Weak emergence in the angular dependence of the critical current density of the high temperature superconductor coated conductor REBCO

Abstract

Extensive critical current density J c measurements are reported as a function of magnetic field B, temperature T, angle θ between the applied field and the surface of the tape, and strain ε, on a REBCO coated conductor. The strain, ε peak (B, T, θ), at which J c (ε app ) is maximised, is a function of B, T, and θ, which is consistent with weakly emergent behaviour. It is described by the chain model that considers competition between twinned domains with different crystallographic orientations and opposing responses under an applied uniaxial strain.Detailed effective upper critical field B * c2 (T, ε app , θ = 0) data are presented that show universal temperature and strain scaling. They lead to an accurate flux pinning relation for the volume pinning force,q , where b = B/B * c2 (T, ε app , θ = 0) and p and q are constants, and are used to help parameterise the scaling behaviour of the angular J c data more accurately in those cases where B * c2 cannot be measured directly. We derive approximate analytic in-field expressions that explain how the fraction, f, of a-domains amongst the a-and b-domains affects the strain dependence of the critical parameters and conclude that in our tape, f = 0.4, and the strain at which J c is the same in both domains is ε JcA=JcB = 0.15 %. We report a sharp peak in J c as the applied field approaches alignment with the ab-plane and the unusual result that with it, a suppression of the index of transition N also occurs. We find that the effective upper critical field B * c2 increases as the field angle approaches the ab-plane significantly faster than any available theoretical model for the upper critical field B c2 .In addition, we conclude that a weak-emergence description is not limited to high temperature superconductors, but also describes some low-temperature superconductors.

Training and Upgrading Tokamak Power Plants with Remountable Superconducting Magnets

“…It should include all the key technologies and identify whether fission power plants can be replaced on a commercial footing by fusion power plants that produce no long-term high-level waste, reduce proliferation of nuclear weapons in a increasingly carbon-free world, and provide long-term energy security for base load electricity production. [156], ARC [5], CFETR [193,206], ITER [1,109], SPARC [2,207], JET [166,208,209], JT60-SA [103,110], KSTAR [210,211,212], EAST [213,214,215], WEST [216,217], MAST-U [153,218] and SST-1 [219,220] [108,111,130,134], and B c2 (T ) = B c2 (0)(1 − t) s for REBCO [120].…”

“…B * c2 (0) and T * c for quaternary Nb-Ti were taken from [126], all other parameters are from ITER specification Nb-Ti. The value of A * for REBCO was found by fitting to literature data [136], all other parameters were taken from measurements on REBCO tapes [120]. Nb 3 Sn parameters were taken from [111].…”

“…The exciting new results from MIT which achieved a field of > 20 T [118,119] at elevated temperatures (20 K) in a fusion relevant coil, demonstrate REBCO cables are on a fast track to fusion applications [36]. REBCO's ≈ 90 K critical temperature [120] allows for large temperature margins in cable design and higher operation temperature that reduces cryo-power requirements. However there is more work to be done to demonstrate reliability -it is a ceramic oxide material, that is prone to brittle fracture under tensile strain > 0.3 -0.7 % [121,122] and tape delamination under cyclic loading [38,123].…”

“…All other fitting parameters for this quaternary material were assumed to be the same as for commercial Nb-Ti. The REBCO scaling parameters were taken from previous measurements on SuperPower tapes [120,136]. A comparison between the overall strand and tape critical current densities of commercial Nb-Ti, quaternary Nb-Ti and REBCO at 4.5 K is shown in figure 7.…”

Self-Field Effects in a Josephson Junction Model for ${J_\text{c}}$ in REBCO Tapes

“…where we have used the constraint αn (0) = −|T cn /T c |. The temperature dependence of the Ginzburg-Landau parameter is taken from the Ginzburg-Landau ratio of the critical fields [4] using the standard temperature dependence for the upper critical field [5] and a two-fluid model for the critical field [6]. The temperature dependence of the coherence length is given by the Ginzburg-Landau relation for B c2 (T ) [4].…”