ISSN:
1089-7666
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Ideal linear magnetohydrodynamic (MHD) stability calculations demonstrate reasonable adherence at low aspect ratio (AR〈2) to the Troyon scaling relationship for maximum beta, resulting in a broad regime of stable high-beta equilibria. For a specific low-aspect-ratio case (AR=5/3), a wide range of stable equilibria having volume-averaged beta, 〈β〉, in excess of 20% is found. A systematic approach for estimating the maximum beta is used. First, the aspect ratio is reduced, for fixed shape and profiles, starting from the Troyon optimized case at AR=2.5; the plasma cross-section shape is then varied for fixed profiles at fixed AR=5/3; and finally, pressure and safety factor profiles are varied for fixed shape and aspect ratio. The calculations are carried out for low n (n=1–3), usually with a conducting wall at a radius of 1.5 times the plasma minor radius, for n=∞ ballooning modes, and for Mercier stability. Several additional "spot checks'' on the effects of moving the conducting wall to infinity and of the stability of n=0 and n=4 and 5 modes indicate good stability properties for these, also. The calculations presented here demonstrate a straightforward extrapolation of the Troyon scaling formula to low aspect ratio, in spite of qualitative differences previously noted in low-aspect-ratio equilibria.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.859148
