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The dynamic resistance of a superconductor appears if it carries a direct current (DC) current and is simultaneously exposed to alternative current (AC) magnetic fields if its amplitude is higher than its full penetrated field. Due to its strong anisotropy, the dynamic resistance of high-temperature superconducting (HTS) tape is not only affected by the magnitude of AC magnetic fields but also their orientations. In particular, the dynamic resistance has considerable effect on the current distribution in HTS cables (except for Roebel cables) and even cable-in-conduit conductors made from those HTS cables, except for dissipative loss. This paper presents the behavior of dynamic resistance in an HTS quasi-isotropic strand (Q-IS), which consists of four sub-stacked 2G HTS tapes proposed by our group at North China Electric Power University, while it carries a DC current and simultaneously experiences an AC magnetic field with different magnitudes and orientations. An angular dependence of dynamic resistance in a single 2G HTS tape in an AC magnetic field with various orientations is first performed in simulations and experiments, respectively. The experimental results are in good agreement with the simulated ones, which shows that the dynamic resistance of a Q-IS also exhibits quasi-isotropic characteristics and has an important effect on the distribution of DC transport current. The related results are promising for the design and application of other DC HTS cables, feeders and magnets. [ABSTRACT FROM AUTHOR]

The quench characteristic is a critical issue for the application of superconducting cable. In order to study the process of the quench behavior in the cable accurately, a four-dimensional (4D) quench model for quasi-isotropic superconducting cable was developed and presented, in this paper. We first consider that the materials of the cable are in perfect thermal contact with the neighboring ones, and the radial temperature field and current redistribution at different time and different axial distances during the quench process are obtained. Then, thermal contact resistance (TCR) is considered. In addition, the minimum quench energy (MQE) and the quench propagation velocity (QPV) in axial direction of the two cases are investigated and compared. The results show that the maximum temperature of the heating area (Tmax) is higher and QPVs are greater than the case without considering TCR. In addition, there is temperature gradient in the cross section of the cable. Finally we evaluate the sensitivity of thermal stability for the quasi-isotropic cable on the different values of TCR and positions where TCR is inserted. It is concluded that TCR among REBCO tapes has little effect on MQE and QPV of quasi-isotropic superconducting cable. The results are useful for the application of the quasi-isotropic superconducting cable immersed in liquid nitrogen, and this numerical model can also be used for simulating the quench process of other superconducting cables or conductors. [ABSTRACT FROM AUTHOR]

A full high temperature superconducting (HTS) magnet can operate in persistent current mode (PCM), which has promising application in high magnetic field. A laboratory scale Bitter-like HTS magnet stacked by REBaCuO (RE: rare earth element) annular plates was proposed and it can operate in PCM without current lead and joint resistance. This study focuses on the temporal stability of the magnetic field generated by the magnet, which was energized by the multi-pulsed field magnetization (MPFM) method composed of a solenoid coil and pulsed triangular waveform current source and tested at 77 K (LN2 bath). The characteristics of the magnetic field in the magnet with various pulsed current amplitudes, durations and reversal excitation experiments were systematically researched. Moreover, the numerical simulation of the magnet energized with the pulsed current amplitude 3A was performed and the attenuation of the magnetic field in the magnet was discussed and analyzed. [ABSTRACT FROM AUTHOR]

With the progress of a high-temperature superconducting material production technology, the full superconducting magnets with a high magnetic field above 25 T have been realized for recent years. However, they cannot operate with persistent mode (PCM) since there is difficulty in jointing without resistance or low enough jointing resistance in HTS tapes. The bitter-like HTS magnet is a full superconducting magnet composed of ReBCO annular plates, and the power supply technology is an effective method for achieving PCM. In this paper, we choose inner and outer excitations to energize a bitter-like HTS magnet in 77 K. It was found that the HTS magnet reaches saturation faster by using the inner excitation than the outer excitation for the same bitter-like HTS magnet. The magnetic field was measured with a Hall probe at 77 K. The results illustrated that the inner excitation is much faster than the outer excitation, but the saturation field in former is lower than the latter one. [ABSTRACT FROM AUTHOR]

Nowadays, a conductive cooling cryocooler for superconductor becomes used wildly. But in the absence of liquid helium, heat conduction becomes much difficult, which means conductive cryocooler conductors are more susceptible to disturbances than conductors immersed in liquid helium. A current-sharing temperature is a key design parameter for superconductors’ performance. In this paper, we analyze the issues of current-sharing temperature in the Nb3Sn/Cu conductor. Based on the power law model, we simulate and analyze the effects of power law index, magnetic field, and moderate intrinsic-strain on the current sharing temperature of Nb3Sn/Cu conductor operating in conductive cooling cryocooler, when the temperature of superconductor is aroused by disturbance. [ABSTRACT FROM AUTHOR]

• The study of bending properties has important significance for nuclear fusion and superconducting magnets. • Laminated beam theory can accurately calculate strain distribution through finite element method (FEM) simulation. • A FEM simulation model is established to analyze the critical bending radius of Q-IS strand, and samples are made for testing. • According to the built model, the critical bending radius of Q-IS strand is simulated when bended along different angles. The study of the mechanical properties of superconducting strands plays a very important role in its application in engineering. In this paper, a 3D model based on laminate theory is proposed to study the bending properties of REBCO tape and quasi-isotropic superconducting (Q-IS) strand. Laminated beam theory can not only simplify REBCO tape and superconducting strand to qualitatively analyze strain distribution, but also accurately calculate strain distribution through finite element method (FEM) simulation. A FEM simulation model is established to analyze the critical bending radius of Q-IS strand, and samples are made for testing. According to the built model, the critical bending radius of Q-IS strand is simulated when bended along different angles. The study of bending properties has important significance for the application of superconducting strand in the applications of power transmission, nuclear fusion and superconducting magnets. [ABSTRACT FROM AUTHOR]

• This quasi-isotropic superconducting strand could be applied to high-energy physical magnets or fusion magnets. • This superconducting strand shows quasi-isotropy characteristics in an external magnetic field and also has the advantage of high current density. • According to different transmission requirements, the critical current can be adjusted by stacking copper tapes or copper former of different thicknesses. At the same time, adding copper tapes can improve the thermal stability of superconducting strand. • The effect of thickness of copper tape on critical current for strands stacking REBCO tapes outside and copper tapes inside and stacking REBCO tapes outside on a copper former are studied. • The influence of different stacking methods of copper tapes and superconducting tapes on the critical current was studied. In order to improve the transmission capacity of the second generation REBCO tape, many structures of superconducting strand/cable stacked with REBCO tapes were proposed. Quasi-isotropic superconducting strands (Q-IS) stacking REBCO & copper tapes alternately and stacking REBCO tapes outside with copper tapes inside are proposed in this paper. The critical current of Q-IS strand is simulated based on H-formulation, and strand samples are fabricated and tested. Critical current densities of Q-IS strand in the two stacking patterns are analyzed, indicating that the second stacking pattern can improve the critical current density of a single REBCO tape more than the first pattern. Another kind of Q-IS strand with REBCO tapes placed on a copper former is also proposed, and this kind of strand can be twisted to improve the engineering current density and reduce the AC loss, which can be used in power transmission, large superconducting magnets, fusion application and so on. [ABSTRACT FROM AUTHOR]