Abstract Body

The Photovoltaic-Energy storage-Direct current-Flexibility system (PEDF) can achieve efficient coordination between generation, grid, load, and storage, but it relies heavily on the stability of the DC bus voltage. The loads within buildings are often complex and random, making the issue of DC bus fluctuations a primary research focus.

The prerequisite for bus voltage stability is power balance. In this work, we propose using superconducting magnetic energy storage (SMES) technology to enhance the energy absorption capacity of the entire DC microgrid. First, we analyze the operating mechanism of SMES in response to voltage fluctuations during transient processes. Then, we compare the extent of voltage fluctuations before and after the application of SMES in simulations. Both theoretical and simulation results show that the SMES system can significantly improve the voltage stability of the system on a transient time scale.

Abstract Body

We are developing a liquid hydrogen cooled high-temperature superconducting (HTS) generator. To superconduct the field winding of generator of several hundred MW class, several kA-class high-current assembled conductors are required, and we are now developing a prototype conductor and verifying its electrical and mechanical properties¹). It is necessary to perform the kA-class energization tests of assembled conductors under liquid hydrogen cooling, but the capacity of the current leads of the liquid hydrogen test system built at JAXA's Noshiro Rocket Testing Centre is 500 A²), and it is not easy to modify the system to multi kA-class.

One method of testing large-current low-temperature superconducting (LTS) conductors is the current induction method, in which both ends of the target conductor are short-circuited to form a low-inductance secondary coil that is magnetically coupled to a high-inductance primary coil³). By sweeping the current through the primary coil, a large current is induced in the secondary coil. The same method is expected to be used for large-current energization testing of HTS conductors, but there are several issues that need to be improved. These include the accuracy of the induced current measurement using Rogowski coils, the development of ultra-low resistance connection techniques for HTS conductors, and the resetting of the induced current to zero by conductor quenching.

For this reason, we proposed a new energization method in which AC current is applied to the primary coil and conducted a basic study. As a first step, we manufactured a one-turn short-circuit test coil using a single HTS wire and installed it in a fabricated REBCO field coil2), and conducted an inductive energization test. When the excitation frequency was 1 Hz or less, a phenomenon was confirmed in which the phase difference of the Rogowski coil voltage increased rapidly when the peak value of the secondary current exceeded the Ic of the wire, indicating the possibility of determining the Ic of the secondary conductor using this method. Since the Rogowski coil voltage is measured using a lock-in amplifier, it is highly robust to noise and drift, enabling highly accurate inductive current measurement. The next step was to manufacture and verify prototype short-circuited test coils using multiple HTS wires. The test results will be presented at the conference, and the potential of the AC inductive energization method will be discussed.

References

[1] M. Ohya et al., “Current flow simulation of assembled conductors for field coils of liquid hydrogen-cooled high-temperature superconducting generator,” IEEE Trans. Appl. Supercond., Vol. 33, No. 5 (2023) 4603005.

[2] M. Ohya et al., “Energization test apparatus of HTS coils cooled by liquid hydrogen and manufacture of split-type REBCO external field coil,” J. Phys. Conf. ser., Vol. 2776 (2024) 012010.

[3] G. B. J. Mulder et al., “On the inductive method for maximum current testing of superconducting cables,” Proceedings of the 11th International Conference on Magnet Technology (1990) 479-484.

Acknowledgment

This presentation is based on results obtained from a project, JPNP20004, subsidized by the New Energy and Industrial Technology Development Organization (NEDO).

This work was also supported by NIFS Collaboration Research program (NIFS23KIIA009).

Figure 1. One-turn short-circuit test coil using an HTS wire installed in a REBCO field coil.

