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Roles of ion and electron dynamics in the onset of magnetic reconnection due to current sheet instabilities
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10.1063/1.2979316
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Affiliations:
1 Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
2 National Institute for Fusion Science, Toki 509-5292, Japan and The Graduate University for Advanced Studies, Toki 509–5292, Japan
Phys. Plasmas 15, 092114 (2008)
/content/aip/journal/pop/15/9/10.1063/1.2979316
http://aip.metastore.ingenta.com/content/aip/journal/pop/15/9/10.1063/1.2979316

Figures

FIG. 1.

Schematic image of series A and B. The top figure represents the initial condition in the case of mass ratio 220 which is common in series A and B, while the bottom figures represent the initial conditions for lower mass ratio in series A (left) and in series B (right). The curves convex upward (blue) indicate the initial density profiles. Two curves which have a shape similar to the ∞ symbol in each figure indicate typical meandering orbits. Larger one (green) and smaller one (red) correspond to ion and electron orbits, respectively.

FIG. 2.

Color-coded contour plot of electric field profile at in the run A2, where the profile along the axis is enlarged.

FIG. 3.

Mass ratio dependence of the linear growth rate of LHDI. The growth rates normalized by the generalized lower hybrid frequency are plotted with blue squares for series A and with red crosses for series B, respectively. The relationship between the mass and the growth rate is approximately described by the green lines.

FIG. 4.

(a), (b) Evolution of the fastest-growing LHDI modes (electric field) at for series A [panel (a)] and series B [panel (b)], respectively. (c), (d) Spatial profiles of the LHDI amplitudes for series A [panel (c)] and series B [panel (d)]. The profiles are computed by averaging over the linear growth phase of each mode. Red, green, blue, and purple lines denote the runs A1/B1, A5/B5, A7/B7, and A8/B8, respectively. Numbers attached to the margin denote corresponding mass ratios and wave numbers normalized by the electron gyroradius .

FIG. 5.

(a), (b) Spatial profiles of electron velocity at the saturation phase of LHDI. (c), (d) Spatial profiles of charge density in the vicinity of neutral sheet at the saturation phase of LHDI. The panels (a) and (c) represent the profiles at for series A, and the panels (b) and (d) correspond to those at for runs B1, B4, B5, and B7, and that at for run B8. These profiles are averaged over the direction and the numbers attached to the margin denote corresponding mass ratios.

FIG. 6.

(a), (b) Color-coded contour plots of magnetic field at (a) and (b) in the run A2. (c), (d) Mass ratio dependence of the linear growth rate of the kink modes excited at the neutral sheet in series A (c) and in series B (d), where the red points denote the dominant longer-wavelength mode and the blue points denote the dominant shorter-wavelength mode .

FIG. 7.

Time evolutions of wavy magnetic force terms at the neutral sheet due to the kink modes. (a) Shorter-wavelength kink mode for series A. (b) Shorter-wavelength kink mode for series B. (c) Longer-wavelength kink mode for series A. (d) Longer-wavelength kink mode for series B. The wavy terms due to the longer modes are estimated from the summation of three modes of , 0.472, and 0.703, while those for the shorter-wavelength kink modes are estimated from the summation of three modes of , 1.88, and 2.12. The red, green, and purple lines in panels (a), (b), (c), and (d) denote the runs A1/B1, A3/B3, and A5/B5, respectively.

FIG. 8.

Time evolutions of dc electric field at the neutral sheet in series A where the electric field is plotted in the logarithmic scale. The red (solid), green (dashed), and blue (dotted) lines denote the runs A1, A3, and A5, respectively.

FIG. 9.

Time evolutions of ion temperature anisotropy at the neutral sheet for series A (left) and B (right), respectively. The red, green, blue, and purple lines denote the runs A1/B1, A3/B3, A4/B4, and A5/B5, respectively. The numbers attached to the margin denote corresponding mass ratios.

FIG. 10.

Color-coded contour plots of ion distribution function at initial equilibrium (left) and its variation from the initial equilibrium at (right) for the run A3, where the purple vertical line represents . White dots (a), (b), (c), (d), and (e) on the plane correspond to the velocities , , , , and , respectively.

FIG. 11.

Turning points of meandering ions as a function of particle velocity at the neutral sheet in the initial equilibrium for series A. Colored curved lines indicate the location of the meandering particles with the same turning point in the velocity space at the neutral sheet. The black curved lines represent contours of the absolute value of the velocity. The blue points (a), (b), (c), (d), and (e) correspond to the examples of the velocity at the neutral sheet in the same manner as in Fig. 10.

FIG. 12.

Relationship between the growth rate of the kink mode and the ion temperature anisotropy. The red crosses (+) denote the simulation results for series A and numbers in the figure denote mass ratio for each run. The blue diagonal crosses (×) denote those for series B. Solid line represents the theoretical relationship of the ion-ion kink mode estimated from Fig. 15 in Ref. 42.

Tables

Table I.

Simulation parameters for simulation series A.

Table II.

Simulation parameters for simulation series B.

/content/aip/journal/pop/15/9/10.1063/1.2979316
2008-09-25
2014-04-16

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