Sherwood 2015

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approvedrw_greenwald.pdf2015-04-09 09:33:58Roscoe White
approvedisland.pdf2015-01-15 08:46:52Roscoe White

Thermal island destabilization and the Greenwald limit

Author: Roscoe B. White
Requested Type: Consider for Invited
Submitted: 2015-01-15 08:42:37

Co-authors: D.A. Gates, D.P. Brennan

Contact Info:
Princeton University
P.O. Box 451
Princeton, NJ   08543

Abstract Text:

Magnetic reconnection is ubiquitous in the magnetosphere, the solar
corona, and in toroidal fusion research discharges.
In a fusion device a magnetic island saturates at a width which produces a minimum in the magnetic energy of the configuration.
At saturation the modified current density profile, a function of the flux in the island, is essentially flat, the growth rate proportional to the difference in the current at the O-point and the X-point. Further modification of the current density profile
in the island interior causes a change in the island stability and
additional growth or contraction of the saturated island. Because field lines in an island are isolated from the outside plasma an island can heat or cool preferentially depending on the balance of Ohmic heating and radiation loss in the interior, changing the resistivity and hence the current in the island.
A model of island destabilization due to radiation cooling of the island is constructed, and the effect of modification of the current within an island is calculated. An additional destabilization effect is described, and it is shown that a small imbalance of heating can lead to exponential growth of the island. A destabilized magnetic island near the plasma edge can lead to plasma loss, and because the radiation is proportional to plasma
density and charge, this effect can cause an impurity dependent density limit.

This talk or paper should be followed immediately by a paper by D. Brennan and myself on the same topic.

March 16-18, 2015
The Courant Institute, New York University