Search

The plasma sheath causes the spacecraft’s communication signal to attenuate dramatically during the re-entry period, which seriously threatens the astronauts. However, valid experimental protocols have not been obtained hitherto. To realize the propagation of electromagnetic waves in negative permittivity background of the plasma sheath, alumina columns are embedded in the plasma background to form plasma photonic crystals, which can support the coupling of evanescent waves between the alumina columns. We experimentally demonstrate the realization of communication in blackout scenario by achieving a complete passing band in the plasma cutoff region. For high frequency communications in the plasma sheath, electromagnetic wave propagation based on topological edge states is also experimentally demonstrated. Furthermore, we realize a triply-degenerate Dirac cone formed dynamically at the center of the Brillouin zone by modulating the electron density, where electromagnetic wave exhibits high transmittance and does not experience phase accumulation at the Dirac point. Our work thus not only provides an effective approach to overcome the communication blackout problem, but the design can also be served as a promising experimental platform to explore topological electromagnetic phenomena.

This paper has established a relatively comprehensive model for ultra-low frequency (ULF) current induced by thermal pressure gradients and its propagation. In the ULF current excitation model, we decomposed the current into a constant term unaffected by altitude and a product with a function significantly influenced by altitude. Combining this with the EISCAT background, we determined that for modulation frequencies below 5 Hz, the optimal height for ULF current excitation corresponds to the critical frequency height. We calculated the ionospheric currents at heating altitudes of 332 km for modulation frequencies of 5 Hz; the corresponding maximum currents were 1.03 × 10−10 A·m−2. By incorporating the current into the ULF waves propagation model based on magnetoionic theory, we found that the electromagnetic field energy is mainly concentrated in the horizontal direction, indicating that the energy primarily propagates outward through magnetosonic waves. The dominant components are the electric field component Ey and the magnetic field component Bz, whose maximum values reached 1.1 μV·m−1 and 1.5 pT. Unfortunately, magnetosonic waves cannot propagate downward due to the sharp variation in the real part of the refractive index between 200 and 300 km. However, the shear Alfvén waves component By can propagate downward, and there is still an intensity of approximately 0.1 pT at the bottom of the ionosphere, which is because the refractive index of shear Alfvén waves is most uniform in the parallel magnetic field direction, allowing By to propagate parallel to the magnetic field effectively. [ABSTRACT FROM AUTHOR]

A sub-wavelength particle with a total scattering cross section that exceeds the single channel limit is referred to as a superscatterer, which can provide ability to control light in nanoscale. A variety of superscatter structures have been suggested, most of them are typically constructed with strong forward scattering but minor backscattering. This unusual behavior can be attributed to the superposition of resonant modes in adjacent angular momentum channels. We reveal the mechanism of super backscattering for subwavelength column, which can be formed by recombining non-adjacent resonant modes, as confirmed by our numerical analysis. [ABSTRACT FROM AUTHOR]

The twig edge states in graphene‐like structures are viewed as the fourth states complementary to their zigzag, bearded, and armchair counterparts. In this work, a rod‐in‐plasma system in a honeycomb lattice with twig edge truncation under external magnetic fields and lattice scaling is studied and it is shown that twig edge states can exist in different phases of the system, such as quantum Hall (QH) phase, quantum spin Hall (QSH) phase, and insulating phase. The twig edge states in the negative permittivity background exhibit robust one‐way transmission properties immune to backscattering and thus provide a novel avenue for solving the plasma communication blackout problem. Moreover, it is demonstrated that corner and edge states can exist within the shrunken structure by modulating the on‐site potential of the twig edges. Especially, helical edge states with the unique feature of pseudospin‐momentum locking that can be excited by chiral sources are demonstrated at the twig edges. These results show that the twig edges and interface engineering can bring new opportunities for more flexible manipulation of electromagnetic waves. [ABSTRACT FROM AUTHOR]

This work deals with the numerical and experimental investigation of atmospheric pressure dielectric barrier discharges (DBDs). In the experiment, the current and voltage of DBD sustained in an argon flow in coaxial discharge cell are measured. Numerical models are based on the drift-diffusion theory of gas discharges. Different modelling approaches, where the electron kinetics is determined on the basis of the Maxwellian electron energy distribution function (EEDF), vs models with more realistic EEDF obtained from the solution of the electron Boltzmann equation are implemented. The effect of energy loss due to heating of the gas is considered. [ABSTRACT FROM AUTHOR]

Plasma blackout, which contains ablative impurities, strongly attenuates the signal of the reentry spacecraft. Traditional methods focus on mitigating electron densities and impurities around the antenna, and metamaterial-based electromagnetic methods have yet to be proven experimentally. We simulate the plasma blackout problem using laboratory plasma supported by gas discharge technology. Alumina pillars are embedded in the plasma background to form plasma photonic crystals, while topological phase transitions are achieved by shrinking and expanding pillars within a unit cell. The topological edge states (TESs) that are insensitive to weak impurities in the transport path are verified theoretically and experimentally. We introduce the glide-reflection (GR) symmetry in the nontrivial lattices to obtain the gapless edge states, which are exclusively observed in the acoustic systems. Meanwhile, the Δω of the gapless TES increases with the electron densities, ensuring a wide communication bandwidth. Furthermore, the strong coupling of heterostructure with GR symmetry in plasma photonic crystals is elucidated. Our work not only provides a new approach to the blackout communication problem but can also serve as a nascent experimental platform to investigate topological electromagnetic phenomena. [ABSTRACT FROM AUTHOR]

We present a theoretical and numerical study of drift current model in the ionosphere by incorporating the ohmic heating model and the magnetohydrodynamic (MHD) momentum equation. Based on these equations, the ionospheric electron temperature and drift current are investigated. The results indicate that the maximum change of electron temperature Δ T e is about 570 K, and the ratio is Δ T e / T e ~48 %. The maximum drift current density is 8 × 10−10 A ⋅ m −2, and its surface integral is 5.76 A. Diamagnetic drift current is the main form of current. The low collision frequency between charged particles and neutral particles has little effect on the current, and the collision frequency of electrons and ions is independent of the drift current. The current density profile is a flow ring. We present the effective conductivity as a function of the angle between the geomagnetic field and the radio wave; the model explains why the radiation efficiency in Kotik's experiment was strongest when the X wave is heating along the magnetic dip angle. [ABSTRACT FROM AUTHOR]