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Optimizing coil configurations for AC loss reduction in REBCO HTS fast-ramping magnets at cryogenic temperatures

Superconductivity 2022年第3期3卷 133-142页

作者： Zhenan Jiang Honghai Song Wenjuan Song rodney a.badcock Robinson Research Institute Victoria University of WellingtonWellingtonNew Zealand Department of Physics and Astronomy State University of New York at Stony BrookNew YorkUSA James Watts School of Engineering University of GlasgowGlasgowUK

AC loss is one of the critical issues for designing REBCO fast‐ramping magnets operating at cryogenic *** are many ways to reduce AC loss for coil ***,it is not clear which method is the most effective way to minimize AC loss in the coil windings for a given Ampere‐*** this work,we numerically studied coil configurations of several small superconducting magnets constructed from 12 mm SuperPower REBCO coated conductors,for fast‐ramping application with the same Ampere‐turns to identify the lowest AC loss among *** HTS magnets have a total turn number of 50 and inner diameter of 30 cm,carrying AC current operating in the temperature range of 20–40 K at 25 *** incorporated several existing loss reduction strategies including spacing between the turns for single pancake coils,grading Ic values for the solenoid configuration,and applying flux diverters to shape the magnetic field around the coil *** simulation was implemented using a homogenized H‐*** all studied loss reduction methods,the use of flux diverters has the largest impact in AC loss *** AC loss values in the solenoid winding comprising a stack of five single pancake coils with 0.1 mm turn‐to‐turn gap with the flux diverters agree well with those in the single pancake coil for 2 mm turn‐to‐turn gap with the flux *** type coil configurations with flux diverters generate much smaller AC loss than the single pancake type with flux diverters when they generate the same center magnetic field.

关键词： Fast ramping magnet AC loss reduction H‐formulation REBCO Flux diverters

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The impact of magnetic field periodicity on the hysteresis loss in superconducting magnetic bearings

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Superconductivity 2023年第1期5卷 55-62页

作者： Mohammad Siamaki James G.Storey Lars Wiesehoefer rodney a.badcock Paihau-Robinson Research Institute Victoria University of Wellington76 Sydney StreetLower Hutt 5012New Zealand Fachhochschule Südwestfalen Lindenstraße 5359872 MeschedeGermany

Since the discovery of high‐temperature superconductors(HTS),superconducting magnetic bearings(SMB)have attracted much attention for practical applications such as flywheel energy storage systems,electrical machines,gyroscopes,etc.,because of their ability to provide passive stable levitation under high‐load *** providing contactless linear and rotational motion,SMBs gradually decelerate by AC losses mainly generated by magnetic field *** main component of AC losses at low rotational speeds is hysteresis loss,which is said to be independent of rotational speed,intrinsic to HTS,and proportional to the cube of magnetic field *** the state‐of‐the‐art analytical expression of hysteresis loss in SMBs captures the general physics of the loss mechanism,it ignores the periodicity of the magnetic field in one complete rotation of the *** this paper,the analytical expression of hysteresis loss is modified,taking into account the impact of magnetic field periodicity and the distribution of loss over the bearing *** new expression is tested by performing spin‐down experiments with magnets of different levels of inhomogeneity in an actual SMB *** impact of magnetic field inhomogeneity on the dynamic behaviour of the bearing is also *** results show consistency between modified analytical calculations and experimental data.

关键词： Superconducting bearings Hysteresis loss

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I_(c) measurement of twisted multifilamentary MgB_(2) wires with non-magnetic sheath over a wide range of temperatures and fields

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Superconductivity 2023年第4期8卷 84-89页

作者： Yukai Qiao Matt Rindfleisch Mike Tomsic Michael D.Sumption Naoyuki Amemiya rodney a.badcock Nicholas M.Strickland Zhenan Jiang Robinson Research Institute Victoria University of WellingtonWellingtonLower Hutt 5012New Zealand Hyper Tech Research Inc ColumbusOH 43228USA Department of Materials Science and Engineering The Ohio State UniversityColumbusOH 43210USA Department of Electrical Engineering Kyoto UniversityKyoto 615-8510Japan

All‐superconducting rotating machines have the potential for meeting the high power density and high efficiency required for electrical aircraft ***,very high AC loss encountered in superconducting armature windings could hinder their *** MgB_(2) wires are one of the promising candidates for the stator windings,due to their potentially low AC loss properties with small filament size and twist *** the first step,the dependence of critical current and n‐value on magnetic fields and temperatures I_(c)(B,T)and n(B,T),which are basic input parameters for AC loss simulation,needs to be *** this work,we present transport I_(c)measurements in three non‐magnetic multifilamentary MgB_(2) wires(MgB_(2)/Nb/CuNi/CuZn):one large wire with a 0.70 mm diameter and 25 mm twist pitch,and two small wires with a 0.48 mm diameter each and a 10 mm and 30 mm twist pitch respectively.A four‐probe direct current method is used to measure I_(c) of the MgB_(2) wires with variations in temperature(15-35 K)and magnetic field(0-5.5 T).Full I_(c) data for the small wire with 10 mm twist pitch was obtained,and the n‐values were mostly less than *** the I_(c) data for the large wire at low fields was more limited due to heating,the n‐values were higher and could be up to around *** difference is attributed to the different filament *** also found that there is no significant hysteresis in the transport critical current measured by decreasing or increasing magnetic fields due to the non‐magnetic *** non‐hysteretic characteristic is critical for lowering AC loss because the additional losses from magnetic sheaths can be *** the magnetic‐field dependence of critical current density,an empirical expression has been developed that provides suitable extrapolations to lower fields for the large wire.

关键词： Transport critical current MgB_(2)wire A four‐probe direct current method

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A full-wave HTS flux pump using a feedback control system

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Superconductivity 2023年第4期8卷 26-33页

作者： James H.P.Rice Ben P.P.Mallett Dominic A.Moseley Alexander Petrov Heng Zhang Steven Wray rodney a.badcock Paihau-Robinson Research Institute Victoria University of WellingtonLower Hutt 5012New Zealand UK Atomic Energy Authority Culham Science CentreAbingdon OX143DBUnited Kingdom

Transformer‐rectifier flux pumps are DC superconducting power supplies capable of charging superconducting magnets to high currents and stored magnetic ***,we demonstrate a full‐wave superconducting flux pump assembled from high‐temperature superconducting(HTS)wire that utilizes superconducting switches controlled by applied magnetic field.A negative DC offset occurs in the superconducting secondary of the circuit during operation which is related to the output load current.A feedback control system is proposed and demonstrated to account for the negative DC *** the primary current proportional to the load current during operation allowed for the maximum output of the flux pump to be increased from 35 A to more than 275 *** results are reproduced using a coupled electrical‐and magnetic–circuit model formulated in the MATLAB Simulink®package.

关键词： High‐temperature superconductor Flux pump Power supply Circuit modelling High current

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