Stability Properties of the URAGAN-2M Torsatron

A more accurate model of the helical coils has changed previous stability results, which were obtained with a model that used only three filaments for each half-coil. With the improved model, Mercier stability is obtained for parabolic pressure profiles at peak beta values of up to 3% for the standard configuration, which now has an average minor radius ā = 23.3 cm. For a configuration with a smaller plasma radius, ā = 15.2 cm, the maximum peak beta, 5.0%, is limited by equilibrium. The addition of a toroidal field reduces the rotational transform to <0.5. This configuration has access to the second stability regime for Mercier modes when narrow pressure profiles are used at low beta.