Applied-field magnetoplasmadynamic (AF-MPD) thrusters have been proposed as highly propellant-efficient thrusters for satellites and spacecraft. The electromagnets for these devices have only been reducible to practical dimensions with the maturation of high-temperature superconductors. We report the development and ground testing of such a magnet which has been designed and constructed with the intention of deploying to the International Space Station and testing in orbit. The magnet is of dimensions suitable for accommodating a small thruster, will be cooled by a miniature space-compatible cryocooler and energized by a flux pump. It can generate a magnetic field of up to 760 mT operating at around 77 K in that configuration. A passive magnetic shield has been incorporated in order to comply with stray-field requirements of the ISS when operating at the target operational field of 300 mT.

A spacecraft re-entering the Earth's atmosphere must endure extremely high heat loads. These heat loads are created by the rapid deceleration of the spacecraft causing shock waves which in turn create a high-temperature plasma. Passive thermal protection based on ablative materials is the current solution for spacecraft heat shielding, but it is limited by material durability. As an alternative, magnetic heat shielding has shown great potential to deflect and redirect the plasma. However, fully understanding of the concept requires further experimental validation. Paihau-Robinson Research Institute has designed and built a high-temperature superconductor (HTS) system, which will be used to test the magnetic heat shielding concept at the German Aerospace Centre's (DLR) shock tunnel, where realistic flow conditions for hypersonic flight configurations are created. This paper reports the design of the HTS system with some preliminary experimental results on its performance. The shock wave stand-off distance is calculated based on the designed field (2T), which will be compared with the experimental data using a high-speed camera at DLR's shock tunnel in 2025.

Particle irradiation offers a route to incorporating additional flux pinning centres in high-temperature superconducting wires with minimal disruption to the pre-existing defect landscape, thereby further enhancing the critical current in a controllable fashion. This work is a comprehensive study of the fluence-dependence of proton irradiation using protons of two energies, 2.5 and 1.2 MeV, in enhancing the critical current performance in commercially available (Y,Dy)Ba2Cu3O7-delta coated conductors. A sequence of fluences covering the range from 1 x 1015 to 5 x 1016 protons cm-2 was used in the irradiation process to study the flux pinning in this material. The resulting samples were characterized using field angle-dependent transport critical current measurements over a range of temperatures from 20 K to 77.5 K and magnetic fields up to 8 T, thus covering the wide range of operating conditions. Optimisation of fluence for highest performance at each energy resulted in a similar level of isotropic critical current enhancement, a factor 2.6 improvement at 20 K and 8 T, but with a significant difference in the optimised fluence in each case. The lower energy 1.2 MeV protons produce this enhancement at a three-fold lower fluence compared to 2.5 MeV protons, a result of their higher electronic energy loss. The different samples are analysed within the framework of the maximum entropy model, helping to understand the vortex dynamics before and after irradiation.

AC loss is a critical issue for high-temperature superconducting (HTS) applications. Earlier studies have focused on ac loss in HTS conductors carrying sinusoidal currents. However, HTS conductors in some applications carry non-sinusoidal currents, and hence it is essential to study ac loss under those conditions. This study presents simulated ac loss of a REBCO stack and coil winding carrying currents with square, trapezoidal, and triangular waveforms. The simulation method is based on the T-A formulation implemented in COMSOL Multiphysics 6.0. AC loss dependence on frequency and n -value is also investigated. The simulation results show ac loss varies with current waveforms for both the stack and coil winding—loss magnitude is largest under square waveform, followed by trapezoidal, sinusoidal, and triangular waveform. Surprisingly, ac loss of the stack decreases with increasing frequency as f − 2/n , while f −1/ n for the coil winding. The difference between the ac loss values in the stack and coil winding under different current waveforms becomes smaller with increasing n -value. With an infinitely large n -value, the difference in the ac loss values for all different waveforms may disappear, as the critical state model suggests.

A large portion of the pipe infrastructure used in the chemical processing industry is susceptible to corrosion under insulation (CUI). Eddy current-based magnetic sensing is one of the methods that can be used as an early detector of this corrosion. However, the large sensor-to-pipe distances used in this method, due to the presence of insulation, limits the sensitivity to corrosion. This paper will describe the development of instrumentation and methods based on eddy current sensing with thin-film magnetic sensors. In particular, it focuses on the influence of the sensor angle relative to the radial magnetic field. The influence of this parameter on the amplitude of the measured signal was investigated by both finite element simulations and experimental observations. The measured magnetic field was found to be highly sensitive to small changes in sensor angle, with the estimated depth of a defect changing at a rate of 11.2 mm/degree of sensor rotation for small angles. It is also shown that a sensor aligned with the radial direction should be avoided, with an optimal sensor angle between 0.5 and 4 degrees. With the sensor in this angle range, the simulations have shown it should be possible to resolve the depth of corrosion to a resolution of 0.1 mm.

