Damping rates of waves in a switched magnetoplasma medium:longitudinal propagation

The interaction of a circularly polarized electromagnetic wave with a switched-on magnetoplasma medium is considered. A static magnetic field in the direction of propagation is assumed to be present, resulting in longitudinal propagation. The incident wave splits into three waves whose frequencies are different from that of the incident wave. It is shown that these waves ultimately damp out if the plasma is even slightly lossy. The damping of the waves is interpreted in terms of their attenuation with distance and decay with time as they propagate in the lossy plasma. The attenuation-length and decay-time constants of the waves are obtained, and their dependence on the incident-wave frequency and the gyrofrequency is examined. Optimum parameters for an experiment to detect these waves are suggested     

电磁捕集器的设计

本文叙述了一个静电堵漏会切型等离子体约束系统。基本设计参数为:电极所在之处磁场达10kG;堵漏电压为10kV;等离子体密度～10~(12)cm。;离子温度>O.5keV;约束时问>5ms。 该装置可用作为等离子体积累与加热、电势屏蔽、静电堵漏轴对称串级镜端塞的研究。     

Particle-in-cell simulation for the effect of magnetic cusp on discharge characteristics in a cylindrical Hall thruster

The cylindrical Hall thruster has the good prospect of serving as a miniaturized electric propulsion device.A 2 D-3 V particle-in-cell plus Monte Carlo(PIC-MCC) method is used to study the effect of the magnetic cusp on discharge characteristics of a cylindrical Hall thruster.The simulation results show that the main ionization region and the main potential drop of the thruster are located at the upstream of the discharge channel.When the magnetic cusp moves toward the anode side,the main ionization region is compressed and weakened,moving upstream correspondingly.The ionization near the cusp is enhanced,and the interaction between the plasma and the wall increases.The simulation results suggest that the magnetic cusp should be located near the channel exit.     

Plasma losses in a toroidal theta-pinch with superposed hexapole

A toroidal theta-pinch discharge with superposed non-helical hexapole field is investigated. The characteristic data of the discharge are: major diameter 52 cm, minor inner diameter of the vacuum vessel 6 cm, maximum magnetic field between 10 and 21 kG, rise time (quarter-cycle) 3.0 μs, maximum temperature between 40 and 100 eV, maximum density between 1 and 3×10¹⁶ cm^?3, beta-values between 0.3 and 1. The plasma confinement times are determined by measuring particle density, temperature and plasma radius. The confinement times are compared with those of models which account for cusp losses, resistive losses, and Bohm diffusion. Measured confinement times are consistent with those expected from cusp losses with a cusp slit-width of one ion gyro-radius. Above electron temperatures of 20 eV, resistive losses are negligible. Bohm diffusion is not consistent with measurements, but is of the same order of magnitude.     

The Influences of the Magnetic Field Strength on the Magnetic Confinement of Primary Electrons in an Ion Source

This paper deals with the simulation of trajectories of energetic electrons under the influence of a multi-cusp magnetic field produced by a permanent magnet assembly in a ring cusp geometry which is designed for supporting a plasma based ion source. The primary electrons are assumed as being emitted from a cathode located coaxially with the cylindrical discharge chamber. The volume of the region occupied by the electron trajectories and the magnetic trapping time were evaluated and plots are presented showing the effects of the surface magnetic field strength of the magnets on the volume and the mean confinement time of primary electrons in the ion source.     

Interaction of a Plasma Beam with a Transverse Magnetic Barrier

The interaction of an energetic He plasma beam with a quasi step-like transverse magnetic barrier is reported. When the rate of flow of momentum in the incident beam is less than the pressure of the magnetic field, a collisionless electrostatic shock is observed to form in front of the barrier as a result of the drastic compression of the plasma. The initially cold plasma is substantially thermalized by the shock and the electron density is increased by a factor of four. In the opposite limit the plasma penetrates the barrier in a flute-like manner.     

Magnetotransport in a dual waveguide coupled by a finite barrier： Energy filter and directional coupler

We propose in this paper that a dual waveguide coupled by a finite barrier be able to serve as an energy filter under a perpendicular magnetic field. In the waveguide direction, the conductance exhibits a periodic square-wave pattern in which the miniband is controlled by the magnetic and potential modulation. The electrons with energies in the miniband can completely transfer along one waveguide while the other electrons undergo filtration. Compared with the coupled waveguide without magnetic modulation, the structure under magnetic field is found to be a good directional coupler. By adjusting the potential barrier and magnetic field, the electrons input from one port of waveguide can transfer to any other ports.     

