Critical error fields for locked mode instability in tokamaks

Journal Article · Wed Jul 01 00:00:00 EDT 1992 · Physics of Fluids B; (United States)

DOI:https://doi.org/10.1063/1.860017· OSTI ID:7285240

La Haye, R J; Fitzpatrick, R; Hender, T C; Morris, A W; Scoville, J T; Todd, T N ^[1]

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1. General Atomics, San Diego, California 92138 (United States)

Otherwise stable discharges can become nonlinearly unstable to disruptive locked modes when subjected to a resonant {ital m}=2, {ital n}=1 error field from irregular poloidal field coils, as in DIII-D (Nucl. Fusion {bold 31}, 875 (1991)), or from resonant magnetic perturbation coils as in COMPASS-C ({ital Proceedings} {ital of} {ital the} 18{ital th} {ital European} {ital Conference} {ital on} {ital Controlled} {ital Fusion} {ital and} {ital Plasma} {ital Physics}, Berlin (EPS, Petit-Lancy, Switzerland, 1991), Vol. 15C, Part II, p. 61). Experiments in Ohmically heated deuterium discharges with {ital q}{approx}3.5, {ital {bar n}} {approx} 2 {times} 10{sup 19} m{sup {minus}3} and {ital B}{sub {ital T}} {approx} 1.2 T show that a much larger relative error field ({ital B}{sub {ital r}21}/{ital B}{sub {ital T}} {approx} 1 {times} 10{sup {minus}3}) is required to produce a locked mode in the small, rapidly rotating plasma of COMPASS-C ({ital R}{sub 0} = 0.56 m, {ital f}{approx}13 kHz) than in the medium-sized plasmas of DIII-D ({ital R}{sub 0} = 1.67 m, {ital f}{approx}1.6 kHz), where the critical relative error field is {ital B}{sub {ital r}21}/{ital B}{sub {ital T}} {approx} 2 {times} 10{sup {minus}4}. This dependence of the threshold for instability is explained by a nonlinear tearing theory of the interaction of resonant magnetic perturbations with rotating plasmas that predicts the critical error field scales as ({ital fR}{sub 0}/{ital B}{sub {ital T}}){sup 4/3}{ital {bar n}}{sup 2/3}. Extrapolating from existing devices, the predicted critical field for locked modes in Ohmic discharges on the International Thermonuclear Experimental Reactor (ITER) (Nucl. Fusion {bold 30}, 1183 (1990)) ({ital f}=0.17 kHz, {ital R}{sub 0} = 6.0 m, {ital B}{sub {ital T}} = 4.9 T, {ital {bar n}} = 2 {times} 10{sup 19} m{sup {minus}3}) is {ital B}{sub {ital r}21}/{ital B}{sub {ital T}} {approx} 2 {times} 10{sup {minus}5}.

• DOE Contract Number: AC03-89ER51114
• OSTI ID: 7285240
• Journal Information: Physics of Fluids B; (United States), Vol. 4:7; ISSN 0899-8221
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
TOKAMAK DEVICES
MODE LOCKING
MAGNETOHYDRODYNAMICS
PLASMA CONFINEMENT
PLASMA MACROINSTABILITIES
TEARING INSTABILITY
TOROIDAL CONFIGURATION
ANNULAR SPACE
CLOSED CONFIGURATIONS
CLOSED PLASMA DEVICES
CONFIGURATION
CONFINEMENT
FLUID MECHANICS
HYDRODYNAMICS
INSTABILITY
MAGNETIC FIELD CONFIGURATIONS
MECHANICS
PLASMA INSTABILITY
SPACE
THERMONUCLEAR DEVICES
700340* - Plasma Waves
Oscillations
& Instabilities- (1992-)
700310 - Plasma Confinement- (1992-)