Formation of inner structure of a reconnection separatrix region

We present multipoint spacecraft observations at the dayside magnetopause of a magnetic reconnection separatrix region. This region separates two plasmas with significantly different temperatures and densities, at a large distance from the X line. We identify which terms in the generalized Ohm's law balance the observed electric field throughout the separatrix region. The electric field inside a thin approximately c/omega pi Hall layer is balanced by the j x B/ne term while other terms dominate elsewhere. On the low density side of the region we observe a density cavity which forms due to the escape of magnetospheric electrons along the newly opened field lines. The perpendicular electric field inside the cavity constitutes a potential jump of several kV. The observed potential jump and field aligned currents can be responsible for strong aurora.     

Kinetic structure of the electron diffusion region in antiparallel magnetic reconnection

Strong electron pressure anisotropy has been observed upstream of electron diffusion regions during reconnection in Earth's magnetotail and kinetic simulations. For collisionless antiparallel reconnection, we find that the anisotropy drives the electron current in the electron diffusion region, and that this current is insensitive to the reconnection electric field. Reconstruction of the electron distribution function within this region at enhanced resolutions reveals its highly structured nature and the mechanism by which the pressure anisotropy sets the structure of the region.     

Two-scale structure of the electron dissipation region during collisionless magnetic reconnection

Particle-in-cell simulations of collisionless magnetic reconnection are presented that demonstrate that reconnection remains fast in very large systems. The electron dissipation region develops a distinct two-scale structure along the outflow direction. Consistent with fast reconnection, the length of the electron current layer stabilizes and decreases with decreasing electron mass, approaching the ion inertial length for a proton-electron plasma. Surprisingly, the electrons form a super-Alfvénic outflow jet that remains decoupled from the magnetic field and extends large distances downstream from the x line.     

平行电磁场中H-光剥离电子轨道分岔现象的研究

当改变能量、位置或场强等参数时,电磁场中里德堡态的原子、分子和离子等体系将出现分岔现象,从而导致波函数在分岔点附近发散,半经典闭合轨道理论不再适用.本文分析并计算了平行电磁场中H-光剥离电子轨道的分岔现象,并采用统一近似的方法进行定域修正,从而消除了分岔点的奇异性,得到了合理的光剥离电子流的分布.     

Magnetohydrodynamic theories of magnetic field reconnection

This article is concerned with a review of the prominent magnetohydrodynamic theories proposed to date to explain magnetic field reconnection. These theories fall into three categories: (i) resistive tearing-mode instability, (ii) steady externally driven processes, (iii) nonsteady externally driven processes. The purpose of this article is to give on the analytical side - (i) a detailed discussion including a critical appraisal of the existing pr ominent theories of magnetic reconnection, (ii) a further elaboration and more correct versions and extensions of some of the existing theories of magnetic reconnection, and a review of the laboratory and computational work on the problem. The controversies that surround the application of these theories to problems involving explosive releases of magnetic energy are discussed.     

Motion of electron with anomalous moments in parallel electric and magnetic fields

An accurate solution is obtained for the Dirac equation describing the motion of an electron with anomalous moments in constant, homogeneous, and parallel electric and magnetic fields. The system of solutions obtained is shown to be orthogonal and complete with respect to the scalar product defined in the null plane X^oX³=const. The solutions obtained pass smoothly in the limit to steadystate solutions describing the motion of an electron with anomalous moments in a homogeneous magnetic field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 23–28, January, 1978.It remains to thank V. G. Bagrov for useful discussions of the work.     

Energetic electrons associated with magnetic reconnection in the magnetic cloud boundary layer

Here is reported in situ observation of energetic electrons (～100-500 keV) associated with magnetic reconnection in the solar wind by the ACE and Wind spacecraft. The properties of this magnetic cloud driving reconnection and the associated energetic electron acceleration problem are discussed. Further analyses indicate that the electric field acceleration and Fermi-type mechanism are two fundamental elements in the electron acceleration processes and the trapping effect of the specific magnetic field configuration maintains the acceleration status that increases the totally gained energy.     

