Magnetic surfaces in an axisymmetric torus

Abstract

A method is developed for specifying the boundary equilibrium magnetic surface in an axially symmetric torus by using the absolute values of the magnetic field B = B _s (θ) and the gradient of the poloidal flux ||∇Ψ| = |∇Ψ| _s (θ) in a special flux coordinate system. By setting two surface constants (e.g., the safety factor q and dp/dΨ) and matching the absolute values of the magnetic field and the flux gradient on a closed magnetic surface, it is possible to find all equilibrium magnetic functions (including n · ∇ ln B and the local shear s) and all constants (including the toroidal current J and the shear dμ/dΨ) on this surface. Such a non-traditional formulation of the boundary conditions in solving the stability problem in an axisymmetric torus allows one to impose intentional conditions on plasma confinement and MHD stability at the periphery of the system.