Excitation of Nonsymmetric Waves by Given Sources in a Magnetoplasma in the Presence of a Cylindrical Plasma Channel

We consider the problem of excitation of electromagnetic field by spatially bounded, arbitrary given sources in a magnetoplasma in the presence of a cylindrical plasma channel aligned with an external magnetic field. We obtain a rigorous solution for the total field comprising both the discrete and continuous parts of the spatial spectrum of excited waves. Expressions for the radiation pattern and total radiation power of given sources are analyzed. For the whistler range, we calculate the radiation power of a ring electric current located in a channel with enhanced plasma density. It is shown that in this range, the presence of such a channel can lead to a significant increase in the radiation power of ring currents as compared with the case where the considered sources are immersed in a uniform background magnetoplasma, regardless of their orientation.     

Nonsymmetric Whistler Waves Guided by Cylindrical Ducts with Enhanced Plasma Density

We study the guided propagation of whistler waves whose fields depend on the azimuthal angle in cylindrical plasma-waveguide channels (density ducts) aligned with an external magnetic field and surrounded by a uniform magnetoplasma. The main attention is paid to ducts with enhanced plasma density. It is shown that, under certain conditions, such ducts are capable of guiding proper (eigen) modes and improper leaky modes. We present the results of analysis of the dispersion properties and field structures of nonsymmetric modes guided by cylindrical ducts in the whistler frequency range.     

Whistler Wave Emission from a Modulated Electron Beam in a Collisional Magnetoplasma in the Presence of a Density Duct

We study the radiation from a modulated electron beam injected along the axis of a cylindrical density duct in a magnetoplasma. An expression for the average power lost by the beam at the modulation frequency is obtained and analyzed. It is shown that in the case of Cerenkov resonance of the beam with a weakly damped whistler mode of an enhanced-density duct, a noticeable increase in this power is possible compared with the case where the beam is injected in a homogeneous background magnetoplasma. Based on the results of numerical calculations performed for conditions of the Earth's ionosphere, we give estimates of an increase in the power radiated from the beam in the whistler frequency range in the presence of a cylindrical duct with enhanced density. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 9, pp. 730–742, September 2005.     

Wave emission from a VLF plasma-waveguide antenna system under ionospheric conditions

We study a VLF plasma-waveguide antenna system having the form of a field-aligned quasicylindrical enchancement of plasma density, which relaxes gradually to the background magnetoplasma with distance from the given source. A model enabling one to calculate both the total radiated power and the power distribution over the spatial spectrum of radiated waves is proposed. It is shown that this plasma antenna is useful for increasing the power going to the long-wave part of the spatial spectrum of whistler waves excited in the ambient plasma. Concrete estimates for terrestrial ionospheric conditions are given.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 2, pp. 210–225, February, 1996.The work of the first two authors was supported in part by the Russian Foundation for Fundamental Research (Project codes No. 95-02-05001 and No. 94-02-05447-a, respectively). The work of the third author (A. V. Kudrin) was supported by the Russian Foundation for Fundamental Research under Grant No. 96-02-18666.     

Whistler waves guided by ducts with enhanced density in a collisional magnetoplasma

We study the guided propagation of whistler waves along cylindrical ducts with enhanced density in a collisional magnetoplasma. It is shown that under certain conditions, the presence of comparatively small dissipative losses due to electron collisions in a plasma medium can lead to significant changes in the dispersion characteristics and field structures of whistler modes guided by such ducts compared with the case of a collisionless plasma. We present the results of numerical calculations showing such changes in the properties of whistler modes. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 1, pp. 31–49, January 2008.     

Propagation effects in the radio interferometry of polarized radiation: II. Fluctuations of polarized radiation in a random magnetoplasma

This paper analyses fourth-order moments of polarized radiation passing through magnetoactive plasma with random irregularities both in electron density and in magnetic field. We consider the new propagation effect arising from chiral properties of random magnetoplasma. That is, the lens formed by the same irregularities of magnetic field may be characterized by refractive properties of opposite sense vis-a-vis the rotation of the wave polarization vector. This produces an appearance of slight circular polarization fluctuations arising from initially nonpolarized radiation. Analysis of the polarized radiation fluctuations may allow the spatial spectrum of magnetic field irregularities to be detected. The enhanced level of the circularly polarized component, and the share of fluctuations owing to magnetic field irregularities, can be readily observed at low frequencies only, say, in the radiation passing through the solar chromosphere or the Jovian and terrestrial ionosphere, (magnetosphere).     