Thermodynamic characteristics of a nonrelativistic electron in constant parallel electric and magnetic fields

The large statistical sum of a noninteracting nonrelativistic electron gas in constant parallel electric and magnetic fields is calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 64–67, September, 1979.     

Quasi-two-dimensional electron gas in a non-quantizing magnetic field and strong non-quantizing electric field

A calculation is performed to determine the transverse electric field E_y formed in quasi-two-dimensional superlattices in a strong drift field E_x and a weak magnetic field that is perpendicular to the plane of the superlattice (H‖OZ). When the electronic energy spectrum is nonadditive, the field E_y includes both the Hall factor and a spontaneous transverse electric field that exists whetherH is present or not. The situation when the specimen is in a closed circuit with a resistor on the OY axis is examined. As the function E_x, the field E_y is multivalued (multistable) and variable. The stability of the branches of the function E_y(E_x) is determined using a specially introduced (kinetic) “potential” whose minimum corresponds to the steady state of a nonequilibrium electron gas. Volgograd State Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 46–51, July, 1996.     

Magnetoresistance of a two-dimensional electron gas in a parallel magnetic field

The conductivity of a two-dimensional electron gas in a parallel magnetic field is calculated. We take into account the magnetic-field-induced spin-splitting, which changes the density of states, the Fermi momentum, and the screening behavior of the electron gas. For impurity scattering, we predict a positive magnetoresistance for low electron density and a negative magnetoresistance for high electron density. The theory is in qualitative agreement with recent experimental results found for Si inversion layers and Si quantum wells.     

Compressibility of a two-dimensional electron gas in a parallel magnetic field

The thermodynamic compressibility of a two-dimensional electron system in the presence of an in-plane magnetic field is calculated. We use accurate correlation energy results from quantum Monte Carlo simulations to construct the ground state energy and obtain the critical magnetic field B_c required to fully spin polarize the system. Inverse compressibility as a function of density shows a kink-like behavior in the presence of an applied magnetic field, which can be identified as B_c. Our calculations suggest an alternative approach to transport measurements of determining full spin polarization.     

New measure of the dissipation region in collisionless magnetic reconnection

A new measure to identify a small-scale dissipation region in collisionless magnetic reconnection is proposed. The energy transfer from the electromagnetic field to plasmas in the electron's rest frame is formulated as a Lorentz-invariant scalar quantity. The measure is tested by two-dimensional particle-in-cell simulations in typical configurations: symmetric and asymmetric reconnection, with and without the guide field. The innermost region surrounding the reconnection site is accurately located in all cases. We further discuss implications for nonideal MHD dissipation.     

Significant discrepancy between the ionization time for parallel and anti-parallel electron emission in sequential double ionization

The ionization time in sequential double ionization with an elliptically polarized laser pulse has been examined theo- retically using a semiclassical method. The significant discrepancy between the ionization time for parallel and anti-parallel electron emission is predicted numerically for the first time. The impact of the carrier envelope phase offset is also studied in this work.     

Motion of an electron from a point source in parallel electric and magnetic fields

Negative ions undergoing near-threshold photodetachment in a weak laser field provide an almost pointlike, isotropic source of low-energy electrons. External fields exert forces on the emitted coherent electron wave and direct its motion. Here, we examine the spatial distribution of photodetached electrons in uniform, parallel electric and magnetic fields. The interplay of the electric and magnetic forces leads to a surprising intricate shape of the refracted electron wave, and multiple interfering trajectories generate complex fringe patterns in the matter wave. The exact quantum solution is best understood in terms of the classical electron motion.     

Evidence for electron acceleration up to approximately 300 keV in the magnetic reconnection diffusion region of earth's magnetotail

We report direct measurements of high-energy particles in a rare crossing of the diffusion region in Earth's magnetotail by the Wind spacecraft. The fluxes of energetic electrons up to approximately 300 keV peak near the center of the diffusion region and decrease monotonically away from this region. The diffusion region electron flux spectrum obeys a power law with an index of -3.8 above approximately 2 keV, and the electron angular distribution displays strong field-aligned bidirectional anisotropy at energies below approximately 2 keV, becoming isotropic above approximately 6 keV. These observations indicate significant electron acceleration inside the diffusion region. Ions show no such energization.     

