Generation of Extra-Ordinary Mode Radiation by an Electrostatic Pump in a Two-Electron-Temperature Plasma

Coherent wave-wave coupling can produce radiation with a high efficiency. Recently, there has been a great deal of interest in the study of electro-magnetic wave generation in magnetized plasmas. We have investigated theoretically the effect of finite ion temperature on the parametric instability of an electro-static upperhybrid pump into an X-mode nonthermal radiation and low frequency ion waves in a two electron temperature plasma. The latter may include the lower-hybrid, the electron-acoustic and the ion-cyclotron waves. The loss cone distribution existing permanently at low altitudes acts as a free energy source generating the upper-hybrid waves. The upper-hybrid waves can also be present because of a linear instability produced by runaway electrons. Nonlinear dispersion relation and the growth rates are derived for each case using the hydrodynamical model. We find extra numerical factor arising due to the ions of finite temperature in the growth rate expression. This study may be useful in magnetosphere, auroral ionosphere, solar wind, solar radio bursts, and laboratory plasmas where ion has finite temperature and electrons have two distinct energy distributions.     

Low-Frequency Radiation from an Axisymmetric Current in an Ionospheric Plasma

We consider the radiation of low-frequency electromagnetic waves from an axisymmetric current and propagation of these waves in a homogeneous ionospheric plasma with Hall and Pedersen conductivities. We obtain an analytical expressions for the fields excited by pulsed radial and ring currents. It is shown that electromagnetic radiation propagates as a wave inside a cone along the magnetic field. The field propagation outside the cone is described by a diffusion law. The spatio-temporal characteristics of the signal are determined by the ionospheric conductivities.     

Measurement of Landau damping and the evolution to a BGK equilibrium

Linear Landau damping and nonlinear wave-particle trapping oscillations are observed with standing plasma waves in a trapped pure electron plasma. For low wave amplitudes, the measured linear damping rate agrees quantitatively with linear Landau damping theory. At larger amplitudes, the wave initially damps at the Landau rate, then regrows and oscillates, approaching a steady state, as predicted by O'Neil in 1965 [Phys. Fluids 8, 2255 (1965)]]. This BGK equilibrium is observed to decay slowly due to external dissipation.     

Radiation of a charge moving over the diffraction grating

The states of a charged particle with a finite free path are determined in the field of a resonant electromagnetic wave. The exact resonance conditions, the modulation and beam instability mechanisms, the charge and current densities (Ohm's law) are obtained for the collisionless beam of resonance particles. Quantum theory of radiation is developed for the resonant adiabatic interaction between a particle and a wave taking into account the interaction with a constant magnetic field induced at the grating surface by the charge and nonresonant waves. The radiation power, the spectrum, and the range of generated frequencies are determined. The results obtained can be used in the plasma and solid-state theories and in electronics.     

Characterization and Suppression Techniques for Degree of Radiation Damping in Inversion Recovery Measurements

Radiation damping is a phenomenon in which transverse nuclear magnetization couples with the current in a coil used in nuclear magnetic resonance experiments. This results in an additional magnetic field that increases the relaxation pathway for the magnetization, which then relaxes back to equilibrium more quickly. Radiation damping has been shown to affect longitudinal relaxation time (T₁) measurement in inversion recovery experiments. In this work, we demonstrate that the extent of radiation damping depends upon the T₁ of the sample. Radiation damping difference spectroscopy is used to characterize the severity of radiation damping, while gradient inversion recovery is used for radiation damping suppression in T₁ measurements. At field strength of 9.4 T, for the radiation damping characteristic time (T_rd) of 50 ms, these investigations show non-negligible radiation damping effects for T₁ values greater than T_rd, with severe distortions for T₁ longer than about 150 ms, showing reasonable agreement with the predicted T_rd. We also report a discrepancy between published expressions for the characteristic radiation damping time.     

Trapped-particle instability leading to bursting in stimulated Raman scattering simulations

Nonlinear, kinetic simulations of stimulated Raman scattering (SRS) under laser-fusion conditions present a bursting behavior. Different explanations for this regime have been given in previous studies: saturation of SRS by increased nonlinear Landau damping [K. Estabrook et al., Phys. Fluids B 1, 1282 (1989)]], and detuning due to the nonlinear frequency shift of the plasma wave [H. X. Vu et al., Phys. Rev. Lett. 86, 4306 (2001)]]. Another mechanism, also assigning a key role to the trapped electrons is proposed here: the breakup of the plasma wave through the trapped-particle instability.     

