skip to main content

SciTech ConnectSciTech Connect

Title: DISCHARGE IMPROVEMENT THROUGH CONTROL OF NEOCLASSICAL TEARING MODES BY LOCALIZED ECCD IN DIII-D

A271 DISCHARGE IMPROVEMENT THROUGH CONTROL OF NEOCLASSICAL TEARING MODES BY LOCALIZED ECCD IN DIII-D. Neoclassical tearing modes (NTMs) are MHD modes which can limit the performance of high beta discharges in tokamaks, in some cases leading to a major disruption. The destabilizing effect which results in NTM growth is a helical decrease in the bootstrap current caused by a local reduction of the plasma pressure gradient by seed magnetic islands. The NTM is particularly well suited to control since the mode is linearly stable although nonlinearly unstable, so if the island amplitude can be decreased below a threshold size the mode will decay and vanish. One means of shrinking the island is the replacement of the missing bootstrap current by a localized current generated by electron cyclotron current drive (ECCD). This method has been applied to the m=3/n=2 neoclassical tearing mode in DIII-D, in H-mode plasmas with ongoing ELMs and sawteeth, both of which generate seed islands periodically. In the case of the 3/2 mode, full suppression was obtained robustly by applying about 1.5 MW of ECCD very near the rational surface of the mode. When the mode first appears in the plasma the stored energy decreases by 20%, butmore » after the mode is stabilized by the ECCD the beta may be raised above the initial threshold pressure by 20% by additional neutral beam heating, thereby generating an improvement in the limiting beta of nearly a factor 2. An innovative automated search algorithm was implemented to find and retain the optimum location for the ECCD in the presence of the mode.« less
Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
OSTI Identifier:
813959
DOE Contract Number:
AC03-99ER54463
Resource Type:
Conference
Resource Relation:
Conference: Conference title not supplied, Conference location not supplied, Conference dates not supplied; Other Information: THIS IS A PREPRINT OF A PAPER TO BE SUBMITTED FOR PUBLICATION IN NUCLEAR FUSION.; PBD: 1 Oct 2002
Research Org:
GENERAL ATOMICS (US)
Sponsoring Org:
(US)
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ALGORITHMS; AMPLITUDES; BOOTSTRAP CURRENT; CYCLOTRONS; DECAY; DOUBLET-3 DEVICE; ELECTRONS; HEATING; ISLANDS; MAGNETIC ISLANDS; MODE RATIONAL SURFACES; PERFORMANCE; PLASMA PRESSURE; STORED ENERGY