Current Status in Building a Compact and Mobile HTS MRI Instrument

Self Cite

Magnetic switches apply AC magnetic fields to DC current-carrying high temperature superconducting (HTS) tapes to generate DC voltages and are commonly used in the persistent current switches (PCSs) and flux pumps to charge HTS-coated conductor magnets. Normally, they are made of copper field coils and iron cores with narrow air gaps for the HTS tape to pass through. However, the perpendicular components of the self-field of the HTS tape in the air gap can be enhanced by the iron cores and cause a critical current reduction of up to 40% to the tape. If ignored, this reduction, rather than the magnets themselves, will limit the current carrying capability of the HTS magnets. To tackle this problem, we present analytical approximations to calculate the self-field distribution of a superconducting tape between iron cores. The approximate solutions are based on the method of images in electromagnetics to simplify the derivation and are then verified by the experiments and 3D finite element method models using the T–A formulation. The solutions are universal and can be applied to almost all the magnetic switches currently in use. A case study of typical magnetic switches shows that the solutions can be used to determine the critical current reduction quickly and accurately, analyse the influence of different parameters, and simplify the design process of magnetic switches. The results can significantly benefit the design and optimisation of PCSs and flux pumps for HTS magnet charging systems in the future.

Section: Introductionmentioning

confidence: 99%

Analytical approximations for the self-field distribution of a superconducting tape between iron cores

Hao

Dong

Yang

et al. 2022

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“…In this case, the flux linkage ψ P from the flux pump to loop 2 can be written as equation (2). And the mutual inductance between the flux pump and loop 2 , M p , can be obtained as equation (3), where i m is the current in the copper coil of the flux pump,…”

Section: Electromagnetic Semi-analytical Modelmentioning

confidence: 99%

“…High temperature superconducting (HTS) magnets have the advantages of high current carrying capacity, high thermal * Author to whom any correspondence should be addressed. stability, high critical magnetic field and temperature, and therefore, can be used in many fields [1][2][3][4][5]. There are two magnetizing methods for the existing HTS magnets, one is to energize the magnet directly with the current generated by an external power supply, and the other is to use the induced current to power the magnet by inductive mode, such as by flux pump, field cooling method, zero field cooling method and so on.…”

Section: Introductionmentioning

confidence: 99%

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

Zhu,

Wang,

Gao

et al. 2023

We propose a new flux pump driven non-soldering closed-loop (NSCL) high temperature superconducting (HTS) magnet free of any soldering joints throughout the magnet for persistent current mode (PCM) operation. All the superconducting parts of the magnet are wound directly with HTS closed-loop ring split from an 8 mm REBCO tape using our new cutting scheme free of any soldering requirements. The magnet contains two single-pancake coils connected in series forming a closed circuit through two parallel bridge branches. Two thermal switches set on the two bridge branches control the on–off of the two bridges. A copper coil with iron core installed around one of the bridges is employed as the flux pump to drive the HTS magnet. An electromagnetic-thermal semi-analytical modelling method is proposed to analyse the pumping process by which the transport current in the magnet is calculated. The theoretical limit equation of the saturation current is improved as well. The proposed method can predict the current of the NSCL HTS magnet during the pumping process and provide results that are close to experiments. Experiments verify both the feasibility of the proposed flux pump driven NSCL HTS magnet and the modelling method. The results show that the NSCL HTS magnet works well in the PCM, which provides inspiration to the design of PCM operation of high field HTS magnets. The proposed modelling method also helps guide the design of different forms of HTS magnets and the flux pumps driving them.

“…The HTS bridge consists of four parallel tapes (each has I c0 = 298 A at 77 K), and uses the turningback structure which can effectively cancel out the induction voltage. This flux pump could be potentially used to charge an emerging HTS magnet for an ultra-compact MRI scanner [108].…”

Section: Applications Using Dynamic Resistancementioning

confidence: 99%

Dynamic resistance and dynamic loss in a ReBCO superconductor

Zhang

Shen²,

Chen³

et al. 2022

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Dynamic resistance is a time-averaged direct current (DC) resistance in superconducting materials, which typically occurs when a superconductor is carrying a transport DC while simultaneously subject to a time-varying magnetic field. Dynamic resistance has recently attracted increasing attention as it not only causes detrimental dynamic loss in superconducting devices such as the Nuclear Magnetic Resonance (NMR) magnets and superconducting machines, but on the other hand, the generated dynamic voltage can be exploited in many applications, e.g., high temperature superconducting (HTS) flux pumps. This article reviews the physical mechanism as well as analytical, numerical modelling, and experimental approaches for quantifying dynamic resistance during the last few decades. Analytical formulae can be conveniently used to estimate the dynamic resistance/loss of a simple superconducting topology, e.g., a single rare-earth-barium-copper-oxide (ReBCO) tape. However, in a complex superconducting device such as a superconducting machine, the prediction of dynamic resistance/loss has to rely on versatile numerical modelling methods before carrying out experiments, especially at high frequencies up to the kHz level. The advantages, accuracies, drawbacks, and challenges of different quantification approaches for dynamic resistance/loss in various scenarios are all inclusively discussed. The application of dynamic resistance in HTS flux pumps is also presented. It is believed that this review can help enhance the understanding of dynamic resistance/loss in superconducting applications, and provide a useful reference for future superconducting energy conversion systems.