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Title: On the resonance amplification of magnetic perturbations near the threshold of tearing instability in a tokamak

Using a cylindrical model, a relatively simple description is presented of how a magnetic field perturbation stimulated by a low external helical current or a small helical distortion of the boundary and generating magnetic islands penetrates into a plasma column with a magnetic surface q=m/n to which tearing instability is attached. Linear analysis of the classical instability with an aperiodic growth of the perturbation in time shows that the perturbation amplitude in plasma increases in a resonant manner as the discharge parameters approach the threshold of tearing instability. In a stationary case, under the assumption on the helical character of equilibrium, which can be found from the two-dimensional nonlinear equation for the helical flux, there is no requirement for the small size of the island. Examples of calculations in which magnetic islands are large near the threshold of tearing instability are presented. The bifurcation of equilibrium near the threshold of tearing instability in plasma with a cylindrical boundary, i.e., the existence of helical equilibrium (along with cylindrical equilibrium) with large islands, is described. Moreover, helical equilibrium can also exist in the absence of instability.
Authors:
;  [1]
  1. National Research Centre Kurchatov Institute (Russian Federation)
Publication Date:
OSTI Identifier:
22472019
Resource Type:
Journal Article
Resource Relation:
Journal Name: Plasma Physics Reports; Journal Volume: 41; Journal Issue: 12; Other Information: Copyright (c) 2015 Pleiades Publishing, Ltd.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BIFURCATION; DISTURBANCES; ELECTRIC CURRENTS; EQUILIBRIUM; MAGNETIC FIELDS; MAGNETIC ISLANDS; MAGNETIC SURFACES; NONLINEAR PROBLEMS; PLASMA; TEARING INSTABILITY; TOKAMAK DEVICES; TWO-DIMENSIONAL SYSTEMS