负氢离子源中电子能量沉积三维数值模拟研究

本文理论计算了多峰离子源永磁体, 采用二体碰撞模型(binary collision)处理电子之间的库仑碰撞, 采用空碰撞(null-collision)方法处理电子与氢元素相关粒子, 开发了全三维PIC-MCC模拟算法, 并利用该算法模拟了多峰离子源中电子沉积过程, 分析了多峰磁场对电子的空间和能量分布影响, 结果显示: 电子的非均匀分布起源于高能电子在引出区的B× ▽B漂移.     

Three-dimensional PIC/MCC simulation of electron deposition in JAEA 10 A ion sources

A systematic research on the electron deposition process in the JAEA 10 A ion source is carried out by using a particle-in-cell/Monte Carlo collision simulation, which is based on a full three-dimensional self-developed code. Two parts are studied. One is the space and energy distribution of fast and slow electrons, the other is the vibration excitation collisions between electrons and hydrogen moleculars. The results show that the inhomogeneity of electrons comes from the Y direction drift of the fast electrons(Te 25 eV) due to the action of the magnetic fields. This drift also increases the number of vibration excitation collisions in the-Y direction, and results in the increase of Hain the-Y direction,eventually leading to the-Y drift of H-. It explains the spatial non-uniformity in the JAEA 10 A ion source.     

Calculation of characterisctics of electron drift in neon under a DC electric field

The features of the energy distribution function of electrons drifting in a monatomic gas are analyzed. The case of electron drift in neon under typical experimental conditions for dust structures in plasma is considered. The results of calculation of the energy balance of electrons and drift characteristics in an electric field at strengths of 0.1 < E/N < 1000 Td taking into account inelastic collisions are presented.     

Radial Distributions of Dusty Plasma Parameters in a DC Glow Discharge

A non‐stationary non‐local kinetic model for radial distributions of dusty plasma parameters based on the solution of Boltzmann equation for electron energy distribution function is presented. Electrons and ions production in ionizing collisions and their recombination on dust particle surface were taken into account. The drift‐diffusion approximation for ions was used. To obtain the self‐consistent radial distribution of electric potential the Poisson equation was used. It is shown that at high dust particle density the recombination of electrons and ions can exceed their production in ionization collisions in the region of dusty cloud. In this case the non‐monotonous radial distribution of the electric field is formed, the radial electric field becomes reversed and the radial electron and ion fluxes change their direction toward the center of the tube (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mechanisms for formation of the electron distribution function in the positive column of discharges under Langmuir-paradox conditions

The form of the electron distribution function in the positive column of low-pressure discharges is examined under conditions such that the electron mean free path exceeds the vessel radius. Its formation is analyzed taking all major factors into account, including elastic and inelastic collisions, radial and axial electric fields, and the loss of fast electrons to the wall. It is shown that the main mechanism controlling the fast part of the distribution function is the loss of electrons to the wall, which is determined by the scattering of electrons into a comparatively small loss cone that depends on the relationship between the axial and radial components of the velocity. Since the elastic collision rate for all elements has a weak dependence on the energy beyond the ionization threshold, ultimately the high-energy part of the electron energy distribution function in the positive column of low-pressure discharges is nearly Maxwellian. The subthreshold portion of the distribution function, in turn, is determined by the energy diffusion, in a comparatively strong field, of Maxwellian electrons which arrive after inelastic collisions. The final electron distribution function is well approximated by an exponential with a single slope over the entire energy range. Only within a narrow range of scattering angles is the electron distribution function strongly depleted by the loss of electrons to the vessel walls. In the end, it is concluded that this phenomenon, like the Langmuir paradox, may be related to aspects of the physics of the formation of the electron distribution function owing to a combination of already known mechanisms, rather than to a hypothetical mechanism for thermalization of the electrons, as assumed up to now in the literature. A comparison of solutions of the model kinetic equation given here with published Monte Carlo calculations and experimental data shows that they are in good agreement. Zh. Tekh. Fiz. 69, 34–41 (November 1999)     

