Mark Ainslie

King's College London | KCL · Department of Engineering

Superconducting rotating machines are more efficient, smaller and lighter than conventional ones. Thus, they can reduce energy consumption and can be an enabling technology in applications that require light-weight machines. Using high temperature superconducting (HTS) materials in machines simplifies cooling designs compared to using low temperatu...

Bulk high-temperature superconducting materials can trap magnetic fields up to an order of magnitude larger than conventional permanent magnets. Recent advances in pulsed field magnetization (PFM) techniques now provide a fast and cost-effective method to magnetize bulk superconductors to fields of up to 5 T. We have developed a portable, desktop b...

The discovery of REBCO (rare-earth barium copper oxide) materials with high critical temperatures, and the continued advancements in the fabrication of REBCO coated conductors with extremely high critical current densities, has enabled the development of ultra-high-field (> 20 T) compact and large-scale thermonuclear fusion devices. At present, aro...

High-power density all-superconducting rotating machines have potential for application in electrical aircraft motors. However, superconductors in the armature windings of such rotating machines carry AC currents under AC/rotating magnetic fields, resulting in AC losses For. reducing AC loss, low-cost, round magnesium diboride (MgB2) wires are one...

Accurate numerical modelling of bulk rare-earth barium cuprate ((RE)BCO) high-temperature superconductors requires measured data of the temperature and magnetic field dependence of the critical current density, J c , and flux-flow exponent, n . However, there is limited published J c and n data for modern (RE)BCO bulks. In this work, transport and...

The magnetic field optimization of RE-Ba-Cu-O (REBCO, RE = rare earth) bulk superconducting undulators is a fundamental step toward their implementation in an accelerator driven photon source, like a synchrotron or a free electron laser. In this article, we propose a sorting algorithm to reduce the undulator’s phase error based on the reconstructio...

Breakthrough in Superconducting Magnet Strength and Stability Iron-based superconductors are promising for uses like quantum computing and superstrong magnets. However, improving their superconducting properties is challenging. This study aimed to improve these properties in a specific superconductor, K-doped Ba122, using Bayesian optimization. The...

A novel concept for a compact high-field magnet coil is introduced. This is based on stacking slit annular discs cut from bulk (RE)BCO ceramic in a Bitter-like architecture. Finite-element modelling shows that a small 20-turn stack (with a total coil volume of <20 cm ³ ) is capable of generating a central bore magnetic field of >2 T at 77 K and >20...

Magnetic drug targeting (MDT) is one of the most effective drug delivery systems for multi-disease therapy. Since a bulk superconducting magnet could generate a superior magnetic field strength and gradient, there is great potential for achieving MDT external to the body. In this work, a three-dimensional Y-shaped blood vessel and bulk superconduct...

No-insulation (NI) high-temperature superconductor (HTS) coil possess inherent advantages compared with their insulated (INS) counterparts, including enhanced current density, improved mechanical integrity, thermal stability, and self-protecting properties, making them a more appealing technological choice for high-field magnets, rotating machines,...

Flux pumps provide a promising solution for contactless charging of high- temperature superconducting (HTS) coils, eliminating the need for bulk current leads and reducing the heat burden for the cryogenic system. Characterizing the nonlinear effects of an HTS coil charged by a flux pump and understanding the dynamics of the charging process is ess...

We report on the performance of a new type of helical undulator based on bulk single-grain GdBa2Cu3O7−δ high-temperature superconductors. The 104-mm-long prototype with a period length of 16 mm and a magnetic aperture of 4 mm achieves an on-axis field above 2.5 T at a temperature of 10 K. This undulator technology has the potential to change the de...

It is necessary to fabricate (RE)BCO bulk high temperature superconductors in the form of individual single grains in order to maximise the length scale over which current flows, and hence trapped magnetic field. However, inherent difficulties in the grain growth process place limitations on the diameter and height of the single grain that may be a...

The practical magnetization of arrays of multiple single grain, bulk high temperature superconductors (HTSs) is essential for practical applications, such as trapped flux rotating machines, magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR). We report a systematic investigation of the pulsed field magnetization (PFM) of a bulk as...

A prototype MgB2 bulk with a diameter of 20 mm and a thickness of 2 mm was synthesized using the MVT (Magnesium Vapor Transport) method, which can realize dense and high-purity MgB2 bulks by transporting and diffusing pure magnesium vapor into boron pellets. Owing to its superior Jc-B characteristic, the obtained bulk by the MVT method exhibited, c...

