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2007_02_14_romero_talamas_icc_oral_presentation_v02.pdf2007-02-20 14:19:39Carlos Romero-Talamas

The search for reconnection and helicity during formation of a bounded spheromak

Author: Carlos A. Romero-Talamas
Requested Type: Consider for Invited
Submitted: 2006-12-18 17:26:51

Co-authors: H. S. McLean, E. B. Hooper, R. D. Wood, L. L. LoDestro, J. M. Moller

Contact Info:
Lawrence Livermore National Laboratory
7000 East Ave.
Livermore, California   94550

Abstract Text:
Studies at the Sustained Spheromak Physics Experiment (SSPX) are being conducted to understand how spheromaks are formed inside a magnetic flux conserver when driven by coaxial helicity injection, and how this process can be optimized. Essential to obtaining the spheromak’s closed flux surfaces is magnetic reconnection, which has been observed during large gun voltage spikes (> 1kV) both at the experiment by means of magnetic probes [1] and in numerical simulations [2] using NIMROD, a 3D resistive MHD code. The experimental observations, however, are insufficient to discern between multiple reconnection events in the volume (suggested by the NIMROD simulations), or a single reconnection event in which open flux surfaces acquire enough helicity to form the topological link that results in open and closed surfaces in the driven spheromak.

High-speed images taken during this time show a large kink in the column of open magnetic flux that forms shortly after breakdown. The kink also coincides with the first large voltage spike. The light arriving at the camera (mostly Hα) diminishes rapidly during this time due to an increasing degree of ionization, and thus it is not possible to follow the column’s evolution using only the imaging system.

To complement the imaging observations, a magnetic probe consisting of two linear arrays of chip inductor clusters that measure Bx, By, and Bz, is being constructed. The probe is designed to be inserted through a narrow port, and then be opened using a specially designed mechanism that allows measurements, including reconnection, at various positions in a large fraction of the plasma volume.

A computer program that simulates the magnetic field produced by current-carrying flux ropes having arbitrary shapes, including multiple kinks and knots, has been developed to aid in the double probe signal analysis. The program includes synthetic probes that mimic the double probe, and will be used to fit the experimental signals to kink models guided by the high-speed images. These analyses are expected to yield information about the helicity content in the column before reconnection, and measure the latter whenever it occurs near the probe.

Work supported by U.S. DOE under Contract No. W-7405-ENG-48 at UC LLNL, and the Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas (CMSO).

[1] C. A. Romero-Talamás, et al., Phys. Plasmas 13, 022502 (2006).
[2] E. B. Hooper, et al., Phys. Plasmas 12, 092503 (2005).

Characterization: E6

Ordering of abstract according to H. S. McLean

University of Maryland

Innovative Confinement Concepts Workshop
February 12-14, 2007
College Park, Maryland

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