Kinetic theory of monochromatic waves bunching in a low-voltage beam discharge in rare gases

The kinetic theory of phase focusing, that is bunching in a low-voltage beam discharge in rare gases (LVBD) during the propagation of longitudinal electrostatic oscillations at the Knudsen numbers of the order of unity have developed. The anomalous relaxation of the almost monoenergetic electron beam in momentum and energy is described for the case when this process cannot be explained by electron–atom collisions. The paper has shown the important role of electrons that have the beam energy and isotropic directional distribution, which is formed as a result of elastic collisions between the beam electrons and atoms. The dependence of the anomalous relaxation length on parameters of the LVBD in rare gases is studied.The developed theory makes it possible to quantitatively interpret experimental data on the LVBD under conditions when the electron mean free path is of the order of the interelectrode gap. According to these data, regardless of the density of the charged particles in the LVBD plasma in rare gases, five Langmuir plasma wavelengths fit along the length of the anomalous relaxation of the electron beam. The study of the electron beam dynamics laws in a plasma is important for the development of plasma-electrical devices, where the beam discharge is applied, namely: widely used all-movable stabilizers, sources of intense electromagnetic radiation, controlled elements of electronic circuits, plasma chemical reactors, etc.     

Electron distribution function in a weakly ionized He-Hg mixture

The electron energy distribution functions for He-Hg mixture in a uniform electric field are calculated for differentE/N and relative mercury concentration? from fundamental cross-section data. The Boltzmann equation is applied considering the elastic and inelastic collisions of electrons with neutrals of the both components. From these distributions and elastic collision cross-section (for He and Hg) drift velocity, diffusion coefficient and mean electron energy are computed. The electron energy losses in elastic and inelastic collisions over the considered region of the parameters are discussed.     

Potential formation in a bounded two-electron temperature plasma system with floating collector that emits electrons

Formation of the plasma potential in a plasma that contains energetic electrons and is bounded by a floating collector that emits electrons is studied theoretically. The problem is treated by a static. kinetic plasma-sheath model of Schwager and Birdsall [Phys. Fluids B2 (1990) 1057], which we have extended in order to include additional energetic electron population. The distribution of these electrons is assumed to be a high-temperature Maxwellian. They are called hot electrons. In the paper we study effects of the density and temperature of the hot electrons on the formation of the plasma potential. The model shows that for certain densities and temperatures of the hot electron population plasmas with two different plasma potentials can coexist in the system. These two plasmas are separated spatially by a double layer. For the case when there is no emission of electrons from the collector, results of the model are compared with computer simulation and very good agreement between the model and the simulation is found. The simulation also confirms existence of two plasmas with two different potentials separated by a double layer.     

Nonlinear simulations of peeling-ballooning modes with anomalous electron viscosity and their role in edge localized mode crashes

A minimum set of equations based on the peeling-ballooning (P-B) model with nonideal physics effects (diamagnetic drift, E×B drift, resistivity, and anomalous electron viscosity) is found to simulate pedestal collapse when using the new BOUT++ simulation code, developed in part from the original fluid edge code BOUT. Nonlinear simulations of P-B modes demonstrate that the P-B modes trigger magnetic reconnection, which leads to the pedestal collapse. With the addition of a model of the anomalous electron viscosity under the assumption that the electron viscosity is comparable to the anomalous electron thermal diffusivity, it is found from simulations using a realistic high-Lundquist number that the pedestal collapse is limited to the edge region and the edge localized mode (ELM) size is about 5%-10% of the pedestal stored energy. This is consistent with many observations of large ELMs.     

