Ballooning Stability of the Compact Quasiaxially Symmetric Stellarator

Redi, M. H. ; Canik, J. ; Dewar, R.L. ; Johnson, J. L. ; Klasky, S. ; Cooper, W. A. ; Kerbichler, W.

Princeton University. Plasma Physics Laboratory.

关键词: Axial Symmetry;    70 Plasma Physics And Fusion Technology;    Plasma Confinement;    Computerized Simulation;    Stellarators;   

DOI  :  10.2172/788263
RP-ID  :  PPPL-3612
RP-ID  :  AC02-76CH03073
RP-ID  :  788263

美国|英语

来源: UNT Digital Library

【 摘 要 】

The magnetohydrodynamic (MHD) ballooning stability of a compact, quasiaxially symmetric stellarator (QAS), expected to achieve good stability and particle confinement is examined with a method that can lead to estimates of global stability. Making use of fully 3D, ideal-MHD stability codes, the QAS beta is predicted to be limited above 4% by ballooning and high-n kink modes. Here MHD stability is analyzed through the calculation and examination of the ballooning mode eigenvalue isosurfaces in the 3-space [s, alpha, theta(subscript ''k'')]; s is the edge normalized toroidal flux, alpha is the field line variable, and theta(subscript ''k'') is the perpendicular wave vector or ballooning parameter. Broken symmetry, i.e., deviations from axisymmetry, in the stellarator magnetic field geometry causes localization of the ballooning mode eigenfunction, with new types of nonsymmetric, eigenvalue isosurfaces in both the stable and unstable spectrum. The isosurfaces around the most unstable points i n parameter space (well above marginal) are topologically spherical. In such cases, attempts to use ray tracing to construct global ballooning modes lead to a k-space runaway. Introduction of a reflecting cutoff in k(perpendicular) to model numerical truncation or finite Larmor radius (FLR) yields chaotic ray paths ergodically filling the allowed phase space, indicating that the global spectrum must be described using the language of quantum chaos theory. However, the isosurface for marginal stability in the cases studied are found to have a more complex topology, making estimation of FLR stabilization more difficult.