Bifurcation of equilibria between with and without a large island in the large helical device

A rapid bifurcation of the equilibria with and without a large island ( n / m = 1/1) has been observed in the medium to high beta large helical device discharges. A large island imposed by an external resonant field is suddenly suppressed nearly perfectly by the plasma effects when the beta at the ι/2π = 1 surface exceeds a critical value. The critical beta value is nearly proportional to the externally imposed resonant field normalized by the main field strength.