典型甚低频电磁波对辐射带高能电子的散射损失效应

辐射带中高能电子与空间甚低频电磁波由于波粒共振相互作用发生投掷角散射, 进而沉降入稠密大气而损失. 为研究甚低频电磁波对辐射带中高能电子的散射作用机制, 本文基于准线性扩散理论, 利用库仑作用和波粒共振相互作用扩散系数的物理模型, 得到了两组典型甚低频电磁波与高能电子波粒共振相互作用的赤道投掷角弹跳周期平均扩散系数, 并分析了甚低频电磁波共振散射作用与大气库仑散射作用对不同磁壳及不同能量的辐射带电子扩散损失的影响规律. 以磁壳参数L=2.2, 能量E=0.5 MeV的辐射带电子作为算例, 采用有限差分方法数值求解扩散方程, 计算分析了电子单向通量和全向通量随时间的沉降损失演化规律. 研究结果表明: 当电子能量大于0.5 MeV, 磁壳参数大于1.6时, 甚低频电磁波的共振散射作用显著; 随着磁壳参数或电子能量的增大, 斜传播甚低频电磁波引起的高阶共振相互作用越来越大; 电子全向通量近似随时间呈指数函数形式衰减.     

Radiation from an Electric Dipole Surrounded by a Plasma Cylinder with a Cavity

We solve the problem of the influence of a small-radius (ka1) isotropic plasma cylinder with a coaxial free-space cavity on the radiation from a source of electromagnetic waves to an outer region of free space. Conditions of the resonance radiation are obtained and characteristics of this radiation as functions of the relative size of the cavity are studied. We show that the resonance frequency splits into two frequencies such that the transmission coefficients at these frequencies can exceed the resonance transmission coefficient for the plasma cylinder without a cavity. The results obtained are compared with the case of emission from a two-layer spherical plasma resonator.     

Controlled Space Radiation concept for mesh-free semi-analytical technique to model wave fields in complex geometries

Numerical modelling of the ultrasonic wave propagation is important for Structural Heath Monitoring and System Prognosis problems. In order to develop intelligent and adaptive structures with embedded damage detector and classifier mechanisms, detailed understanding of scattered wave fields due to anomaly in the structure is inevitably required. A detailed understanding of the problem demands a good modelling of the wave propagation in the problem geometry in virtual form. Therefore, efficient analytical, semi-analytical or numerical modelling techniques are required. In recent years a semi-analytical mesh-free technique called Distributed Point Source Method (DPSM) is being used for modelling various ultrasonic, electrostatic and electromagnetic wave field problems. In the conventional DPSM approach point sources are placed along the transducer faces, problem boundaries and interfaces to model incident and scattered fields. Every point source emits energy in all directions uniformly. Source strengths of these 360° radiation sources are obtained by satisfying interface and boundary conditions of the problem. In conventional DPSM modelling approach it is assumed that the shadow zone does not require any special consideration. 360° Radiation point sources should be capable of properly modelling shadow zones because all boundary and interface conditions are satisfied. In this paper it is investigated how good this assumption is by introducing the ‘shadow zone’ concept at the point source level and comparing the results generated by the conventional DPSM and by this modified approach where the conventional 360° radiation point sources are replaced by the Controlled Space Radiation (CSR) sources.     

静电电子回旋脉塞与静电自由电子激光

笔者提出了静电电子回旋脉塞的概念,并在三位博士生的共同努力下,建立了静电电子回旋脉塞的线性及非线性理论。接着,笔者又提出利用静电回旋系统建立静电自由电子激光的概念(此种静电自由电子激光目前在国际上简称为Orbitron自由电子激光),随即又建立了这种自由电子激光的线性理论并进行了数值计算。 陈晓东、欧阳征标和硕士生徐晓曦在他们的学位论文中,完成了静电电子回旋脉塞机理的实验论证工作。实验结果和理论计算较好地相符。 上述一系列的工作均已得到国际的公认。本文就是这一系列工作的基本总结。     

短圆管换能器辐射阻抗

辐射阻抗是换能器最重要的辐射声场特性参数之一,影响着换能器的谐振频率、频带宽度、效率以及辐射声功率等.随着圆管换能器半径和高度的不断变化,想直接得到声场瑞利积分的解析解是十分困难的.该文通过建立经验公式模型来解决此问题.首先,通过有限元软件计算圆管换能器辐射阻抗的数值解.然后利用MATLAB工具进行曲线拟合.经过反复逼...     

