Development of 46-kA Nb/sub 3/Sn conductor joint for ITER Model Coils

Abstract

Ahtrud -The conductor Joint is one of the key technologics for superconducting coils. A butt type joint has been successfully developed for Ihe ITER magnets.The 46kA NbSSn conductors arc conncctcd by the diffuslon bonding technique in vacuum, after the reaction of NbJSn. The advantage o f this joint is low losses against pulse fietd, because the compacted part is very small compared with other types of joint. I5 butt joints have alrcady bcon fabricated in the ITER CS Model Coil, According to the test results of the full-size conductor samples, these butt joints will be operated stably in the pulsc operation, because the temperature increase due to ac losses and Joule heating by jolnt resistance is very small and the joint has sufficiently high temperature margin,

Development of the Joints for ITER Central Solenoid

“…The CS butt joint is the extension from the butt joint developed by JAERI for the CS Model Coil Outer Module [3]. However, there are several differences in fabrication: a) the butt joining tool needs to be assembled and sealed around connecting conductors, and b) the straight section where the joint is made is very short in order to prevent the joint to "bulge" from the winding pack too much.…”

Development of the Butt Joint for the ITER Central Solenoid

“…In the interface of the joint the strands are highly compacted to a very low void fraction -(5-8%) to ensure large area of the contact. Studies performed by the Japanese Home Team [3] revealed that the diffusion bond takes place only between copper portions of the cross section in the superconducting strands, sleeve and copper strands. The bronze area does not fuse.…”

“…Study [7] performed with ANSYS predicted that the strain of the butt joint interface will be stretched by only slightly less than the jacket -to 0.1%, and the butt joint interface will see 22 kN tensile load. At ultimate strength of the butt joint of 40-50 kN [3] there is a serious concern regarding mechanical and electrical integrity of the joint under such high cyclic load.…”

“…The butt joint fabrication procedure of bonding was developed during ITER EDA [3]. The CS butt joint will use these parameters as a starting point and will verify its applicability to the CS conductor.…”

“…The lap joint design is more structurally reliable and offers a better uniformity in current distribution [2]. The butt joint had lower AC losses and was insensitive to orientation of the transverse varying magnetic field [3]. Based on successful CS Model coil experience, ITER selected an in-line butt joint that would occupy about the same space envelop as the conductor.…”