Reconnection in presence of guide fields

Details Reconnection in presence of guide fields Reconnection in presence of guide fields

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm61a0476r&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SM61A-0476

Astronomy and Astrophysics

Astrophysics

2724 Magnetopause, Cusp, And Boundary Layers, 2764 Plasma Sheet, 7835 Magnetic Reconnection, 7843 Numerical Simulation Studies

Scientific paper

Many physical systems observed in laboratory experiments, in space and astrophysics plasmas can be modeled as simple current sheet with a magnetic field reversal (Harris sheet). However, often additional components of the magnetic field need to be considered. In the Earth's magnetopause, there is an out of plane magnetic field (referred to as guide field) of strength comparable to the lobe field on either side of the Harris sheet. In astrophysical systems, such as jets from accretion disks, the magnetic field is believed to be primarily aligned with the current and can be represented by a Harris sheet with a very strong guide field, much larger than the lobe field. In magnetic confinement fusion devices, reconnection develops in presence of strong toroidal fields and the configuration can be represented by a Harris sheet in the poloidal plane with a strong guide field in the toroidal direction. To understand better the role of the guide field the implicit PIC code CELESTE has been applied. The advantage of the implicit formulation in the present case is to allow one to exceed the time step limitation imposed by the rapid gyromotion in the guide field. Normal explicit codes are limited to weak guide fields to respect this stringent time step limitation. Furthermore, a linear theory [1] for the stability of current sheets has been extended to include the additional processes caused by the guide field. Our results show that the reconnection rate is adversely affected by the guide field and that the structure of the reconnection region is altered dramatically. The dissipation layer still breaks up into two layers as without a guide field but the physics in each layer is modified. To understand the physics of the dissipation layer we compare the results of the PIC simulations with linear theory. The agreement is remarkable and several features of the simulations can be explained by linear effects alone. [1] Daughton W.S., PHYSICS OF PLASMAS, 6, 1329 (1999)

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