Anomalous light-induced drift of lithium atoms in a mixture of noble gases

This paper is a theoretical study of the spectral features of the velocity of light-induced drift (LID) of lithium atoms (⁷Li and ⁶Li) in a binary mixture of noble gases: Ne + Ar, Ne + Kr, and Ne + Xe. The spectral shape of the LID signal is predicted to depend strongly on the fraction ξ of neon in the buffer mixture in the range ξ≈0.8–0.9 (ξ=N _Ne/N _b, where N _Ne is the neon concentration, and N _b is the total concentration of the buffer particles). When the velocity of anomalous LID is treated as a function of the radiation frequency, it is found to have one, three, five, or seven zeros and to differ substantially from the dispersion-curve-like behavior with one zero predicted by the standard LID theory with velocity-independent transport collision rates. The reason for these additional zeros of the drift velocity is the alternating-sign dependence on the lithium-atom velocity of the relative difference of transport rates of collisions between buffer particles and excited and unexcited atoms. What is also established is that the anomalous LID of lithium atoms can be observed at almost all temperatures, depending on the value of ξ. At a fixed temperature, anomalous LID can be observed only in a narrow range of values of the fraction of neon in the buffer mixture, Δξ≈0.02. The results make possible highly precise testing in the LID experiments of the interatomic potentials used in calculations of the velocity spectrum of anomalous LID. Zh. éksp. Teor. Fiz. 116, 1587–1600 (November 1999)     

电子回旋共振放电的电离特性PIC/MCC模拟(Ⅱ)——数值模拟与结果讨论

采用粒子模拟与蒙特卡罗相结合(PIC/MCC)的方法，应用电磁模型，编写了准三维的电子回旋共振(ECR)放电电离过程的模拟程序，得到了ECR放电过程中电子与离子的相空间分布、电磁场分布.通过对这些分布随时间演化的分析，得出ECR加热发生在ω≈ω_c0且垂直于轴向的区域；ECR区域，微波能量几乎全部耦合给电子，获得能量的电子通过与中性粒子的电离碰撞产生了大量的带电粒子；随着放电的进行，大量带电粒子通过频繁的碰撞，分布由各向异性逐渐趋于各向同性. 关键词： 电子回旋共振放电 粒子模拟 蒙特卡罗 电离     

Relaxation of bound electrons in elastic collisions with infinitely heavy particles

The recombination relaxation of bound electrons in collisions with infinitely rigid, infinitely heavy spheres is considered. The relaxation mechanism is due to a change in the electron scattering from the spheres. The distribution functions of bound electrons and the recombination time due to that mechanism are obtained. The characteristics of the relaxation are the same as for the Thompson recombination mechanism (caused by energy transfer from the electron to a third particle) to within replacement of the mass of the third particle by the ion mass.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 48–53, April, 1996.     

潘宁源放电的全三维电磁粒子模拟/蒙特卡罗碰撞数值算法研究

深入研究潘宁放电的物理机制, 研制了全三维高品质算法粒子模拟软件(PIC), 设计并添加了相应物理情景的蒙特卡罗碰撞模块(MCC), 并对电子、氢分子离子(H₂⁺)、氢正离子(H⁺)、氢三正离子(H₃⁺)同时进行了跟踪, 成功研制了全三维电磁PIC/MCC数值算法. 结合国内研究较热的潘宁放电模型, 对该算法进行模拟验证. 模拟结果显示: 采用有效的滤波算法能抑制电磁数值噪声, 电子能量呈麦克斯韦分布, 由于电子的径向漂移和加速导致离子源顶端H₂⁺产量较大. 关键词： 潘宁离子源 高品质算法 粒子模拟/蒙特卡罗     

Electron Kinetics in the Cathode Region of a Glow Discharge and in Hollow Cathodes

On the basis of an improved cascade model a multi-group theory for studying the electron kinetics in the cathode region of a glow discharge and in hollow cathodes is developed. The secondary electrons newly created by ionization are taken into account. The electrons are divided in groups with respect to the interval where they were created or where they made an inelastic collision. The inelastic collisions and the forward scattering are assumed to dominate. The mean energies of two neighbouring groups are taken to be different by the ionization energy or by parts of it. For the flux densities of the various electron groups a set of ordinary first order differential equations and corresponding boundary conditions are obtained and solved for He. These formulae are valid for any electric potentials. The results relatively well agree with those of Monte Carlo simulations. The first Townsend ionization coefficient differs substantially from that resulting from the Townsend formula. The velocity distribution function spatially varies and contains several groups of fast electrons. Using the detour factor the angular scattering can be included in the calculations.     

