The large coil task and results of testing U.S. coils

The United States, EURATOM, Japan, and Switzerland have collaborated since 1978 in development of superconducting toroidal field coils for fusion reactor applications. The United States provided a test facility and three coils; the other participants, one coil each. All coils have the same interface dimensions and performance requirements (stable at 8 T), but internal design was decided by each team. Two U.S. coil teams chose bath-cooled NbTi, 10-kA conductors. One developed a Nb3Sn conductor, cooled by internal flow, rated at 18 kA. All U.S. coils have diagnostic instrumentation and imbedded heaters that enable stability tests and simulated nuclear heating experiments. In single-coil tests, each coil operated at full current in self-field (6.4 T). In six-coil tests that began in July 1986, one U.S. coil and the Japanese coil have been successfully operated at full current at 8 T. The other coils have operated as background coils while awaiting their turn as test coil. Coil tests have been informative and results gratifying. The facility has capably supported coil testing and its operation has provided information that will be useful in designing future fusion systems. Coil capabilities beyond nominal design points will be determined.