Radiation response behaviour of Al codoped germano-silicate SM fiber at high radiation dose

Radiation response behaviour of Ge + Al doped SM fiber fabricated by the solution doping process has been studied at room temperature with respect to 1310 nm transmission wavelength under three different dose rates of 200, 400 and 600 Rad/min to compare with that of standard Er doped as well as Ge doped SM fibers. Their radiation sensitivity has been observed with variation of dose rates, transmission wavelength along with their recovery nature. Radiation response behaviour of Al doped SM fiber is found to be slightly non-linear in nature with very low dose rate dependency. No saturation level was found upto 13 Krad cumulative dose. Thermobleaching as well as photobleaching phenomena have also been studied. Gamma irradiated Al doped preform shows an absorption peak at around 300 nm due to generation of Al (E′) defect center and gets annihilated after thermobleaching process. Gamma irradiated Al doped SM fiber shows prominent photobleaching effect on their optical attenuation with respect to the 850 nm transmission wavelength. From ESR study resonance signals for Al³⁺ related radiation-induced defect centers are not clearly observed in this study. A very weak hyperfine pattern has been observed for gamma irradiated Al doped preform sample. The high radiation sensitivity along with linear response behaviour, low recovery and almost dose rate independence behaviour of the material system of Ge + Al codoped SM core optical fiber under gamma radiation shows their potential for application as fiber optic radiation sensor in comparison to the universal standard erbium doped SM fiber.     

宽带微波馈入对于具有常规磁场构型的ECR离子源性能的提高

As clearly demonstrated at several laboratories,the performances of electron-cyclotron resonance (ECR)ion sources can be enhanced by increasing the physical sizes(volumes)of embedded ECR zones.En- larged ECR zones have been achieved by engineering the central magnetic field region of these sources so they are uniformly-distributed"volumes"in resonance with single-frequency rf power.Alternatively,the number of ECR surfaces in conventional minimum-B geometry sources can be increased by heating their plasmas with multiple,discrete frequency microwave radiation.Broadband rf power offers a simple,low cost and arguably more effective means for increasing the physical sizes of the ECR zones within the latter source type.In this article,theoretical arguments are made in support of the volume effect and the charge-state enhancing ef- fects of broadband microwave radiation(bandwidth:200MHz)plasma heating are demonstrated by comparing the high-charge-states of Ar ion beams,produced by powering a conventional minimum-B geometry,6.4GHz ECR ion source,equipped with a biased disk,with those produced by conventional bandwidth(bandwidth:～1.5MHz)radiation.     

Radiation from a spherically distributed,rotating charge

Radiation emission from a spherically distributed charge, undergoing simultaneously translational and rotational motion, is studied. The angular velocity is assumed to be proportional to the translational velocity of the center of mass. It is shown that in this case the spectral-angular distribution of the radiation can be represented as a product of the spectralangular distribution of the radiation of a point charge by the form factor, which depends on the method employed to distribute the charge and take into account its intrinsic rotation. As an example, synchrotron radiation from a rotating charge distributed over a sphere is investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 36–39, September, 1991.In conclusion it is the authors' pleasant duty to thank Professor V. G. Bagrov for his interest in this work and for helpful discussions.     

A Possible Dusty Microplasma Source of Mid-Infrared Radiation

Microplasmas have been discussed as novel sources of photons in the ultraviolet to infrared (IR). Recently, the addition of dust to a microplasma has been discussed in various contexts. In this paper, we theoretically investigate thermal radiation from heated dust in microplasmas to explore dusty microplasmas as possible sources of mid-IR (MIR) radiation. We consider grains that are selective absorbers (and, thus, selective emitters) in the MIR. Heating of the dust by impinging plasma and cooling of the dust by conduction and thermal radiation are studied for a range of plasma parameters and dust sizes. Possible applications of such sources may include spectroscopy since many gases absorb strongly in the MIR.      

