[Seminars] EFI Colloquium Today!
holly2 at uchicago.edu
Mon May 22 10:47:40 CDT 2017
EFI COLLOQUIUM TODAY
Monday May 22, 2017
Small reception following
Speaker: Walter Gekelman (UCLA)
Title: The collision of magnetic flux ropes, magnetic reconnection and non-local Ohm’s law
Abstract: Magnetic flux ropes are bundles of twisted magnetic fields and their associated current. They are common on the surface of the sun (and presumably all other stars) and are observed to have a large range of sizes and lifetimes. They can become unstable and resulting in coronal mass ejections that can travel to earth and indeed, have been observed by satellites. Single and multiple flux ropes have been reproducibly generated in the LArge Plasma Device (LAPD) at UCLA. Using a series of novel diagnostics the following key quantities, B, Vp, u, n, Te(u is the plasma flow and Vp the plasma potential) have been measured at more than 48,000 spatial locations and 7,000 time steps. The figure below is experimental data showing field lines in the two flux ropes (colored in yellow and blue), The Quasi-separatrix layer, Q (a region where reconnection occurs) and the field on a plane transverse to the background magnetic field.
Every term in Ohm’s law is evaluated across and along the local magnetic field and the plasma resistivity derived. Ohm’s law does not yield a physically meaningful resistivity and the data meets a condition for non-locality. The Kubo AC conductivity yields meaningful results for the global resistivity. Time domain structures (spiky electric fields) are observed to move from the reconnection region to the edges of the current channels.
Work done at the Basic Plasma Science Facility at UCLA, which is supported by DOE and NSF.
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