Physics – Plasma Physics
Scientific paper
Feb 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996prnc.rept.....g&link_type=abstract
Technical Report, Princeton Univ. Observatory NJ United States
Physics
Plasma Physics
Accretion Disks, Astrophysics, Magnetic Field Reconnection, Internal Waves, Magnetohydrodynamic Stability, Boundary Conditions, Plasma Physics, Tidal Waves, Rotating Disks
Scientific paper
The PI further explored an m = 1 internal-wave instability of accretion disks that he had previously discovered. In brief, tidal distortions of the disk destabilize internal waves -- nearly incompressible disturbances whose wavelength is comparable to the disk thickness or smaller. These waves require either a radial gradient in specific angular momentum, or a vertical gradient in entropy or molecular weight; both gradients should be of a sign that normally makes for stable oscillations, but nevertheless these waves are parametrically destabilized by tides. It had been shown earlier by Vishniac & Diamond that m = 1 internal waves may transport angular momentum radially through the disk, but a robust mechanism for exciting the waves had been lacking. Previous research pointed out that since other processes may also transport angular momentum, the parametric internal-wave instability may be most important in limiting the outer radius of the disk, because tidal excitation of the waves entails a retarding torque on the disk and a transfer of angular momentum to the companion. The process of magnetic reconnection is also of considerable importance to understanding many important astrophysical problems. In rotating accretion disks it provides a natural saturation limit to the Balbus Hawley instability. In order for reconnection to happen in a highly conducting plasma it is first necessary that a very thin current layer develop. The thinner the layer that is reached the faster the resulting reconnection. Any two dimensional reconnection problem can actually be broken into two parts, a global one and a local one. The global conditions provide a complete set of boundary conditions for the local problem of the physics in the reconnection layer. The purpose of this research is to understand a magnetic reconnection experiment being carried out at the plasma physics laboratory, the MRX. However, the test of the agreement of the analysis with the experiments will also be a test of how well we understand the reconnection phenomena in a real laboratory situation. In addition, it is hoped that detailed experimental probing of the layer itself will aid understanding of the general process of magnetic reconnection.
Goodman Jeremy
Kulsrud Russell M.
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