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Phase space structure of the electron diffusion region in reconnection with weak guide fields
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View: Figures


Image of FIG. 1.
FIG. 1.

Time slice from an open-boundary PIC simulation of anti-parallel reconnection. (a) Acceleration potential . (b) Magnetic field strength B. (c) Pressure anisotropy . (d) Out of plane current density (normalized to ). (e) Distribution function just upstream of the electron diffusion region at the point marked with circles. The color plot shows data from the PIC code, while the black contour lines are from the analytic form of f in Appendix.

Image of FIG. 2.
FIG. 2.

Plots of reconstructed distribution function along a cut at . Velocity units are in terms of c. (a) Distribution function averaged over , and , where is the Lorentz factor. (b) Moments of the electron distribution for a cut along the z axis passing through the x-line. From left to right, the density, fluid velocity, diagonal, and off-diagonal components of the pressure tensor are plotted. The dashed lines show the data from the PIC simulation while the solid lines show the reconstructed moments. Density and pressure components are normalized to and the value of outside the layer.

Image of FIG. 3.
FIG. 3.

Electron distribution within neutral sheet. (a) Isosurface of the distribution at x-line. The different colors correspond to the number of times the electrons are reflected in the layer. (b) Electron orbits from x-line with 0, 1, and 2 reflections. Color plot is in-plane electric field , with contours of in-plane projection of magnetic field lines.

Image of FIG. 4.
FIG. 4.

(a) and (b) Isosurfaces of the distribution at above and below x-line at (x, z) = (206.25, 200). The red region lies in , the blue in . Note the relative displacement in of the red and blue surfaces as z increases, causing a gradient in . (c) and (d) Isosurfaces of the distribution at to the left and right of the x-line. Rotation of the distribution along the layer causes the gradient in . (e) and (f) distribution of particles taken from PIC simulation at . (g) and (h) The distributions in (a), (b) after integrating over and , showing the and contributions separately (making the displacement in clearer). Vertical axis units are arbitrary. The red line represents , while the blue is for .

Image of FIG. 5.
FIG. 5.

(a) Electron distributions averaged over at the x-line from simulations in which the force of on the electrons is modified. In the left plot, there is no elongation due to the absence of . The center plot shows the distribution in the unmodified simulation, while there is increased electron acceleration in the final plot, where has been effectively doubled. (b) Comparison of the reconstructed distribution using (from simulation data) and 0 (assuming only magnetic trapping). The importance of the parallel potential in determining the length of the fingers is evident. Note that the data in (a) and (b)come from two different sets of simulations.

Image of FIG. 6.
FIG. 6.

Changes in the reconnection geometry as the guide field is increased from 0 to . The left column shows the in-plane electric field , while the right column shows the electron flow velocity (in this figure, the x-axis is shifted such that the x-line is located at ). The electron Alfvén speed is 0.3c, so electrons in the jets are moving at this velocity.

Image of FIG. 7.
FIG. 7.

Electron distributions at the x-line from simulations of reconnection with increasing guide fields. From left toright, , and . At the largest guide field, the elongated electron jet is no longer present and the field geometry is different.

Image of FIG. 8.
FIG. 8.

(a) Isosurfaces of the electron distribution at the x-line for . Colors show the number of times an electron is reflected before reaching the x-line. (b) Trajectory of an electron reaching the point marked (b) in velocity space from the left and exiting from the right. Likewise for (c).

Image of FIG. 9.
FIG. 9.

Four different views of isosurfaces of the electron distribution at the x-line for . Colors show the number of times an electron is reflected before reaching the x-line, and only regions with electrons with 0, 1, and 2 reflections are shown.

Image of FIG. 10.
FIG. 10.

A demonstration of the evolution of the velocity space positions of electrons in the fingers. Electrons from the zero-reflection finger in (a) follow the trajectories in (c) until they reach the one-reflection finger at the x-line (b). The distribution in (a) is taken from the average x position of the crossings of the three trajectories.

Image of FIG. 11.
FIG. 11.

Electron distributions at the x-line from full mass ratio simulations. From left to right, the (antiparallel), , and . The antiparallel distribution has the same structure as in the mass ratio 400 antiparallel simulation, while the cases are similar to larger guide field simulations at mass ratio 400.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Phase space structure of the electron diffusion region in reconnection with weak guide fields