低杂波电流驱动中的雪崩逃逸增强及鱼骨不稳定性

等离子体中存在的一定数量的高能逃逸电子（E≥1MeV)通过大角度库仑散射从等离子体中碰撞出二次电子，二次电子被低杂波有效地加速成为逃逸电子，这些逃逸电子又被正反馈回等离子体，形成雪崩现象。在此过程中，一部分获得较大横向动量的二次电子或由低杂波驱动的高能电子可能被香蕉轨道捕获，这些被捕获在磁岛中的电子与某种模式的磁场扰动共振时，就出现鱼骨不稳定现象。     

Synchrotron radiation intensity and energy of runaway electrons in EAST tokamak

A detailed analysis of the synchrotron radiation intensity and energy of runaway electrons is presented for the Experimental Advanced Superconducting Tokamak(EAST). In order to make the energy of the calculated runaway electrons more accurate, we take the Shafranov shift into account. The results of the analysis show that the synchrotron radiation intensity and energy of runaway electrons did not reach the maximum at the same time. The energy of the runaway electrons reached the maximum first, and then the synchrotron radiation intensity of the runaway electrons reached the maximum.We also analyze the runaway electrons density, and find that the density of runaway electrons continuously increased. For this reason, although the energy of the runaway electrons dropped but the synchrotron radiation intensity of the runaway electrons would continue rising for a while.     

超热电子与金黑腔靶作用产生硬X射线的蒙特卡罗模拟

激光打靶产生大量麦氏分布的超热电子,与金腔靶相互作用产生硬X射线.利用蒙特卡罗方法,对超热电子在金腔靶中的传输进行了研究,模拟了在不同超热电子温度、份额下硬X射线谱的变化及在不同腔体尺寸、腔壁厚度情况下,硬X射线谱的变化情况,给出硬X射线产生效率的决定因素.利用硬X射线谱反推得到的超热电子信息与蒙特卡罗程序模拟结果相结合的方法,获得金腔内部超热电子初始信息. 关键词： 热电子 超热电子 蒙特卡罗方法 硬X射线     

Plasmonic secondary electron emission from alkali metals

One of the authors (Gornyi) has demonstrated earlier the possibility of plasmonic secondary electron emission (PSEE). Here electrons striking a solid substance excite in it plasmons, which then break up and in turn excite electrons. These electrons, upon being emitted into vacuum, form clusters of secondary electrons with definite energy levels. When energy-loss spectra of electrons are compared with energy spectra of secondary electrons and with work-function curves for secondary electrons, all of them plotted for lithium, sodium, and potassium, then the occurrence of the PSEE phenomenon in these metals can be established. The PSEE explains the peaks along the energy spectra and the work-function curves for secondary electrons. These peaks were not understood before.     

The origin and elimination of spurious peaks in threshold electron photoionization spectra

Autoionization electrons in threshold photoionization spectra are known to occur. The effect of such electrons on the interpretation of threshold electron spectra is discussed and a new method is described which enables one to discriminate between zero kinetic energy electrons and energetic electrons in photoionization experiments with little ambiguity. The method largely overcomes the main problem present in some previously described threshold electron studies; namely, the line-of-sight transmission of energetic electrons which gives rise to non-threshold electron peaks. A rejection ratio of 25 is readily obtained for 0.038 eV electrons compared with threshold (zero kinetic energy) electrons and the (small) transition probability for energetic electrons falls off more rapidly than for analysers previously described. Design parameters based on electron trajectory calculations are given for the analyser used, and photoionization results on argon are presented.     

Influence of Coulomb force between two electrons on double ionization of He-like atoms

In strong-field double ionization,two electrons are ionized by intense laser field.These two electrons move in the laser field and the state is described by a Coulomb-Volkov state,where the repulsive Coulomb state describes the relative motion of the two electrons and the Volkov state describes the center-of-mass motion of the two electrons in the laser field.In the frame of scattering theory,we derive a simple analytical formula of the double ionization of He-like atoms.The effect of the Coulomb force between two electrons on the double ionization process is discussed.Numerical studies disclose that the Coulomb force enhances the ionization rate of high-energy electrons but suppresses the ionization rate of the lowest-energy electrons.     

Observation of trapped and passing runaway electrons by infrared camera in the EAST tokamak

In EAST, synchrotron radiation is emitted by runaway electrons in the infrared band, which can be observed by infrared cameras. This synchrotron radiation is mainly emitted by passing runaway electrons with tens of Me V energy. A common feature of radiation dominated by passing runaway electrons is that it is strongest on the high field side. However,the deeply trapped runaway electrons cannot reach the high field side in principle. Therefore, in this case, the high field side radiation is expected to be weak. This paper reports for the first time that the synchrotron radiation from trapped runaway electrons dominates that from passing runaway electrons and is identifiable in an image. Although the synchrotron radiation dominated by trapped runaway electrons can be observed in experiment, the proportion of trapped runaway electrons is very low.     

