Experimental study of current-driven turbulence during magnetic reconnection

Magnetic reconnection is an important process in magnetized plasmas ranging from the laboratory to astrophysical scales. It enables the release of magnetic energy believed to power solar flares and magnetospheric substorms. Reconnection also controls the evolution of the topology of the magnetic field, enabling deleterious instabilities, such as the sawtooth instability in fusion experiments, to transport plasma across the experiment's minor radius. Notably, simple estimates of the finite reconnection rate due to classical resistivity fail to explain the fast and explosive nature of reconnection observed in these systems. A major goal of reconnection research is to determine which mechanisms enable "fast" reconnection to occur. This thesis studied the fluctuations arising in the plasma during magnetic reconnection experiments on the Versatile Toroidal Facility (VTF), with a primary goal of testing whether "anomalous resistivity" due to micro-instabilities can speed the reconnection process. Fluctuations were studied using impedance-matched, high-bandwidth Langmuir probes. Strong, broadband fluctuations, with frequencies extending from near the lower-hybrid frequency [fLH = (fcefci)1=2] to the electron cyclotron frequency fce were found to arise during the reconnection events. Based on frequency and wavelength measurements, lower-hybrid waves and Trivelpiece-Gould waves were identied. The lower-hybrid waves appear to be driven by strong perpendicular drifts or gradients which arise due to the reconnection events; an appealing possibility is strong temperature gradients.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Physics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2009

Author dc:creator

• Fox, William Randolph, II

Advisor dc:contributor.advisor

• Miklos Porkolab.

• Physics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/52784

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/52784