Issues with Modeling a Tunnel Communication Channel through a Plasma Sheath

We consider two of the most relevant problems that arise when modeling the properties of a tunnel radio communication channel through a plasma layer. First, we studied the case of the oblique incidence of electromagnetic waves on a layer of ionized gas for two wave polarizations. The resonator parameters that provide signal reception at a wide solid angle were found. We also took into account the unavoidable presence of a protective layer between the plasma and the resonator, as well as the conducting elements of the antenna system in the dielectric itself. This provides the first complete simulation for a tunnel communication channel. Noise immunity and communication range studies were conducted for a prospective spacecraft radio line.

Modeling the Lunar Wake Response to a CME Using a Hybrid PIC Model

In the solar wind, a low-density wake region forms downstream of the nightside lunar surface. In this study, we use a series of 3D hybrid particle-in-cell simulations to model the response of the lunar wake to a passing coronal mass ejection (CME). Average plasma parameters are derived from the Wind spacecraft located at 1 au during three distinct phases of a passing halo (Earth-directed) CME on 2015 June 22. Each set of plasma parameters, representing the shock/plasma sheath, a magnetic cloud, and plasma conditions we call the mid-CME phase, are used as the time-static upstream boundary conditions for three separate simulations. These simulation results are then compared with results that use nominal solar wind conditions. Results show a shortened plasma void compared to nominal conditions and a distinctive rarefaction cone originating from the terminator during the CME’s plasma sheath phase, while a highly elongated plasma void reforms during the magnetic cloud and mid-CME phases. Developments of electric and magnetic field intensification are also observed during the plasma sheath phase along the central wake, while electrostatic turbulence dominates along the plasma void boundaries and 2–3 lunar radii R M downstream in the central wake during the magnetic cloud and mid-CME phases. The simulations demonstrate that the lunar wake responds in a dynamic way with the changes in the upstream solar wind during a CME.

Generation of Cold Magnetized Relativistic Plasmas at the Rear of Thin Foils Irradiated by Ultra-High-Intensity Laser Pulses

A scheme to generate magnetized relativistic plasmas in a laboratory setting is proposed. It is based on the interaction of ultra-high-intensity sub-picosecond laser pulses with few-micron-thick foils or films. By means of Particle-In-Cell simulations, it is shown that energetic electrons produced by the laser and evacuated at the rear of the target trigger an expansion of the target, building up a strong azimuthal magnetic field. It is shown that in the expanding plasma sheath, a ratio of the magnetic pressure and the electron rest-mass energy density exceeds unity, whereas the plasma pressure is lower than the magnetic pressure and the electron gyroradius is lower than the plasma dimension. This scheme can be utilized to study astrophysical extreme phenomena such as relativistic magnetic reconnection in laboratory.

Analysis of Hypersonic Platform-Borne SAR Imaging: A Physical Perspective

The usage of a hypersonic platform for remote sensing application has promising prospects, especially for hypersonic platform-borne synthetic aperture radar (SAR) imaging. However, the high-speed of hypersonic platform will lead to extreme friction between the platform and air, which will cause the ionization of air. The ionized gas forms the plasma sheath wrapped around the hypersonic platform. The plasma sheath will severely affect the propagation of SAR signal and further affect the SAR imaging. Therefore, hypersonic platform-borne SAR imaging should be studied from a physical perspective. In this paper, hypersonic platform-borne SAR imaging under plasma sheath is analyzed. The SAR signal propagation in plasma sheath is computed using scatter matrix method. The proposed SAR signal model is verified by using a ground experiment system. Moreover, the effect of attenuation caused by plasma sheath on SAR imaging is studied under different SAR parameters and plasma sheath. The result shows that attenuation caused by plasma sheath will degrade the SAR imaging quality and even cause the point and area targets to be submerged into the noise. The real SAR images under plasma sheath also illustrate this phenomenon. Furthermore, by studying imaging results under different SAR and plasma parameters, it can be concluded that the severe degradation of SAR imaging quality appears at condition of high plasma sheath electron density and low SAR carrier frequency. The work in this paper will be beneficial for the study of hypersonic platform-borne SAR imaging and design of hypersonic SAR imaging systems in the future.

The ion transit effects on the sheath dynamics inthe intermediate radiofrequency regime: excitationsof ion-acoustic waves and solitons

The capacitively coupled plasma is investigated kinetically utilizing the particle- in-cell technique. The Argon (Ar) plasma is generated via two radio-frequencies. The plasma bulk density increases by increasing the voltage amplitude of the high frequency (≥ 13.56 MHz) which is much greater than the ion plasma frequency. The intermediate radio-frequencies ( ≈ 1 MHz) which are comparable to the ion plasma frequency causes a broadening of the ion energy distribution considerably, i.e., ions gain energies above and lower than the time-averaged energy. The good agreement between published experimental results and our theoretical calculations via the Ensemble- in-Spacetime model confirms the modulation of ions around time-averaged values. Intermediate frequencies allow ions to respond partially to the instantaneous electric field. The response of ions to the instantaneous electric field is investigated semi- analytically. The dispersion relation of the plasma sheath and bulk are derived. Stable ion acoustic modes are found. The ion-acoustic modes have two different velocities and carry energy from the sheath edge to the electrode. Also, intermediate frequencies excite solitons in the plasma sheath; the results may help to explain the ion density, flux, and energy modulation, and, consequently, the broadening of the ion energy distribution.

Surface effects in a capacitive argon discharge in the intermediate pressure regime

One-dimensional particle-in-cell/Monte Carlo collisional (PIC/MCC) simulations are performed on a capacitive 2.54 cm gap, 1.6 Torr argon discharge driven by a sinusoidal rf current density amplitude of 50 A/m2 at 13.56 MHz. The excited argon states (metastable levels, resonance levels, and the 4p manifold) are modeled self-consistently with the particle dynamics as space- and time-varying fluids. Four cases are examined, including and neglecting excited states, and using either a fixed or energy-dependent secondary electron emission yield due to ion and/or neutral impact on the electrodes. The results for all cases show that most of the ionization occurs near the plasma-sheath interfaces, with little ionization within the plasma bulk region. Without excited states, secondary electrons emitted from the electrodes are found to play a strong role in the ionization process. When the excited states, secondary electron emission due to neutral and ion impact on the electrodes are included in the discharge model, the discharge operation transitions from α-mode to γ-mode, in which nearly all the ionization is due to secondary electrons. Excited states are very effective in producing secondary electrons, with approximately 14.7 times the contribution of ion bombardment. Electron impact of ground state argon atoms by secondary electrons contributes about 76 % of the total ionization; primary electrons, about 11 %; metastable Penning ionization, about 13 %; and multi-step ionization, about 0.3 %.