A 10 mm-period, high-temperature superconducting (HTS) undulator consisting of twenty staggered-array GdBa2Cu3O7-x (GdBCO) bulk superconductors has been fabricated and tested successfully. Each GdBCO disk was machined into a half-moon shape with micro-meter accuracy and shrink-fitted into a slotted oxygen-free copper disk which provided pre-stress...

Bulk rare-earth barium cuprate (REBCO) high-temperature superconductors are attractive for many electromagnetic applications due to their ability to support large current densities and trap large magnetic fields. At present, magnetisation techniques are the predominant method of measuring the critical current density, $J_\text {c}$ , for bulk sup...

The high-temperature superconducting (HTS) dynamo enables injection of large DC currents into a superconducting coil, without the need for bulky and thermally-inefficient current leads. For practical applications of such technology – like energizing superconducting coils in superconducting rotating machines and NMR/MRI magnets – modelling and under...

High-temperature superconducting (HTS) rare-earth barium copper oxide (REBCO) coated conductors with outstanding critical current density under high fields can help realize a high-field path toward magnetic-confinement fusion. REBCO cabling methods such as conductor on round core (CORC) cables, twisted stacked tape conductor (TSTC) cables, and Ruth...

(RE)-Ba 2 Cu 3 O 7−δ bulk superconductors acting as permanent trapped field magnet analogues have been shown to trap fields in excess of 17 T. However, the occurrence of thermomagnetic instabilities during their magnetisation process can limit their performance. In 2019, Naito et al. trapped 15.1 T in a (Y)-BaCuO bulk-pair under applied fields of u...

The high-temperature superconducting (HTS) dynamo enables injection of large DC currents into a superconducting coil, without the need for thermally-inefficient current leads. Because of this important advantage, there is significant interest in using such technology to energise superconducting coils in superconducting rotating machines and NMR/MRI...

Interactions between inhomogeneous magnetic fields and a superconductor lie at the heart of several high-temperature superconducting (HTS) devices. An example is the situation where the magnetic field from a small permanent magnet (PM) is applied to a coated-conductor HTS tape, such that flux penetrates the superconductor. The PM field is highly sp...

When used as trapped field magnets (TFMs), single grain, bulk high-temperature superconducting (HTS) rings are promising candidates for the generation of strong, uniform magnetic fields for nuclear magnetic resonance (NMR). The pulsed field magnetisation (PFM) technique provides a low cost, compact and portable method to magnetise these samples as...

(RE)-Ba-Cu-O ring bulks, used as trapped field magnets, show great promise as a compact and lightweight source for generating the magnetic fields required for nuclear magnetic resonance (NMR). The inhomogeneities introduced by the growth process of such bulks pose a challenge to the required field uniformity for NMR. In this study, we model a stack...

Magnetic lens, exploiting the induced screening current, may concentrate the spatial magnetic flux. This concept has been realized by several research groups using GdBCO and/or MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bulk superconductors. The limitation of the magnitude of concentra...

Pulsed field magnetization (PFM) and field-cooled magnetization (FCM) have been carried out for GdBaCuO disk-shaped bulks fabricated by two-step buffer-assisted (BA)-top seeded infiltration growth (TSIG) technique, and the results are compared with those of bulks fabricated by conventional top seeded melt growth (TSMG) technique. In both PFM and FC...

One potential application of magnetized RE-Ba-Cu-O (where RE = rare earth or Y) bulk superconductors is as a high-field alternative to conventional permanent magnets in desktop NMR and MRI systems. Pulsed field magnetization (PFM) is one of the most promising practical methods of magnetizing such bulks. However, the trapped fields obtained by PFM a...

Bulk, single grain RE-Ba-Cu-O [(RE)BCO] high temperature superconductors (HTS) could potentially be used to generate stable magnetic fields for MRI and NMR. In these applications, however, the homogeneity of the magnetic field is of critical importance. As a result, the spatial distribution of critical current density, Jc, within the bulk single gr...

MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in bulk form shows great promise as an inexpensive, lightweight alternative to bulk (RE)-Ba-Cu-O materials to act as trapped field magnets (TFMs), which can replace permanent magnets in applications such as desktop high-field magnet systems an...

In order to optimize the design of undulators using high-temperature superconductor (HTS) bulks we have developed a method to estimate the critical current density (J_{c}) of each bulk from the overall measured magnetic field of an undulator. The vertical magnetic field was measured along the electron-beam axis in a HTS bulk-based undulator consist...

