Resonant Joule phenomena in a magnetoplasma

The present state of research of resonant Joule interactions of collisional plasmas with electromagnetic waves, including both the problems of plasma heating and wave dynamics, is reviewed. The controlled development of non-linear wave processes in gaseous and solid-body plasmas in radiowave and microwave ranges via resonant heating is discussed. The series of thermal bistability effects, produced by electron-temperature hysteresis near Langmuir and cyclotron resonances, is considered. The geometrical resonances of absorption in layered structures and bounded volumes are illustrated. Localization of dissipation phenomena near resonant regions in heterogeneous and anisotropic magnetoplasmas is analyzed. Relativistic and quantum effects in resonant collisional attenuation of waves in a plasma are shown. Some analogous tendencies in Joule wave phenomena are marked in plasmas characterized by very different physical conditions-from laboratory devices up to cosmic objects.     

Effect of Joule heating on the electroosmotic microvortex and dielectrophoretic particle separation controlled by local electric field

Dielectrophoresis (DEP) technology has become important application of microfluidic technology to manipulate particles. By using a local modulating electric field to control the combination of electroosmotic microvortices and DEP, our group proposed a device using a direct current (DC) electric field to achieve continuous particle separation. In this paper, the influence of the Joule heating effect on the continuous separation of particles is analyzed. Results show that the Joule heating effect is caused by the local electric field, and the Joule heating effect caused by adjusting the modulating voltage is more significant than that by driving voltage. Moreover, a non-uniform temperature distribution exists in the channel due to the Joule heating effect, and the temperature is the highest at the midpoint of the modulating electrodes. The channel flux can be enhanced, and the enhancement of both the channel flux and temperature is more obvious for a stronger Joule heating effect. In addition, the ability of the vortices to trap particles is enhanced since a larger DEP force is exerted on the particles with the Joule heating effect; and the ability of the vortex to capture particles is stronger with a stronger Joule heating effect. The separation efficiency can also be increased because perfect separation is achieved at a higher channel flux. Parameter optimization of the separation device, such as the convective heat transfer coefficient of the channel wall, the length of modulating electrode, and the width of the channel, is performed.     

一级相变磁制冷材料的基础问题探究

由于一级相变磁制冷材料发生磁相变时有晶胞体积的突变,相变过程中有相变潜热存在,其磁化过程中有许多磁学问题有待于进一步探究.本文以LaFe13-xSix合金为研究对象,在现有对磁一级相变基础问题的分析基础上,对一级相变材料中系统熵变、等温熵变、绝热温变、热滞、磁滞、铁磁与顺磁态两相共存的温度区间和磁场区间、制冷能力的计算等磁学基础问题进行了较为细致的探究.分析表明,在忽略完全铁磁态和顺磁态对磁热效应的贡献时,Maxwell方程和Clausius-Clapeyron方程计算熵变的值具有等效性.等温磁化过程中升温和降温曲线包围的面积SABCE(磁滞的大小),实际上是升温过程和降温过程中磁场做的净功,等于相变潜热之差.磁滞和热滞的大小与磁化过程数据测量的时间有关,测量时间越长则滞后越小,当相变是平衡相变则滞后为零.另外,对温度和磁场诱导磁相变过程进行了分析,提出了一级相变磁制冷材料制冷能力的不同计算模型.本文对一级相变磁制冷材料的磁学基础问题研究有一定的参考价值.     

Nonlinear Electrostatic Ion‐Acoustic Waves in the Solar Atmosphere

Basing on recent solar models, the excitation of ion‐acoustic turbulence in the weakly‐collisional, fully and partially‐ionized regions of the solar atmosphere is investigated. Within the frame of hydrodynamics, conditions are found under which the heating of the plasma by ion‐acoustic type waves is more effective than the Joule heating. Taking into account wave and Joule heating effects, a nonlinear differential equation is derived, which describes the evolution of nonlinear ion‐acoustic waves in the collisional plasma.     

基于MULTI2D-Z程序的Z箍缩动态黑腔形成过程模拟

对辐射流体力学程序MULTI-2D进行改造,增加磁场演化方程程序模块,自洽地在运动方程模块中增加洛伦兹力,在能量方程模块中增加欧姆加热,将它改造成辐射磁流体力学程序MULTI2D-Z.验证了新增磁场程序模块的可靠性,并发现温度和密度的增大会抑制磁场的扩散,负径向速度梯度的流体对流也会抑制磁场的扩散.利用改造好的MULTI2D-Z程序模拟了峰值为8 MA的脉冲电流驱动的钨丝阵Z箍缩动态黑腔形成过程.得到了X光功率(约30 TW)和能量(约300 k J)、泡沫辐射温度(约120 eV)、箍缩轨迹等模拟结果.在动态黑腔形成过程中,磁场主要分布在钨主体等离子体中;辐射向内传播,烧蚀泡沫柱而使它膨胀;辐射热波在被撞击的泡沫柱中传播,其传播速度比物质温度传播得快,当辐射热波传播到中心轴时泡沫柱中的辐射场变得比较均匀,并且除了冲击波处外辐射温度与物质温度基本上没有分离.这些模拟结果可增强人们对磁场扩散和对流规律以及动态黑腔形成机制的理解,同时表明了MULTI2D-Z程序可成为Z箍缩及其应用的新的程序模拟工具.     

