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Graduate Student Seminar - 12/03/2010

"Suppression of Energetic Electron Transport by Double Layers in Flares"

by Tak Chu Li

Friday, December 3, 2010 -- 12:00 p.m.
Large Conference Room, 1207 Energy Research Facility

Advisor:  Professor James Drake

Recent observations from RHESSI revealed coronal hard x-ray emissions came from an above-the-loop-top source. it is not clear how the flare-accelerated electrons stayed above the loop top for a prolonged period of time. Using particle-in-cell simulations, we set up an initial system of very hot electrons in contact with cold electrons parallel to the local magnetic field and let it evolve over time. After a short phase of diffusion, a large-amplitude, localized electrostatic electric field (in the form of a classic double layer) spontaneously emerges at the boundary between the hot and cold electrons. Ion acoustic waves excited by the cold electron drift in response to hot electron transport are observed to accompany the emergence. The double layer then suppresses the hot electron transport into the cold region. It expands over time and therefore enhances the suppression. The barrier supports a significant temperature drop between the two regions that is sustained for the duration of the simulation. The dynamics of the double layer and the associated transport suppression are being explored.

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