引导磁场对收集极中电子能量沉积的影响

理论分析了引导磁场对收集极材料中电子运动的约束作用,推导了引导磁场作用下二次电子的逃逸条件,利用蒙特卡罗方法计算了引导磁场作用下电子束在收集极中的能量沉积规律。研究结果表明:引导磁场对电子在材料内部的运动约束作用很弱,对二次电子有强约束作用;大部分二次电子经拉莫回旋再次轰击在收集极上被收集,逃逸的二次电子沿引导磁场方向进入束波作用区;增大电子的入射角度时,束流密度的降低和二次电子的再次入射降低了收集极中电子的最大沉积能量密度,提高了收集极的耐电子轰击能力。     

Transition from gas-kinetic to minimal metal-type conductivity in a supercritical fluid of metal vapor

We have proposed a peculiar model of the plasma of dense metal vapors, containing atoms embedded into the electron jelly, as well as free (thermally ionized) electrons and ions. The main feature of the model is the presence of the electron jelly existing at any density of the atomic component. The number of electrons in the jelly increases under compression. The process of its formation can be called the “cold” ionization, or pressure ionization. The composition of the gas–plasma mixture, including the concentration of atoms and electrons in the jelly, as well as the concentration of free thermally ionized electrons and ions, has been calculated. The conductivity of dense vapors is determined by the sum of the conductivities of thermal electrons (which is calculated using the Frost formula) and jelly electrons (which is calculated by the Regel–Ioffe formula for the minimal metal-type conductivity). The concentration of thermal electrons decreases and the concentration of jelly electrons increases upon compression of the vapor. Accordingly, the conductivity varies from the conductivity of thermal electrons to the conductivity of jelly electrons, continuously passing through the minimum. The calculated values of the conductivity of supercritical metal vapors are in satisfactory agreement with experimental results.     

化学成键的元素中的退化费米气体中的束缚电子对

Cooper考虑一对电子在一个安稳的费米球面上相互作用着,指出这种相互作用是由声子和屏蔽库仑场导致的,在电子间存在一种净的吸引作用,结果这对电子能够形成一个束缚态.我们给出的是对于元素之中有化学键的形成,甚至电了发生了转移,电负性高的元素得到了电子,电负性低的元素失去了电子时退化费米气体中的束缚电子对的描述.     

Die Elektronenbewegung im Neutralgas bei hohen elektrischen Feldern

In strong electric fields the acceleration of the electrons by the field exceeds the deceleration by collisions with neutral molecules. Thus run-away or beam electrons are produced. This paper investigates the motion of the beam electrons in a neutral gas considering ionization processes by electron-molecule-impacts. We start with a time independent current of primary electrons (case a) and a space independant density of primary electrons (case b). The further development of the velocity distribution is calculated. For a molecular hydrogen gas the amplification of the initial electrons, the average ionization, and the velocity distribution of the electrons as a function of space or time respectively is given. The average ionization has an asymptotic solution, which becomes valid, when one primary electron has produced by ionization an avalanche of approximately 100 electrons. The Townsend coefficient α for high values of the field strength is independant of space only in the region of this asymptotic solution.     

ECRH of trapped electrons in laboratory magnetoplasmas

Heating of plasma electrons by high power millimeter wave fields at cyclotron harmonic resonance is studied. A mirror field is modelled for the local trapping of electrons. It is shown that superthermal electrons can be generated as the consequence of the ECRH of trapped electrons.     

Radiation dose from reentrant electrons

In estimating the crew exposures during an extra vehicular activity (EVA), the contribution of reentrant electrons has always been neglected. Although the flux of these electrons is small compared to the flux of trapped electrons, their energy spectrum extends to several GeV compared to about 7 MeV for trapped electrons. This is also true of splash electrons. Using the measured reentrant electron energy spectra, it is shown that the dose contribution of these electrons to the blood forming organs (BFO) is more that 10 times greater than that from the trapped electrons. The calculations also show that the dose-depth response is a very slowly changing function of depth, and thus adding reasonable amounts of additional shielding would not significantly lower the dose to BFO.     

Effective interaction of electrons in quantum wells

Effects of electron-phonon interaction on the interaction between electrons in semiconductor quantum wells are considered. It is found that the direct Coulomb potential between electrons in a quantum well is smaller than that in bulk semicondutors. The antisymmetric modes of the confined bulk phonons and interface phonons have no contribution to the effective interaction of electrons. If a well is narrow enough, the effective interaction between electrons caused by interaction with interface phonons may exceed that by interaction with confined bulk phonons. In narrower wells the effective interaction potential of electrons produced by phonons is stronger, but decreases rapidly with increasing distance between electrons.     