The nonlinear optical properties of nanotubes with spiral defects in a longitudinal magnetic field

It is demonstrated that the anisotropic transfer of photon momentum to an electronic subsystem results in induction of a photon-drag EMF in a standing electromagnetic wave along the axis of a nanotube with a spiral defect, which confirms the assumption found in the literature that the occurrence of such an effect in the presence of an external magnetic field is possible not only in 2-D systems but also in nanotubes with a spiral symmetry. One of the potential mechanisms of inducing the EMF connected with the spatial asymmetry of the electron-phonon interaction in a nanotube with a spiral defect is considered. This mechanism allows for such an EMF to occur upon heating the electron system by the Joule heat of the photon-drag current that flows through the nanotube.     

Stationary structure of a high-frequency discharge maintained by a distributed electromagnetic source in the presence of an external magnetic field

The stationary structure of an axisymmetric high-frequency discharge maintained by a given source in an external dc magnetic field is investigated. The source is assumed to be a current wave that travels over the discharge tube surface in the direction of the external magnetic field. The source current has a single azimuthal component and its frequency belongs to the lower hybrid range. The main emphasis is placed on the special case where the electron heat conduction length across the external magnetic field exceeds considerably the tube radius. The dependences of discharge plasma parameters on the current amplitude and propagation constant along the tube have been found for this case. The results of numerical calculations of the distributions of the field and the power of the Joule loss in a discharge are presented.     

Application of vacuum arc cathode spot model to graphite cathode

A model of near-electrode processes is applied here to describe the behavior of cathode spots on graphite cathode in vacuum arc. The physical model is based on a kinetic treatment of cathode evaporation, electron emission from the cathode, and plasma production. The model consists of physical assumptions and a system of equations that are formulated in the paper. Spot parameters, such as cathode erosion rate, cathode potential drop, cathode surface temperature, current density, electric field, and plasma density, temperature, and velocity in the near-electrode region are calculated numerically. The calculation includes the dependence of spot parameters on spot current and spot lifetime. The variation of spot parameters as a function of spot lifetime are very strong at lifetimes shorter than 10 μs. The calculations indicate that Joule heating in the cathode body is significant, and may exceed cathode heating by the ion heat flux. Calculated spot parameters are compared with the corresponding experimental data for relatively low arc currents (<100 A) and their agreement is discussed     

Internal dynamics of a plasma propelled across a magnetic field

When a plasma is pushed across a magnetic field by some nonelectromagnetic force, ions and electrons get turned in opposite directions by the magnetic field. This creates an internal current as well as sheaths at the plasma surfaces and results in an electric field which allows the plasma to maintain some, or even most of its initial momentum in the form of E&oarr;×B&oarr; drift. An exact analysis of that process is presented for the internal region of the plasma. The energy provided by the initial push is used, in part, to create some gyrations inside the plasma. When the rest energy density of the plasma exceeds twice the magnetic energy density (or when the Alfven speed is less than c), there will be enough energy to spare for the plasma to continue across the magnetic field at half its initial momentum. Two cases are considered: an impulsive start and a gentle push such as provided by gravity. The amplitude of the resulting internal gyrations becomes small in the second case. The frequencies of the gyrations are those of extraordinary modes of very long spatial wavelength     

Observation of Localized Electron Cyclotron Resonance Heating in a Magnetic Mirror

A right-hand circularly polarized (RHCP) electron cyclotron wave is launched along the axis of a steady-state magnetically confined plasma column. Detailed measurements of the spatial variation of electron temperature, density, plasma potential, and wave amplitude about the resonance zone are presented. In particular, data are presented where the temperature increase due to electron cyclotron resonance heating (ECRH) is strongly localized near the resonance position. A numerical wave heating model has been developed for electrons in a magnetic mirror and is found to be in qualitative agreement with observations.     

