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1.
The radial distributions of ions,electrons and dust particles in the positive colum of glow discharges are investigated in a tripled-pole diffusion model.The dust particles are mainly trapped in the region around the column axis where the electrostatic potential is the highest.The presence of the dust particles results in the ion density increasing and the electron density decreasiung in the dust-trapped region.The dust-trapped region is wider for a higher dust temperature or a smaller particulate redius.The ions and electrons in the dust-free region away from the column axis are in ambipolar diffusion. 相似文献
2.
Quanming Lu 《中国物理 B》2022,31(8):89401-089401
Magnetic reconnection underlies the physical mechanism of explosive phenomena in the solar atmosphere and planetary magnetospheres, where plasma is usually collisionless. In the standard model of collisionless magnetic reconnection, the diffusion region consists of two substructures: an electron diffusion region is embedded in an ion diffusion region, in which their scales are based on the electron and ion inertial lengths. In the ion diffusion region, ions are unfrozen in the magnetic fields while electrons are magnetized. The resulted Hall effect from the different motions between ions and electrons leads to the production of the in-plane currents, and then generates the quadrupolar structure of out-of-plane magnetic field. In the electron diffusion region, even electrons become unfrozen in the magnetic fields, and the reconnection electric field is contributed by the off-diagonal electron pressure terms in the generalized Ohm's law. The reconnection rate is insensitive to the specific mechanism to break the frozen-in condition, and is on the order of 0.1. In recent years, the launching of Cluster, THEMIS, MMS, and other spacecraft has provided us opportunities to study collisionless magnetic reconnection in the Earth's magnetosphere, and to verify and extend more insights on the standard model of collisionless magnetic reconnection. In this paper, we will review what we have learned beyond the standard model with the help of observations from these spacecraft as well as kinetic simulations. 相似文献
3.
Direct measurements of a collisionless current channel during driven magnetic reconnection are obtained for the first time on the Versatile Toroidal Facility. The size of the diffusion region is found to scale with the electron drift orbit width, independent of the ion mass and plasma density. Based on experimental observations, analytic expressions governing the dynamical evolution of the current profile and the formation of the electrostatic potential that develops in response to the externally imposed reconnection drive are established. This time response is closely linked to the presence of ion polarization currents. 相似文献
4.
Magee RM Den Hartog DJ Kumar ST Almagri AF Chapman BE Fiksel G Mirnov VV Mezonlin ED Titus JB 《Physical review letters》2011,107(6):065005
Complementary measurements of ion energy distributions in a magnetically confined high-temperature plasma show that magnetic reconnection results in both anisotropic ion heating and the generation of suprathermal ions. The anisotropy, observed in the C(+6) impurity ions, is such that the temperature perpendicular to the magnetic field is larger than the temperature parallel to the magnetic field. The suprathermal tail appears in the majority ion distribution and is well described by a power law to energies 10 times the thermal energy. These observations may offer insight into the energization process. 相似文献
5.
On 1 April 2001, the Polar satellite crossed a subsolar magnetopause associated with antiparallel magnetic fields. Over a width approximately 6 magnetosheath ion skin depths (approximately 3 magnetospheric ion skin depths), perpendicular ion flows different from E x B/B(2) as well as Hall magnetic and electric field signatures were observed. At a smaller scale, the electron flow decoupled from the magnetic field near a deep minimum in the magnetic field strength. Separatrices were identified as boundaries of low frequency electric field turbulence associated with density minima and parallel electric fields. The reconnection rate was less than 2% of the asymptotic Alfvén speed. 相似文献
6.
Khotyaintsev YV Vaivads A André M Fujimoto M Retinò A Owen CJ 《Physical review letters》2010,105(16):165002
We report in situ observations of high-frequency electrostatic waves in the vicinity of a reconnection site in the Earth's magnetotail. Two different types of waves are observed inside an ion-scale magnetic flux rope embedded in a reconnecting current sheet. Electron holes (weak double layers) produced by the Buneman instability are observed in the density minimum in the center of the flux rope. Higher frequency broadband electrostatic waves with frequencies extending up to f(pe) are driven by the electron beam and are observed in the denser part of the rope. Our observations demonstrate multiscale coupling during the reconnection: Electron-scale physics is induced by the dynamics of an ion-scale flux rope embedded in a yet larger-scale magnetic reconnection process. 相似文献
7.
