相对论Klystron双流放大器电子注的成形

 相对论双流放大器是一种结构简单、高效率的高功率微波器件。其作用机理是沿同一方向传播的两束同心的环形电子束之间的双流不稳定性。这种双流不稳定性导致两个电子束之间的能量交换,最后由输出腔变成微波放大输出。相对论双流放大器成功的关键之一就是同一方向传播的两束同心的环形电子束的成形,利用MAGIC粒子模拟程序,对相对论双流放大器电子注的成形进行了粒子模拟。通过粒子模拟,证实了选择合适的参数来形成两束环形同心束是可行的。     

Characteristic features of the development of two-stream instability of electron beams in the presence of spatially localized perturbations

A study is made of the evolution of a spatially localized perturbation in the form of a Gaussian packet during two-stream instability in a plasma. It is shown that, on the whole, the moving perturbation is decelerated and its shape is distorted; moreover, the higher the group velocity of the packet, the higher the deceleration rate.     

Relativistic two-stream instability

We study the (local) propagation of plane waves in a relativistic, non- dissipative, two-fluid system, allowing for a relative velocity in the “background” configuration. The main aim is to analyze relativistic two-stream instability. This instability requires a relative flow—either across an interface or when two or more fluids interpenetrate—and can be triggered, for example, when one-dimensional plane-waves appear to be left-moving with respect to one fluid, but right-moving with respect to another. The dispersion relation of the two-fluid system is studied for different two-fluid equations of state: (i) the “free” (where there is no direct coupling between the fluid densities), (ii) coupled, and (iii) entrained (where the fluid momenta are linear combinations of the velocities) cases are considered in a frame-independent fashion (e.g.no restriction to the rest-frame of either fluid). As a by-product of our analysis we determine the necessary conditions for a two-fluid system to be causal and absolutely stable and establish a new constraint on the entrainment.     

Analysis of the electron cyclotron maser instability

A single nonlinear equation which describes the temporal evolution of the field amplitude of the electron cyclotron maser instability is derived self-consistently. The results deduced from this nonlinear equation are found to agree well with those of particle simulation.     

Relativistic electron cyclotron theory,revisited

Summary The stages of the relativistic theory leading from the Maxwell-Vlasov system to the absorption and emission coefficients for electromagnetic electron cyclotron waves in a thermonuclear magnetoactive plasma are critically followed, with a particular attention to the approximations involved. Simple and general forms are obtained, holding to arbitrary order in the electron Larmor radius expansion. The applicability limits of the lowest order in this expansion are analysed.     

On the excitation of ion cyclotron and electron cyclotron waves by beams of charged particles

The instabilities of the electrostatic waves of a hot plasma in a magnetic field, excited by beams of charged particles, have been studied in some special cases within the framework of the linear theory. We are interested in short-wavelength oscillations with a transverse wavelength compareable with the Larmore radius of ions or electrons, with frequencies in the vicinity of the harmonic cyclotron frequency of ions or electrons. Expressions have been derived for the increments of these instabilities in the case of a beam with an isotropic distribution function in the velocity space, as well as with an anisotropic distribution function. The influence of the beam temperature on the character of the instabilities and the conditions of formation of the instabilities are discussed, and the order of magnitude of the increments is estimated.The authors thanks J. Václavík and V. Kopecký for valuable discussions and comments.     

离子通道回旋电子注受激辐射非线性理论

文中对散射波自洽增长的时间响应进行了数值模拟计算,研究了离子密度、电子注入射能量对电磁散射波的功率、频率以及工作效率的非线性影响 关键词： 电磁辐射 非线性 高功率毫米波源 等离子体     

On the kineteic theory of electron cyclotron maser

This paper starts from the kinetic theory to expound the method of characteristics. Influence of the equilibrium distribution functionf _o upon analyzed result is fully investigated. Dispersion equation is rigorously derived in waveguide coordinate system in case of interaction between TE _mn field in a circular waveguide and a single momentum ring-shaped electron beam. In the meantime, we make some critical review of previous papers and clarify their confusion and ambiguities.     

