High temperature superconducting (HTS) magnets energized by flux pumps are capable of carrying heavy current without heat leakage derived from current leads and thus desirable for many applications. However, the soldering resistance is still an obstacle for the persistent operations of the HTS magnets. Here, we propose a closed-loop HTS magnet magnetized by flux pump with thermal switches. The magnet consists of closed-loop double-pancake (DP) coils wound by a rare-earth barium copper oxide (REBCO) tape on which a slit is cut to form a closed-loop ring within which current can flow without encountering the soldering resistance. Another REBCO tape is soldered on the closed-loop ring to form a pump bridge and a flux pump consists of a copper coil with iron core is set arround the pump bridge. There exist a group of manganese copper wires wound on the closed-loop ring and the pump bridge respectively as thermal switches. A piecewise semi-analytical solution is suggested to investigate the charging process by which the transport current in the magnet is calculated. Experiments are carried out to verify the feasibility and rationality of the magnet and the solution. The results show that the magnet can be operated in a persistent current mode, and thus, this study represents a practical solution for persistent operation of the HTS magnets. Besides, the proposed solution can effectively explain and predict the saturation current of the suggested magnet, which can, therefore, guide the design of other forms of the HTS magnets and flux pumps.

The qualities of superconducting conductors are usually characterized by their critical current and n-value. In this paper, the critical current and the n-value of the second-generation (2G) high temperature superconducting (HTS) conductors considering the temperature-field dependence are predicted by a back propagation (BP) neural network as Jc(B,θ,T) and n(B,θ,T). There exists correlation between the critical current and the n-value, thus in our BP neural network, the tasks of estimating the critical current and the n-value can be carried out in one network. The outputs to predict the critical current and the n-value share the same hidden layers of the network, and therefore the critical current and the n-value can be calculated simultaneously. The critical current and the n-value of HTS conductors vary from different manufacturers and even for the same manufacturer but different production batches.

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