Keywords: High-temperature superconductor, Assembled conductor, Inductive energization test, Liquid hydrogen

Abstract Body

In the aircraft industry, there is a strong need to reduce carbon dioxide emissions. New technological innovations are needed to achieve virtually zero carbon dioxide emissions [1]. One of these innovations is the aircraft electric propulsion systems using superconducting technology [2]. In our previous works, we developed triaxial superconducting cables [3]. We confirmed that 95% of transmission loss could be reduced compared to XLPE cables as an energy-saving effect through validation tests. However, they were heavy for the superconducting electric propulsion aircraft system [4]. Therefore, we have newly developed high-capacity and lightweight stacked superconducting cables with REBa₂Cu₃O_y (RE, rear earth) coated conductors (CCs) for superconducting propulsion systems for aircraft [4], [5]. Moreover, there is a need to design a small and lightweight cable termination structure. In this study, we demonstrated the electrode architecture of the stacked CCs superconducting cable terminations.

In the simple electrode architecture, the critical current (Ic) properties in the stacked CCs cables show the degradation of 40 – 60% at liquid nitrogen compared with a total Ic value of CCs. From its result, we need to design an electrode architecture which is suitable for the stacked CCs cables. Furthermore, we also report their results in detail.

Abstract Body

The Fukushima Daiichi nuclear power plant suffered an accident as a result of the 2011 earthquake. As a result, radioactive materials were released into the atmosphere. Afterwards, the radioactive materials were deposited in the soil due to rainfall. The government removed the topsoil and decontaminated the soil. Approximately 13 million cubic meters of contaminated soil were generated during the decontamination process, and processing it requires a huge amount of time and money. Therefore, there is a need for a method to efficiently treat contaminated soil. Therefore, we proposed a method to selectively remove clay minerals that have a high radiation dose due to their adsorption properties of caesium, which make up most of the contaminated soil. In conventional methods, magnetic separation of paramagnetic materials requires a combination of a strong magnetic field of about 5 T or more and a high gradient magnetic field with ferromagnetic filaments. Therefore, we have proposed a separation concept of the selection tube magnetic separation method in which the drag force acting on the particles to be separated is reduced as much as possible to an almost weightless state by fluid control, and a low magnetic field is used as the source of the magnetic field for the magnetic attraction force required for the separation. Under laminar flow, the particle size distribution of particles suspended in the tube depends on their streamlines (velocity distribution). The width of the particle size distribution can be precisely controlled by magnetic force. In our previous study, we have been shown from calculations that more precise separation is possible by using a solenoid-type superconducting magnet as the magnetic field source, placing a magnetic filter inside the selection tube, and controlling the magnetic force acting on the particles in a vertical downward direction. The results showed that smaller particles could be adsorbed at the same flow rate by using it in combination with magnetic separation. Thus, it was found that by using magnetic separation in combination, the water flow rate can be increased by 10 times when adsorbing particles of the same particle size, which may lead to an improvement in processing speed. And, for actual magnetic separation with selection tube, it is necessary to guide the targeted particles in a desired magnetic field area inside the bore of a superconducting magnet, and we had been succeeded in sending the particles in a desired magnetic field area by using a multi-stage selection tube [1], [2].

In this study, a superconducting solenoid magnet was applied as the magnetic field generator, sieved vermiculite particles (volume magnetic susceptibility of 7.0 × 10^-4) were measured with a particle size analyzer, and the flow velocity in the tube was determined from calculations with the targeted particle diameter of the particles to be separated as 4 µm, and a selection tube superconducting magnetic separation experiment was conducted. The experimental system is shown in Fig. 1-(a). A magnetic filter (made of SUS430 with a wire diameter of 0.6 mm) was placed in a selection tube and an external magnetic field of 2 T was applied. A two-stage selection tube was used, and the target particles were suspended in the separation area. As shown in Figure 1-(b), particles were captured on the magnetic filter, with a peak at about 4 µm particle size, confirming that vermiculite with a particle size appropriate for the calculated flow velocity was captured. High gradient magnetic separation experiments were conducted using a small-scale selection tube with a superconducting magnet of the solenoid type under a low magnetic field. Magnetic separation of paramagnetic particles of several microns in diameter was possible at a maximum applied magnetic field of 2 T, demonstrating that the magnetic separation method using selection tubes is effective for the separation of paramagnetic materials.

