(stellarators/magnetohydrodynamics/equilibrium and stability code/n

An ideal magnetohydrodynamic equilibrium and stability code is used to study ballooning modes in torsatrons. The most dangerous modes turn out to be those with low poloidal and toroidal wave numbers. Beta limits for equilibrium and stability are determined for an e = 2 ultimate torsatron with large e = 1 and f = 3 sidebands. The study of equilibrium and stability for torsatrons is a chal- lenging problem in ideal magnetohydrodynamics because these devices are not axisymmetric. They are similar to stellarators in that the confining fields are generated by currents flowing in helical coils passing around a torus (1, 2). Recent progress in the development of computational methods has provided important new theoretical tools in this area (3-5). Codes have been written to calculate nonaxisymmetric toroidal equilibria and to test their stability. Other codes have been written to trace magnetic lines and to describe magnetic surfaces in harmonic stellarator fields. In this study we announce results about equilibrium and stabil- ity of torsatrons found by using these computer codes. Special attention is devoted to the prediction of beta limits for an ulti- mate torsatron experiment called WISTOR-U that is being de-