The simulation of the electromagnetic wave propagation plays an important role in solving the communication blackout issue. Finite element analysis software package COMSOL is employed by us to model the electromagnetic wave propagation in the presence of the non-uniform reentry plasma sheath in this paper. The propagation characteristics of the electromagnetic wave are analyzed by the observation of the field distributions. The electromagnetic wave with s polarization begins to attenuate as an exponential function at the cut-off position. The mode conversion takes place for the p polarization wave when the real part of the plasma permittivity is close to 0. The wave reflection, transmission, and absorption coefficients as a function of the frequency are calculated and analyzed. The absolute agreements between the results calculated by COMSOL model and by the layered model are achieved. The difference of the coefficients between s and p polarization waves can be explained by the presence or absence of the mode conversion. Conclusions in this paper can be the foundation to employ the COMSOL to study the interactions between the electromagnetic wave and the plasma.
Scattering of ion cyclotron range of frequency (ICRF) waves by plasma density perturbations in the edge has been previously studied with the help of antenna code RAPLICASOL (2020, Nucl. Fusion, 60, 096001). The further interesting question is whether the density perturbations have an effect on ion cyclotron resonance heating (ICRH) in the core. In this paper, FEM based 2D full wave code integrating the core with edge is used to study this issue. The analytical density perturbations are applied to study the influence of density perturbations on field distribution, power deposition, waves coupling and power partition among different species in the core and the fraction of energy dissipation in SOL. The influence of density perturbations becomes global and significant when the poloidal size of the density blob is comparable to the perpendicular wavelength. In addition, the amplitude and the radial size of the density blob are positively related to the strength of waves scattering. Finally, a typical experiment on EAST is chosen and the influence of realistic density perturbations on ICRH is evaluated.
“Communication blackout” is such a consequence that the attenuation of electro-magnetic (EM) waves becomes drastic when the frequency of EM waves is near or below the oscillation frequency of plasmas. Deep comprehension on the propagation characteristics of EM waves in the plasma sheath plays an important role in solving this issue. However, relevant works in the literature are almost based on the cold plasma sheath model, neglecting the temperature of the plasmas as well as the spatial dispersion effect. We apply COMSOL Multiphysics software to simulate and study the spatial dispersion effect in the warm plasma sheath in this paper. The mode conversion between EM waves and Langmuir waves in the warm plasmas is observed. The characteristics of field distributions in the warm plasma sheath are different from the cold plasma sheath distinctly, when the resonance between EM waves and the plasmas happens. The reflection and absorption coefficients are also influenced accordingly. The research in this paper gives an insight into EM waves propagation in the warm re-entry plasma sheath and supplies a better comprehension on the interaction between EM waves and the plasma sheath.
The rotation angle of the static magnetic field compared with the toroidal direction should not be ignored for many ion cyclotron range of frequency (ICRF) antenna designs. The antenna coupling code based on the variational theory is employed to analyze the influence of the rotation angle of the static magnetic field on the ICRF antenna coupling on EAST theoretically. A comprehensive analysis of the variation of the coupling resistance dependent on the rotation angle is under taken. The shift of the power spectra as a function of parallel and perpendicular wave numbers is analyzed. The variation of the current distributions also supports the conclusions associated with the ICRF wave coupling. The results and conclusions in this paper will benefit the ICRF antenna design and the experiments relevant to the ICRF wave coupling.
Electromagnetic wave (EMW) penetration through an overdense plasma sheath is a critical subject in solving the “communication blackout” issue. Based on the numerical electron fluid numerical simulations, the linear mode conversion between EMW and electron acoustic waves (EAWs) was examined in the unmagnetized nonuniform plasma sheath with two-temperature electron population. The first resonant position of EMW in the plasma sheath is crucial to stimulate EAW efficiently, while the second one plays an important role in electromagnetic radiation from EAW. Owing to the mode conversion and EAW propagation, a channel can be opened in the overdense nonuniform plasma sheath for EMW. The transmission efficiency of EMW will be reduced remarkably for lacking a low density region where the mode conversion takes place.
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