Single-particle trajectories in a cusped magnetic field

The trajectories of a single charged particle in relation to the cusp axis and cusp plane in a cusped magnetic field are numerically studied. The results show that the particle reflected by the cusp field forms a double helix; i.e., the helix itself makes a helical motion. The location of the reflection point extends well into the injection side of the cusp plane, suggesting that a diverging magnetic field of appropriate geometry may be able to reflect a charged particle. However, the location of the reflection point does not alter the nature of the trajectory     

On the containment of plasma in stationary magnetic and high-frequency fields I

The stationary state of a collisionless plasma in a magnetic mirror is analyzed provided that a strong h.f. field is present. The h.f. field frequency is somewhat higher than the electron cyclotron frequency. The pressure acting on the plasma and the height of the h.f. potential barrier are derived in particular. The h.f. potential yields the possibility of eliminating the loss cone in the velocities distribution. The upper limits, which the electron temperature must not exceed, are derived. If an appropriate stationary magnetic field is used, the required incident wave power can be diminished and the allowable electron temperature can be increased. Some new results concerning the case of a homogeneous magnetic field are presented.     

Mechanism of diffusion of positively charged dust particles in a photoemission cell under microgravity conditions

The decay of a dusty plasma in a photoemission cell under microgravity conditions is investigated on the basis of the method of nonlocal moments. It is founds that plasma decay in space experiments occurs in accordance with the mechanism of free electron diffusion followed by dust particle drift. An analytic solution is found for the evolution of radial distributions of the dust particle concentration and the electric field under the experimental conditions. The effect of abnormally high temperatures of dust particles is considered. The effect of axial magnetic fields on the decay of dusty plasma is investigated. It is shown that the plasma decay in a magnetic field is governed by the ambipolar diffusion mechanism, the decay being prolonged up to 10³ s in a magnetic field on the order of 10³–10⁴ G in strength.     

低速度零散会切电子枪的设计和数值仿真

根据拉格朗日方程对电子在平滑会切磁场中的径向波动与速度零散的关系进行讨论。运用Matlab,Magic软件相互结合的方法设计电子枪结构和磁场。用Matlab程序模拟单电子在给定电场、磁场中的运动,分析了单电子径向速度对零散的影响,并优化磁场分布。设计的磁场可以有效地减小单电子束径向速度,降低电子束速度零散。用Magic软件对电流为1 A、能量为30 keV的电子束在优化磁场中的运动进行仿真,得到的电子束速度比约为2,速度零散小于2.5%,轴向速度零散小于8.5%。     

Maser based on cyclotron resonance in a decaying plasma

The features of generating electromagnetic radiation in a two-level cyclotron maser whose active medium is a decaying nonequilibrium plasma confined in a magnetic field with the mirror configuration have been examined. It has been shown that, even in the absence of a continuously acting source of nonequilibrium particles (inversion of the medium), the system can exhibit the regimes of the quasimonochromatic or pulse generation of radiation owing to a fast monotonic decrease in the instability threshold that is characteristic of the plasma decay. The theory is confirmed by the results of observations of the burst activity of the decaying pulsed-discharge plasma under the conditions of the electron cyclotron resonance in the direct axisymmetric magnetic trap.     

Neutron storage in a magnetic field

The motion of neutrons in magnetic traps is considered for various cases of neutron polarization. The results of implementing such traps in practice and special features of experiments studying magnetic neutron storage are discussed. The problem of neutron losses during injection via magnetic valves can be solved by conjoining a magnetic trap with a converter of cold neutrons into ultracold ones or with a source of ultracold neutrons. Prospects for expanding neutron-storage experiments by invoking a correlation analysis of neutron decay and by using the transport properties of charged particles in a nonuniform magnetic field are analyzed. In such an investigation, the recording of the storage time of neutrons proper can be supplemented with the detection of decay protons and electrons and with a parallel measurement of the asymmetries of proton and electron emission with respect to the magnetic field. A set of relative measurements permits improving the accuracy of an experimental determination of the neutron lifetime and combining this determination with the determination of correlation coefficients. On this basis, it is possible to find directly the ratio of the weak-interaction constants and the constants themselves. The application of the most advanced reactor and accelerator technologies to subcritical electric nuclear devices optimized for generating cold and ultracold neutrons, along with the use of solid deuterium and superfluid helium, creates preconditions for developing a neutron plant and for launching neutron studies at accelerators. Thus, the work that has been done as a development of V.V. Vladimirsky's proposals on magnetic neutron storage is analyzed, and the potential of a further use of ultracold neutrons and magnetic devices for deploying a full-scale precision experiment to study the beta decay of polarized neutrons is demonstrated.     

