THE SUPERCONDUCTING MAGNET SYSTEM FOR THE TOKAMAK PHYSICS EXPERIMENT

The superconducting magnet system for the Tokamak Physics experiment ( TPX) will be the first all superconducting magnet system for a Tokamak , where the poloidal field coils, in addition to the toroidal field co ils are superconducting. The magnet system is designed to operate in a steady slate mode, and to initiate the plasma discharge ohmically. Th e toroidal field system provides a peak field of 4.0 Tesla on the plas ma axis at a plasma major radius of 2.25 m. The peak field on the niob ium 3-tin, cable-in-conduit (CIC) conductor is 8.4 Tesla for the 16 to roidal field coils. The toroidal field coils must absorb approximately 5 kW due to nuclear heating, eddy currents, and other sources. The po loidal field system provides a total of 18 volt seconds to initiate th e plasma and drive a plasma current up to 2 MA. The poloidal field sys tem consists of 14 individual coils which are arranged symmetrically a bove and below the horizontal mid plane. Four pairs of coils make up t he central solenoid, and three pairs of poloidal ring coils complete t he system. The poloidal field coils all use a cable-in-conduit conduct or, using either niobium 3-tin (NB3Sn) or niobium titanium (NbTi) supe rconducting strands depending on the operating conditions for that coi l. All of the coils are cooled by flowing supercritical helium, with i nlet and outlet connections made on each double pancake. The supercond ucting magnet system has gone through a conceptual design review, and is in preliminary design started by the LLNL/MIT/PPPL collaboration. A number of changes have been made in the design since the conceptual d esign review, and are described in this paper. The majority of the des ign and all fabrication of the magnet system will be accomplished by i ndustry, which will shortly be taking over the preliminary design. The magnet system is expected to be completed in early 2000.