Manufacture

The CSMC task has two important objectives:

• to verify the conductor performance under ITER-relevant conditions;
• to demonstrate the major steps in the manufacturing of the conductor and ITER CS coil.

To test conductor, the CSMC can fit an "insert coil" within the bore of the main coil. This insert coil has a single layer, but a full size conductor length ~80 m can be accommodated with a bending radius of about 70 cm. The insert coil has its own power supply and instrumentation. At present, 3 insert coils relevant for ITER are foreseen (one for the CS conductor, one for the TF and one for the PF conductor using NbTi).

The technology required to build the ITER CS coil requires a significant advance on present superconducting coil manufacturing technology. The main manufacturing issues are addressed also in the CSMC conductor, and are now all successfully solved. These include the production of a substantial quantity of Nb₃Sn to a uniform quality, and the jacketing of a cable of this strand using a heavy square section of superalloy "Incoloy 908" to provide structural support against magnetic forces. The conductor has been accurately bent to the winding shape, heat treated in a controlled atmosphere and insulated in an "unspringing" process before stacking to form the winding and impregnating with epoxy resin. Finally, the different layers have been connected by joints on the top and bottom of the coil.

Apart from testing of the insert coil, operation of the main coil will provide verification of the insulation performance under load and demonstrate the integrated performance of joints and conductor for several conductor lengths and two different joint concepts, confirming that manufacturing variability can be controlled.

The CS Model Coil consists of two modules nested inside each other. The Inner Module (upper pictures) has an inner diameter of 1.8 m, outer diameter of 2.7 m and height of 2.8 m. It was made by the USA. The Outer Module (lower pictures) has an inner diameter of 2.7 m, outer diameter of 3.6 m and height of 2.8 m. It was made by Japan.

As shown in the right hand pictures, the complete CSMC assembly has been made in a dedicated test facility provided by the Japanese Home Team.

Major Achievements

• Installation of the CS Model Coil and CS Insert was completed on October 14, 1999.
• Cooldown of the CS Model Coil and Insert was started on November 29, 1999. However, although the coils attained superconductivity on December 16th, a leak was found in a helium pipe used for structure cooling. The coils were then warmed up.
• The leak was identified in the helium pipe at the bottom of the structure,, in the welds along the 19 mm diameter 1.6 mm thick pipe. The bad part of the pipe was cut out and a new pipe inserted and leak tested under pressure.
• After the repair of the leak, cooldown was started on March 13, 2000, and completed on April 6.
• Testing of the CS Model Coil started on April 11. A low current check up to 20% (9.2 kA) of the nominal current (46 kA) was successfully performed.
• Maximum field of 13.5T, maximum current of 46kA and stored energy of 640MJ acheived in April 2000.
• Ramp-up rates of 1.2T/s and rampdown rates of -1.5T/s achieved in insert coils, well above respective goals of 0.4 and -1.2T/s respectively, and completion of 10 000 cycle test in August 2000.

• Testing of TF insert (from September 2000)and NbAl insert (from December 2000)

All four original EDA Parties were directly involved in the project and have contributed to its various elements. The Japanese and US Home Teams are responsible for implementing the project in close collaboration with the Joint Central Team at Naka.