强激光与细锥靶相互作用产生强流高能电子束的研究

本文提出采用了强激光与细锥形靶作用, 产生大量定向高能电子, 用于快点火激光聚变方案研究. 通过PIC 模拟, 研究了细锥靶和激光脉冲的各项参数, 对产生高能电子的影响. 模拟发现, 细锥靶开口10° 时能够产生较多的高能电子, 当开口角度逐渐增大时, 高能电子的能量和数目都有一定程度下降. 若为细锥靶加上预等离子体, 产生的高能电子的数目将大大提高, 而最高的电子能量将会下降. 中等能量的电子加速主要由于激光有质动力加速, 而高能量的电子加速主要由于电子感应加速. 随着激光脉宽的增加, 高能电子的数量直线上升. 关键词： 细锥形靶 电子加速 感应共振加速     

Structure of the direct-current magnetron discharge in neon at different polarities of the electrode system

A dc magnetron discharge in neon is studied at different polarities of the electrode system. It is found that the electron energy distribution function is composed of three groups of electrons: fast electrons accelerated by the strong field of a cathode sheath, slow electrons confined in a potential well due to the space-charge field, and intermediate-energy electrons. It is shown that the energy distribution of the confined electrons is a Maxwell-Boltzmann distribution function, whereas the energy distribution of the intermediate electrons is typical of electron diffusion at a constant total energy. The measured values of the cathode sheath thickness depend on the source polarity.     

Interaction of a high-intensity ultrashort laser pulse with extended nanofilaments of dense plasma

Generation and propagation of fast electrons in laser targets consisting of thin nanofilaments are studied numerically and analytically. Such targets completely absorb laser radiation and exhibit a large coefficient of laser-energy conversion to kinetic energy of a flow of fast electrons. Analytical estimates show that the optimal thickness of the filament is on the order of the skin depth of the laser plasma, while an optimal distance between filaments is on the order of the Debye radius of hot electrons. A bunch of relativistic electrons can propagate as far as several hundred micrometers in such targets, while the fastest electrons can propagate several millimeters. Upon bending of filaments, the flow of electrons propagates along the filaments and can be focused by bringing the filaments together. Laser targets of the discussed composition are used as sources of dense bunches of relativistic electrons and subsequent generation of high-intensity X-ray radiation with their help.     

电子回旋波使磁镜中捕获电子与逃逸电子相互转化

在Littlejohn的带电粒子引导中心拉格朗日体系下,讨论了电子回旋波对磁镜等离子体中捕获电子与逃逸电子的影响,给出了捕获电子变成逃逸电子以及逃逸电子被电子回旋波捕获的条件,并计算了它们的相互转化的概率。 关键词：     

Correlation between valence electronic structure and magnetic properties in RCo_5(R=rare earth) intermetallic compound

The magnetisms of RCo_5(R = rare earth) intermetallics are systematically studied with the empirical electron theory of solids and molecules(EET).The theoretical moments and Curie temperatures agree well with experimental ones.The calculated results show strong correlations between the valence electronic structure and the magnetic properties in RCo_5 intermetallic compounds.The moments of RCo_5 intermetallics originate mainly from the 3d electrons of Co atoms and 4f electrons of rare earth,and the s electrons also affect the magnetic moments by the hybridization of d and s electrons.It is found that moment of Co atom at 2c site is higher than that at 3g site due to the fact that the bonding effect between R and Co is associated with an electron transformation from 3d electrons into covalence electrons.In the heavy rare-earth-based RCo_5 intermetallics,the contribution to magnetic moment originates from the 3d and 4f electrons.The covalence electrons and lattice electrons also affect the Curie temperature,which is proportional to the average moment along the various bonds.     

Electron bunching in a Penning trap and accelerating process for CO_2 gas mixture active medium

In PASER(particle acceleration by stimulated emission of radiation),in the presence of an active medium incorporated in a Penning trap,moving electrons can become bunched,and as they get enough energy,they escape the trap forming an optical injector.These bunched electrons can enter the next PASER section filled with the same active medium to be accelerated.In this paper,electron dynamics in the presence of a gas mixture active medium incorporated in a Penning trap is analyzed by developing an idealized ID model.We evaluate the energy exchange occurring as the train of electrons traverses into the next PASER section.The results show that the oscillating electrons can be bunched at the resonant frequency of the active medium.The influence of the trapped time and population inversion are analyzed,showing that the longer the electrons are trapped,the more energy from the medium the accelerated electrons get,and with the increase of population inversion,the decelerated electrons are virtually unchanged but the accelerated electrons more than double their peak energy values.The simulation results show that the gas active medium needs a lower population inversion to bunch the electrons compared to a solid active medium,so the experimental conditions can easily be achieved.