Study of two dimensional field reversed equilibria with plasma outside the separatrix

Two dimensional equilibria of field reversed configuration with plasma outside the separatrix is investigated. By numerical calculation, it is found that the separatrix ( phi =0) becomes spindly asβsub(s) (beta ratio on the surface phi =0) increases. Remarkable is that the surface phi =0 becomes an open surface and no more the separatrix as βsub(s) is increased beyond a critical value, and furthermore, that only axially uniform configurations are obtained when βsub(s) is greater than a second critical value. Existance of the critical values of βsub(s) are explained with use of a long thin plasma model and a condition of axial force balance which takes into account the plasma outside the separatrix. The critical values obtained with this model well agree with the two dimensional numerical results as well as radii of the plasma at the center plane and at the ends of vessel. (author)