Collisionless reconnection in configurations with a minimum in the equatorial magnetic field and with magnetic shear

Journal Article · Wed Mar 01 04:00:00 EST 1995 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/94JA03028· OSTI ID:207161

Pritchett, P L; Buechner, J ^[1]

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1. Max Planck Institut fuer Extraterrestrische Physik, Berlin (Germany)

Two-dimensional (x,z) particle simulations are used to investigate the influence of a minimum in the equatorial magnetic field profile and of a B{sub y} field component (sheared magnetic field) on the occurrence of collisionless reconnection in thin current sheets (R{sub i}/L {approximately} 1, where R{sub i} is the ion gyroradius based on the lobe field B{sub o} and L is the current sheet half thickness). It is shown that the pure ion tearing mode (ion to electron mass ratio M{sub i}/m{sub e}=1) first produces an X line in a region of minimum average (over a tearing wavelength) normal field B{sub z}(x,0) and in the region of minimum current sheet thickness; this need not coincide with the actual minimum in B{sub z}. With a mass ratio M{sub i}/m{sub e}>1 the tearing growth rate is strongly reduced as k{rho}{sub e}{yields}1, where {rho}{sub e} is the electron gyroradius in the B{sub z} field. This is an extension of the stabilization associated with electron confinement to a flux tube previously predicted and observed for a constant equatorial field profile. If the slow growth allowed for k{rho}{sub e}{approx}1 eventually produces an X line, then an {open_quotes}explosive{close_quotes} stage of reconnection occurs in which the electron dynamics no longer inhibits the tearing mode displacement, and the growth rate approaches that for the one-dimensional neutral sheet. The addition of a uniform and static shear field B{sub y}{approx_gt}B{sub z} is found not to remove the stabilizing effect associated with the electron dynamics. The significant differences between the parameter regime of the present simulations and that of analytic treatments of the effect of B{sub y} on thick (R{sub i}/L < 0.1) current sheets are discussed in detail. 39 refs., 13 figs.

• OSTI ID: 207161
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: A3 Vol. 100; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
COLLISIONLESS PLASMA
MAGNETIC RECONNECTION
MAGNETOTAIL
PLASMA SHEET
TEARING INSTABILITY
TWO-DIMENSIONAL CALCULATIONS