A simple screening current simulation method using equivalent circuit model for REBCO pancake coils

Abstract

The screening current induced in rare-earth barium copper oxide (REBCO) tape generates an unwanted irregular magnetic field. The screening current-induced field (SCIF) is a challenging issue for MRI, NMR, and accelerators magnet composed of REBCO coils. A few FEM-based simulation methods have been proposed to estimate the SCIF; however, they require a long computation time.Recently, we have proposed a simple SCIF computation method based on the self and mutual inductances of REBCO pancake coil and screening current radial paths on the top and bottom of pancake coils. Accuracy of the proposed method is not excellent; however, computation time is quite short. In this paper, we report an equivalent circuit model that includes the self and mutual inductances of a REBCO pancake coil and screening current radial path. Moreover, with this proposed method, we can compute SCIF of no-insulation (NI) REBCO pancake coils, while it is not the case with the previously proposed FEM-based simulation method. The proposed method has been validated by experiment. The proposed method is available online.

A newly developed screening current simulation method for REBCO pancake coils based on extension of PEEC model

“…The simulation results of the proposed A-PEEC are shown below, applying to two REBCO magnets: (a) a simple REBCO magnet consisting of 2 double-and 4 single-pancake (2 DP + 4 SP) coils with turn-to-turn insulation [29,42,46], and (b) a 14-T no-insulation (NI) REBCO insert magnet, named LBC3 [16], which generated 14.4 T inside a background field of 31.1 T. The simulated screening current-induced fields of both cases are compared with the measured ones.…”

“…The screening current behaviors may be represented with multiple inductive components [42]. Coupling the screening current equivalent circuit to an NI equivalent circuit [43,44], it is possible to simulate the screening current of NI pancake coils as well as conventional insulated pancake ones [29]. The following circuit equations are solved in the SEC model:…”

“…Figure 5 shows the screening current-induced fields at the magnet center, both the measurement and the simulation results of FEM + TFA, SEC, and A-PEEC. The results of FEM + TFA and SEC were presented in [29]. Here, the screening current-induced field B sc is defined as…”

“…To protect high-field HTS magnet from excessive stress concentration, the screening current behaviors have been discussed [22]. So far, a few screening current simulation methods have been proposed, which include: (a) an axisymmetric finite element method (Axi-FEM) [23,24]; (b) a finite element method with a thin film approximation technique (FEM + TFA) [15,[25][26][27][28]; (c) a simple equivalent circuit (SEC) model [29]; and (d) an advanced partial element equivalent circuit (A-PEEC) model which is shown for an SC simulation in this paper.…”

A non-destructive method for detecting turn-to-turn resistivity distribution in NI REBCO coils

“…A portion of the current in the NI coils will be forced to flow into the inter-turn paths during unsteady conditions such as excitation, demagnetization and quench, resulting in delayed charging and discharging [13], complicated quality degradation in the magnetic field [14,15] and stress concentration problem [16,17]. Additionally, the alternating background magnetic field also induces radial currents in the NI coils or similar cables, which leads to inter-turn losses [18,19], distinct dynamic resistance distribution from the insulated coils [20][21][22], and the redistribution of coil currents and spatial magnetic fields [23].…”