Abstract Details

nwe_icc_2006_.pdf2006-02-24 10:48:05Nicholas Eidietis

Non-inductive production of ST plasmas with washer gun sources on the Pegasus Toroidal Experiment

Author: Nicholas W. Eidietis
Submitted: 2006-01-03 11:49:58

Co-authors: G. Fiksel, R.J. Fonck, G.D. Garstka, E.A. Unterberg, G.R. Winz

Contact Info:
University of Wisconsin-Madison
1500 Engineering Drive
Madison, WI   53706
United States

Abstract Text:
Developing non-inductive startup and efficient fueling techniques is important for the ST and for current-carrying toroidal devices in general. This need is especially acute on the very-low-A Pegasus toroidal experiment due to its limited volt-second capability. Experiments are being conducted to test auxiliary plasma injection and toroidal current drive via DC helicity injection. Dual low-impurity, high-current (1 kA) plasma washer guns have been installed in the lower divertor region of the Pegasus vacuum vessel. These guns act both as helicity and fueling sources. The sources are biased up to –900 V relative to the vessel and initially drive current along helical field lines produced by the toroidal and vertical fields. At high current density, the helical current streams reconnect to form a continuous cylindrical plasma with a net toroidal current. At sufficiently low values of externally applied poloidal field, the toroidal current causes a reversal of the poloidal flux and the plasma relaxes to a tokamak-like configuration. Discharges with toroidal current greater than 25 kA are routinely produced with less than 2 kA of injected current. These high-current plasmas exhibit features indicative of closed flux surfaces, including strong reversal of poloidal flux at the center column, a well-defined edge, significantly increased L/R decay times (> 0.7 ms), observed peaking of the SXR emission at the center of the plasma, significant gas fuelling requirements, and the characteristic n = 1 mode (f=40-100 kHz) which is observed in other helicity-injection-driven toroidal devices. The design of larger array to be installed in Pegasus next year, projected to provide Ip > 100 kA, is also presented.
* Supported by U.S. D.O.E. Grant DE-FG02-96ER54375

Characterization: A3


The University of Texas at Austin

Innovative Confinement Concepts Workshop
February 13-16, 2006
Austin, Texas

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