The magnetohydrodynamlc stability theory of internal ring configurations is developed using a nearly cylindrical, sharp-boundary plasma model* I. INTRODUCTION In this report the stability of a straight configuration with internal rings is investigated. As these configurations are positively stable (in contrast to the neutrally stable theta pinch), the configuration can be imagined to be bent into a torus or a U bend* The positive stability is not altered if the radius of curvature is large

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... h. The internal ring experimental work at Nagoya » was based on /d£/B theory, which is a low-B concept. The closely related problem of stability of the main plasma in ELMO has been solved for arbitrary 8, J and illustrates how the /d£/B criterion generalizes to high 6. The ELMO theory is necessarily rather complicated because of the many degrees of freedom inherent in a diffuse profile. Here, a sharp-boundary, small-6 model is used to obtain, in a relatively simple manner, an overall impression of the stability properties of internal ring configurations. The model is first discussed in a general way, for arbitrary axisymmetric fixed internal currents, and then applied to internal rings. It is also of interest to check the model for the case of ELMO