The objective of the Toroidal Field Model Coil Project is to develop and demonstrate the
superconducting magnet technology to a level that will allow the ITER TF coils to be built with
confidence. It provides for the validation of design and analysis, demonstration of industrial
manufacturing methods, the performance of each component integrated in the magnet, and the testing and demonstration of reliable operation. The programme also drives the development of ITER full-scale conductor including strand, cable, conduit and terminations.
The project is aimed at defining the critical manufacturing steps in this process by the manufacture of a subsize coil and two full size sections of the outer housing. Although the conductor cannot be fully tested for superconducting properties (this is done instead in the L-1 task), the manufacturing has been done to define appropriate tolerance targets, procedures and quality control steps. The test of the subsize coil creates realistic magnetic loads to demonstrate the structural concept. The toroidal field model coil is a "race-track" shaped coil about 4m high and 3m wide, scaled with respect to the full-size ITER TF coils and including the key technical features and manufacturing approaches foreseen for the actual ITER TF coils.
 Fig.1 Conductor Insulation and transfer (Ansaldo Energia) |
 Fig.2 Machining of one Radial Plate, 3 m x 4 m x 12 cm thick (performed by Mecaachrome under contract with Nöll) |
 Fig.3 Laser Welding of Conductor Cover Plates (RTM) |
 Fig.4 Forging operations of the TF inner case section 1.5 m x 1.5 m x 3 m long, showing the square hollow tube being bent to the required radius (Kind) |
Fig.1 shows the conductor after heat treatment, opened out by 'unspringing' to give space to wrap with insulation without damaging the superconductor. The insulation has been applied to the lower turns. Fig.2 shows the machining of the radial plate which reinforces the conductor. The conductor is fitted into grooves in this plate. The top of the groove is closed by a cover plate which is laser welded into position, as shown in Fig.3. The case for the model coil is too small to allow the manufacturing processes for a full size coil case to be developed. Two sections of the full size case have therefore been manufactured, one from the inner leg by forging and one from the outer leg, by casting. Fig.4 shows the inner leg section during forging as a hollow tube, before cutting into two U sections.
The assembly of the winding pack was completed over the last 6 months of 1999. The impregnation of the individual radial plates with an outer insulation wrap was finished in July 2000 and the outer joints between pancakes were EB welded in August 2000. The joint insulation was completed and the ground insulation built up in a final impregnation step.
The winding pack has been put into the case and closure welded. Problems were found initially with the quality of this welding (with many defects needing repair) but this has now been resolved by the supplier. Vacuum impregnation of the winding pack-case gap (pre-filled with coated sand granules) was completed in late 2000, and the finished coil delivered to the TOSKA facility at Karlsruhe, Germany, which has been adapted by the European Home Team to accommodate the coil and its test programme.
Assembly and checking of the coil in TOSKA was completed in June 2001 and the cooldown to 4K took 2 weeks. The coil went superconducting on 6th July 2001. On 25th July the coil was ramped to 80kA (above the value needed in ITER and the maximum possible in the facility) with a field of 8T. This is the highest current ever driven in a superconducting coil. The behaviour of all joints and superconductor are as expected, as are the temperature increases during fast ramp-down and safety discharge.
The test programme is continuing to explore the operational limits of the coil and to validate the design codes.
The European Home Team has lead responsibility for implementing the project in collaboration with the Joint Central Team in Naka.