共查询到20条相似文献,搜索用时 265 毫秒
1.
通过Fokker-Planck模拟,研究了等离子体在任意强度的直流电场中产生电流的过程以及电子分布函数的演变过程.研究发现,不同强度的电场中等离子体的行为存在着明显的差别.在弱电场中,电流与电场满足Spitzer公式,且电流产生的响应时间约等于撤销电场后电流衰减的弛豫时间;在中等强度的电场中,电子分布函数呈现为静止Maxwell分布和漂移Maxwell分布之和,而且在中等强度或者强直流电场中弛豫时间也将远远大于响应时间.根据电子分布函数的演变规律,推导了一组类似于流体力学方程的公式,这组方程像Spitzer公式一样简便地描述了等离子体中电流与电场的关系,并且对电场强度没有限制.数值模拟显示这组方程比Spitzer公式更适用于等离子体的混合粒子模拟中.
关键词:
等离子体电流
电子分布函数
Fokker-Planck模拟
Spitzer公式 相似文献
2.
The dynamic evolution of the boundary between the ionosphere and auroral cavity is studied using 1D and 2D kinetic Vlasov simulations. The initial distributions of three singly ionized species (H+, O+, e-) are determined from space-based observations on both sides of an inferred strong double layer. The kinetic simulations reproduce features of parallel electric fields, electron distributions, ion distributions, and wave turbulence seen in satellite observations in the auroral upward-current region and, for the first time, demonstrate that auroral acceleration can be driven by a parallel electric field supported, in part, by a quasistable, strong double layer. In addition, the simulations verify that the streaming interaction between accelerated O+ and H+ populations continuously replenished by the double layer provides the free energy for the persistent formation of ion phase-space holes. 相似文献
3.
Reza Fallah Reza Khooniki Seyed Mohammad Khorashadizadeh Ali Reza Niknam 《等离子体物理论文集》2021,61(2):e202000086
The influence of relativistic-ponderomotive nonlinearities and the plasma inhomogeneity on the nonlinear interaction between a high-power laser beam and a warm underdense plasma are studied. It is clear that the relativistic ponderomotive force and the electron temperature modify the electron density distribution and consequently change the dielectric permittivity of the plasma. Therefore, by presenting the modified electron density and the nonlinear dielectric permittivity of the warm plasma, the electromagnetic wave equation for the propagation of intense laser beam through the plasma is derived. This nonlinear equation is numerically solved and the distributions of electromagnetic fields in the plasma, the variations of electron density, and plasma refractive index are investigated for two different background electron density profiles. The results show that the amplitude of the electric field and electron density oscillations gradually increase and decrease, during propagation in the inhomogeneous warm plasma with linear and exponential density profiles, respectively, and the distribution of electron density becomes extremely sharp in the presence of intense laser beam. It is also indicated that the electron temperature and initial electron density have an impact on the propagation of the laser beam in the plasma and change the plasma refractive index and the oscillations' amplitude and frequency. The obtained results indicate the importance of a proper choice of laser and plasma parameters on the electromagnetic field distributions, density steepening, and plasma refractive index variations in the interaction of an intense laser beam with an inhomogeneous warm plasma. 相似文献
4.
The mechanisms behind limitation of current of nonrelativistic high-current electron beams in the plasma-filled diode immersed
in the external guiding magnetic field whose intensity is comparable with that of the beam self magnetic field are studied.
It is shown that the beam current is limited by transmission capacity of the double layer between the cathode and anode plasma
on the one hand and, on the other hand, by charge neutralization of the beam and by the decrease of the longitudinal velocity
of the beam electrons under the action of the induced electric field and of the beam self magnetic field. The effect of the
beam self fields on its cross-sectional current density and energy distributions is studied. Results of the numerical simulations
are in good agreement with the experimental data. 相似文献
5.
Li YT Yuan XH Xu MH Zheng ZY Sheng ZM Chen M Ma YY Liang WX Yu QZ Zhang Y Liu F Wang ZH Wei ZY Zhao W Jin Z Zhang J 《Physical review letters》2006,96(16):165003
A novel fast electron beam emitting along the surface of a target irradiated by intense laser pulses is observed. The beam is found to appear only when the plasma density scale length is small. Numerical simulations reveal that the electron beam is formed due to the confinement of the surface quasistatic electromagnetic fields. The results are of interest for potential applications of fast electron beams and deep understanding of the cone-target physics in the fast ignition related experiments. 相似文献
6.
7.
采用自洽场离子球模型,研究类氢氖基态1s的电离势随等离子体电子温度及电子密度的变化规律,计算得到基态电离势的百分偏移量随等离子体电子密度的变化关系,拟合结果表明两者的对数值满足很好的线性关系.该结果对计算等离子体电离态分布及光谱模拟具有一定意义. 相似文献
8.
