Nonlinear development of collisionless driven reconnection and the consequent energy conversion process between the field and particles in a sheared magnetic field are investigated by means of a two-and-one-half-dimensional particle simulation. Magnetic reconnection takes place in two steps irrespective of a longitudinal magnetic field, but the growth rate of the reconnection field varies in proportion to the E؋B drift velocity at an input boundary. It is clearly observed that the triggering mechanism of collisionless driven reconnection for the fast growing phase changes from an electron meandering dominance in a weak longitudinal field to an electron inertia dominance in a strong field. The electron acceleration and heating take place in the reconnection area under the influence of reconnection electric field, while the electron energy is converted to the ion energy through the action of an electrostatic ͑ambipolar͒ field excited by magnetic compression in the downstream. It is also found that, in the presence of a longitudinal magnetic field, the electron acceleration by the reconnection field takes place effectively and the generated force-free current is maintained for a long period while forming an asymmetric spatial profile of current layer. © 1997 American Institute of Physics. ͓S1070-664X͑97͒00302-9͔
Driven magnetic reconnection in a collisionless plasma, "collisionless driven reconnection," is investigated by means of two-and-one-half-dimensional particle simulation. Magnetic reconnection develops in two steps, i.e., slow reconnection, which takes place in the early stage of the compression when the current layer is compressed as thin as the orbit amplitude of an ion meandering motion (ion current layer), and subsequent fast reconnection, which takes place in the late stage when the electron current is concentrated into the narrow region with a spatial scale comparable to the orbit amplitude of an electron meandering motion (electron current layer). The global dynamic evolution of magnetic reconnection is controlled by the physics of the ion current layer. The maximum reconnection rate is roughly in proportion to the driving electric field. It is also found that both ion heating and electron heating take place in accordance with the formation of two current layers and the ion temperature becomes two or more times as high as the electron temperature.
Generation of anomalous resistivity and dynamical development of collisionless reconnection in the vicinity of a magnetically neutral sheet are investigated by means of a three-dimensional particle simulation. For no external driving source, two different types of plasma instabilities are excited in the current layer. The lower hybrid drift instability ͑LHDI͒ is observed to grow in the periphery of current layer in an early period, while a drift kink instability ͑DKI͒ is triggered at the neutral sheet in a late period as a result of the nonlinear deformation of the current sheet by the LHDI. A reconnection electric field grows at the neutral sheet in accordance with the excitation of the DKI. When an external driving field exists, the convective electric field penetrates into the current layer through the particle kinetic effect and collisionless reconnection is triggered by the convective electric field earlier than the DKI is excited. It is also found that the anisotropic ion distribution is formed through the anomalous ion heating by the DKI.
A new simulation method has been developed to investigate the excitation and saturation processes of toroidal Alfven eigenmodes (TAE modes). The background plasma is described by a magnetohydrodynamic (MHD) fluid model, while the kinetic evolution of energetic alpha particles is followed by the drift kinetic equation. The magnetic tluctuation of n=2 mode develops and saturates at the level of 1.8X 10m3 of the equilibrium field when the initial beta of alpha particles is 2% at the magnetic axis. after saturation, the TAE mode amplitude shows an oscillatory behavior with a frequency corresponding to the bounce frequency of the alpha particles trapped by the TAE mode. The decrease of the power transfer rate from the alpha particles to the TAE mode, which is due to the trapped particle effect of a finite-amplitude wave, causes the saturation. From the linear growth rate the saturation Ievel can be estimated. 0 1995 American Institute of Physics.
Long time scale evolution of collisionless driven reconnection in an open system is investigated by means of two-dimensional full particle simulation based on an open boundary model. Collisionless reconnection is externally driven by the plasma inflow, which is mainly controlled by two key parameters of an external driving electric field, i.e., the strength E0 and the early nonuniformity scale xd. The strength E0 controls reconnection rate, while the scale xd controls the current layer shape and thus the magnetic-field configuration. It is found that the dynamical behavior of collisionless reconnection is sensitive to xd and less to E0 in our simulation parameter range. In the small xd case, the system evolves toward a steady state in which the reconnection rate is balanced with the external driving field E0. As xd increases, the reconnection evolution exhibits an intermittent phenomenon because of the frequent excitation of magnetic islands near the original X point.
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