Increasingly ambitious space missions rely upon the advancement of propulsion systems, and innovations in electric propulsion represent a vital step toward potential solutions. Electric propulsion research has indicated improved thruster performance at higher magnetic fields, but real-world implementations have been encumbered by available magnet technology. In this study, a new class of superconducting magnet designed for such space applications is demonstrated. A central cathode electrostatic thruster was paired with a conduction cooled high temperature superconducting magnet operated in non-pulsed mode. Using Xe propellant, thrust of 38--73 mN was measured at a central bore magnetic field of 1.13 T and on-anode field of 1.28 T, and the thruster's specific impulse was throttled between 1050s and 1450s. The peak thruster efficiency was 18.7%, inclusive of the power consumption of the magnet subsystems. This was performed without the onset of plasma instabilities, and is the first case in the literature of a high temperature superconducting plasma thruster operating at > 1 T.

We have used silver-ion irradiation and proton irradiation to produce point-like and spherical defects in REBa 2 Cu 3 O 7 coated conductors. We compare the resulting pinning landscape for optimized fluences and show that proton irradiation gives a slightly greater pinning enhancement at 20 K, but in the same samples silver irradiation gives significantly better pinning enhancement at 65 K. We attribute this to the relative sizes of the defects and to the distribution of defects resulting from the different ion collision rates.

In rapid-cycling synchrotrons (RCSs), superferric magnets wound with high-temperature superconductors are energized by ac current with a dc offset. However, the presence of the dc offset may increase the ac loss in the magnets. To investigate the influence of the dc offset on ac loss of superconductors, simulations of a single high-temperature superconducting (HTS) tape and a four-tape stack carrying various combinations of ac currents with dc offsets were carried out using the T - A formulation. The 4 mm-wide REBCO HTS tape considered in this work was SuperPower wires with a self-field critical current of 104.98 A. For both the single tape and the four-tape stack, the amplitude of ac current ranges from 0.1 to 0.9 times their respective critical currents, while the dc offset varies from 0 to 0.8 times their respective critical currents. Regarding the four-tape stack, the simulated critical current of 88.9 A was employed. The normalized current density and perpendicular magnetic field distributions of the single tape and the four-tape stack were presented for different ac and dc values. Compared to the cases without the dc offset, small dc offsets almost have no influence on ac loss of both the single tape and the four-tape stack, while a significant loss increase is observed with high dc offsets. For a given combination of ac current and dc offset, the influence of the dc offset on ac loss is more pronounced in the four-tape stack than in the single tape.

In high-temperature superconducting (HTS) power devices, the presence of iron cores changes the magnetic field profile around the HTS coil windings, potentially affecting their AC loss characteristics. AC loss measurements for HTS coil windings coupled with an iron core using the electrical method can lead to a significant error, owing to the indirect estimation of the iron core loss through using a copper test coil. To investigate the cause of the experimental error and the influence of an iron core on coil AC losses, transport AC losses of REBCO double pancake coil (DPC) assemblies coupled with an iron cylinder were measured. A 40-turn 1DPC and an 80-turn 2DPC assembly wound with 4 mm SuperPower wire were employed in the measurements. To ensure the same iron core loss using the HTS coil assembly and the copper coil, 2D finite element method simulations were conducted iteratively to design the iron core and the copper coil to get the same local magnetic field distributions in the designed iron core for the two cases. The main cause of the error is due to the difference in local magnetic flux densities in the iron core generated by the HTS coil assembly and the copper coil even when the ampere-turns of the coils are identical. We showed that the simulation-guided measurement method can assure accurate AC loss measurement in the HTS coil assemblies coupled with iron cores. Compared with the AC losses in the 1DPC and 2DPC coil assemblies without the iron cylinder, the presence of the iron cylinder significantly increases the coil losses. Frequency dependence is observed in the coil AC losses of the 1DPC and 2DPC assemblies when coupled with the iron cylinder. This is due to the eddy current induced in the iron cylinder generating a magnetic field, which influences the coil AC loss.

High-temperature superconducting (HTS) technology provides an alternative approach to achieve compact transformers. Addressing AC loss in the HTS winding is crucial for HTS transformer applications. Most numerical AC loss studies on HTS transformers have neglected the influence of iron cores. This work carries out an AC loss study to explore the impact of an iron core on the HTS windings in a 3-phase HTS 1 MVA transformer coupled with it. AC loss simulations for the transformer winding both with and without the iron core are conducted by adopting the three-dimensional (3D) T-A homogenization method. When the iron core is incorporated, the saturation magnetic fields of iron materials, flux diverters (FDs) with different geometries, and variations in turn spacings in the LV winding composed of Roebel cables are considered to investigate their influence on the AC loss of the transformer winding. The inclusion of the iron core leads to a 1.2% increase in AC loss for the transformer winding while simulating at the rated current. We attribute this slight difference to the non-inductive winding structure of the transformer winding, where a strong magnetic field generated in the space between the LV and HV windings effectively shields the influence of the iron core.

