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.     

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.     

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.     

On the possibility of natural formation of a transverse wave with a phase velocity lower than the velocity of light

The formation of a transverse wave with a phase velocity lower than the velocity of light, which can exist in an equilibrium plasma without a slow-wave structure in zero magnetic field, is described. It involves the transformation of a transverse wave with trapped electrons, traveling along the magnetic field, into a slow transverse wave after the removal of the magnetic field. During the evolution of the wave with trapped electrons, the magnetic induction decreases very slowly in the direction of the wave propagation. As a result, the velocity at which electrons are in resonant interaction with the wave increases; therefore, the electrons fall to the bottom of potential wells. Under the influence of the trapped electrons, the phase velocity of the wave decreases and becomes lower than the velocity of light. It becomes equal to the velocity at which the electrons are in resonance interaction with the wave at the instant when the magnetic field vanishes. It is demonstrated that a transverse wave with a velocity lower than the velocity of light can exist in an equilibrium plasma even after the magnetic field vanishes; in this case, the flow of trapped electrons serves as a slow-wave structure.     

Der Einfluß metastabiler Atome auf den statischen Durchschlag in Argon

A gas discharge in argon is initiated by an ultraviolet light pulse which releases 10⁵ electrons at the cathode within 20 nsec. The time of built-up for the static breakdown is found to be in the order of msec. The oscillogram of the current near breakdown shows a fast component consisting of several successive avalanches caused by secondary electrons liberated by ions at the cathode and a slow component which is due to the electrons liberated by metastable atoms at the cathode. The second Townsend coefficient for argon ions and a nickel cathode is determined to beγ ₊= 2.5·10^?3. The amount of electrons liberated by metastables at static breakdown is 25% of the total number of secondary electrons. The mean life-time of the metastables at 1,1 Torr and an electrode separation of 10 mm is found to be 2.2 msec, which is mainly due to de-exciting collisions at the electrodes.     

中低温稠密等离子体电子压强的自洽场计算

 对含温有界自洽场平均原子结构中自由电子的判据作了修改,用分波法和Fermi-Dirac统计处理自由电子。在计算电子压强时考虑了共振态和交换、库仑关联对压强的影响。计算并与实验比较了Ni、Cu的零温电子压强。以Fe、Pb为算例,展示了本模型的适用性。     

强激光场下原子超快动力学过程中的能量交换

利用三维经典系综模型,研究了整个系综两电子(Ar原子为例)从激光场吸收的能量对激光参数(波长、激光强度和椭偏率)的依赖关系.结果显示,当激光强度固定,波长增加时,整个系综两电子从激光场吸收的能量整体呈上升趋势,但不同强度下趋势略有差异.在较低强度时整个系综两电子从激光场吸收的能量对波长的依赖关系呈现持续平稳增加的趋势,在较高强度时呈现先缓慢减小再快速增大的趋势.对强度的依赖关系在不同波长时呈现两个有趣的交叉点.对椭偏率的依赖关系在较低强度时呈现先逐渐减小再缓慢增大的趋势;在中等强度时呈现一个“阶梯型”即先缓慢增大再逐渐减小最后缓慢增大;在更高强度时呈现先逐渐增大再逐渐减小的趋势.为了解释整个系综两电子从激光场吸收的能量对激光参数的依赖关系,把整个系综的动力学过程分为双电离、单电离、受挫单电离和受挫双电离4种通道.然后分析各个通道的特征及其如何主导整个系综两电子从激光场吸收的能量的变化趋势.分析结果表明,整个系综两电子从激光场吸收的能量对波长、激光强度和椭偏率的依赖均是由于某种通道主导整个系综两电子从激光场吸收的能量的结果.     

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.     

Spatial distribution of high-energy electron emission from water plasmas produced by femtosecond laser pulses

High energy electrons emitted by water plasmas produced by a single or a multiple laser pulse are investigated. The multipulse mode greatly enhances the generation and the temperature of hot electrons. Directional emission of high energy electrons over 25 keV is observed in two symmetric directions with respect to the laser axis and at 46 degrees from the directions of the laser electric field. Two-dimensional particle-in-cell simulations reproduce well the experimental results and indicate that the acceleration mechanism of the high energy electrons is due mainly to the resonance absorption at the edge of the spherical droplets formed by the leading pulse.     

Spectra of electrons and X-ray photons in a diffusive nanosecond discharge in air under atmospheric pressure

The spectra of electrons and X-ray photons generated in nanosecond discharges in air under atmospheric pressure are investigated theoretically and experimentally. Data for the discharge formation dynamics in a nonuniform electric field are gathered. It is confirmed that voltage pulses with an amplitude of more than 100 kV and a rise time of 1 ns or less causing breakdown of an electrode gap with a small-radius cathode generate runaway electrons, which can be divided into three groups in energy (their energy varies from several kiloelectronvolts to several hundreds of kiloelectronvolts). It is also borne out that the formation of the space charge is due to electrons appearing in the gap at the cathode and a major contribution to the electron beam behind the foil comes from electrons of the second group, the maximal energy of which roughly corresponds to the voltage across the gap during electron beam generation. X-ray radiation from the gas-filled diode results from beam electron slowdown both in the anode and in the gap. It is shown that the amount of group-3 electrons with an energy above the energy gained by runaway electrons (in the absence of losses) at a maximal voltage across the gap is much smaller than the amount of group-2 electrons.     

