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Title: Island-induced bootstrap current on the saturation of a thin magnetic island in tokamaks

Abstract

It is shown that island-induced bootstrap current density, which results from the symmetry breaking of the vertical bar B vertical bar when an island is embedded in the equilibrium magnetic field B, modifies the evolution equation and the saturation level for a thin magnetic island in tokamaks. This modification is independent of the fraction of the equilibrium bootstrap current density. It is found that island-induced bootstrap current density increases the saturation level for modes with positive values of {delta}{sup '}. Here, {delta}{sup '} is the stability parameter for the linear tearing modes.

Authors:
 [1]
  1. Engineering Physics Department, University of Wisconsin, Madison, Wisconsin 53706 (United States)
Publication Date:
OSTI Identifier:
20974936
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 4; Other Information: DOI: 10.1063/1.2730500; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BOOTSTRAP CURRENT; EQUILIBRIUM; ISLANDS; MAGNETIC FIELDS; MAGNETIC ISLANDS; MAGNETOHYDRODYNAMICS; PLASMA; PLASMA CONFINEMENT; TEARING INSTABILITY; TOKAMAK DEVICES

Citation Formats

Shaing, K. C. Island-induced bootstrap current on the saturation of a thin magnetic island in tokamaks. United States: N. p., 2007. Web. doi:10.1063/1.2730500.
Shaing, K. C. Island-induced bootstrap current on the saturation of a thin magnetic island in tokamaks. United States. doi:10.1063/1.2730500.
Shaing, K. C. Sun . "Island-induced bootstrap current on the saturation of a thin magnetic island in tokamaks". United States. doi:10.1063/1.2730500.
@article{osti_20974936,
title = {Island-induced bootstrap current on the saturation of a thin magnetic island in tokamaks},
author = {Shaing, K. C.},
abstractNote = {It is shown that island-induced bootstrap current density, which results from the symmetry breaking of the vertical bar B vertical bar when an island is embedded in the equilibrium magnetic field B, modifies the evolution equation and the saturation level for a thin magnetic island in tokamaks. This modification is independent of the fraction of the equilibrium bootstrap current density. It is found that island-induced bootstrap current density increases the saturation level for modes with positive values of {delta}{sup '}. Here, {delta}{sup '} is the stability parameter for the linear tearing modes.},
doi = {10.1063/1.2730500},
journal = {Physics of Plasmas},
number = 4,
volume = 14,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • When a magnetic island is embedded in toroidally symmetric tokamaks, the toroidal symmetry in |B| is broken [K. C. Shaing, Phys. Rev. Lett. 87, 245003 (2001)] . Here, B is the magnetic field. This broken symmetry induces an additional bootstrap current density in the vicinity of the island. It is illustrated that this island induced bootstrap current density modifies the island evolution equation and imposes a lower limit on the absolute value of the tearing mode stability parameter |{Delta}{prime}| for the island to be unstable. This lower limit depends on the local poloidal plasma beta {beta}{sub p}, the ratio ofmore » the plasma pressure to the poloidal magnetic field pressure. If {beta}{sub p} is high enough, the magnetic island is stable. This mechanism provides an alternative route to stabilize the island.« less
  • When a magnetic island is embedded in toroidally symmetric tokamaks, the toroidal symmetry in |B| is broken [K. C. Shaing, Phys. Rev. Lett. 87, 245003 (2001)]. Here, B is the magnetic field. This broken symmetry induces an additional bootstrap current density in the vicinity of the island. It is illustrated that this island induced bootstrap current density modifies the island evolution equation and imposes a lower limit on the absolute value of the tearing mode stability parameter {delta}{sup '} for the island to be unstable. This lower limit depends on the local poloidal plasma beta {beta}{sub p}, the ratio ofmore » the plasma pressure to the poloidal magnetic field pressure. If {beta}{sub p} is high enough, the magnetic island is stable. This mechanism provides an alternative route to stabilize the island.« less
  • By calculating radio frequency current drive (RFCD) and the bootstrap current in a consistent kinetic manner, we find synergistic effects in the total noninductive current density in tokamaks [1]. We include quasilinear diffusion in the Drift Kinetic Equation (DKE) in order to generalize neoclassical theory to highly non-Maxwellian electron distributions due to RFCD. The parallel plasma current is evaluated numerically with the help of the FASTEP Fokker-Planck code [2]. Current drive efficiency is found to be significantly affected by neoclassical effects, even in cases where only circulating electrons interact with the waves. Predictions of the current drive efficiency are mademore » for lower hybrid and electron cyclotron wave current drive scenarios in the presence of bootstrap current. (c) 1999 American Institute of Physics.« less
  • The bootstrap current in tokamaks is determined in the low collision frequency regime for arbitrary values of the aspect ratio and effect charge. The resulting expression should be useful for a quantitative analysis of currents in tokamaks.