Electrical resistance of Nb₃Sn/Cu splices produced by electromagnetic pulse technology and soft soldering

Abstract

The electrical interconnection of Nb 3 Sn/Cu strands is a key issue for the construction of Nb 3 Sn based damping ring wigglers and insertion devices for third generation light sources. We compare the electrical resistance of Nb 3 Sn/Cu splices manufactured by solid state welding using Electromagnetic Pulse Technology (EMPT) with that of splices produced by soft soldering with two different solders. The resistance of splices produced by soft soldering depends strongly on the resistivity of the solder alloy at the operating temperature. By solid state welding splice resistances below 10 n can be achieved with 1 cm strand overlap length only, which is about 4 times lower than the resistance of Sn96Ag4 soldered splices with the same overlap length. The comparison of experimental results with Finite Element simulations shows that the electrical resistance of EMPT welded splices is determined by the resistance of the stabilizing copper between the superconducting filaments and confirms that welding of the strand matrix is indeed achieved. EMPT allows interconnecting the ductile, unreacted strands, which reduces the risk of damaging the brittle reacted Nb 3 Sn strands.To be published in Superconductor Science and Technology Geneva, Switzerland CERN-ATS-2011-230 AbstractThe electrical interconnection of Nb 3 Sn/Cu strands is a key issue for the construction of Nb 3 Sn based damping ring wigglers and insertion devices for third generation light sources. We compare the electrical resistance of Nb 3 Sn/Cu splices manufactured by solid state welding using Electromagnetic Pulse Technology (EMPT) with that of splices produced by soft soldering with two different solders. The resistance of splices produced by soft soldering depends strongly on the resistivity of the solder alloy at the operating temperature. By solid state welding splice resistances below 10 nΩ can be achieved with 1 cm strand overlap length only, which is about 4 times lower than the resistance of Sn96Ag4 soldered splices with the same overlap length. The comparison of experimental results with Finite Element simulations shows that the electrical resistance of EMPT welded splices is determined by the resistance of the stabilizing copper between the superconducting filaments and confirms that welding of the strand matrix is indeed achieved. EMPT allows interconnecting the ductile, unreacted strands, which reduces the risk of damaging the brittle reacted Nb 3 Sn strands.

Electromechanical behaviour of REBCO tape lap splices under transverse compressive loading

“…The resistance of such splices is determined by the resistance of the high purity Cu matrix through which the current flows from the superconducting filaments of the conductors to be interconnected. Contact resistances can be neglected [22]. 14 The resistance of soldered Nb-Ti or Nb 3 Sn splices depends significantly on the electrical resistivity of the solder that is used [23].…”

“…In this article we compare REBCO tape splice resistances with those of other superconductors, notably Bi-2223 tape and MgB2 wires, and with Nb-Ti and Nb 3 Sn lap splice resistances that we have reported previously [8]. The electromechanical splice properties are important for applications where the splices are submitted to substantial mechanical loads.…”

Fabrication of NbTi superconducting joint by electromagnetic forming method

“…The electromagnetic forming (EMF) technology is based on the Faraday's law of electromagnetic induction resulting in repulsive Lorentz body forces between two conductive bodies carrying opposed currents [12]. It has the advantages of high strain rates plastic deformation, self-cleaning surface, high bonding force, no-lubricant, contact-free, good repeatability and high production rate.…”

“…The EMF technology is new for the superconducting jointing application. D. Schoerling manufactured Nb 3 Sn/Cu splices using EMF method for horizontal racetrack damping wiggler magnet [12]. But the superconductors in the joint haven't realized metallurgical bonding.…”

The Electrical Resistance of Rutherford-Type Superconducting Cable Splices

“…DISCUSSION AND CONCLUSION 168 In the following discussion it is assumed that the influence 169 of the solder resistance on the overall splice resistance can 170 be neglected. This assumption is based on the resistivity re-171 sults obtained for the solder material [13], and on resistance 172 measurements of splices soldered with different solder alloys 173 [14]. The resistance of Nb-Ti/Cu Rutherford-type cables lap 174 Because of the strong field dependence of the critical current 205 density of Nb-Ti and Nb 3 Sn superconductors, there is always a 206 huge margin in terms of critical current density for splices that 207 are outside the high field region of a magnet.…”