Comparing linear ion-temperature-gradient-driven mode stability of the National Compact Stellarator Experiment and a shaped tokamak

One metric for comparing confinement properties of different magnetic fusion energy configurations is the linear critical gradient of drift wave modes. The critical gradient scale length determines the ratio of the core to pedestal temperature when a plasma is limited to marginal stability in the pl...

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Bibliographic Details
Published in:Physics of plasmas 2013-02, Vol.20 (2)
Main Authors: Baumgaertel, J. A., Hammett, G. W., Mikkelsen, D. R.
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
Adiabatic flow
CONFIGURATION
CRITICAL TEMPERATURE
CROSS SECTIONS
ELECTRON TEMPERATURE
H-MODE PLASMA CONFINEMENT
Instability
ION TEMPERATURE
PLASMA
PLASMA DRIFT
PLASMA INSTABILITY
PLASMA SIMULATION
Plasmas
STABILITY
STELLARATORS
TEMPERATURE GRADIENTS
THERMONUCLEAR REACTORS
TOKAMAK DEVICES
TURBULENCE
Turbulent flow
WAVE PROPAGATION
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Summary:One metric for comparing confinement properties of different magnetic fusion energy configurations is the linear critical gradient of drift wave modes. The critical gradient scale length determines the ratio of the core to pedestal temperature when a plasma is limited to marginal stability in the plasma core. The gyrokinetic turbulence code GS2 was used to calculate critical temperature gradients for the linear, collisionless ion temperature gradient (ITG) mode in the National Compact Stellarator Experiment (NCSX) and a prototypical shaped tokamak, based on the profiles of a JET H-mode shot and the stronger shaping of ARIES-AT. While a concern was that the narrow cross section of NCSX at some toroidal locations would result in steep gradients that drive instabilities more easily, it is found that other stabilizing effects of the stellarator configuration offset this so that the normalized critical gradients for NCSX are competitive with or even better than for the tokamak. For the adiabatic ITG mode, NCSX and the tokamak had similar adiabatic ITG mode critical gradients, although beyond marginal stability, NCSX had larger growth rates. However, for the kinetic ITG mode, NCSX had a higher critical gradient and lower growth rates until a/LT≈1.5 a/LT,crit, when it surpassed the tokamak's. A discussion of the results presented with respect to a/LT vs. R/LT is included.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.4791657