The concept of a high-gradient trapped field magnet (HG-TFM), which incorporates a hybrid system of two (RE)BaCuO superconducting bulk components with different functions, was proposed in 2021 by the authors based on the results of numerical simulations. The HG-TFM as a desktop-type magnet can be a more effective way to generate a higher magnetic f...

During quasi-static magnetization of bulk superconductors using field-cooled magnetization (FCM) from high fields at low temperatures, such bulks are sometimes broken, which is believed to be mainly due to an electromagnetic force – and subsequent stress – larger than the fracture strength. However, a ring bulk can break, even during pulsed field m...

Achieving low AC-loss armature windings is a key challenge to enable all-HTS motors. Large AC-loss is induced in the HTS armature windings through interaction with the rotating magnetic field generated by the rotor. To reduce the AC loss in the armature windings, it is important to minimize the impact of the rotating magnetic field, especially the...

One of the potential applications of ring-shaped, single grain RE-Ba-Cu-O bulk superconductors is in desktop magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) systems as an alternative to conventional permanent magnets. The higher magnetic field available from magnetized bulk superconductors could significantly improve the perfo...

Superconducting machine designs have historically focused on an isolated, cryogenic rotor and conventional (copper) stator due to unacceptable levels of AC loss in a superconducting stator. Thus, AC loss reduction in the armature windings is one of the key issues for achieving practical all-superconducting motors that could deliver an unprecedented...

The development of a new hard x- ray beamline I-TOMCAT equipped with a 1 m long short-period bulk high-temperature superconductor undulator (BHTSU) has been scheduled for the upgrade of the Swiss Light Source at the Paul Scherrer Institute. The very hard x -ray source generated by the BHTSU will increase the brilliance at the beamline by over one o...

The intrinsic mechanical properties of single‐grain RE‐Ba‐Cu‐O bulk high‐temperature superconductors can be improved by employing a thin‐wall geometry. This is where the samples are melt‐processed with a predefined network of artificial holes to decrease the effective wall thickness. In this study, the tensile strengths of thin‐wall YBCO disks were...

Dynamo-type flux pumps can be employed to energize high-temperature superconducting (HTS) magnets to maintain the steady current mode or in rotor windings of electrical HTS motors and generators to inject the current without the need for current leads. To understand the complicated operating working mechanism of the flux pump it is necessary to stu...

Bulk superconductors can act as trapped-field magnets with the potential to be used for many applications such as portable medical magnet systems and rotating machines. Maximising the trapped field, particularly for practical magnetisation techniques such as pulsed field magnetisation (PFM), still remains a challenge. PFM is a dynamic process in wh...

The development of a new hard x-ray beamline I-TOMCAT equipped with a 1-meter-long short-period bulk high-temperature superconductor undulator (BHTSU) has been scheduled for the upgrade of the Swiss Light Source (SLS 2.0) at the Paul Scherrer Institute (PSI). The very hard x-ray source generated by the BHTSU will increase the brilliance at the beam...

The high-$T_c$ superconducting (HTS) dynamo exploits the nonlinear resistivity of an HTS tape to generate a DC voltage when subjected to a varying magnetic field. This leads to the so-called flux pumping phenomenon and enables the injection of DC current into a superconducting coil connected to the dynamo without current leads. In this work, the pr...

In this work, we have verified experimentally an all-(RE)BaCuO hybrid trapped field magnet lens (HTFML) using only one cryocooler and a special technique named the ‘loose contact method’. In the experimental setup, only the inner magnetic lens was tightly connected to the cold stage and cooled at all times, and the outer trapped field magnet (TFM)...

The charging/discharging delays in superconducting coils wound without insulation (NI coils) are a major drawback of the technique. While removing the insulation improves safety margins the increase in the characteristic time constant _c can make a coil unfit for a particular purpose. It is widely accepted for instance that NI coils will...

The expanding capabilities of HTS flux pumps and rectifiers to provide kA+ currents necessitates the exploration of high-current switching phenomenon. One such phenomenon, the dynamic resistance, occurs in type-II devices carrying dc transport currents while exposed to ac magnetic fields. In the following, finite element analysis of the threshold f...

A high-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconducting (HTS) dynamo enables the injection of large DC currents into a superconducting circuit, without the requirement for current leads. In this work, we attempt to explain the frequency dependence of such dynamos/flux pumps rep...

For high-temperature superconducting (HTS) maglev, an electromagnet guideway unit (EMGU) that can form an electromagnet guideway (EMG) with a small gap, or even no gap, between EMGUs has been designed. The longitudinal magnetic fields along a single EMGU and two EMGUs arranged in a line were first investigated through measurement and simulation. Th...