We investigate changes to the pinning landscape in ion-irradiated coated conductors through comparisons of critical current and n -values as a function of field, field angle and temperature, where n is the power law exponent in the current density-electric field relation, ${\bm{E\ }} = {{\bm{E}}}_{\bm{c}}\ {({{\bm{J}}/{{\bm{J}}}_{\bm{c}}})}^{\bm{n}}$ . Many models of J c have been developed but models of n -value are rare in the literature. The n -value can be interpreted as the sensitivity of E to J or in the context of a maximum entropy analysis n can be related to a constraint on the vortex system. We investigated samples of (Y,Dy)BCO coated conductor tapes from AMSC irradiated with 50 to 150 MeV Ag ions, and measured J c and n -values at temperatures from 20 to 77 K and fields up to 8 T at all field angles. As n -values arise from vortex pinning behavior we model the angle dependence using the maximum entropy distributions we have previously used for J c (θ) analysis. Fitting with these distributions shows the n -values are the outcome of the combined defect structures interacting with vortices. The changes in n -value with field and temperature are not simply correlated with J c values, for example, n -values often have a broad c -axis centered peak with no correlation to a peak in J c . At higher temperatures n -values generally have no peak centered on the ab -plane. Irradiation along the c -axis changes n -values in a broad angular range. The n -value is sometimes interpreted as a measure of the energy barrier associated with thermal creep, but from our observations we propose that it is a measure of the dimensionality of the vortex system.

Particle irradiation using light ions and heavy ions is found to be an effective method to introduce flux-pinning centers into REBCO films and coated conductors. The degree of enhanced critical current at various conditions depends upon the size, morphology, and orientation of ion tracks. Proton irradiation to the optimised fluence results in greater isotropic enhancement at lower temperatures, the enhancement decreases as temperature increases. Silver ion irradiation on the other hand gives a greater enhancement at higher temperature but limited to particular angular ranges. We compare the results of these two types of irradiation and then produce a mixed pinning landscape with a combination of the two. We find a nearly isotropic enhancement in Ic at lower temperatures and an enhancement about the c -axis direction, similar but broader than silver irradiation alone, at higher temperatures.

A 6.5 MVA/25 kV high-temperature superconducting (HTS) transformer for the Chinese Fuxing high-speed train has been proposed to replace the oil-based transformers while achieving higher efficiency, lighter weight, and minimized volume. The high targeted efficiency (>99%) makes ac loss reduction a vital issue. HTS coated conductors generally exhibit asymmetric critical current characteristics as a function of magnetic field angle $I_{c}$ ( $B$ , $\theta$ ), leading to a nontrivial influence on the ac loss of coil windings. The fast computing $T$ – $A$ homogenization method is proposed to calculate the ac loss of the 6.5 MVA/25 kV traction transformer with large turn numbers. The variables, $T$ and $A$ , are the current and magnetic vector potentials, respectively. The ac loss of the transformer windings is analyzed for various coil configurations with and without flux diverters considering $I_{c}$ ( $B$ , $\theta$ ). At the rated current and 65 K, employing the flux diverters with a square-shape cross section, the total ac loss is decreased by 73.7% and an extra 150-W loss reduction was also obtained. Moreover, an additional reduction of 37 W is realized upon utilizing the asymmetric $I_{c}$ ( $B$ , $\theta$ ) characteristic. The reduced 187 W in ac loss at 65 K corresponds to a reduction in ambient power requirement of over 5.6 kW. Therefore, considering asymmetric $I_{c}$ ( $B$ , $\theta$ ) can lead to a nontrivial reduction in ac loss, even incorporating flux diverters.

The magnetic performance of ferrite based soft magnetic composite materials (SMCs) have been investigated for inductive power transfer (IPT) applications in roads. The magnetic permeabilities and magnetic losses of SMCs were characterized for varying ferrite particle size fractions and particle loadings. The magnetic performance of the crushed ferrite powders were 2-3 times higher than expected based on magnetic particle theory for spherical magnetic particles. Findings were confirmed by comparing the magnetic performance of SMCs made from spherically ground ferrite powders. The good agreement of magnetic relative permeability measurements and related analytic models have shown that the key parameters affecting the relative permeability of SMCs are the magnetic particle loading, the magnetic particle aspect ratio and related shape factor, and interparticle align-ment. Similarly, the measured magnetic power loss densities measurements in the low field limit (mu r < 100) compared well with magnetic loss models where there is an inverse relationship to the magnetic relative permeability. Therefore, the best performance for ferrite SMCs is to be achieved by maximising the magnetic relative permeability which also minimises the power losses for a given B.

