2010 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. I I, NO. I, MARCH 2001 Design, Fabrication and Test of the React and Wind, Nb3Sn, LDX Floating Coil B.A. Smith, J.H. Schultz, zyxwvuts A. Zhukovsky, A. Radovinsky, C. Gung, P.C. Michael, J.V. Minervini, J. Kesner, D. Gamier, M. Mauel, G. Naumovich, zyxw and R. Kocher Abstract-The Levitated Dipole Experiment (LDX) is an innovative approach to explore the magnetic confinement of fusion plasma. A superconducting solenoid (floating coil) is magnetically levitated for up to 8 hours in the center of a 5-meter diameter vacuum vessel. The floating coil maximum field is 5.3 T, and a react-and-wind Nb3Sn conductor was selected to enable continued field production as the coil warms from 5 K during the experiment up to a final temperature of about 10 K. The coil is wound using an 18-strand Rutherford cable soldered into a half-hard copper channel, and is self protected during quench. The coil is insulated during winding and then vacuum impregnated with epoxy. The impregnated coil is tested with 2 zyxwvut kA operating current at 4.2 K, and then a single, low resistance joint is formed at the outer diameter of the coil before the coil is enclosed in its toroidal helium vessel. This paper presents details of the coil design and manufacturing procedures, with special attention to the techniques used to protect the coil from excessive strain damage throughout the manufacturing process. zyxwvutsrq Index Terms-coil fabrication, levitated dipole, Nb3Sn,quench protection, react-and-wind, soldered joints I. INTRODUCTION HE Levitated Dipole Experiment (LDX) seeks to investigate steady state, high beta plasma operation with near-classical magnetic confinement through the use of a superconducting solenoid which is levitated inside of a large vacuum vessel. Levitated coils for plasma research are not new zyxwvutsrqpo [ 11, [2]. LDX, however, focuses on maximizing magnetic flux expansion, and this sets the experiment apart from earlier devices. As a fusion device, it is based on a concept first proposed by Hasagawa [3]. An overview of the experiment is available [4], and details on other aspects of the experiment, including the floating coil conductor fabrication [5], the BSSCO-2223 levitating coil [6], and the NbTi charging coil [7] are being published. The floating solenoid coil (F-coil) T Manuscript received September 17, 2000. This work was supported by the US. Department of Energy under Grant No. DE-FG02-98ER54458 B.A. Smith, J.H. Schultz, A. Zhukovsky, A. Radovinsky, C. Gung, P. C. Michael, J.V. Minervini, J. Kesner are with the Plasma Science and Fusion Center at Massachusetts Institute of Technology, Cambridge, MA 02139 USA (telephone: 617-258-7852, e-mail: smith @psfc.mit.edu). D. Gamier is with Columbia University, NY, NY 10027 USA. He is currently on assignment at the Plasma Science and Fusion Center at Massachusetts Institute of Technology, Cambridge, MA 02139 USA (telephone: 6 17-258-8997, e-mail: gamier@psfc.mit.edu). M. Mauel is with Columbia University, NY, NY 10027 USA. (telephone: 212-854-4455, e-mail: mauel@columbia.edu). G. Naumovich, and R. Kocher are with Everson Electric Company, Bethlehem, PA 18017 USA, (Telephone: 610-264-861 1, e-mail: gnaumovich@eversonelec.com). will operate inside a helium pressure vessel that is itself surrounded successively by a lead thermal shield and an outer vacuum vessel, all of which form a toroidal structure capable of taking up to 10 g crash loads. Details of the cryostat design are published [8]. This entire 580 kg structure will be levitated inside a 5-meter diameter vacuum vessel during the experiment. This paper describes the details of the completed floating coil fabrication and test activities prior to the assembly of the coil into the helium vessel. 11. FLOATING COL OVERVIEW The floating (F) coil (Fig 1) is a 0.4 H solenoid winding that operates persistently through a low resistance lap-solder joint formed at the winding outer diameter (OD). When the F- coil is charged to full current, the peak field on the winding is about 5.3 T. Prior to daily operation, the coil is cooled in the charging station to about zyxw 5 K via retractable helium transfer lines which connect into extensions from the F-coil heat exchanger tubing (Fig. 1). The F-coil is charged to full current by the simultaneous discharge of the charging coil. During an experimental run, the coil is expected to slowly warm from about 5 K to close to 10 K over the course of about 8 hours. At full current of 2070 At 5.3 T the F-coil current sharing temperature is about 10.8 K. i'oncakr winding zyxwvut n Quench or0 tection HMI/ Eccobond zyxwv ?I soaked oldered lop joint - ~~~ wrap (top arid hottoo?) changer tube R-388--- Fig. I. Floating coil winding (dimensions in mm) is contoured to fit into a toroidal shell. Heat exchanger tubes for recooling are also shown. Finished coil has about 720 turns. The coil is wound from a continuous length of about 1500 m of conductor (Fig. 2) comprised of an 18-strand, Nb3Sn Rutherford cable which has been heat treated and soldered into a half-hard, RRR=80 copper channel. The index (n-) value for the soldered conductor was measured in the range of l0.5-8223/01$10.00 zyxwvut 0 2001 IEEE