Spectral and angular distribution of slow electrons emitted by hydrogen atoms in collisions with fast highly charged ions

The ionization of hydrogen atoms with the emission of slow electrons in collisions with fast highly charged ions is considered. Analytical expressions are obtained for the singly and doubly differential ionization cross sections and for a quantity which characterizes the angular asymmetry in the escape of slow electrons. A unique feature of the momentum balance for collisions that lead to the emission of slow electrons is discussed. Zh. Tekh. Fiz. 67, 13–18 (July 1997)     

Many-electron effects in atomic processes

The major role of the collectivization of electrons in atoms and quasiatomic formations is demonstrated. The random-phase approximation with exchange, which permits allowance for these effects, is discussed in detail. The need to extend the scope of this approximation when some processes are considered, which is achieved by combining it with perturbation theory, is noted. The role of the collective effects is illustrated by the results of recently performed calculations of the photoionization cross sections of atomic iodine and its positive and negative ions, the single-electron ionization of Xe⁺, resonance-enhanced photon emission in collisions of electrons with atoms and quasiatomic formations, the nondipole corrections to the angular distribution of photoelectrons, and the probabilities of two-electron transitions in which all the energy is released in the form of a single photon. Zh. Tekh. Fiz. 69, 31–35 (September 1999)     

近玻尔速度氙离子激发钒的K壳层X射线

测量了2.4—6.0 MeV Xe~(20+)离子轰击V靶表面过程中辐射的X射线.计算了V的K壳层X射线发射截面,并将实验结果与平面波恩近似、ECPSSR、两体碰撞近似的理论计算进行了对比.讨论了近玻尔速度非对称碰撞过程中,BEA模型估算高电荷态重离子激发内壳层电离的修正因素.结果表明,综合考虑库仑偏转和有效电荷态修正后,BEA理论与实验结果符合较好.     

Eine quantitative Deutung der Elektronengruppen im elektronenstrahlerzeugten He-Niederdruckplasma mit Hilfe der Boltzmannschen Stoßgleichung

Neglecting electron-electron collisions the velocity distribution of plasma electrons in a beam generated He-low pressure plasma is evaluated with help of Boltzmann equation. The energy distribution of secondary electrons generated by the electron beam is considered applying the atom collision theory ofGryzinski. The resulting velocity distribution of plasma electrons shows group character. The “temperatures” of the ultimate and secondary electrons and their density ratio are in satisfying agreement with experiment.     

Calculation of stopping power for partially stripped ions using an oscillator model

Collision of swift ions with atoms was considered in this paper. The projectile and target atoms were modeled as assemblies of quantum oscillators and it was assumed that both, target and projectile could be excited or ionized, without charge exchange. The model presented here is an extension of the one given by Sigmund and Haagerup [Phys. Rev. A 34, 892 (1986)]. The number of electrons bound to the projectile, as a function of the projectile velocity, was used from Cabrera-Trujillo et al. [Phys. Rev. A 55, 2864 (1997)]. Contributions to energy loss from excitation of the projectile and targets were separately considered. It has been found that projectile excitation contributes up to 20% to the total energy loss in the lower energy region. Comparisons with other authors, including SRIM 2003, are also given and good agreement was found.     

Non-Maxwellian Electron Velocity Distribution Resulting from Electron-SF6 Attachment Collisions

A model reaction system is considered consisting of a heat bath of argon atoms (c) and small concentrations of SF₆-molecules (m) and electrons (e) (number densities: n_e ? n_m ? n_c). Within the model the time behaviour of the electron velocity distribution function is studied under the influence of elastic electron-argon collisions and electron SF₆ attachment collisions. On the basis of the distribution function time-dependent macroscopic quantities (kinetic electron temperature. nonequilibrium rate constant of the attachment reaction) are calculated.