Self-consistent Modeling of the IcI_c of HTS Devices: How Accurate do Models Really Need to Be?

Numerical models for computing the effective critical current of devices made of HTS tapes require the knowledge of the Jc(B,theta) dependence, i.e. of the way the critical current density Jc depends on the magnetic flux density B and its orientation theta with respect to the tape. In this paper we present a numerical model based on the critical state with angular field dependence of Jc to extract the Jc(B,theta) relation from experimental data. The model takes into account the self-field created by the tape, which gives an important contribution when the field applied in the experiments is low. The same model can also be used to compute the effective critical current of devices composed of electromagnetically interacting tapes. Three examples are considered here: two differently current rated Roebel cables composed of REBCO coated conductors and a power cable prototype composed of Bi-2223 tapes. The critical currents computed with the numerical model show good agreement with the measured ones. The simulations reveal also that several parameter sets in the Jc(B,theta) give an equally good representation of the experimental characterization of the tapes and that the measured Ic values of cables are subjected to the influence of experimental conditions, such as Ic degradation due to the manufacturing and assembling process and non-uniformity of the tape properties. These two aspects make the determination of a very precise Jc(B,theta) expression probably unnecessary, as long as that expression is able to reproduce the main features of the angular dependence. The easiness of use of this model, which can be straightforwardly implemented in finite-element programs able to solve static electromagnetic problems, is very attractive both for researchers and devices manufactures who want to characterize superconducting tapes and calculate the effective critical current of superconducting devices

Numerical Study on Magnetization Characteristics of Superconducting Conductor on Round Core Cables

This paper presents numerical study on magnetization characteristics of conductor on round core (CORC) cable. Numerical-models introduced in this paper are based on finite-element method (FEM) with simplified structure, optimized assumptions and settings. Magnetization performance of CORC cables is represented by both full coupled model and isolated model. These numerical models are verified by experiments on CORC cables made of commercial HTS tapes. On basis of this, two topics are discussed in this paper: one is the magnetic shielding effect of superconducting layers in CORC cables; the other one is the end effect of magnetization loss in short CORC cables. Conclusions obtained in this paper will be helpful to understand the working mechanism of CORC cable and also useful in design of large-scale magnets based on CORC cables

Design and Testing of Coils Wound Using the Conductor-On-Round-Tube (CORT) Cable

Alternative concept for winding of coils from high-temperature superconducting tapes has been investigated. Conductor-On-Round-Tube (CORT) conductors with tapes helically wound on a metallic tube have been manufactured and used to wind single layer coils with the bore diameters between 116 and 325 mm wound and tested in the dc regime. Results were analyzed with the help of numerical calculations considering the critical current density dependence on magnetic field derived from the short sample measurement. We have also modified the standard approach by including the fluctuations of critical current along the tape length into the calculations. Results have shown that the uniformity of critical current is essential for achieving predictable cable and coil performance