Theoretical beta limits and stability in noncircular tokamaks including internal separatrices
Tokamaks achieve stability against MHD localized interchange instabilities through toroidally produced average magnetic well and through shear of the magnetic field lines. If the plasma beta exceeds a critical value, ballooning modes can be driven unstable by plasma pressure gradients in local regions of unfavorable curvature. The critical ..beta.. for these pressure-driven modes depends on the current density profiles, with flatter profiles being favored. However, these have steep current density gradients and are destabilizing for the current-driven external kinks and axially symmetric modes in the absence of wall stabilization. Hence, complementary studies of pressure- and current-driven modes are required to optimize tokamaks for maximum stable ..beta.. with respect to both classes of instability. The techniques used include a fully global, numerical variational analysis of the ideal MHD theory of computed equilibria; approximate, semi-analytical localized interchange and ballooning analyses of this theory; a kinetic theory extension of the local ballooning analysis that includes the effects of individual particles and electrostatic fields neglected in ideal MHD; and an approximate, semi-analytic kink and incompressible axially symmetric mode analysis, valid for equilibria with elongated cross sections.
- Research Organization:
- General Atomics, San Diego, CA (United States)
- DOE Contract Number:
- EY-76-C-03-0167-038
- OSTI ID:
- 6624655
- Report Number(s):
- GA-A-15062; CONF-780811-28; TRN: 79-002555
- Resource Relation:
- Conference: 7. conference on plasma physics and control, Innsbruck, Austria, 23 Aug 1978
- Country of Publication:
- United States
- Language:
- English
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