A. Bourquard

Joints for large superconducting conductors

Abstract Large fusion magnets call for high-current conductors (up to 60 kA). This has been achieved by the cable-in-conduit conductor concept. The connection of these conductors has to take into account several demanding boundary conditions: a large number of strands (around 1000), a low resistance at high current (1–2 nΩ), low losses in pulsed field operation, Nb3Sn heat treatment, helium tightness control, limited available space. A conceptual design was developed by the CEA, based on the connection of two separate twin boxes clamped together, according to the lap-joint concept. These boxes are machined out of an explosive bonding plate (jacket material/copper), and the electrical connection is achieved by tin–lead soldering of the facing copper soles. After qualification of the explosive bond and validation of the joint concept in the laboratory, the technology was transferred to the industry within the framework of the manufacture of the ITER Toroidal Field Model Coil (TFMC). In addition, three full-size joint samples (FSJS), relevant to different jacket materials and joining techniques, were manufactured by the industry and successfully tested in the SULTAN facility at CRPP, Villigen. The paper reports on the results of the laboratory tests, describes the transfer of technology to industry, and lastly presents some typical experimental results.

Design and manufacture of a prototype NbTi full-size joint sample for the ITER poloidal field coils

Abstract The design of the poloidal field (PF) coils of the International Thermonuclear Experimental Reactor (ITER) relies on the use of 45 kA NbTi cable-in-conduit conductors. An R&D programme is carried out jointly between CEA and ENEA to acquire knowledge on the behaviour of such conductors. In addition to the manufacture and tests of two subsize joint samples at CEA Cadarache, the design of a poloidal field full-size-joint sample (PF-FSJS) has been carried out. This sample is composed of two conductor legs made of stainless steel-jacketed NbTi full size cables, of a lower joint built according to the “twin box” concept developed at CEA, and of two upper terminals to be connected to the facility current leads. A description of the sample design, the techniques used for the different manufacturing steps of the conductor legs, the terminations and the assembly is related. This prototype sample will be tested in the Sultan test facility at Villigen (Switzerland) and will be a model for the manufacture of joints for the PF coils.

Completion of the ITER Toroidal Field Model Coil

In the scope of the ITER EDA a Toroidal Field Model Coil (TFMC) has been manufactured accompanied by a thorough Quality Assurance (QA) test program. This large superconducting coil has been conceptually designed by the ITER European Home Team (EUHT) and manufactured by European industry. The coil is being completed and will be tested at the Forschungszentrum Karlsruhe in spring 2001. The race track shaped winding is made of a cable-in-conduit conductor in a circular 316LN stainless steel jacket. From this conductor five double pancake (DP) modules were fabricated. Results of conductor and DP manufacture were already presented at previous conferences and are therefore only summarized here. The paper concentrates on the subsequent manufacturing steps, namely the stacking of the DP modules, the insulation and impregnation of the winding pack, the outer joint manufacture by electron beam welding, the assembly of the winding pack with the stainless steel case, the mounting of the helium pipes, the sensors and the busbars. To assemble the coil into the TOSKA facility and to fit it to the EU-LCT coil a heavy Inter-Coil Structure (ICS) has been built, in which the TFMC will rest on four wedges.

NbTi superconducting busbars for the ITER TFMC

Abstract The ITER Toroidal Field Model Coil (TFMC) uses an Nb 3 Sn superconducting conductor that operates up to 80 kA. The TFMC busbars are dual channel superconducting cable-in-conduit conductors designed for operation at 80 kA using the NbTi superconducting material. The busbar system is split into two parts: one linked to the coil, and the other to the current leads. Three different joining systems have been developed for connecting the busbars to the coil, to the current leads and between each other. The design is described and the R and D carried out is reported.

Assembly in the test facility, acceptance and first test results of the ITER TF model coil

As a joint European effort an ITER Toroidal Field Model Coil (TFMC) was manufactured in industry and has been assembled in the TOSKA test facility of the Forschungszentrum Karlsruhe. After cool down and acceptance tests of the racetrack shaped coil made of a Nb/sub 3/Sn cable in conduit conductor the first test campaign started in July 2001 reaching the design current of 80 kA within one week. This paper describes the assembly in the test facility, summarizes the acceptance tests before and after cool down, and reports on the first test results.

Specific fabrication techniques of the Polo model coil and its components

Poloidal field coils of Tokamak machines are characterized by their pulsed operation needed for plasma ramp up and control. They have to sustain operation faults such as plasma disruptions in their superconducting state. A low-loss conductor, low-loss structural reinforcement and a high-voltage insulation system are needed for fulfilling these requirements. The basis for this technology has been developed for a superconducting model coil. The fabrication technique applied for the coil and some high-voltage related components are described. >

Manufacture, assembly and QA of the ITER toroidal field Model Coil

The conceptual design of the ITER TF Model Coil (TFMC) was produced by the European Home Team based on the ITER TF coil design. The test configuration in the TOSKA facility of FZK comprises the TFMC coupled with the existing European LCT coil by an intercoil structure (ICS). The elements of the TFMC are being constructed by European industry under the supervision of ITER European Home Team and are currently nearing completion. The primary objectives of the TFMC program are to gain experience of all aspects of the coil manufacturing process (including QA methods) and to establish realistic manufacturing tolerances for the actual ITER TF coils. At the current state of the project many of these objectives have already been achieved. The various technical problems encountered during engineering design and manufacture have been solved and have produced very useful information which can be applied in the ITER procurement documents for the TF coil system. This paper presents a description of the manufacturing process and related QA procedures.

MANUFACTURING OF THE POLO MODEL COIL

A superconducting poloidal field model coil as needed for tokamaks was constructed by GEC ALSTHOM within the Polo project of KfK Karlsruhe. The fabrication procedures for the coil with a strong stainless steel jacketed conductor are described and compared with conventional copper coils.

Completion of the Polo model coil

A superconducting poloidal field model coil as needed for tokamaks has been constructed by GEC ALSTHOM within the Polo project in effective collaboration with Forschungszentrum Karlsruhe, Institut fur Technische Physik, Germany. The manufacturing procedures for the coil and its terminals are described.