Effects of Ion-to-Electron Mass Ratio on Electron Dynamics in Collisionless Magnetic Reconnection 总被引:3,自引:0,他引:3
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A 2 1/2-dimensional electromagnetic particle-in-cell (PIC) simulation code is used to investigate electron behaviour in collisionless magnetic reconnectfon. The results show that the ion/electron mass ratio (mi/me) almost has no impact on the reconnection rate, however it can significantly affect electron behaviour in the diffusion region. For the case with larger mass ratio, the width of electron current sheet becomes smaller and the outflow region along the separatrix is smaller, hence the peak of the electron outflow speed is essentially larger. Density cavities and the parallel electric field E// along the separatrix can be found in the case with larger mass ratio, which may have significant influences on the acceleration and heating of the electrons near the X point. 相似文献
8.
Formation of electron depletion layer and parallel electric field in the separatrix region of anti-parallel magnetic reconnection
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《中国物理 B》2019,(7)
It is generally accepted that during collisionless magnetic reconnection, electrons flow toward the X line in the separatrix region, and then an electron depletion layer is formed.In this paper, with two-dimensional(2 D) particle-in-cell(PIC)simulation, we investigate the characteristics of the separatrix region during magnetic reconnection.In addition to the electron depletion layer, we find that there still exists an electric field parallel to the magnetic field in the separatrix region.Because a reduced ion-to-electron mass ratio and light speed are usually used in PIC simulation models, we also change these parameters to analyze the characteristics of the separatrix region.It is found that the increase in the ion-to-electron mass ratio makes the electron depletion layer and the parallel electric field more obvious, while the influence of light speed is less pronounced. 相似文献
9.
The PWI/WFC data onboard Geotail during one burst time interval when Geotail is skimming a magnetic reconnection diffusion region in the near-Earth magnetotail is carefully analyzed.Both the whistler-mode wave and the electrostatic solitary wave are found within the region with density depletion on the boundary layer near the magnetic reconnection X-line.The whistler-mode wave is electromagnetic whistler wave propagating quasi-parallel to the ambient field with a small angle between the wave vector and the ambient magnetic field.The whistler-mode wave associated with ESWs suggests that enhanced electromagnetic whistler-mode fluctuations can also be generated after the decay of the ESWs,which is different from the 2-D PIC simulation results. 相似文献
10.
Quantitative, comprehensive, analytical model for magnetic reconnection in Hall magnetohydrodynamics
Dissipation-independent, or "fast", magnetic reconnection has been observed computationally in Hall magnetohydrodynamics (MHD) and predicted analytically in electron MHD. However, a quantitative analytical theory of reconnection valid for arbitrary ion inertial lengths, d{i}, has been lacking and is proposed here for the first time. The theory describes a two-dimensional reconnection diffusion region, provides expressions for reconnection rates, and derives a formal criterion for fast reconnection in terms of dissipation parameters and d{i}. It also confirms the electron MHD prediction that both open and elongated diffusion regions allow fast reconnection, and reveals strong dependence of the reconnection rates on d{i}. 相似文献
11.
12.
Observations of an extremely elongated electron diffusion region occurring during fast reconnection are presented. Cluster spacecraft in situ observations of an expanding reconnection exhaust reveal a broad current layer ( approximately 10 ion skin depths thick) supporting the reversal of the reconnecting magnetic field together with an intense current embedded at the center that is due to a super-Alfvénic electron outflow jet with transverse scale of approximately 9 electron skin depths. The electron jet extends at least 60 ion skin depths downstream from the X-line. 相似文献
13.
