Design Concept for the Gem Detector Magnet

K conceptual design is presented for the Superconducting Super Collider GEM detector solenoid magnet. The magnet has symmetric, independent vacuum vessel enclosed halves, each with a warm bore of 18 m and containing a superconducting solenoid coil. The coils use cable-in-conduit conductor with an aluminum sheath wound at a nominal 19 m diameter in a single layer against an aluminum bobbin. The overall length of the solenoid is 30 m. The operating current in the conductor is 50 kA, which generates a central field of 0.8 T and a stored energy of 2,5 GJ. Each half solenoid is comprised of 12 modules which are electrically joined with a low resistance joint and mechanically bolted together. The unique features of this magnet are the conductor design itself and the large coil diameter, which demands an on-site winding and assembly operation. The use of a natural convection thermosiphon loop for thermal radiation cooling eliminates plumbing complications associated with double-jacketed cable-in-conduit conductors. Locating the aluminum sheath outside the conduit for quench protection enables optimizing the copper-to-superconductor ratio inside the conduit for stability alone. The conceptual design for the magnet, including the design for the detector dependent magnetics, the superconducting coils and coil. structure (cold mass), the coil winding process, the vacuum vessel and liquid nitrogen shields, the cold mass supports and the magnet assembly procedure are described.