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Graduate Student Seminar - 04/03/2009

"A Statistical Model of Magnetic Islands in a Large Current Layer"

by Raymond Fermo

Friday, April 3, 2009 -- 12:00 p.m.
Large Conference Room, 1207 Energy Research Facility

Advisor:  Professor James Drake

The formation of secondary magnetic islands in electron current layers is well documented by 2-D full particle simulations of magnetic reconnection and by observational data in the magnetotail and magnetopause. However, the dynamics of these magnetic islands in very large-scale current layers, such as those in the corona or the magnetopause, are not yet well understood. To retain the small-scale physics of particle-in-cell codes in these large-scale systems, a statistical model is developed. The island distribution is characterized by two independent parameters: the flux contained in the island and the area enclosed by it. An evolution equation for this distribution function is derived, based on rules (verified by PIC simulations) which govern the small-scale generation of secondary islands, the rates of island growth, and island merging. The steady state distribution of islands reveals that the largest islands, which result from multiple mergers, contain distinctly reduced magnetic fields compared with the ambient value. The distribution of islands is used to predict observable quantities such as the maximum island size, typical magnetic field strengths, and power laws. These predictions can be compared with observations from magnetospheric satellites such as THEMIS.

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