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Title: Magnetic Island Induced Bootstrap Current on Island Dynamics in Tokamaks

Authors:
 [1];  [2]
  1. University of Wisconsin
  2. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
968595
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 13; Journal Issue: 2
Country of Publication:
United States
Language:
English

Citation Formats

Shaing, K. C., and Spong, Donald A. Magnetic Island Induced Bootstrap Current on Island Dynamics in Tokamaks. United States: N. p., 2006. Web. doi:10.1063/1.2169773.
Shaing, K. C., & Spong, Donald A. Magnetic Island Induced Bootstrap Current on Island Dynamics in Tokamaks. United States. doi:10.1063/1.2169773.
Shaing, K. C., and Spong, Donald A. Sun . "Magnetic Island Induced Bootstrap Current on Island Dynamics in Tokamaks". United States. doi:10.1063/1.2169773.
@article{osti_968595,
title = {Magnetic Island Induced Bootstrap Current on Island Dynamics in Tokamaks},
author = {Shaing, K. C. and Spong, Donald A},
abstractNote = {},
doi = {10.1063/1.2169773},
journal = {Physics of Plasmas},
number = 2,
volume = 13,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • 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
  • 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.
  • A kinetic theory for the nonlinear evolution of a magnetic island in a collisionless plasma confined in a toroidal magnetic system is presented. An asymptotic analysis of a Grad-Shafranov equation including neoclassical effects such as island bootstrap current defines an equation for the time dependence of the island width. Initially, the island bootstrap current strongly influences the island evolution. As the island surpasses a certain critical width the effect of the island bootstrap current diminishes and the island grows at the Rutherford rate. For current profiles such that ..delta..'<0 the island bootstrap current saturates the island.
  • 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