Materials and Processes Selection for SSC Collider Dipole Magnets

Abstract

Considerable research and development effort has gone into design and production of prototype model dipole and quadrupole magnets for the superconducting super collider (SSC) at the Central Design Group, Brookhaven National Laboratory (BNL), Fermi National Accelerator Laboratory (FNAL), Lawrence Berkeley Laboratory (LBL), and Texas Accelerator Center (TAC), in addition to work done at CERN. Experience gained by GDSS in designing and building MFTF, PMS, and LCP magnets was merged with the work obtained by the SSC Central Design Group and other accelerator magnet programs in making decisions on selection of materials and processes for the collider dipole magnets. The two overwhelming issues in CDM design are high reliability and high producibility of magnets at a low practical cost. The GDSS Materials and Process Engineering group took a close look at the SSCL design, the selection of materials, and processes, and conducted trade studies based on current CDM requirements and past material selection, design, and fabrication experience. GDSS recommended some changes, notably: (1) change of beam tube material from Type 21Cr-6 Ni-9Mn CRES to Type 304LN CRES, (2) superconductor cable-to-cable insulation scheme from one layer of polyimide film and a single barber pole wrap of fiberglass-epoxy to two layers of polyimide film with a polyimide-type adhesive, (3) substitution of machined G10 CR fiberglass epoxy end pieces with less costly and mass-producible injection or resin transfer molded end pieces, and (4) substitution of precision machined, shrink-fit metal and composite re-entrant cold mass support posts with less expensive and mass-producible injection or resin transfer molded posts. The last two changes are not final and need development testing, which is underway. Several other changes are under consideration, including replacement of extruded Al 6063-T6 liquid cryogenic line with Type 304L CRES and coating the beam tube copper plating with a very thin layer of gold for reducing photo-desorption and protecting copper plating from oxidation. The superconductor material remains the same, SSCL optimized, high homogeneity, multi-filamentary Nb-47% Ti wire with copper stabilizer. The cold mass skin and the end domes shall be fabricated from Type 304LN CRES, a proven material with which GDSS has past fabrication experience, and with an extensive design data base. This choice will be extremely valuable for preparing the code case for ASME compliance approval of the cold mass structure.