Abstract Details

Presentation:submitted:by:
icc06_wangv3.pdf2006-03-21 15:34:54Zhehui Wang

Observation of the enhanced helicity injection mode in a rotating plasma annulus

Author: Zhehui Wang
Submitted: 2005-12-21 19:45:23

Co-authors: C.W.Barnes, D.C.Barnes,H.Li,J.Si, and C.M.Ticos

Contact Info:
Los Alamos National Laboratory
MS E526
Los Alamos, NM   87545
USA

Abstract Text:
Helicity injection using coaxial plasma gun is a well-established and important technique for plasma generation and/or sustainment for innovative confinement concepts such as spheromaks, Field-Reversed Configuration (FRC)’s (by way of merging spheromaks), and Spherical Tori (ST)’s. One of the key challenges in helicity injection is to maximize the coaxial gun voltage since helicity injection rate is determined by Vg Phi_g, the product of the gun voltage (Vg) and embedded magnetic flux (Phi_g) that connects the gun cathode to the anode. We have observed for the first time that, when the externally applied magnetic flux remains the same, two modes of operation exist in an annulus configuration with a coaxial plasma gun at one end. A distinct feature of the configuration is the existence of a section of the cathode where externally applied electric field (E) is perpendicular to applied magnetic field (B). In the so-called “normal? mode of operation, the plasma gun current-voltage (IV) characteristics behave as if the annulus does not exist, and the gun voltage resistively decays within a few ms. In the so-called “enhanced helicity injection? mode, the gun voltage is larger compared with the normal mode and decays more slowly. Both multichord Doppler spectroscopy and Mach probe show that a quasi-steady rotation is established in the enhanced helicity injection mode. Edge measurements show at least ten-fold increase in density and optical emission from ions, consistent with radially outward motion due to the centrifugal force. The results show for the first time that tuning plasma flow (rotation in particular) can become an important way to control helicity injection using coaxial plasma guns.

Characterization: E3

Comments:

The University of Texas at Austin

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

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