Heavy-ion irradiation of solids produces damage tracks with radii typically of the order of 1 nm, depending on the ion species and energy. In cuprate superconductors this is close to the coherence length, which makes these defects highly effective flux pinning centers. Varying the ion-beam energy allows tuning of the dimensionality of the defects created, with higher-energy ions tending to produce columnar tracks and lower-energy ions tending to produce point-like defects. Starting with consistent production-standard REBCO tape from American Superconductor we have explored the energy-dependence of silver-ion irradiation and characterized the irradiated samples with angle-dependent transport critical current measurements. Using silver ions with energies in the range 50 MeV to 150 MeV and fluence of 4 × 1011 ions/cm2 we have been able to tune the irradiation-induced damage from point-like defects to columnar tracks, manifesting in changes to the pinning landscape ranging from isotropic critical current enhancement to the production of strong peaks in the angle dependence of critical current.

In-road inductive power transfer (IPT) charging systems that can couple power across an air gap without any physical contact, will make EVs easier to charge. Current IPT systems typically use solid ferrite materials to improve magnetic coupling. Although ferrite is good for guiding magnetic fields, it is very brittle and a large solid block of ferrite would not survive within a road’s structure. Strong robust magnetic materials are required so that vehicles can run over charging pads built into the road without destroying them. This will require innovative affordable solutions and new magnetic material sources to meet these needs in an economically viable way.

AC loss is one of the greatest obstacles for high-temperature superconducting (HTS) applications. In some HTS applications, coated conductors carry non-sinusoidal currents. Thus, it is important to investigate the effect of various waveforms on AC loss in coated conductors. In this work, transport AC loss in a 4 mm - wide REBCO coated conductor carrying sinusoidal and non-sinusoidal currents, is numerically investigated. The current amplitudes, the frequency of the transport current, and n-value are varied. Non-sinusoidal transport current waveforms studied include square, five types of trapezoidal, and triangular waveforms. Simulated results show that, for a given current amplitude, AC loss for the square current waveform is the greatest, that for the triangular waveform is the smallest. The sequence of AC loss in the conductor for different current waveforms coincides with the penetration depth, which implies the penetration depth determines the AC loss of the coated conductor. Furthermore, the transport AC loss in the conductor was found to decrease with frequency as f-2/n for non-sinusoidal transport current.

Normal-incidence irradiation by 100 MeV Ag ions is used to improve flux pinning in previously optimised commercial REBCO tapes from the American Superconductor Corporation. We observe distinct critical-current anisotropy enhancements below and above 40 K. Above 40 K a strong c -axis peak appears in the angular dependence of the critical current, as is usually expected upon the introduction of columnar defects. The critical current is enhanced significantly but only for a limited range of field angles. Close to the parallel-field direction there is no enhancement or even a reduction in critical current. Below 40 K, on the other hand, the enhancement is much broader with respect to field angle, creating an almost isotropic response at 20 K, 3 T. The absence of a prominent c -axis peak does not indicate a lack of pinning, since the absolute value of the critical current still increases by a factor of 2.8 compared to an unirradiated sample. Instead, we postulate that pre-existing point-like pinning centres act to mediate an interaction between the existing planar and newly-introduced columnar pins, broadening both contributions. The point-like pins become less effective with increasing temperature as the coherence length increases, leading to a reduction in this interaction and a separation of the individual peaks relating to planar and columnar pins. At 20 K, we achieve an enhancement in the angular-minimum critical current by a factor of 2.7, in a material that had already been process-optimised for low-temperature pinning.

High-temperature superconducting traction transformers (HTSTTs) have the merits of small size and lightweight in comparison with their conventional counterparts. This article reports the development progress of a 6.6 MVA HTSTT operating at 65 K, including the design, testing, and system cooling. The introduction of flux diverters and an optimized winding design realized a short-circuit impedance higher than 43% and AC loss less than 3 kW. The insulation structure was designed to pass insulation tests specified in standard in China GB/T 25120-2010. An open cooling system with reduced pressure was developed, which realized the efficiency of the 6.6 MVA HTSTT above 99%. Before assembling the prototype transformer, we conducted tests for critical current and dielectric performance of the HTS double pancake coils (DPCs) used in high-voltage (HV) and low-voltage (LV) windings to verify the current-carrying and insulation performances of each DPC. Finally, we measured the critical current and no-load loss of the HTSTT prototype at 77 K. Test results showed that the mass of the transformer is 33% less than conventional transformers. At 77 K, the critical current of the LV winding and HV winding is higher than 700 A and 50 A, respectively. Moreover, the HTSTT on a no-load test reached the test voltage of 25 000 V and loss of 6 kW. In the next step, we will continue to conduct experimental research, and verify the feasibility of the HTSTT on the train, and develop a circulating cooling system, all meeting the commercial requirements of the HTSTT.