Abstract
Joint-free (RE)Ba2Cu3Ox (REBCO) coil based on ‘wind-and-flip’ technique has been developed to generate a persistent magnetic field without power supply. This paper is to study the magnetization characteristics of the joint-free REBCO coil by field cooling, in order to trap higher field. A joint-free pancake coil is wound by REBCO tapes and the field cooling magnetization test is performed on it. An approximate numerical model based on H-formulation is built for this coil to analyze its magnetization behavior, which is validated by the experimental results Analysis show that a persistent direct current is induced in the coil during the field cooling operation, which generates the trapped field. The induced current of the joint-free coil shows an intrinsic non-uniform distribution among turns. Increasing the magnetization field and critical current of REBCO conductors can considerably increase the trapped field. But the trapping factor (the rate of trapped field to background magnetization field) reaches a maximum value (60 % for the test coil). This maximum value is an intrinsic characteristics for a fabricated coil, which only depends on the coil’s geometry structure. With a same usage of REBCO tapes, the trapping factor can be improved significantly by optimizing the coil structure to multiple pancakes, and it can approach 100 %.
Highlights
Second-generation high temperature superconductor (2G HTS) REBCO has always suffered the problem of superconducting joints, which leads to the technique challenges for persistent current REBCO coils.[1,2,3]
E and J are electrical field and current density respectively. They show a nonlinear relationship for REBCO conductors, which is represented in Eq 2
The results show that increasing the critical current of the REBCO tape can significantly increase the trapped field when the critical current in a low range (Ic
Summary
High stable fields are trapped in these tests.[8,26,27,28,29,30] Researches have focused on the field shielding function of this joint-free coil, which has been validated by experiments.[13,14] Both the field trapping and filed shielding result from induced current, and they share a same underlying mechanism. Existing researches on this joint-free REBCO coil focus on experimental validation of magnetization methods. The trapping factor is analyzed, and measures are proposed to increase the trapped field and trapping factor by field cooling
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