The physical understanding and numerical modelling of superconducting devices which exploit the high performance of second generation high temperature superconducting tapes (2G-HTS), is commonly hindered by the lack of accurate functions which allow the consideration of the in-field dependence of the critical current. This is true regardless of the manufacturer of the superconducting tape. In this paper, we present a general approach for determining a unified function Ic(B, θ), ultimately capable of describing the magneto-angular dependence of the in-field critical current of commercial 2G-HTS tapes in the Lorentz configuration. Five widely different superconducting tapes, provided by three different manufacturers, have been tested in a liquid nitrogen bath and external magnetic fields of up to 400 mT. The critical current was recorded at 90 different orientations of the magnetic field ranging from θ = 0°, i.e., with B aligned with the crystallographic ab-planes of the YBCO layer, towards ±90°, i.e., with B perpendicular to the wider surfaces of the 2G-HTS tape. The whole set of experimental data has been analysed using a novel multi-objective model capable of predicting a sole function Ic(B, θ). This allows an accurate validation of the experimental data regardless of the fabrication differences and widths of the superconducting tapes. It is shown that, in spite of the wide set of differences between the fabrication and composition of the considered tapes, at liquid nitrogen temperature the magneto-angular dependence of the in-field critical current of YBCO-based 2G-HTS tapes, can be described by a universal function Ic(f(B), θ), with a power law field dependence dominated by the Kim’s factor B/B0, and an angular dependence moderated by the electron mass anisotropy ratio of the YBCO layer.

This paper presents a comprehensive AC loss study of a circular HTS coil. The AC losses from a circular double pancake coil were measured using the electrical method. A 2D axisymmetric H-formulation model using FEM package COMSOL Multiphysics has been established, which was able to make consistency with the real circular coil used in the experiment. To model a circular HTS coil, a 2D axisymmetric model provided better accuracy than a general 2D model, and was also more efficient than a 3D model. Three scenarios have been analysed: Scenario 1 AC transport current and DC magnetic field (experiment and simulation); Scenario 2 DC transport current and AC magnetic field (simulation); Scenario 3 AC transport current and AC magnetic field (simulation and experimental data support). The angular dependence analysis on the coil under the magnetic field with the different orientation angle  has been carried out for all three scenarios. For Scenario 3, we investigated the effect of relative phase difference ∆ between AC current and AC field on the total AC loss of the coil. To summarise, we have carried out a current/field/angle/phase dependent AC loss (I, B, , ∆) study of circular HTS coil, which could potentially benefit the future design and research of HTS AC systems.

High-T c Superconducting (HTS) flux pumps are capable of injecting flux into a superconducting circuit, which can achieve persistent current operation for HTS magnets. In this paper, we studied the operation of a rectifier-type HTS flux pump. The flux pump employs a transformer to generate high alternating current in its secondary winding which is connected to an HTS load shorted by an HTS bridge. A high frequency AC field is intermittently applied perpendicular to the bridge, thus generating flux flow. The dynamic resistance caused by the flux flow "rectifies" the secondary current, resulting in a direct current in the load. We have found that the final load current can be easily controlled by changing the phase difference between the secondary current and bridge field. Bridge field of frequency ranging 10Hz-40Hz, magnitude ranging 0-0.66T was tested. Flux pumping was observed for field magnitude of 50mT or above. We have found that both higher field magnitude and higher field frequency result in a faster pumping speed and a higher final load current. This can be attributed to the influence of dynamic resistance. The dynamic resistance measured in the flux pump is comparable with the theoretical calculation. The experimental results fully support a first order circuit model. The flux pump is much more controllable than travelling wave flux pumps based on permanent magnets, which makes it promising for practical use.

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This paper presents the measurement and simulation of Alternating Current (AC) losses on the Stabilizer-free and Copper Stabilizer High Temperature Superconducting (HTS) Tapes: SuperPower SF12100 and SCS12050. The AC loss measurement utilised electrical method to obtain overall losses with AC transport currents. The 2D H-formulation by COMSOL Multiphysics has been used to simulate the real geometry and multi-layer HTS tapes. Ferromagnetic AC losses of substrate have been assumed to be ignored as the substrates of SF12100 and SCS12050 are non-magnetic. Hysteresis AC losses in the superconducting layer, and eddy-current AC losses in copper stabilizer, silver overlayer and substrate were concerned in this investigation. The measured AC losses were compared to the AC losses from simulation, with 3 cases of different AC frequency 10, 100, and 1000 Hz. The eddy-current AC losses of copper stabilizer at frequency 1000 Hz were determined from both experiment and simulation. The estimation of AC losses with frequency at 10000 Hz was also carried out using simulation method. Finally, the frequency dependence of AC losses from Stabilizer-free Tape and Copper Stabilizer Tape were compared and analysed.