Mechanical reinforcement for RACC cables in high magnetic background fields

Abstract

Operable in liquid helium, liquid hydrogen or liquid nitrogen, high temperature superconductor (HTS) cables are investigated as future alternatives to low temperature superconductor (LTS) cables in magnet applications. Different high current HTS cable concepts have been developed and optimized in the last years—each coming with its own benefits and challenges. As the Roebel assembled coated conductor (RACC) is the only fully transposed HTS cable investigated so far, it is attractive for large scale magnet and accelerator magnet applications when field quality and alternating current (AC) losses are of highest importance. However, due to its filamentary character, the RACC is very sensitive to Lorentz forces. In order to increase the mechanical strength of the RACC, each of the HTS strands was covered by an additional copper tape. After investigating the maximum applicable transverse pressure on the strand composition, the cable was clamped into a stainless steel structure to reinforce it against Lorentz forces. A comprehensive test has been carried out in the FBI facility at 4.2 K in a magnetic field of up to 12 T. This publication discusses the maximum applicable pressure as well as the behaviour of the RACC cable as a function of an external magnetic field.

Effect of transverse compressive monotonic and cyclic loading on the performance of superconducting CORC® cables and wires

“…A major benefit of CORC ® conductors over the TSTC is that transverse compressive loads applied to CORC ® conductors are always applied to the wide side of the tapes, as long as the deformation of the CORC ® conductor remains mainly elastic. The tapes are much more resilient to transverse stress in this direction, potentially eliminating the need to provide external support to the CORC ® conductor that may be an inevitable requirement for the TSTC, but also for Roebel cables [31,32].…”

Quench and stability of Roebel cables at 77 K and self-field: Minimum quench power, cold end cooling, and cable cooling efficiency

“…But it is much less stable with respect to an externally applied disturbance which quickly initiates film boiling. Analysis using eqn (8) shows that a surface-applied Gd as small as 11 kW/m 2 would be sufficient to drive the currentcarrying cable normal.…”

“…Numerous high-field magnets and insert magnets have been demonstrated using HTS conductors and a few high-field HTS-hybrid research magnets are nearly complete for user facilities [3][4][5][6]. Bi:2212 cables will likely require a high-pressure, atmospherically-controlled, wind-and-react, and epoxy impregnated magnet manufacturing process while Rare-Earth Barium Copper Oxide (ReBCO) will be react-and-wind, have simpler insulation options, and may not require epoxy impregnation depending on the stresses and cable type [7][8][9][10]. The structure of Bi:2212 Rutherford cable is similar to the NbTi and Nb3Sn Rutherford cables that are presently used, but ReBCO cables are quite different.…”

Transverse pressure effect on superconducting Nb3Sn Rutherford and ReBCO Roebel cables for accelerator magnets

“…Although the flat ReBCO tape is much more resilient to transverse pressure than bare Nb 3 Sn round wire, there are significant effects due to stress concentrations between the assembled meander-shaped ReBCO strands [85,[161][162][163]. Therefore, Roebel cables used in accelerator type coils must also be impregnated.…”

“…The Lorentz force generated in such magnets leads to sizeable transverse pressure on the superconducting cables, in the present 15 to 20 T magnet designs of the order of 150 MPa or even above [91]. Contrary to single ReBCO coated conductors, a bare Roebel cable, starts to degrade already under transverse stress below 50 MPa due to stress concentrations [161][162][163]. In order to use this type of cable in high field magnets additional reinforcement is thus required.…”