Critical behavior of magnetically confined plasma regimes.

Plasmas confined in a toroidal magnetic configuration can be characterized by different operational regimes, i.e., distinctive features of the spatial distributions of pressure and current. The poloidal current density is identified as a critical quantity allowing us to discriminate the regimes and an analytical criterion to predict transitions between regimes is derived. The theory also yields a formula which defines current alignment requirements for steady state in a precise way. An analogy with the topological approach of phase transition theory is pointed out and discussed.