A closed-loop high temperature superconducting magnet energized by flux pump and its piecewise semi-analytical solution

Abstract

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.

Miniaturized HTS linear flux pump with a charging capability of 120 A

“…However, equation (4) indicates that if the width of the flux profile is reduced, a high output current may also be achieved without increasing the size of the system. Based on the above principle, a linear flux pump device was designed with narrow iron teeth to obtain a narrow moving flux profile.…”

“…However, HTS coils cannot operate in persistent current * Author to whom any correspondence should be addressed. mode (PCM) alone because of non-negligible joint resistance and internal flux creep [4][5][6][7]. The traditional power supply to HTS coils is mainly through current leads, which are bulky with considerable thermal leakage, adding to the long-term operating costs of the system [8].…”

A flux pump driven non-soldering closed-loop HTS magnet and its electromagnetic-thermal semi-analytical modelling method

“…New cutting scheme. Inspired by the previous cutting method we used [18], which produces a closed-loop HTS ring with only one loop, we can now easily extend it to realize a closed-loop HTS ring with two loops.…”

“…Figure 1(a) shows the cutting method we used before [18], in which there is a slit cut in the REBCO tape to form the closed-loop HTS ring with only one loop. To produce the closed-loop HTS ring with two loops as required in this paper, we can cut the tape directly to form such a ring following what is shown in figure 1(b), the total length of the tape to be discarded is l-360 mm, where l is the length of 8 mm tape.…”

“…Recently, we have proposed a closed-loop HTS magnet [18] containing two single-pancakes (SPs) excited and demagnetized by a flux pump, which can run without encountering any soldering joints in the stable state, but during the pumping process, the soldering joints can still not be avoided. Although a piecewise semi-analytical solution of the pumping process is deduced and the two theoretical limits of saturation current injected by the flux pump are given for the magnet, the influence of temperature were not considered in the solution and the shared resistance and inductance were simplified as separated, which might have impacted on the accuracy of the semianalytical solution and thus restrict the actual application.…”