高通鸟笼线圈激发螺旋波等离子体特性研究

研制了高通鸟笼线圈,使用氩气作为工质气体对射频天线的工作性能进行了初步评估。利用COMSOL5.4模拟出了鸟笼天线在13.56MHz的工作频率下,电场和磁场呈线性极化分布。对鸟笼线圈进行了电路结构解剖,推导出了其谐振频率计算公式。利用热耦合红外测温仪测试了正常工作状态下的鸟笼线圈外表温度明显低于传统射频天线,电容器最高温度仅65.8°。使用光谱仪对螺旋波等离子体放电光谱特性进行诊断。通过朗缪尔探针诊断了不同压强和磁场强度下螺旋波等离子体密度,在1.0Pa、600Gs、射频功率700W条件下等离子体密度达到1.62×10¹⁸m^-3。诊断了正向功率和反向功率对应的等离子体密度,其与磁滞现象变化趋势雷同。测试了螺旋波等离子体的径向密度分布,其在轴心处密度达到最高。探究了无磁场条件下等离子体特性,其密度值不会发生大幅度跃迁,纵向磁场是引发螺旋波等离子体放电的关键因素,低压条件下有利于得到更低的电子温度,最低达到2.67eV。表明鸟笼线圈低热耗、高馈入的特性使其在激发大体积的高密度螺旋波等离子体方面具有明显优势,可以投入到下一阶段氢气螺旋波等离子体的激...     

Infrared thermography based defect detection in ferromagnetic specimens using a low frequency alternating magnetic field

A new active infrared thermography based technique is proposed for defect detection in ferromagnetic specimens using a low frequency alternating magnetic field induced heating. The test specimens (four mild steel specimens with artificial rectangular slots of 8.0, 5.0, 3.3 and 3.0 mm depths) are magnetized using a low frequency alternating magnetic field and by using an infrared camera, the surface temperature is remotely monitored in real time. An alternating magnetic field induces an eddy current in the specimen which increases the specimen temperature due to the Joule’s heating. The experimental results show a thermal contrast in the defective region that decays exponentially with the defect depth. The observed thermal contrast is attributed to the reduction in induction heating due to the leakage of magnetic flux caused by magnetic permeability gradient in the defective region. The proposed technique is suitable for rapid non-contact wide area inspection of ferromagnetic materials and offers several advantages over the conventional active thermography techniques like fast direct heating, no frequency optimization, no dependence on the surface absorption coefficient and penetration depth.     

Parametric Instability of Surface Waves on the Second Harmonic of Electron Cyclotron Frequency in a Plasma Layer

The parametric instability of surface waves on the second harmonic of electron cyclotron frequency (SWCF) in a plasma filled dielectric wave guide is examined in a kinetic approximation. The studied surface waves are extraordinary polarized modes and propagate across the external steady magnetic field. The amplitude of the electrical pump wave is assumed to be small. Simple expressions for increments of the parametric instability of the SWCF are calculated. The otained results can be used in controlled fusion researches in order to avoid undesirable regimes of plasma periphery heating in that fusion devices which use the resonance electron cyclotron heating method.     

Toroidal Effect on Lower Hybrid Current Drive in Tokamak

In the review paper of N. J. Fish, the topics concerning the basic theory of lower hybrid wave heating and current drive are presented. In the consideration of radio-frequency heating and current drive of tokamak plasma near the lower hybrid frequency, the parallel wave length is imposed by the coupling device parallel to the magnetic field and is modified by gradients along the field. The important effects are found on wave penetration and damping when the toroidal aspect ratio is low. It may be possible to change the plasma current via electron Landau damping with a coupler rf power spectrum.     

Anisotropic ion heating and tail generation during tearing mode magnetic reconnection in a high-temperature plasma

Complementary measurements of ion energy distributions in a magnetically confined high-temperature plasma show that magnetic reconnection results in both anisotropic ion heating and the generation of suprathermal ions. The anisotropy, observed in the C(+6) impurity ions, is such that the temperature perpendicular to the magnetic field is larger than the temperature parallel to the magnetic field. The suprathermal tail appears in the majority ion distribution and is well described by a power law to energies 10 times the thermal energy. These observations may offer insight into the energization process.     

Z箍缩动态黑腔形成过程MULTI程序一维数值模拟

Z箍缩动态黑腔能够高效地将Z箍缩丝阵等离子体动能转换为黑腔辐射能,为驱动惯性约束靶丸聚变提供高品质的X射线辐射场.利用一维双温多群辐射磁流体力学程序MULTI-IFE,研究了"聚龙一号"装置驱动电流条件下的Z箍缩动态黑腔形成基本物理过程.数值模拟结果表明,在动态黑腔形成过程中,辐射热波的传播速度比冲击波的传播速度更快,比冲击波更早到达泡沫中心,使中心区域的泡沫在冲击波到达前就已具有较高的辐射温度.对于"聚龙一号"装置动态黑腔实验0180发次采用的负载参数,辐射热波和冲击波在泡沫中的传播速度分别约为36.1 cm/μs和17.6 cm/μs,黑腔辐射温度在黑腔形成初期约80 eV,在冲击波到达泡沫中心前可达100 eV以上,丝阵等离子体外表面发射的X射线能量集中在1000 eV以下.本文给出了程序采用的计算模型、美国"土星"装置丝阵内爆计算结果和"聚龙一号"装置动态黑腔实验0180发次模拟结果.     

