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Abstract. In order to improve economic and environmental suitability of tokamak fusion reactors, both the accomplishment of high beta plasmas and the practical use of low activation materials to reduce the amount of radioactive waste are crucially important. Although low radio-activation ferritic steel is considered as a most promising candidate for structural material in DEMO reactors, the influence of a ferromagnetic property in the ferritic steel on MHD stability and beta limits has been poorly investigated so far. The effect of ferritic steel on MHD stability can be regarded as an additional factor to deteriorate the stability in a close relationship with stability for resistive wall mode (RWM). This paper finds substantial influences of residual magnetism in passively stabilizing wall on ideal MHD stability, i.e., ``ferromagnetic wall mode'', even though the ferromagnetism is sufficiently saturated at a high toroidal field (ratio of permeability to vacuum one is typically about 2) and shows evaluations of deterioration of the beta limit due to the ferromagnetic property for the first time.
IAEA 2003
