Experiments on skin depth thick current sheets with Alfvénic Scintillations

Details Experiments on skin depth thick current sheets with Alfvénic Scintillations Experiments on skin depth thick current sheets with Alfvénic Scintillations

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsm43b..07g&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #SM43B-07

Physics

2159 Plasma Waves And Turbulence, 2471 Plasma Waves And Instabilities, 2487 Wave Propagation (6934), 2708 Current Systems (2409), 2772 Plasma Waves And Instabilities

Scientific paper

Exploring the formation and dynamics of sheet-like current structures in plasmas is key to understanding phenomena ranging from auroral arcs, to reconnection in the earth's magnetosphere, to disruptions of tokamak plasmas. We present results from a laboratory experiment designed to produce a thin electron sheet of current within a uniform, magnetized ambient plasma. The experiment is conducted in the Large Plasma Device (LaPD) at UCLA. The linear device is 20 meters in length and one meter in diameter. The electron current sheet is produced using a thin, biased copper plate inserted into the plasma. The initial dimensions of the sheet are 0.4 by 45 ion Larmour radii, ρ i, perpendicular to B0. Two main observations are made. First, in addition to the electron flow in the sheet, a thin (2ρ {i}) sheet of parallel ion flow is measured using a mach probe. This flow has an 'S'-shape in the cross-field plane. Second, a deep (20%) and broad (8ρ i) density cavity forms which gives rise to the spontaneous growth of drift-Alfven waves along the steepest density gradient contours. These waves, which appear as spontaneous scintillations are measured by correlating the fluctuating density and magnetic fields on planes parallel to the background field. The waves are also correlated with cross-field particle flux and lead to a relaxation of the density gradient. The correlations are made apparent in computer generated movies. The current sheet is also host to high frequency waves (ω ≥ ω L_H) as measured with microprobes. An attempt will be made to relate the experimental results to naturally occuring current systems in space.

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