A robust and reliable in-situ magnetization method is essential for exploiting the outstanding magnetic flux trapping ability of bulk superconductors in practical applications. We report a 4.8 T peak trapped magnetic field, B T , achieved at 30 K in a 36 mm diameter GdBa 2 Cu 3 O 7- δ –Ag bulk superconductor using pulsed field magnetization (PFM)....

In this work, we propose a new concept of a high gradient trapped field magnet (HG-TFM). The HG-TFM is made from (RE)BaCuO bulk superconductors, in which slit ring bulks (slit-TFMs) are tightly stacked with TFM cylinders (full-TFMs), and state-of-the-art numerical simulations were used to investigate the magnetic and mechanical properties in detail...

Bulk high temperature superconductors based on the rare-earth copper oxides can be used effectively as trapped field magnets capable of generating large magnetic fields. The top-seeded infiltration growth (TSIG) processing technique can provide a more homogeneous microstructure and therefore more uniform superconducting properties than samples grow...

A backward computation method has been developed to accelerate modelling of the critical state magnetization current in a staggered-array bulk high-temperature superconducting (HTS) undulator. The key concept is as follows: i) a large magnetization current is first generated on the surface of the HTS bulks after rapid field-cooling (FC) magnetizati...

The high-T c superconducting (HTS) dynamo is a promising device that can inject large DC supercurrents into a closed superconducting circuit. This is particularly attractive to energise HTS coils in NMR/MRI magnets and superconducting rotating machines without the need for connection to a power supply via current leads. It is only very recently tha...

High-Tc superconducting (HTS) dynamos are experimentally proven devices that can produce large (more than a kiloamp) dc currents in superconducting circuits, without the thermal leak associated with copper current leads. However, these dc currents are theoretically controversial, as it is not immediately apparent why a device that is topologically...

High-field magnets are essential across a range of scientific disciplines and significant advances in high-field magnet technology continue to be made as scientists seek improved performance and ever-higher magnetic fields. High-temperature superconducting (HTS) magnets offer the possibility of higher magnetic fields with a smaller magnet footprint...

The hybrid trapped field magnet lens (HTFML) is a promising device that is able to concentrate a magnetic field higher than an applied background field continuously, even after removing a background field, which was conceptually proposed by the authors in 2018. We have numerically investigated the HTFML performance, consisting of a REBaCuO cylindri...

The high-Tc superconducting (HTS) dynamo is a promising device that can inject large DC supercurrents into a closed superconducting circuit. This is particularly attractive to energise HTS coils in NMR/MRI magnets and superconducting rotating machines without the need for connection to a power supply via current leads. It is only very recently that...

The finite element method has been used extensively in recent years to solve various problems related to applied superconductivity and provides a useful tool for analysing and predicting experimental results. Based on a recently-developed modelling framework, implemented in the finite element software package COMSOL Multiphysics, investigations on...

We have performed numerical simulations of the electromagnetic hoop stress, σ θ , in a REBaCuO disk bulk reinforced by a metal ring during pulsed-field magnetization (PFM) using a solenoid coil, in which the superconducting characteristics of the bulk material were assumed to have realistic J c - B - T ones. The compressive and tensile σ θ stresses...

A hybrid trapped field magnet lens (HTFML) can reliably generate a concentrated magnetic field, B c , in the centre of the magnetic lens higher than the trapped field of the trapped field magnet (TFM) and the applied magnetic field, B app , even after the external magnetizing field decreased to zero. In this paper, the performance of HTFMLs consist...

We have performed numerical simulations of the electromagnetic, thermal and mechanical properties of a REBaCuO ring-shaped bulk with various reinforcement structures during pulsed-field magnetization (PFM). Compressive and tensile electromagnetic stresses, σ θ mag , are developed in the ring-shaped bulk during the ascending and descending stages of...

A hybrid trapped field magnet lens (HTFML) is a promising device that is able to concentrate a magnetic field higher than the applied field continuously, even after removing an external field, which was conceptually proposed by the authors in 2018. In this study, we propose a new additional advantage of the HTFML, which could be applicable for magn...

The hybrid trapped field magnet lens (HTFML), proposed by the authors in 2018, is a promising device that is able to concentrate a magnetic field higher than the applied field continuously, even after removing the external applied field. In this study, we have investigated the optimized performance of the HTFML consisting of a GdBaCuO magnetic lens...