Bridge-Type Mechanical Lap Joint of a 100 kA-Class HTS Conductor having Stacks of GdBCO Tapes

Abstract

In this paper, we reported design, fabrication and test of a prototype 100-kA-class high-temperature superconducting (HTS) conductor, especially for joint section, to be used for segmented HTS helical coils in the FFHR-d1 heliotron-type fusion reactor. The conductor has a geometry of three rows and fourteen layers of Gadolinium Barium Copper Oxide HTS (GdBCO) tapes embedded in copper and stainless steel jackets and has a joint section with bridge-type mechanical lap joint. We introduced improved method to fabricate the joint based on pilot experiments and we were able to apply a current of ∼ 120 kA at 4.2 K, 0.45 T to the sample without quench at joint. The obtained joint resistance was ∼ 2 nΩ, which was lower than our previous data. Though joint resistance increased with a rise in current and magnetic field, predicted joint resistance in the environment of actual helical coil in the FFHR-d1 was small enough to properly run the cryoplant of the reactor.

Magnet design with 100-kA HTS STARS conductors for the helical fusion reactor

“…To realize the joint-winding, a bridge-type mechanical lap joint with a staircase-like structure has been developed at Tohoku Univ. as a viable technique to obtain a face-to-face connection of YBCO surfaces [7,8]. Welding of the stainless steel jacket is employed to ensure the mechanical strength of the joint section.…”

“…The sample was tested in the superconductor testing facility at NIFS [7][8][9][10]. The central part of the conductor sample was thermally insulated using a GFRP jacket.…”

Design Status of the Structural Components of the Helical Fusion Reactor FFHR-d1

“…For example, the helical fusion reactor might be efficiently constructed using a high temperature superconductor (HTS) with jointwinding. A prototype HTS with a bridge-type mechanical lap joint successfully achieved 100 kA at 20 K and a low-resistance (1.8 nΩ) at 4 K [10,11]. A detailed welding method for the joint section is also being investigated.…”

Fundamental Investigation on Tensile Characteristics of a Mechanical Lap Joint of REBCO Tapes

“…We plan to connect the REBCO tapes at the joint section using a bridgetype mechanical lap joint that has two joint sections with a staircase-like structure to make face-to-face connection of REBCO surfaces. Indium foils are inserted in between [10]- [12] and the outer stainless steel jacket is welded to have high tensile strength. In the mechanical joint, joint surfaces are just mechanically contacted with pressure, which is different from a soldered joint and a diffusion bonding.…”