Radiation of whistler-band wares in magnetoactive plasma. II

The whistle-band radiation of the ring magnetic current in a magnetoactive plasma is studied. Principal attention is given to the dependence of the distribution of the radiated power over the space spectrum of the excited plane waves (whistlers conical-refraction waves, and plasma waves) on the radiator dimensions and the magnetic-field distribution over the ring. It is shown that most of the power radiated by ring magnetic currents in the examined frequency band goes into plasma waves, regardless of the radiator dimensions.Scientific-Research Radio-Physics Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35 No. 8, pp. 631–640, August, 1992.     

等离子体中相对论电子的同步曲率辐射特性研究

根据同步曲率辐射理论推导了在等离子体环境中,不同磁场条件下的相对论性电子的吸收系数和发射系数表达式，计算了电子的发射强度，并且在此基础上研究了同步曲率辐射机制的脉泽效应.研究了两种磁场位型，第一种是强度均匀但弯曲的磁场，第二种是偶极磁场，结果发现了一些偶极磁场下特有的辐射特性.考虑到在天体的环境下电子具有的不同的能谱分布，分别选用了三种典型的能谱分布(幂率分布，高斯分布，热分布)进行了研究，通过计算负吸收和脉泽放大效应在发射强度上的表现后， 发现在某些天体物理环境中，同步曲率辐射在等离子体中的确存在脉泽放大效应.这些研究结果对太阳系中行星外层辐射的研究和宇宙中的射电高亮温度等问题的研究可能提供有益的帮助. 关键词： 同步曲率辐射 负吸收 脉泽效应     

Alfvén waves in the electron-nuclear plasma in the peripheral crust of a neutron star as a residual effect of a supernova explosion

The conservation of magnetic flux in the evolution and collapse of massive stars suggests that Alfvén magnetoplasma oscillations can be excited in an isolated neutron star by residual (after the supernova explosion) disturbances of the magnetized electron-nuclear plasma localized in the peripheral crust of the star. The frequencies of the poloidal Alfvén oscillations are calculated in the uniform magnetic field approximation, and it is found that the periods of the oscillations fall into the time interval of the periodicity of radio pulsar radiation. This coincidence of the periods could mean that, at least for some pulsars observed in the radio range, the electromagnetic activity is due to converstion of the energy of magnetoplasma oscillations into electromagnetic radiation. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 9, 593–598 (10 November 1996)     

A model for steady-state large-volume plasma generation

A simple scheme for generating a uniform, steady-state, large-volume plasma is presented. The weakly magnetized plasma is created by direct ionization of the background gas by low-energy electrons generated from thermionic filaments. An annular arrangement of the filaments ensures a uniform plasma density in the radial direction as predicted by theory. Experiments have been performed to characterize the plasma generated in such a configuration. In order to explain the experimental observation, a bulk plasma theory based on plasma transport by means of cross-field diffusion is developed. As assumed in the theoretical model, the experimental measurements indicate a uniform plasma density along the axis. Both the theory and experiment indicate that the plasma density is a function of the square of the external magnetic field. The theory also predicts the plasma density to be proportional to the neutral density to the two-thirds power, in agreement with the experimental data. The experimental data agree well with theoretical prediction for a broad range of system parameters     

有限磁场作用下填充环形等离子体波导中功率流密度的计算

 在考虑有限磁场的作用下,得到了填充等离子体的圆柱光滑波导中各场分量的表达式,然后导出了功率流密度的计算式。通过计算得出等离子体的密度和厚度对功率流密度有极大的影响,并分析了其机理。     

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在HL-2A装置孔栏位形放电的等离子体实验中,电子回旋辅助加热期间观察到了等离子体约束改善的现象,并对等离子体从低约束模式(L模)向约束改善模式转换时的等离子体线平均电子密度、等离子体储能、分界面内辐射功率、能量约束时间、Hα辐射等进行了研究。同时,分析了电子密度和等离子体辐射功率的空间分布随时间的演化。对改善约束的相关功率(辅助加热、欧姆加热功率和损失功率)进行了分析,并研究了等离子体约束改善转换时的边界净输入功率(阈值)与电子线平均密度和环向磁场的关系。     

Radiated power of oscillators traveling in a moving medium

We consider the radiation from oscillating electric and magnetic dipoles moving with constant velocity directed parallel or antiparallel to the velocity of the surrounding medium. It is assumed that the medium in its rest frame is isotropic and has no spatial dispersion. We obtain expressions for the spectral density of the radiated power. In the case of a nondispersive medium, algebraic expressions for the total radiated power in the regime of “subluminal relative motion” are also obtained. In particular, it is shown that the energy loss of a source is negative if it moves in the direction of the superluminal motion of the medium and the source velocity is somewhat smaller than the medium velocity. It is noted that this phenomenon takes place for a smaller difference between the velocities of the source and the medium compared with a similar phenomenon for nonoscillating sources. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 4, pp. 316–328, May 2007.     

