A 3 T magnet system for MAGNUM-PSI

The FOM-Institute for Plasma Physics is preparing the construction of Magnum-psi, a magnetized (3 T), steady-state, large area (100 cm²), high-flux (up to 10²⁴ H⁺ ions m^-2s^-1) plasma generator. Magnum-psi will be used to study plasma-surface interaction in conditions similar to those in the divertor of ITER and fusion reactors beyond ITER. The active magnetic field region is required to be 4 meter long, 1 meter diameter and steady state. This, together with the need for minimization of the running costs, makes the application of superconducting coils imperative. The magnet system will be unique because of its maximum transparency to provide optimal radial access to the experimental region inside the magnet bore. In this contribution we present a magnet configuration that consists of 5 cylindrical, conduction cooled NbTi coils. These generate an axial field of 3 T with a maximum field on the coils below 6 T. Two cryogenic structures are proposed: the discrete coils are either placed within separate cryostats or are supported by a single cylinder in a shared cryostat with 32 room temperature view ports. Room temperature iron rings close to the outer coils reduce the axial forces that would otherwise put severe constraints on the mechanical structure. The field will most probably be passively shielded by an iron dome at 2 meters from the cryostat.