Collisionless instability of thin current sheets in the presence of sheared parallel flows

Journal Article · Fri Aug 15 00:00:00 EDT 2008 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2968459· OSTI ID:21120527

Roytershteyn, V ^[1]; Daughton, W ^[2]

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1. Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (United States)
2. Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

The first results of an ongoing investigation of the influence of sheared parallel flows on the onset of collisionless magnetic reconnection in thin current sheets are reported. In particular, an exact kinetic equilibrium that incorporates flow with a symmetric profile into the well-known Harris model is proposed and its linear stability is described. The complete linearized Vlasov-Maxwell system is solved using a numerical approach that introduces no approximations regarding the shape of the particle orbits or relative magnitude of the different components of the electromagnetic potentials. Thus accurate results are obtained in a difficult, but practically important limit where the characteristic length scales for the variation of the equilibrium magnetic field and flow are comparable to the ion kinetic length scales. In particular, the dispersion relation for an instability that produces magnetic reconnection is traced as a function of the flow speed V{sub 0} at the center of the sheet, starting with the collisionless tearing mode at V{sub 0}=0. The effects of the sheared flow are shown to qualitatively depend on the thickness of the current sheet. In relatively thick sheets the characteristic features of the dispersion relation depend mostly on the value of the flow shear. In this regime there exist regions of the parameter space where the flow is destabilizing. However, the growth rate of the instability never significantly exceeds that of the collisionless tearing mode and the mode is always stabilized at high enough values of V{sub 0}. When the sheet is thinner than the ion gyroradius in the asymptotic magnetic field, the flow shear introduces strong non-Maxwellian features into the equilibrium distribution function. In this regime, the flow is purely stabilizing for the equilibrium considered. The instability produces magnetic reconnection in all the parameter regimes considered. Finally, the results of the linear analysis are verified using large-scale particle-in-cell simulations.

• OSTI ID: 21120527
• Journal Information: Physics of Plasmas, Vol. 15, Issue 8; Other Information: DOI: 10.1063/1.2968459; (c) 2008 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
APPROXIMATIONS
ASYMPTOTIC SOLUTIONS
BOLTZMANN-VLASOV EQUATION
CURRENTS
DISPERSION RELATIONS
DISTRIBUTION FUNCTIONS
EQUILIBRIUM
IONS
LENGTH
MAGNETIC FIELDS
MAGNETIC RECONNECTION
MAGNETOHYDRODYNAMICS
MAXWELL EQUATIONS
PLASMA
PLASMA SIMULATION
SHEAR
TEARING INSTABILITY
THICKNESS