Abstract
The instability of a Harris current sheet under a broad range of finite guide field is investigated using a linearized gyrokinetic electron and fully kinetic ion particle simulation code. The simulation is carried out in the twodimensional plane containing the guide field along and the current sheet normal along . In this particle model, the rapid electron cyclotron motion is removed, while the realistic mass ratio , finite electron Larmor radii, and waveparticle interactions are kept. It is found that for a finite , where is the asymptotic antiparallel component of magnetic field, three unstable modes, i.e., modes A, B, and C, can be excited in the current sheet. Modes A and C, appearing to be quasielectrostatic modified twostream instability/whistler mode, are located mainly on the edge of the current sheet. Mode B, on the other hand, is confined in the current sheet center and carries a compressional magnetic field perturbation along the direction of electron drift velocity. Our new finding suggests that mode B may contribute directly to the electron anomalous resistivity in magnetic reconnection. In the cases with extremely large , the wave modes evolve to a globally propagating instability. The simulation shows that the presence of finite modifies the physics of the current sheet significantly.
This work was supported by DOE Grant No. DEFG0205ER54826 to Auburn University and DOE Grant No. DEFG0394ER54736 and NSF Grant No. ATM0335279 to UCI. Computer resources were provided by the NERSC supercomputer center and the Arctic Region Supercomputer Center (ARSC). The authors thank P. H. Yoon and W. Zhang for helpful discussions.
I. INTRODUCTION
II. LINEARIZED GKe/FKi SIMULATION MODEL
A. GKe/FKi scheme in approximation
B. Initial and boundary conditions
III. SIMULATION RESULTS
A. Mode A
1. dependence
2. dependence
3. dependence
B. Mode B
C. Mode C
D. General cases with multiple modes
E. Case with strong guide field
IV. SUMMARY
Key Topics
 Magnetic fields
 30.0
 Whistler waves
 21.0
 Electrical resistivity
 17.0
 Magnetic reconnection
 16.0
 Plasma instabilities
 14.0
Figures
Simulation results of case 1 (mode A). (a) Contours of the perturbed electromagnetic field , plasma density , , and in the 2D simulation plane. The dashed lines mark , and scales in the colorbars are amplified by a factor of . (b) Eigenfunctions of corresponding quantities, where the red (blue, black) line represents the real (imaginary, absolute value) part. The dashed lines mark and .
Simulation results of case 1 (mode A). (a) Contours of the perturbed electromagnetic field , plasma density , , and in the 2D simulation plane. The dashed lines mark , and scales in the colorbars are amplified by a factor of . (b) Eigenfunctions of corresponding quantities, where the red (blue, black) line represents the real (imaginary, absolute value) part. The dashed lines mark and .
Simulation results of case 1. (a) The relative powers of predominant components and , with , as a function of real frequency at different locations of , 0.5, 1, 1.5, 2, 2.5, and . The vertical dashed line marks the real frequency . (b) The power of with as a function of time at different locations at , 1, 1.5, and . The longdashed line represents with . (c) Time series plot of as a function of at .
Simulation results of case 1. (a) The relative powers of predominant components and , with , as a function of real frequency at different locations of , 0.5, 1, 1.5, 2, 2.5, and . The vertical dashed line marks the real frequency . (b) The power of with as a function of time at different locations at , 1, 1.5, and . The longdashed line represents with . (c) Time series plot of as a function of at .
Hodograms of magnetic field in plane in (a) case 1 at , (b) case 2 at , and (c) case 3 at . The arrows indicate the direction from upstream to downstream against . The field quantities are normalized to their maximum value in each case.
Hodograms of magnetic field in plane in (a) case 1 at , (b) case 2 at , and (c) case 3 at . The arrows indicate the direction from upstream to downstream against . The field quantities are normalized to their maximum value in each case.
Eigenfunctions of and with , 6.8, and 13.6 in mode A. The dashed lines mark and .
Eigenfunctions of and with , 6.8, and 13.6 in mode A. The dashed lines mark and .
Real frequency and growth rate of mode A (a) as a function of for guide field and 0.2 and =0.033, (b) as a function of electron , for and =6.8 and (c) as a function of for =6.8 and =0.033.
Real frequency and growth rate of mode A (a) as a function of for guide field and 0.2 and =0.033, (b) as a function of electron , for and =6.8 and (c) as a function of for =6.8 and =0.033.
Simulation results of case 2 (mode B): (a) contours and (b) eigenfunctions of various quantities. The dashed lines in the top (bottom) panel mark ( and ). Scales in the colorbars are amplified by a factor of .
Simulation results of case 2 (mode B): (a) contours and (b) eigenfunctions of various quantities. The dashed lines in the top (bottom) panel mark ( and ). Scales in the colorbars are amplified by a factor of .
Real frequency and growth rate of mode B (a) as a function of for , , and and (b) as a function of for , and .
Real frequency and growth rate of mode B (a) as a function of for , , and and (b) as a function of for , and .
Simulation results of case 3 (mode C): (a) contours and (b) eigenfunctions of various quantities. The dashed lines in the top (bottom) panel mark ( and ). Scales in the colorbars are amplified by a factor of .
Simulation results of case 3 (mode C): (a) contours and (b) eigenfunctions of various quantities. The dashed lines in the top (bottom) panel mark ( and ). Scales in the colorbars are amplified by a factor of .
Real frequency of modes A, B, and C and growth rate of eigenmode (a) as a function of for , , and and (b) as a function of for , , and .
Real frequency of modes A, B, and C and growth rate of eigenmode (a) as a function of for , , and and (b) as a function of for , , and .
The relative powers of perturbed electromagnetic quantities as a function of the real frequency at different ’s for (a) case 4 and (b) case 5.
The relative powers of perturbed electromagnetic quantities as a function of the real frequency at different ’s for (a) case 4 and (b) case 5.
Simulation results of case 6 for extremely large guide field : (a) contours and (b) eigenfunctions of various quantities. Scales in the colorbars are amplified by a factor of .
Simulation results of case 6 for extremely large guide field : (a) contours and (b) eigenfunctions of various quantities. Scales in the colorbars are amplified by a factor of .
Tables
Typical parameters for generation of current sheet instabilities.
Typical parameters for generation of current sheet instabilities.
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