Field of an Electric Dipole Surrounded by a Small Plasma Spheroid with a Cavity

Abstract

We obtain and analyze a solution of the boundary-value problem for the field of an electric dipole centered in a vacuum cavity inside a small plasma spheroid. The influence of the cavity size on the field enhancement in an outer vacuum region is analyzed as a function of the curvature of the plasma-spheroid surface. The results are compared with the case of a sphere with similar cavity.This paper is the continuation of works [1][2][3][4][5][6][7][8][9][10][11][12] devoted to studying the influence of small plasma regions around a dipole source on its radiation into an outer vacuum region. Such studies are aimed at analyzing possibilities of enhancement of radiation from a small plasma region. The studies were performed for plasma regions of different shapes ranging from a circular or elliptic cylinder to a sphere and a prolate or oblate spheroid. The effect of the shape of a plasma Fig. 1.region was revealed and some estimates of the influence of an ion sheath formed around sources in plasmas [13,14] and modeled by a vacuum sheath were performed. The presence of a continuous isotropic plasma region [1-6] around a source leads to an increase in the field in an outer vacuum region by 1-2 orders of magnitude compared with the case where the plasma region is absent, provided the amplitude of the feeding current at a single resonant frequency determined by the plasma-region shape remains intact. The presence of an external magnetic field [7-10] or allowance for an ion sheath [11,12] around the source in plasma leads to splitting the resonant frequency into two frequencies and can enhance this effect.In this paper, we study the influence of the ion sheath on the far-zone field of a source surrounded by a plasma spheroid of small electrical sizes k p a 1, where k p = ω p /c, ω p is the electron plasma frequency, a is the major semiaxis of the spheroid, and c is the speed of light in free space.We consider the radiation field of an electric dipole centered in a small prolate plasma spheroid with the major and minor semiaxes a and b, respectively (Fig. 1), and the eccentricity e. The dipole is aligned with the symmetry axis of the spheroid. The ion sheath around the source is modeled by a small vacuum spheroid with the semiaxes a 1 and b 1 and the same eccentricity e. The model of an inner cavity with a sharp boundary is simplified and neglects the influence of the region with the relative dielectric permittivity ε = 0. We plan to consider this influence in future works. The distance 2d 1 between the foci of the inner spheroid is assumed to vary from the minimum value determined by the dipole length to the value almost * Yulia.Afanasyeva@paloma.spbu.ru

Antenna radiation enhanced by a negative permittivity material: plasma

“…6 shown the influence of antenna frequency, plasma layer width and collision frequency on radiation intensity [6]. Also, the effect of plasma layer with different shape is considered [7].…”

Field of an electric dipole surrounded by a nonuniform cylindrical plasma sheath

“…An increase in the radiation from antennas sur- rounded by plasma sheathes of various shapes (circular or elliptic cylindrical, spherical, and spheroidal) for the same current as in the sheathless antenna was considered for the model of a plasma sheath in the form of a homogeneous or piecewise-homogeneous medium with a step-like transition of dielectric permittivity between a vacuum layer (ε = 1) and a plasma layer with the negative real part of dielectric permittivity [1][2][3][4][5][6]. In those works, the region in which the real part of dielectric permittivity went to zero was not considered, although this region predominantly affects the formation of the source field in the cases analyzed in [7,8].…”