf in a dc sheath. The resulting dust potential will be called the dust dc self-bias potential Udc and is generally a sensitive function of the ac potential amplitude and of the ratio ωch/ω between the so-called dust charging frequency ωch and the ac frequency ω. The difference between Udc and Uf maximizes for ωch≪ω and approaches 0 for ωch≫ω. We propose that the dust dc self-bias effect is important in all plasmas having a rapid potential variation and always has to be taken into account when calculating the charge and the force on dust particles in such plasmas. Since levitation of dust particles above surfaces normally requires negative dust particles, the dust dc self-bias effect may explain why some experiments indicate that levitation of dust particles is easier in rf discharges than in dc discharges.