Confinement time exceeding one second for a toroidal electron plasma

Nearly steady-state electron plasmas are trapped in a toroidal magnetic field for the first time. We report the first results from a new toroidal electron plasma experiment, the Lawrence Non-neutral Torus II, in which electron densities on the order of 10(7) cm(-3) are trapped in a 270-degree toroidal arc (670 G toroidal magnetic field) by application of trapping potentials to segments of a conducting shell. The total charge inferred from measurements of the frequency of the m=1 diocotron mode is observed to decay on a 3 s time scale, a time scale that approaches the predicted limit due to magnetic pumping transport. Three seconds represents approximately equal to 10(5) periods of the lowest frequency plasma mode, indicating that nearly steady-state conditions are achieved.     

Influence of super-strong magnetic field on the electron chemical potential and β decay in the stellar surroundings

In this paper, considering the quantum effect of electrons in a super-strong magnetic field, the influence of a super-strong magnetic field on the chemical potential of a non-zero temperature electron is analyzed, the rates of β decay under the super-strong magnetic field are studied, and then we compare them with the case without a magnetic field. Here, the nucleus 63Co is investigated in detail as an example. The results show that a magnetic field that is less than 1010 T has little effect on the electron chemical potential and β decay rates, but the super-strong magnetic field that is greater than 1010 T depresses the electron chemical potential and improves the β decay rates clearly.     

Leak widths resulting from plasma diffusion in a magnetic cusp

Several formulas describing cusp leak widths are derived using different assumptions on the natures of the crossfield diffusion and the plasma flow parallel to the magnetic field.     

Particle-in-cell simulation for different magnetic mirror effects on the plasma distribution in a cusped field thruster

Magnetic mirror used as an efficient tool to confine plasma has been widely adopted in many different areas especially in recent cusped field thrusters. In order to check the influence of magnetic mirror effect on the plasma distribution in a cusped field thruster, three different radii of the discharge channel(6 mm, 4 mm, and 2 mm) in a cusped field thruster are investigated by using Particle-in-Cell Plus Monte Carlo(PIC-MCC) simulated method, under the condition of a fixed axial length of the discharge channel and the same operating parameters. It is found that magnetic cusps inside the small radius discharge channel cannot confine electrons very well. Thus, the electric field is hard to establish. With the reduction of the discharge channel's diameter, more electrons will escape from cusps to the centerline area near the anode due to a lower magnetic mirror ratio. Meanwhile, the leak width of the cusped magnetic field will increase at the cusp. By increasing the magnetic field strength in a small radius model of a cusped field thruster, the negative effect caused by the weak magnetic mirror effect can be partially compensated. Therefore, according to engineering design, the increase of magnetic field strength can contribute to obtaining a good performance, when the radial distance between the magnets and the inner surface of the discharge channel is relatively big.     

Magnetic field and finite barrier-height effects on the polarizability of a shallow donor in a GaAs quantum wire

The binding energy and the polarizability are estimated for a shallow donor confined to move in a GaAs quantum well wire (QWW) with a rectangular and square cross-section under the action of an axial magnetic field. In this work, the Hass variational method within the effective mass approximation is used in the case of infinite and finite barrier QWWs. We present our results as a function of the size of the wire and for several values of the magnetic field strength. It is found that the magnetic field strongly reduces the polarizability. The finite barrier-height effect is important for smaller well widths. For higher fields and large wire, the effects of the magnetic field are predominant and the barrier potential is a small perturbation.     

会切磁场中大回旋电子束产生的研究

研究了会切磁场产生的机理。通过对Moster-Molnar 模型的探讨, 建立了会切磁场的物理模型。在会切磁场理论分析和数值模拟基础上, 探讨了影响会切磁场设计的因数; 利用拉格朗日公式求解了会切磁场中电子运动轨迹。探讨了会切磁场与大回旋空心会切电子枪的关系, 得到了改进会切电子枪性能的一些一般性结论。     

Single Particle Trajectories in a Nonadiabatic Cusp Magnetic Field Configuration

Charged particle trajectories are numerically analyzed in a cusp magnetic field. One of the significant observations is that the initial phase of the particle is a critical parameter controlling the conversion of the parallel component of velocity to the perpendicular component. This conversion is also studied for different magnetic field gradient scale lengths in the cusp field region.