RELAXED AND PARTIALLY RELAXED MAGNETIC EQUILIBRIA IN TIGHT-ASPECT-RATIO TORI

Force-free equilibrium magnetic fields in tight-aspect-ratio toroidal configurations are investigated. The study is mainly directed to modelling field configurations in the 'rodomak', a modification to the SPHEX gun-injected spheromak in which a current-carrying rod is inserted along the geometric axis. A family of analytical relaxed states (del x B = muB, mu constant) is presented for a torus of rectangular cross section, with boundary conditions allowing for flux embedded in the walls, representing the gun. Numerically calculated fields in SPHEX geometry, with mu profiles relevant to the driven phase of operation, are also given. The dependence of the field configurations and global quantities such as energy, helicity and toroidal current on the controlling parameters (gun flux, gun current and rod current) and geometry is discussed.