Bifurcated equilibria in two-dimensional MHD with diamagnetic effects

In this work, we analyse the sequence of bifurcated equilibria in two dimen sional reduced magnetohydrodynamics. Diamagnetic effects are studied un der the assumption of a constant equilibrium pressure gradient, not altered by the formation of a magnetic island. The formation of an island when the sy mmetric equilibrium becomes unstable is studied as a function of the tearin g-mode stability parameter Delta' and of the diamagnetic frequency, by empl oying fixed-point numerical technique and an initial-value code. At larger values of Delta', a tangent bifurcation takes I,lace, above which no small- island solutions exist. This bifurcation persists up to fairly large values of the diamagnetic frequency (of the order of one-tenth of the Alfven freq uency). The implications of this phenomenology for the intermittent MHD dyn amics observed in tokamaks is discussed.