具有空心阴极放电特征的射频放电的两电子组模型

 运用两电子组模型，考虑了射频放电中的α过程和γ过程两种电离机制，并结合流体模型，研究了中等气压下窄电极间隙容性耦合射频放电在运行模式转变区的等离子体密度以及电离速率分布等特性。理论研究表明，γ电离过程在高电流模式运行中起主要作用，并证实了此类放电中存在显著的电子摆钟效应，具有类似于空心阴极放电的特征。     

飞秒激光-等离子体相互作用中快电子能量分布

 采用不同量程的电子谱仪与LiF热释光探测器相配合，测量了飞秒激光 等离子体相互作用中产生的快电子能量分布。结果显示快电子能量分布的一致性和多个重要特征与国外同类实验和计算机模拟结果相似。快电子能谱在低能处产生凹陷是由于冷电子的回流产生的；几种加速机制共同作用是能谱在100~350 keV范围内出现平台的原因；快电子的有效温度较好地满足共振吸收的温度定标律是由于反射激光加速与共振吸收机制均是通过朗道阻尼或波破对电子进行加速的。     

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.     

Convoy electrons produced at glancing angle scattering of MeV HeH+ ions from a crystal surface

Abstract

Convoy electrons produced at glancing angle scattering of MeV HeH⁺ ions from an atomically clean (001) surface of SnTe crystal are observed. Energy spectrum of the convoy electrons shows a peak broader than that at scattering of atomic projectiles and the most probable energy of convoy electrons at HeH⁺ scattering is larger than those at scattering of isotachic He ions. This acceleration of convoy electrons is qualitatively explained by the force due to surface wake induced by Coulomb exploding fragment He²⁺ and H⁺.     

Resonance phenomena in low-energy electron scattering by planar crystalline nanostructures

Multiple scattering of low-energy electrons by a nanostructure consisting of planar crystalline films is analyzed. It is demonstrated that, at a particular ratio between the geometric and potential parameters of the system, there arise resonance states of scattered electrons in which the transmission coefficient of electrons increases drastically. Narrow transparency windows that correspond to almost complete transmission of the electron beam are formed at specific distances between the films in the resonance structure. A method for quantum-mechanical calculation of the parameters of the resonance structure is proposed.     

Spin polarized tunneling at finite bias

A mesoscopic spin valve is used to determine the dynamic spin polarization of electrons tunneling out of and into ferromagnetic (FM) transition metals at finite voltages. The dynamic polarization of electrons tunneling out of the FM slowly decreases with increasing bias but drops faster and even inverts with voltage when electrons tunnel into it. A free-electron model shows that in the former case electrons originate near the Fermi level of the FM with large polarization whereas in the latter, electrons tunnel into hot electron states for which the polarization is significantly reduced. The change in sign is ascribed to the matching of the electron wave function inside and outside the tunnel barrier.     

Deceleration and acceleration of fast electrons in a dense gas in an electric field

The propagation of electrons in a gas at energies higher than the excitation energy of the K shell of the gas atoms is simulated numerically. Calculations show that, without a field, the penetration depth of the electrons into a gas heavier than nitrogen is limited primarily by their elastic collisions with atomic nuclei. For electrons moving in an electric field, the effect of elastic collisions is that there is no definite electric field strength above which an electron with a given energy will be continuously accelerated. Even in an electric field much stronger than the critical one, only a fraction of electrons are accelerated. The remaining electrons turn back due to elastic collisions and lose their energy in deceleration by the field. In this case, the propagation velocity of the centroid of the electrons tends to a constant value.     

Fast method of calculating electronic stopping in a material

The main processes determining the distribution function of nonrelativistic stopping electrons in a material are analyzed. It is established that electrons change direction of their motion mainly because of scattering on nuclei of the material at small angles. This property of the Coulomb interaction is used to fasten numerical computations of the parameters of stopping electrons.     

Anomalous passage of ultrarelativistic electrons in thick single crystals in axial channeling

The dynamics of ultrarelativistic axially channeled electrons in thick crystals is studied. It is revealed that a certain fraction of initial electrons have anomalously large dechanneling depths. It is shown also that the dechanneling depth in heavy and light crystals are comparable. In some cases, the number of channeled electrons can strongly increase at the expence of quasi-channeled electrons.

The problem of quasichanneling is also considered.