Nonlinear gain of a dipole antenna immersed in a collisionless plasma

This paper presents an investigation of the effect of collisionless plasma on the equatorial gain of a high power dipole antenna. The plasma experiences a ponderomotive force in the non-uniform radiation field and the electron density gets redistributed; the plasma gets depleted in the centre and the near equatorial zone of the antenna. This nonuniformity in the electron density (hence in the dielectric constant) tends to converge the electromagnetic power to the equatorial zone. For typical parameters a 20% (i.e., ∼1 dB) enhancement in the gain of the antenna has been predicted within the limits of the perturbation theory. Work partially supported by NSF (USA)     

等离子体天线输入阻抗测量及分析

通过矢量网络分析仪测量了不同激励功率条件下柱形等离子体天线系统的输入阻抗随频率的变化关系,实验结果表明柱形等离子体天线输入阻抗具有明显的谐振特性.结合放电管的等效电路模型与柱形等离子体天线输入电流特性,定性分析了等离子体天线输入阻抗变化与等离子体参数之间的关系.此种测量方法有助于等离子体天线动态重构特性的研究和实现快速阻抗匹配. 关键词： 等离子体天线 输入阻抗 表面波     

Toward the theory of a loop antenna in an anisotropic plasma

We consider the problem of determining the current distribution along a loop antenna consisting of an infinitely thin perfectly conducting strip coiled into a ring. The antenna is immersed in an anisotropic plasma medium perpendicular to the external magnetic field and is excited by a given EMF. Primary attention is focused on the frequency band in which the excitation of electrostatic waves is possible. The problem is reduced to solving a system of integral equations with logarithmic and singular kernels. Using the solution of these equations, we found expressions for the antenna current distribution and input impedance. The analysis of these expressions is presented. Radiophysical Research Institute, Lobachevsky State University, Nizhny Novgorod, Russia. Translated from izvestiya Vysshikh Uchbnykh Zavedenii, Radiofizika, Vol. 41, No. 3, pp. 358–373, March, 1998.     

Resonance cones of a magnetic ring antenna in an anisotropic plasma

A theory of convergent and divergent resonance cones in the near zone of a magnetic ring antenna in a cold magnetized plasma is developed. A comparison with the electric ring exciter is made. Density variations due to the rf field ponderomotive force are estimated.     

Guiding of an electromagnetic pulse in a plasma immersed in combined wiggler and axial magnetic fields

We present a new plasma-based method of guiding an electromagnetic pulse. The scheme consists of an inhomogeneous magnetic field and a uniform density plasma, in contrast to existing schemes that rely on transverse plasma density gradients but need not be magnetized. The refractive index of a magnetized plasma depends on the strength and direction of the magnetic field as well as the plasma density. A guiding channel is formed by using field inhomogeneity to generate the desired transverse profile of the index of refraction. The concept is analyzed with an envelope equation and, for the specific example of a wiggler magnetic field, with a two-dimension particle-in-cell simulation. A simplified model of this scheme as producing a magnetic wall in analogy to metallic waveguides is presented, for which corresponding approximate relations for the guided mode axial wavelength and radius are derived as functions of the plasma and magnetic field parameter. These are seen to be in good agreement with particle-in-cell simulation results. Since the desired inhomogeneity of the refractive index can be made easily when the electromagnetic wave frequency is close to the cyclotron frequency, this guiding scheme is most readily applied in the microwave regime.     

Excitation of plasma waves by an externally applied electromagnetic wave to a nonuniform classical plasma

Radiation-driven plasma wave equations (RWE's) are derived from the basic dynamical plasma equations through restaining the external radiation source terms and significant nonlinear terms under the simplified assumptions used by Zakharov [1]. Excitation processes of the transverse plasma waves, Langmuir waves by an externally applied electromagnetic wave to a nonuniform unmagnetized plasma are investigated by means of rough numerical simulations based on RWE's. The results show that the amplitude of the transverse plasma waves is sensitive to their effective damping rate and that the radiation-induced density profile modification looks like a step, which are in qualitative agreement with analytical results.Published in Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 8, pp. 959–987, August, 1996.One of the authors (Li) wishes to thank V.L. Ginzburg, E. Mjølhus, B. Thidé, N.S. Erokhin, J.Y. Liu, J.W. Lee, T.D. Carozzi, and J. Bergman for helpful oral discussions on this topic. Li also wants to thank M. Matsuoka for the kind hospitality during his year-long stay at RIKEN, where this work was completed.     

Excitation of wake-fields in an electron-positron plasma by an ultrarelativistic proton beam

The excitation of one-dimensional nonlinear relativistic wake-waves in an electron-positron plasma by an ultrarelativistic proton beam is discussed on the basis of a self-consistent analytical model. It is shown that in contrast to a common plasma with heavy ions these waves are have an oscillation character at any ratio of the beam density and that of the electron-positron plasma.     

Synthesis of an optimal radiometer with frequency filtering of the input signal

Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 3, pp. 247–253, March, 1991.     

The input impedance of the dielectric resonator antenna

Dielectric cylinders of very high permittivity have been used in the past as resonant cavities, but since the structure is not enclosed by metallic walls, electromagnetic fields do exist beyond the geometrical boundaries of the structure and part of the power is radiated. Through the proper choice of geometry and permittivity this radiation can become the dominant feature of the structure and become an efficient antenna for use at millimeter wave frequencies. Both experimental and theoretical investigations of a variety of these dielectric resonator antennas have been undertaken. In particular, the input impedance of a probe-fed cylindrical structure was examined in detail and a comparison of theoretical and experimental results was made.     

The phenomenon of stochastic resonance in a single-mode laser system with an input periodical signal

Using the linear approximation method, we study a single-mode laser system driven by colored pump noise and quantum noise with coupling between the real and imaginary parts when the laser is operated well above threshold. The steady state mean intensity fluctuation C(0) and signal-to-noise ratio (SNR) are calculated. It is found that there is a maximum in SNR when there is a minimum in the fluctuation of laser system if the coupling coefficient between real and imaginary parts of the quantum noise equals zero.     

A fluid model of the current-voltage characteristics of an electron emitting electrode immersed in a two electron temperature plasma

The current voltage characteristics of a negatively biased electron emitting electrode immersed in a two-electron temperature plasma are analyzed by a simple one dimensional fluid model. Based on the assumption that the electron density in the pre-sheath region obeys the Boltzmann law the Bohm criterion is derived in the form of a transcendental equation for the Mach number, which can have up to 3 solutions. According to these solutions the ion velocity at the sheath edge can be determined either by the hot or by the cool electron temperature. When it is determined by the cool electron temperature and the hot electron temperature is high enough the critical electron emission current from the collector can have a very pronounced local maximum and a minimum when regarded as a function of the electrode potential. Because of that the current voltage characteristics of the electrode may exhibit up to 3 different floating potentials. This result is in good agreement with the experimental observations reported in [J. Appl. Phys. 63, 5674 (1988)].     

Excitation of an optical satellite by thermal electron oscillations of a lithium plasma

An optical satellite excited by thermal electron plasma oscillations is observed near the 2P–3P forbidden line of a dense lithium plasma. The observations are compared with predictions of second order time-dependent Stark theory.