Laboratory modeling of physical processes in the ionosphere modified by powerful radio emission

We present the results of the laboratory modeling of physical processes occurring in the ionosphere during active experiments on the ionospheric modificaton by powerful radio emission. The process of nonuniform thermo-diffusion of a magnetoplasma due to local electron heating is studied under the conditions modeling the ionospheric F layer. It is revealed by direct measurements that thermo-diffusion and diffusion are accompanied by excitation of macroscopic eddy currents. In this case, electrons and ions diffuse along and across the magnetic field, respectively, and the eddy current is carried by particles of the background plasma. As a result, a magnetic-field-aligned density depletion rapidly forms in the plasma. The possibility of trapping and guided propagation of Langmuir waves in such a plasma inhomogeneity is demonstrated. Conditions are found under which the wave trapping and the formation of the inhomogeneity occur in a self-consistent regime, i.e., Langmuir waves are trapped in a small-scale inhomogeneity which, in turn, is formed due to local plasma heating by the field of the trapped waves. Such nonlinear wave trapping takes place only above a certain threshold, which significantly increases in the vicinity of gyroharmonics. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 8, pp. 731–746, August 2007.     

Influence of electric and magnetic fields on the shock wave configuration at the diffuser inlet

The possibility is investigated of influencing the shock wave configuration in a xenon plasma flow at the inlet of a supersonic diffuser by applying electric and magnetic fields. Flow patterns resulting from interaction of the plasma with external fields in the entire diffusor volume and its different sections are compared. The patterns are obtained by the Schlieren method using two recording regimes: individual frames or a succession of frames. The study focuses on the normal shock wave formation process under strong MHD interaction over the whole diffuser volume. Basic factors affecting the plasma flow velocity in the diffuser under externally applied fields are compared, namely, the ponderomotive force and the Joule heating of the gas by the electric field, which decelerate the supersonic flow, and the heat removal to the external electric circuit producing the opposite effect. It has been shown that the external fields are most effective if applied to the inlet part of the diffuser, while the flow in the diffuser section, where there is a large density of dissipative structures, is not readily responsive to external factors. It is suggested that the measure of response can be estimated by the energy that goes to the shock wave formation as a result of the flow interaction with the diffuser walls.     

Numerical simulation and experimental validation of multiphysics field coupling mechanisms for a high power ICP wind tunnel

We take the established inductively coupled plasma(ICP) wind tunnel as a research object to investigate the thermal protection system of re-entry vehicles. A 1.2-MW high power ICP wind tunnel is studied through numerical simulation and experimental validation. The distribution characteristics and interaction mechanism of the flow field and electromagnetic field of the ICP wind tunnel are investigated using the multi-field coupling method of flow, electromagnetic, chemical, and thermodynamic field. The accuracy of the numerical simulation is validated by comparing the experimental results with the simulation results. Thereafter, the wind tunnel pressure, air velocity, electron density, Joule heating rate, Lorentz force, and electric field intensity obtained using the simulation are analyzed and discussed. The results indicate that for the 1.2-MW ICP wind tunnel, the maximum values of temperature, pressure, electron number density, and other parameters are observed during coil heating. The influence of the radial Lorentz force on the momentum transfer is stronger than that of the axial Lorentz force. The electron number density at the central axis and the amplitude and position of the Joule heating rate are affected by the radial Lorentz force. Moreover, the plasma in the wind tunnel is constantly in the subsonic flow state, and a strong eddy flow is easily generated at the inlet of the wind tunnel.     

Second harmonic wave generation from Joule heating in layered organic conductors

The amplitude of a second harmonic wave (SHW) generated from Joule heating as a heat source in organic conductor β-(BEDT-TTF)₂IBr₂ is analyzed as a function of the magnetic field strength and its orientation with respect to the plane of the layers. Angular oscillations of the SHW amplitude are correlated with the angular changes of in-plane conductivity that arise from the periodic dependence of charge carriers velocity on the field orientation. It was found that the nonlinear effect of wave generation leads to a shift between the position of the peaks of the wave amplitude and in-plane conductivity. This allows an important information on the parameter values of organic conductors as well as wave velocity to be obtained. Magnetic field dependence shows that the wave is not strongly attenuated with increasing field and might give insights on the interactions between the electromagnetic, temperature and acoustic oscillations. We found that these observations are completely different compared to those of linear acoustic wave generation. It has been shown that the necessary conditions for observing the nonlinear acoustic wave generation are fulfilled in a wide range of fields and angles that allow the acoustic properties of organic conductors to be studied in detail.