《Physica A》2006,371(2):195-208
The unsteady hydromagnetic Couette flow and heat transfer between two parallel porous plates is studied with the Hall effect and temperature dependent properties. The fluid is acted upon by a constant pressure gradient and an external uniform magnetic field as well as uniform suction and injection applied perpendicular to the parallel plates. A numerical solution for the governing non-linear equations of motion and the energy equation are obtained. The effect of the Hall term and the temperature-dependent viscosity and thermal conductivity on both velocity and temperature distributions is examined. 相似文献
14.
15.
Ono Y Tanabe H Hayashi Y Ii T Narushima Y Yamada T Inomoto M Cheng CZ 《Physical review letters》2011,107(18):185001
Characteristics of the high-power reconnection heating were measured for the first time directly by two-dimensional measurements of ion and electron temperatures. While electrons are heated mainly inside the current sheet by the Ohmic heating power, ions are heated mainly by fast shock or viscosity damping of the reconnection outflow in the two downstream areas. The magnetic reconnection converts the energy of reconnecting magnetic field B(p) mostly to the ion thermal energy, indicating that the reconnection heating energy is proportional to B(p)(2). 相似文献
16.
Wästerby P Orädd G Lindblom G 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,157(1):156-159
The anisotropy, D(parallel)/D( perpendicular ), of water diffusion in fully hydrated bilayers of dimyristoylphosphatidylcholine at 29 degrees C has been measured by pulsed magnetic field gradient (pfg) NMR. By using NMR imaging hardware to produce magnetic field gradients in an arbitrary direction with respect to a stack of macroscopically aligned lipid bilayers, translational diffusion of water was measured as a function of the angle between the direction of the magnetic field gradient and the normal of the lipid membrane. The observed diffusion coefficient is found to depend strongly on this angle. The anisotropy cannot be accurately determined due to the very small value of D( perpendicular ), but a lower limit of about 70 can be estimated from the observed diffusion coefficients. The results are discussed in terms of the relatively low permeability of water across the lipid bilayer, instrumental limitations, and/or possible defects in the lamellae. 相似文献
17.
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
18.
Electron acceleration by the inductive electric field near the X point in magnetic reconnection is an important generation mechanism for energetic electrons. Particle simulations have revealed that most of energetic electrons reside in the magnetic field line pileup region, and a depletion of energetic electrons can be found near the centre of the diffusion region [Phys. Plasmas, 13 (2006) 012309]. We report direct measurement of energetic electron in and around the ion diffusion region in near-Earth tail by the cluster, and our observations confirm the above predictions: a depletion of the high-energy electron fluxes is detected near the centre of the diffusion region. At the same time, the plasma temperature has a similar profile in the diffusion region. . 相似文献
19.
Boozer AH 《Physical review letters》2002,88(21):215005
A magnetic evolution is ideal if it is consistent with the field being embedded in a perfectly conducting fluid. Faraday's law implies the evolution is ideal when the parallel component of the electric field is the derivative of a scalar potential, a condition that generically holds in any local region of space. Reconnection requires the non-existence of such a potential. In systems with two periodic directions, non-existence focuses reconnection onto the surfaces in which the magnetic field lines close on themselves, the rational surfaces. This rational surface effect does not arise in astrophysics but does appear in periodic simulation codes. Effects that could give astrophysical reconnection are discussed. 相似文献
20.
《Physics letters. A》2006,358(2):149-153
By using the equilibrium equations for a hollow cylindrical piezoelectric layer in absence of body forces and taking into the account a magnetized electron beam in hollow region of this system the effects of thermal pressure, electrostatic self field and the strength of external magnetic field of a non-relativistic magnetized electron beam column on radially polarized of an annular cylindrical piezoelectric crystal in the steady state are simulated. The electrostatic potential profile in piezoelectric layer due to the mechanical pressure and electrostatic self field of electron beam are studied. Furthermore the graphs of the difference of potential Δϕ between inner and outer surfaces of piezoelectric versus to electron temperature, density of beam and the strength of external magnetic field are presented. 相似文献