无障板圆形活塞换能器的辐射阻抗*

辐射阻抗是换能器的最重要辐射声场特性参数之一,影响着换能器的谐振频率、频带宽度、效率以及辐射声功率等。经典声学理论用一阶贝塞尔函数和斯特鲁夫函数给出了圆形活塞换能器辐射阻抗的数学表达式,但仅适用于无限大障板条件。该文用ANSYS有限元软件计算了无障板圆形活塞换能器的辐射阻抗,给出了数值解结果,通过与无限大障板条件下的理论结果相比较,显示了二者之间的偏离情况,尤其是在低频时差异显著。为了借助MATLAB工具模拟无障板圆形活塞换能器的辐射阻抗,并给出较准确的数学表达,选择了一系列初等函数以及它们的复合函数进行曲线拟合,最终给出了辐射阻和辐射抗关于ka的函数表达式,在ka值从0.08到20范围内与有限元计算结果很好吻合。     

Angular scattering diagrams of linearly polarized relativistic-intensity electromagnetic radiation in a plasma

Instability of the propagation of nonlinear nonmonochromatic relativistic-intensity electromagnetic waves in a cold subcritical-density plasma is analyzed in three-dimensional geometry. Angular diagrams of their scattering are presented. The calculations show that forward and backward scattering may occur. The radiation in a specific direction is a set of harmonics, propagating against a continuum background, whose frequencies depend on the angle. Radiation at a specific frequency propagates in a set of scattering cones. The azimuthal cone angles depend on frequency. Zh. éksp. Teor. Fiz. 116, 1947–1962 (December 1999)     

Theoretical Analysis of the Resonance Cone in an Inhomogeneous Magnetoplasma Column

The three-dimensional behavior of the high-frequency resonance cone is investigated using an inhomogeneous slab magnetoplasma model under the quasi-static approximation and neglecting ion motion. The effects of finite ky and electron thermal motion are considered numerically, revealing that the cone angle is shifted to a slightly smaller angle and the reflection point is also shifted toward the high density region compared with results under the cold plasma approximation.     

Kadomtsev-Petviashvili (KP) Burgers equation in a dusty plasmas with non-adiabatic dust charge fluctuation by J.-K. Xue

Eur. Phys. J. D 26, 211 (2003) We hereby present several comments on reference [1]: for this model, we present the travelling shock-wave solutions different from that of reference [1], an auto-Bäcklund transformation, and several two-dimensional and non-travelling-wave possibly-observable effects for the future space and laboratory plasma experiments.Received: 23 November 2003, Published online: 20 April 2004PACS: 52.35.Sb Solitons; BGK modes - 52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)     

Trinal Nature of the Excitation of Bulk Plasmons by a Fast Charged Particle at Grazing Incidence on the Interface between Vacuum and a Metal with Strong Spatial Dispersion

The excitation and propagation of bulk and surface (surface waves of transition radiation of plasmons at frequencies above the plasma frequency) plasma waves by incident electrons moving both in vacuum toward the surface of a metal and inside the metal whose boundary elastically and spectacularly reflects internal nonequilibrium electrons have been analyzed. In contrast to work [B. N. Libenson, J. Exp. Theor. Phys. 113, 553 (2011)], attention in this work is focused on the influence of surface effects on bulk-plasmon excitation by incident electrons. The probabilities and spectra of single characteristic energy loss of an intermediate- energy electron (50–500 eV) moving at an angle to the surface of the medium in three regions: in vacuum, in the medium, and again in vacuum after the electron leaves the medium are calculated. The kinetic approximation is used for the dielectric function, where the entire range of the plasmon spectrum is taken into account correctly for the problem under consideration. In the indicated energy range of incident electrons, surface effects, on the one hand, significantly reduces the probability of excitation of bulk plasma waves in the medium with strong spatial dispersion, in particular, as compared to the results obtained in [B.N. Libenson, J. Exp. Theor. Phys. 113, 553 (2011)], where surface effects were disregarded and the probability of bulkplasmon excitation by a 200-eV electron incident and emitted perpendicularly to the boundary is about one third of that in the unbounded medium. On the other hand, at grazing incidence from vacuum, the probability of transition radiation of bulk plasmons increases significantly and can lead to a change in the character of the angular dependence of the intensity of bulk plasma energy loss. Thus, the main result of this work is that a decrease in the glancing angle of the fast electron with respect to the vacuum–metal interface is accompanied both by an increase in the contribution from the transition mechanism to the probability of bulk-plasmon excitation in the vacuum region and by a decrease in the contribution from Cherenkov and bremsstrahlung mechanisms of excitation in the medium. The probability of bulk-plasmon excitation in the vacuum region exceeds the probability of excitation at the further motion of the electron in metallic aluminum at angles of incidence larger than 65°, 70°, and 75° at the energies E = 200, 350, and 500 eV, respectively.