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Title: Characteristic time for halo current growth and rotation

A halo current flows for part of its path through the plasma edge and for part through the chamber walls and during tokamak disruptions can be as large as tenths of the plasma current. The primary interest in halo currents is the large force that they can exert on machine components particularly if the toriodal rotation of the halo current resonates with a natural oscillation frequency of the tokamak device. Halo currents arise when required to slow down the growth of a kink that is too unstable to be stabilized by the chamber walls. The width of the current channel in the halo plasma is comparable to the amplitude of the kink, and the halo current grows linearly, not exponentially, in time. The current density in the halo is comparable to that of the main plasma body. The rocket force due to plasma flowing out of the halo and recombining on the chamber walls can cause the non-axisymmetric magnetic structure produced by the kink to rotate toroidally at a speed comparable to the halo speed of sound. Gerhardt's observations of the halo current in NSTX shot 141‚ÄČ687 [Nucl. Fusion 53, 023005 (2013)] illustrate many features of the theory of halomore » currents and are discussed as a summary of the theory.« less
Authors:
 [1]
  1. Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)
Publication Date:
OSTI Identifier:
22486436
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 10; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; AMPLITUDES; AXIAL SYMMETRY; CURRENT DENSITY; EDGE LOCALIZED MODES; ELECTRIC CURRENTS; NSTX DEVICE; OSCILLATIONS; PLASMA; ROCKETS; ROTATING PLASMA; SOUND WAVES; VELOCITY; WALLS