The magnetisation profiles and ac magnetisation losses in a single layer YBCO thin film caused by travelling magnetic field waves

Abstract

This paper studies the magnetisation and ac magnetisation losses caused by a travelling magnetic wave on a single-layer YBCO thin film. This work provides thorough investigations on how the critical magnetic field gradient has been changed by the application of a travelling wave. Several conditions were studied such as zero-field cooling (ZFC), field cooling (FC) and a delta-shaped trapped field. It was found that the travelling wave tends to attenuate the existing critical magnetic field gradients in all these conditions. This interesting magnetic behaviour can be well predicted by the finite element (FEM) software with the E-J power law and Maxwell's equations. The numerical simulations show that the existing critical current density has been compromised after applying the travelling wave. The magnetisation profile caused by the travelling wave is very different from the standing wave, while the magnetisation based on the standing wave can be interpreted by the Bean model and constant current density assumption. Based on the numerical method, which has reliability that has been solidly proven in the study, we have extended the study to the ac magnetisation losses. Comparisons were made between the travelling wave and the standing wave for this specific YBCO sample. It was found that by applying the magnetic wave of the same amplitude, the ac magnetisation loss caused by the travelling wave is about 1/3 of that caused by the standing wave. These results are helpful in understanding the general magnetism problems and ac magnetisation loss in the travelling magnetic wave conditions such as inside a high temperature superconducting (HTS) rotating machine, etc.

Numerical models for ac loss calculation in large-scale applications of HTS coated conductors

“…The reference model is an H-formulation model including all the tapes (figure 1(a)). H-formulation models have been widely used and verified against experiments for single conductors and coils [20][21][22][23][24][25][26][27] and can therefore be trusted to give a good estimation of the real losses. Besides the surrounding air, we model only the superconducting layers, taking their real thickness into account.…”

Operational research on a high-Tcrectifier-type superconducting flux pump

“…The key point in these flux pumps is to drive at least one part of superconductor normal either by high field or heat. Developed in recent years, HTS flux pumps [8][9][10][11][12][13][14][15] are mainly based on travelling magnetic waves, which was first proposed by Coombs [8]. Bai [9,10] achieved flux pumping using travelling wave generated by linear windings.…”

Magnetization of YBCO film with ac travelling magnetic waves of relatively short wavelengths

“…To understand the above mentioned problem, a "circular-type magnetic flux pump" (CTMFP) device [9][10][11] was previously built, to study the magnetization of HTS YBa 2 Cu 3 O 7-d film in ac travelling magnetic waves. In the CTMFP experiments, both the YBCO film and the applied field are axial-symmetric, while the magnetization behaviour can be directly compared with the classic magnetization model for type-II superconductor.…”

“…An updated numerical model was built based on the FEM method with Maxwell's Equations and the E À J power relationship, to simulate the complete magnetization process during the experiments. The governing equation is expressed as 1,11…”