Laboratory Observation of Large-Amplitude Electrostatic Fluctuations Driven by Magnetic Reconnection

Details Laboratory Observation of Large-Amplitude Electrostatic Fluctuations Driven by Magnetic Reconnection Laboratory Observation of Large-Amplitude Electrostatic Fluctuations Driven by Magnetic Reconnection

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsh42b..03f&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SH42B-03

Physics

7831 Laboratory Studies And Experimental Techniques, 7835 Magnetic Reconnection (2723, 7526), 7839 Nonlinear Phenomena (4400, 6944), 7863 Turbulence (4490)

Scientific paper

We report recent observations of nonlinear electrostatic fluctuations excited during spontaneous reconnection events on the VTF experiment~[1]. Electrostatic fluctuations are observed by small, high-bandwidth, impedance- matched Langmuir probes. Among a large number of wave phenomena, we observe narrow, large-amplitude, positive potential spikes, with fluctuations in probe current on the order of the ion saturation current drawn by the probe, implying ñ/n ~ 1, or e\tilde{φ} / k Te ~ 1. The spikes are observed in conjunction with large inductive electric fields (the "reconnection electric field"). With arrays of such probes we have observed the speed and shape of these propagating structures. The spike drift speed, which is parallel to the electron drift, is roughly 5 106~m/s, or 2vte (vte = \sqrt{2kTe/me}). Based on the drift speed and the time to cross a single probe tip, we infer that the parallel size is 1-2~mm (50-100~λD, or 5-10~ρe). Observations with probes spaced perpendicular to the magnetic field shows that the perpendicular size is also 1-2~mm. Finally, we will discuss our interpretation of the structures and their generation mechanism, with insights from a newly installed electron energy analyzer. [1] J. Egedal, W. Fox, N. Katz, M. Porkolab, K. Reim, and E. Zhang. (2007). PRL 98, 015003. This was supported by DOE contracts DE-FC02-04ER54786 and DE-FG02-06ER54878, and NSF/DOE PHY-0613734

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