The limitation of an explosive instability of two counter-streaming electron beams

Second-order perturbation calculation shows that an explosive instability of three resonantly interacting waves is limited and converted into a multi-periodic process by non-linear terms of the same order as those that destabilize the waves in the first-order approximation.     

Particle simulation of an ultrarelativistic two-stream instability

A two-stream instability in an unmagnetized plasma is examined by a particle-in-cell simulation. Each beam initially consists of cold electrons and protons that stream at a relative Lorentz factor 100. This is representative for plasma close to the external shocks of gamma-ray bursts. An electrostatic wave develops which saturates by trapping electrons. This wave collapses and the resulting electrostatic turbulence gives an electron momentum distribution that resembles a power law with a spectral break. Some electrons reach Lorentz factors over 1000.     

Excitation of electron cyclotron harmonic waves due to helical electron beams in a plasma

Instabilities of electron cyclotron harmonic waves due to the anisotropy of the velocity distribution of electrons which was produced by the injection of the electron beam perpendicular to the magnetic field have been observed.     

Saturation of cyclotron maser instability driven by an electron loss-cone distribution

The resoinance diffusion of electrons in velocity space caused by the excited EM wave fields is considered to be the dominant saturation process of cyclotron maser instability that is driven by an electron loss-cone distribution. An upper-bound of the saturation level is derived analytically. Since the resulting saturation level is low the resonance diffusion is indeed responsible for the saturation of the cyclotron maser instability.     

二维双流不稳定性静电粒子模拟

为研究双温电子等离子体中束流不稳定性的演化过程,用二维粒子模拟(PIC)代码对双温电子束流不稳定性进行了模拟,其中泊松方程用松弛迭代法求解,代码满足电荷守恒、动量守恒和能量守恒条件。在电子双流不稳定性的非线性演化过程中,得到相空间的空洞结构,实空间也相应出现了电子空洞。给出了不稳定性增长率以及相应色散关系。     

Multistream instability of crossed electron beams in a plasma

Multistream instabilities of crossed electron beams in a plasma are investigated analytically. By using successively more complicated models, the instability of a finite number of crossed monoenergetic beams and the instability of an infinite number of crossed monoenergetic beams with different distributions in the azimuthal angle are studied. The conclusion is drawn that an isotropic plasma is unstable against the excitation of longitudinal waves.     

Effect of upflowing field-aligned electron beams on the electron cyclotron waves in the auroral magnetosphere

The role of low density upflowing field-aligned electron beams (FEBs) on the growth rate of the electron cyclotron waves at the frequencies ω _r < Ω_e, propagating downward in the direction of the Earth’s magnetic field, has been analysed in the auroral region at ω _e/Ω_e < 1 where ω _e is the plasma frequency and Ω_e is the gyrofrequency. The FEBs with low to high energy (E _b) but with low temperature (T _‖b) have no effect on these waves. The FEBs with E _b < 1 keV and T _‖b (> 1.5 keV) have been found to have significant effect on the growth rate. Analysis has revealed that it is mainly the T _‖b which inhibits the growth rate (magnitude) and the range of frequency (bandwidth) of the instability mainly in the higher frequency spectrum. The inhibition in the growth rate and bandwidth increases with increase in T _‖b. The FEBs with less E _b (giving drift velocity) reduce growth rate more than the beams with larger E _b. The inhibition of growth rate increases with the increase in the ratio ω _e/Ω_e indicating that the beams are more effective at higher altitudes.      

Electron cyclotron instability

The paper presents a study of the dependence of initiation and development of instability on the cyclotron frequency of electrons in a homogeneous plasma with cold ions and electrons forming two beams which move in the direction of, and opposite to, that of a constant magnetic field. It is demonstrated that for ^{2 2} , the instability can already arise at _pe ² _ce ² , and a brief comparison with the experimental results is carried out.The authors take this opportunity to thank Dr. M. Seidl for his valuable comments and stimulating discussions on this paper.     

Time behaviour of electron cyclotron harmonic waves excited by helical electron beams in a plasma

Time behaviour of instabilities of electron cyclotron harmonic waves due to the anisotropy of the velocity distribution of electrons has been investigated. Measured growth rate was compared with the calculated ones.