Stability of negative central magnetic shear discharges in the DIII-D tokamak

Journal Article · Thu May 01 04:00:00 EDT 1997 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.872366· OSTI ID:560620

Strait, E J; Casper, T A; Chu, M S; Ferron, J R; Garofalo, A; Greenfield, C M; La Haye, R J; Lao, L L; Lazarus, E A; Miller, R L; Navratil, G A; Ren, C; Rice, B W; Semenov, I; Sips, A C; Soeldner, F X; Stallard, B W; Taylor, T S; Turnbull, A D ^[1]

---

1. General Atomics, P.O. Box 85608, San Diego, California 92186-9784 (United States)

Discharges with negative central magnetic shear (NCS) hold the promise of enhanced fusion performance in advanced tokamaks. However, stability to long wavelength magnetohydrodynamic modes is needed to take advantage of the improved confinement found in NCS discharges. The stability limits seen in DIII-D [J. L. Luxon and L. G. Davis, Fusion Technol. {bold 8}, 441 (1985)] experiments depend on the pressure and current density profiles and are in good agreement with stability calculations. Discharges with a strongly peaked pressure profile reach a disruptive limit at low beta, {beta}{sub N}={beta}(I/aB){sup {minus}1}{le}2.5 ({percent}m T/MA), caused by an n=1 ideal internal kink mode or a global resistive instability close to the ideal stability limit. Discharges with a broad pressure profile reach a soft beta limit at significantly higher beta, {beta}{sub N}=4 to 5, usually caused by instabilities with n{gt}1 and usually driven near the edge of the plasma. With broad pressure profiles, the experimental stability limit is independent of the magnitude of negative shear but improves with the internal inductance, corresponding to lower current density near the edge of the plasma. Understanding of the stability limits in NCS discharges has led to record DIII-D fusion performance in discharges with a broad pressure profile and low edge current density. {copyright} {ital 1997 American Institute of Physics.}

• Research Organization: General Atomics
• DOE Contract Number: AC03-89ER51114
• OSTI ID: 560620
• Report Number(s): CONF-961102--
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 5 Vol. 4; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BETA RATIO
CURRENT DENSITY
ELECTRIC DISCHARGES
KINK INSTABILITY
MAGNETIC CONFINEMENT
MAGNETIC FIELDS
MHD EQUILIBRIUM
PLASMA DISRUPTION
PLASMA MACROINSTABILITIES
PLASMA PRESSURE
PLASMA RADIAL PROFILES
TOKAMAK DEVICES