V. Ya. Martens 《Technical Physics》2002,47(11):1389-1396
It is shown experimentally that the plasma of a hollow-cathode reflex discharge is characterized by a nonequilibrium electron velocity distribution. The parameters of the electron distribution, which is approximated by a superposition of two Maxwellian distributions with different temperatures, are estimated. The penetration of the discharge plasma into the hollow cathode at various cathode potentials and a gas pressure of ∼10\t− 2 Pa is studied. It is shown that the plasma parameters in the hollow electrode depend not only on the parameters of the reflex-discharge plasma, but also on the magnitude and configuration of the magnetic and electric fields in the plasma expansion region. It is shown that the plasma penetration can be accompanied by quasineutrality violation and the formation of space-charge double layers. Experiments confirm that the ion current from the nonequilibrium plasma exceeds the Bohm current. 相似文献
9.
Previous 2D simulations of reconnection using a standard model of initially antiparallel magnetic fields have detected electron jets outflowing from the x point into the ion outflow exhausts. Associated with these jets are extended "outer electron diffusion regions." New PIC simulations with an ion to electron mass ratio as large as 1836 (an H(+) plasma) now show that the jets are strongly deflected and the outer electron diffusion region is broken up by a very weak out-of-plane magnetic guide field, even though the diffusion rate itself is unchanged. Jet outflow and deflection are interpreted in terms of electron dynamics and are compared to recent measurements of jets in the presence of a small guide field in Earth's magnetosheath. 相似文献
10.
H. Nowakowska M. Jasiński J. Mizeraczyk 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(2):511-518
We present results from simulations of 2D distributions of the electromagnetic field inside a waveguide-based axial-type microwave
plasma source (MPS) used for hydrogen production via methane reforming. The studies are aimed at optimization of discharge
processes and hydrogen production. We derive equations for determining electromagnetic field distributions and next determine
the electromagnetic field distributions for two cases – without and with plasma inside the MPS. For the first case, we examine
the influence of the length of the inner conductor of the coaxial line on electromagnetic field distributions. We have obtained
standing wave patterns along the coaxial line and found resonances for certain positions of the coaxial line inner conductor.
For the case with plasma inside the MPS, we perform calculations assuming that distributions of plasma parameters are known.
Simulations are done for several values of maximum electron density. We have found that for values of electron density greater
than strong skin effect in the plasma is observed. Consequently, plasma may be treated as an extension of the inner conductor
of the coaxial line. We have used FlexPDE software for the calculations. 相似文献
11.
应用一维相对论电磁粒子模拟程序,详细研究了线性极化强激光入射到无碰撞稀疏密度长等离子体中引起的受激Raman散射、Raman级联散射、级联散射到光子凝聚、以及大振幅电磁孤立子的产生与加速. 通过研究发现:在适当的激光振幅和等离子体状态下,强的光子凝聚现象会导致大振幅电磁孤立子的产生,电磁孤立子可以以静止、向后以及向前加速的形式存在;在密度均匀的等离子体中,电磁孤立子的加速不仅依赖于激光振幅而且依赖于等离子体的长度;电磁孤立子的电磁频率大约为未扰动电子等离子体振荡频率的二分之一左右,孤立子内电磁场的电场具有半周期结构,相应电磁场的磁场以及静电场则具有一个完整的周期结构.
关键词:
粒子模拟
受激Raman散射
Raman级联散射
光子凝聚
电磁孤立子 相似文献
12.
通过在狄拉克方程中考虑德拜休克尔(Debye-Hückel)屏蔽势,研究了类氢离子C5 低能级能量1s(2S1/2),2s(2S1/2),2p(2P1/2和2P3/2)随等离子体电子温度及电子密度的变化规律,计算得到类氢离子C5 能级能量及能级电离势随等离子体环境的变化关系。同时,拟合得到了基于德拜休克尔屏蔽势下相当好的束缚态能级能量随等离子体环境变化的解析公式,利用该公式得到了类氢离子C5 相应各能级发生压致电离的临界电子密度,其结果与其它文献比有很好的可比性。结果表明:束缚态能级能量随等离子体电子温度的升高而减小,随等离子体电子密度的增大而增大。能级能量百分漂移量的对数值与等离子体电子密度的对数值以及等离子体电子温度的对数值之间均呈现出近似线性关系。对计算等离子体电离态分布及光谱模拟具有一定的意义。 相似文献
13.
V. V. Ivanov T. V. Rakhimova A. O. Serov N. V. Suetin A. F. Pal’ 《Journal of Experimental and Theoretical Physics》1999,88(6):1105-1114
Elementary processes in dusty, beam-driven plasma discharges are studied experimentally and theoretically for the first time.
A theoretical model is constructed for a beam-driven plasma containing macroscopic particles. The effect of macroscopic particles
on the electron energy distribution function is estimated assuming a Coulomb field for the particles. The resulting rate of
electron-ion recombination on the macroscopic particles is compared with the electron loss constant calculated from the electron
energy distribution function with an electron absorption constant in the orbital-motion approximation. This approximation,
which is valid in the collisionless case, is found to work satisfactorily beyond its range of applicability. The distributions
of the charged particles and electric fields created by macroscopic particles in a helium plasma are determined. The experimental
data demonstrate the importance of secondary emission by high-energy electrons.
