3-D MHD stability of high-beta free-boundary tokamak plasmas with finite edge-pressure-gradient and limiter stabilization
Ideal and resistive external kink-tearing-ballooning modes are studied for high-beta toroidal tokamak plasmas with a varying pedestal and/or with stabilization due to a limiter. When the pedestal value is small, the mode spectrum peaks near n=1 with a monotonically decreasing growth rate in n, in which case the most unstable mode has a structure similar to an ideal external kink mode. As the pedestal value increases, the linear growth rate decreases for a fixed beta and the mode spectrum tends to broaden. The perturbation becomes localized near the plasma edge resembling the edge relaxation phenomenon in an H-mode tokamak discharge. The stabilizing effect of a limiter on high-beta MHD modes is considered for a finite-size toroidal limiter, a poloidal limiter, and a general limiter. For the latter two types of limiters, a 3-D linear stability analysis is necessary, coupling both poloidal and toroidal modes. The high-beta toroidal case has different characteristics from the zero-beta cyclindrical case; among them is a substantial reduction in growth rate even with modest contact area. Optimum position and size of a limiter are found through extensive parameter studies. A scheme to stabilize the high-beta external kink-tearing mode by means of a set of passive feedback coils is also discussed.
- Research Organization:
- GA Technologies, Inc., San Diego, CA (USA)
- DOE Contract Number:
- AT03-84ER53158
- OSTI ID:
- 6912018
- Report Number(s):
- GA-A-17483; CONF-840616-1; ON: DE84009188
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
700107* -- Fusion Energy-- Plasma Research-- Instabilities
BALLOONING INSTABILITY
CLOSED PLASMA DEVICES
HIGH-BETA PLASMA
INSTABILITY
INSTABILITY GROWTH RATES
KINK INSTABILITY
LIMITERS
PLASMA
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
TEARING INSTABILITY
THERMONUCLEAR DEVICES
THREE-DIMENSIONAL CALCULATIONS
TOKAMAK DEVICES