Intersubband excitations in single-and double-layer electron systems in a parallel magnetic field

The spectrum of neutral intersubband excitations in single and double quantum wells has been studied by the inelastic light scattering method. It is shown that excitation energies in an external magnetic field have an anisotropic component proportional to the dipole moment of excitations along the growth axis of the quantum wells. Consequently, the measurement of excitation energy in a magnetic field makes it possible to experimentally estimate the quantitative measure of asymmetry of the quantum wells (dipole moment of the intersubband transition). In addition, a parallel magnetic field makes it possible to considerably extend the range of momenta studied since it shifts the dispersion curves in the momentum space by the value of the anisotropic component. A new method is proposed for determining the symmetry of double quantum wells. In asymmetric wells, intersubband excitations appear between the layers and have a large dipole moment along the growth axis. In symmetric wells, the magnetic field itself induces the dipole moment of intersubband excitations so that the excitation spectrum does not change upon magnetic field inversion. Analysis of energy anisotropy in intersubband excitations in double quantum wells makes it possible to determine the symmetry of double wells to a high degree of accuracy.     

Structure of the magnetic reconnection diffusion region from four-spacecraft observations

Magnetic reconnection leads to energy conversion in large volumes in space but is initiated in small diffusion regions. Because of the small sizes of the diffusion regions, their crossings by spacecraft are rare. We report four-spacecraft observations of a diffusion region encounter at the Earth's magnetopause that allow us to reliably distinguish spatial from temporal features. We find that the diffusion region is stable on ion time and length scales in agreement with numerical simulations. The electric field normal to the current sheet is balanced by the Hall term in the generalized Ohm's law, E(n) approximately jxB/ne.n, thus establishing that Hall physics is dominating inside the diffusion region. The reconnection rate is fast, approximately 0.1. We show that strong parallel currents flow along the separatrices; they are correlated with observations of high-frequency Langmuir/upper hybrid waves.     

Forced magnetic reconnection and field penetration of an externally applied rotating helical magnetic field in the TEXTOR tokamak

The magnetic field penetration process into a magnetized plasma is of basic interest both for plasma physics and astrophysics. In this context special measurements on the field penetration and field amplification are performed by a Hall probe on the dynamic ergodic divertor (DED) on the TEXTOR tokamak and the data are interpreted by a two-fluid plasma model. It is observed that the growth of the forced magnetic reconnection by the rotating DED field is accompanied by a change of the plasma fluid rotation. The differential rotation frequency between the DED field and the plasma plays an important role in the process of the excitation of tearing modes. The momentum input from the rotating DED field to the plasma is interpreted by both a ponderomotive force at the rational surface and a radial electric field modified by an edge ergodization.     

Crossover behavior of disordered interacting two-dimensional electron systems in a parallel magnetic field

The crossover behavior of disordered interacting two-dimensional electron systems in a parallel magnetic field is analyzed. Using the so-called crossover one-loop renormalization group equations for the resistance and electron-electron interaction amplitudes, experimentally observed transformation of the temperature dependence of the resistance from a reentrant (nonmonotonic) behavior in relatively weak fields to an insulating-type behavior in stronger fields is qualitatively explained. The text was submitted by the authors in English.     

Identification of the electron-diffusion region during magnetic reconnection in a laboratory plasma

We report the first identification of the electron-diffusion region, where demagnetized electrons are accelerated to super-Alfvénic speed, in a reconnecting laboratory plasma. The width of the electron-diffusion region scales with the electron skin depth [ approximately (5.5-7.5)c/omega_{pe}] and the peak electron outflow velocity scales with the electron Alfvén velocity [ approximately (0.12-0.16)V_{eA}], independent of ion mass.