Electrical properties of superconducting joint between composite conductors

Abstract

To investigate the electrical properties of the joint between superconducting multifilamentary wires, we applied a radio frequency superconducting quantum interference device (r.f.-SQUID) voltmeter to measure the extremely small voltage induced across the joint. We measured the time variation of both the current induced in a loop of superconducting wire and the voltage induced across the joint. A voltage sensitivity in the pico-volt range was obtained with this apparatus. Comparisons of currentdecay between superconducting loops with soldered, spot-welded and cold-welded joints were made. A flux creep-like phenomena was seen in the current-decay for the coldwelded and spot-welded joints.

Development of superconducting joints between iron-based superconductor tapes

“…So far, techniques for joining superconductor wires/tapes such as NbTi, BiSCCO, and MgB 2 wires/tapes have been well developed [16][17][18][19][20][21][22][23][24][25]. For the low temperature superconductors, especially for NbTi, joining methods are very mature and convenient for the manufacture of persistent mode magnets.…”

“…Soldering with solder alloy is one choice in commercial magnet manufacturing, and the critical current of the joints can reach as high as 1000 A at 4.2 K and 1 T [20], with resistance in the range of 10 −13 ∼10 −14 Ω. Cold pressing is another good choice to connect the NbTi filaments [21,22]. The current of joints fabricated by this method was as high as 468 A (1 T, 4.2 K).…”

Interpretation of time-dependent current and resistance of HTS closed loop with superconducting joint considering flux creep

“…by measuring the time (t) dependence of the current flowing in a closed loop (I loop ) made of a superconducting wire/tape with a superconducting joint. [1][2][3][4][5][6] The following equation is used to deduce the circuit resistance (R) of the closed loop:…”

“…an inhomogeneous current distribution in the superconducting wire/tape or joint. 1,3,4,6) After settling the fast decay, a subsequent slow decay can be observed.…”

“…Ohki et al reported that a logarithmic current decay was observed in a REBa 2 Cu 3 O y HTS closedloop sample, which suggested voltage generation by flux creep at the joint. 8) Even though other studies have also mentioned the flux-creep effect to explain the decay of the current flowing in a closed loop, 1,4,5) the flux-creep effect has not yet been clarified sufficiently.…”