Zh. éksp. Teor. Fiz. 115, 2020–2036 (June 1999) 相似文献
14.
模拟了强流电子束源阴极表面附近区域数密度约1014 cm-3的等离子体的膨胀过程,观察到等离子体膨胀速度约为1 cm/μs。通过观察不同时刻阴极附近电子和离子的相空间分布、数密度分布和轴向电场分布,分析了等离子体膨胀过程。结果表明:等离子体的产生使得阴极表面电场增强,进而增大阴极的电流发射密度,电流密度增加使得空间电荷效应增强,并使等离子体前沿处的电场减小,当等离子体前沿处的电场减小到零时等离子体向阳极膨胀。讨论了等离子体温度、离子质量、束流密度和离子产生率对等离子体膨胀速度的影响。结果表明:等离子体的膨胀速度随着等离子体温度升高而增大,随离子质量增大而减小,但膨胀速度不等于离子声速;等离子体产生率越小,等离子体膨胀速度越小。 相似文献
15.
Using direct numerical simulations, we calculate the rate of divergence of neighboring magnetic-field lines in different types of strong magnetohydrodynamic turbulence. In the static-magnetic-field approximation, our results imply that tangled magnetic fields in galaxy clusters reduce the electron diffusion coefficient and thermal conductivity by a factor of approximately 5-10, relative to their values in a nonmagnetized plasma. 相似文献
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17.
Sheng ZM Mima K Sentoku Y Jovanović MS Taguchi T Zhang J Meyer-Ter-Vehn J 《Physical review letters》2002,88(5):055004
We propose a mechanism that leads to efficient acceleration of electrons in plasma by two counterpropagating laser pulses. It is triggered by stochastic motion of electrons when the laser fields exceed some threshold amplitudes, as found in single-electron dynamics. It is further confirmed in particle-in-cell simulations. In vacuum or tenuous plasma, electron acceleration in the case with two colliding laser pulses can be much more efficient than with one laser pulse only. In plasma at moderate densities, such as a few percent of the critical density, the amplitude of the Raman-backscattered wave is high enough to serve as the second counterpropagating pulse to trigger the electron stochastic motion. As a result, even with one intense laser pulse only, electrons can be heated up to a temperature much higher than the corresponding laser ponderomotive potential. 相似文献
18.
Large amplitude electromagnetic solitons in intense laser plasma interaction 总被引:1,自引:0,他引:1
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This paper shows that the standing, backward- and forward-accelerated large
amplitude relativistic electromagnetic solitons induced by intense laser pulse in
long underdense collisionless homogeneous plasmas can be observed by particle
simulations. In addition to the inhomogeneity of the plasma density, the
acceleration of the solitons also depends upon not only the laser amplitude but also
the plasma length. The electromagnetic frequency of the solitons is between about
half and one of the unperturbed electron plasma frequency. The electrostatic field
inside the soliton has a one-cycle structure in space, while the transverse electric
and magnetic fields have half-cycle and one-cycle structure respectively. Analytical
estimates for the existence of the solitons and their electromagnetic frequencies
qualitatively coincide with our simulation results. 相似文献
19.
Chang T. Crew G.B. Retterrer J.M. Jasperse J.R. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1989,17(2):186-195
The exotic phenomenon of energetic ion-conic and counterstreaming electron formulation by lower hybrid waves along the discrete auroral field lines in the Earth's magnetosphere is considered. Mean particle calculations, plasma simulations, and analytical treatments of the acceleration processes are described. It is shown that, in the primary auroral electron-beam region, lower hybrid waves could be an efficient mechanism for the transverse heating of ions of ionospheric origin (H + and O+) as well as for the field-aligned heating of the ambient electrons leading to coincident counterstreaming electron distributions. For oxygen ions to be energized by such a wave-particle interaction process, however, some sort of preheating mechanism will be required 相似文献
20.
Bulanov S.V. Esirkepov T.J. Naumova N.M. Pegoraro F. Pogorelsky I.V. Pukhov A.M. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1996,24(2):393-399
We consider the interaction of high-intensity laser pulses with underdense plasmas and address the problem of the excitation of strong and stable wake plasma waves with regular electric fields to provide effective acceleration of charged particles over appreciably long distances. It is known that a relativistically strong laser pulse longer than the wavelength of plasma waves, propagating in a plasma is subject to self-modulation. This may result in a nonstationary behavior of the produced plasma wake field/particle dephasing, and reduced net acceleration. In this paper we present the results of 1(2/2)-D and 2(1/2)-D particle in cell (PIC) simulations which demonstrate that regular wake electric fields may be obtained by a properly shaped laser pulse (sharp steepening of its leading front). These results are relevant to the design of the 100 MeV laser wake field electron acceleration experiment that uses a terawatt picosecond CO2 laser and is under construction at the Brookhaven Accelerator Test Facility 相似文献