Pressure profile effects on the ballooning mode stability of the FED tokamak

The relative dependence of ideal ballooning instability on the pressure profile is studied in a flux-conserving sequence of equilibria with parameters representative of the Fusion Engineering Device (FED). The instability region based on a pressure profile with an exponential dependence on the poloidal flux suggests an improved profile through which a significant increase in the stable beta value is realized. The corresponding change in the pressure function appears to be relatively small in real space. Computational results indicate that the design value of beta in the FED may be achieved and suggest that for sufficiently optimized pressure profiles, ideal high-n MHD stability limits may not have been exceeded in present tokamaks.