HL-2A装置的约束改善和边界净输入功率分析

在HL-2A装置孔栏位形放电的等离子体实验中,电子回旋辅助加热期间观察到了等离子体约束改善的现象,并对等离子体从低约束模式(L模)向约束改善模式转换时的等离子体线平均电子密度、等离子体储能、分界面内辐射功率、能量约束时间、H_α辐射等进行了研究。同时,分析了电子密度和等离子体辐射功率的空间分布随时间的演化。对改善约束的相关功率(辅助加热、欧姆加热功率和损失功率)进行了分析,并研究了等离子体约束改善转换时的边界净输入功率(阈值)与电子线平均密度和环向磁场的关系。     

Enhanced sound transmission from water to air at low frequencies

Excitation of acoustic radiation into the air from a low-frequency point source under water is investigated using plane wave expansion of the source spectrum and Rayleigh reflection/transmission coefficients. Expressions are derived for the acoustic power radiated into air and water as a function of source depth and given to lowest order in the air/water density ratio. Near zero source depth, the radiation into the water is quenched by the source's acoustic image, while the power radiated into air reaches about 1% of the power that would be radiated into unbounded water.     

Sound radiation from point sources in circular motion

The moving-source approach used by Morfey and Tanna for broad-band sound radiation from a point force in circular motion is adopted in this paper to evaluate the sound radiated in the far field due to point sources of random time variation rotating uniformly in a circle at subsonic speed. It is shown that the sound pressure results (overall and spectral density) for the volume velocity source can be easily extracted from the corresponding results for a rotating point force. An expression for the sound field of a point volume displacement source in arbitrary motion is derived and this is applied to the special case of uniform circular motion. The effects of acceleration of the sources due to circular motion on the radiated sound are established. Applications include noise from tip jet rotors, compressors and marine propellers.     

Transformation of the Angular Power Spectrum of Scattered Radiation in a Turbulent Absorbing Magnetoactive Plasma

We consider the oblique incidence of a small-amplitude plane electromagnetic wave on a layer of turbulent absorbing plasma in a uniform external magnetic field. The equations for the first two statistical moments of the angular power spectrum of scattered radiation are derived in the geometrical-optics approximation. We show that two asymmetry factors of the problem, i.e., the oblique incidence and the influence of the anisotropic medium, compensate for each other along a certain direction and impede the appearance of the effect of displacement of the power-spectrum maximum and the effect of anomalous spectrum broadening. We find the condition at which such a case of wave propagation is realized. The dependence of the angular-spectrum shape on the distance from the plasma-layer boundary is studied numerically without using the small-angle approximation. The calculations confirm the results obtained using the geometrical-optics approximation.     

Experimental results of helicon sources

Helicon plasma sources are known as efficient generators of uniform and high density plasma.A helicon plasma source was developed for the investigation of plasma stripping and plasma lenses at the Institute of Modern Physics, CAS.In this paper, the characteristics of helicon plasma have been studied by using a Langmuir four-probe and a high plasma density up to 3.9×10~(13)/cm~3 has been achieved with the Nagoya type Ⅲ antenna.In the experiment, several important phenomena were found: (1) for a given magnetic induction intensity, the plasma density became greater with the increase of RF power; (2) helicon mode appeared at RF power between 300 W and 400 W; (3) the plasma density gradually tended to saturation as the RF power increased to the higher power; (4) a higher plasma density can be obtained by a good match between the RF power and the magnetic field distribution.The key issue is how to optimize the matching between the RF power and the magnetic field.Moreover, some tests on the extraction of ion beams were performed, and preliminary results are given.The problems which existed in the helicon ion source will be discussed and the increase in beam density will be expected by extraction system optimum.     

Resonant transition radiation in plamsa with magnetic inhomogeneities

We calculate the spectrum of the resonant transition radiation generated by a fast charged particle moving in plasma with small-scale random magnetic inhomogeneities. We determine the conditions under which this type of transition radiation dominates over the transition radiation on plasma density inhomogeneities. We discuss possible applications of the resonant transition radiation in astrophysical and geophysical conditions.