References

[1] Development of novel magnetic separation for paramagnetic particles using the selection tube., N.Nomura, F.Mishima, S.Nishijima, IEEE Trans. on Appl. Supercond., 32, (6), 2022.9

[2] Study on multi-stage magnetic separation device for paramagnetic materials operated in low magnetic fields., F. Mishima, A. Nagahama, N. Nomura, S. Nishijima, Progress in Superconductivity and Cryogenics, 25, (3), p.p.13-17, 2023.9

Acknowledgment

This work was supported by JSPS KAKENHI Grant Number 24K15358.

Figure 1. (a) Concept illustration of magnetic selection tube applied Superconducting magnet. The selection tube is located above the center of the maximum magnetic field. Magnetic flux density (B-max) about 2T.

(b) Photo of vermiculite particles captured on a magnetic filter.

Keywords: Magnetic separation, paramagnetic particle, High Gradient Magnetic Separation System, low magnetic field, Selection tube

Abstract Body

We have been researching and developing high-temperature superconducting (HTS) generators that use the cold heat of liquid hydrogen, eliminating the need for a refrigerator ¹⁾. Winding the generator's field coils with REBCO wire results in high efficiency, which is difficult to achieve with existing generators. However, one of the challenges to the practical application of large, high-speed rotating HTS field coils is the mechanical fragility of the REBCO wires and coils. The compressive stress is estimated to be 50 MPa, which is generated by the expected centrifugal force of 8,000 g (rotation radius 0.5 m, rotation speed 3,600 rpm), but previous studies have reported that the I-V characteristics of the REBCO coils decreases from about 10 MPa²⁾. It is necessary to develop a technology to produce high-strength coils that are at least five times stronger than conventional coils. To achieve this, it is essential to investigate the cause of the reversible degradation in the I-V characteristics of the REBCO coils reported in previous studies (the I-V characteristic deteriorates when a load is applied, but returns to its original state when the load is removed).

First, a numerical model of the test coil in the previous study was built to analyze the stress and strain generated inside the superconducting wire when the coil was compressed. Even the internal structures of the REBCO wire, such as the superconducting layer and the silver layer, were modeled in detail. From the results of this simulation, even when a compressive stress of about 10 MPa was applied to the coil, no strain was observed that would lower the Ic of the REBCO wire. It was estimated that the Ic was lowered by a phenomenon other than mechanical.

Next, a test coil was made by winding a double pancake coil (inner diameter 85 mm, outer diameter 95 m) with 4 mm wide REBCO wires and reinforcing it with a SUS case. As a result of the coil compression test, it was confirmed that the I-V characteristic of the coil deteriorated even when a light compressive load was applied, as in the previous report, and that it returned after the load was removed. However, the I-V characteristic slowly deteriorated with time after the start of compression, and it was assumed that there was a reason for the coil temperature to rise during compression. After reconsidering the test configuration, it was found that the reversible decrease in I-V characteristics no longer occurred by providing gas vent paths from the inner circumferential space of the coil. It was determined that the cause of the reversible phenomenon was the increase in pressure and temperature caused by the evaporation of liquid nitrogen in the inner space of the coil when a load was applied. Compression tests were performed with this configuration and the I-V characteristics did not degrade even when the target compression load of 50 MPa was applied, indicating that a high-strength coil design was in sight.

References

[1] M. Ohya et al., “Mechanical simulation and energizing tests of HTS coils for 10 kW generator cooled by liquid hydrogen,” IEEE Trans. Appl. Supercond., Vol. 34, No. 3 (2024) 5201507.

[2] Y. Nagasaki et al., “Axial compressive stress dependence of critical current of REBCO double-pancake coil,” IEEE Trans. Appl. Supercond., Vol. 31, No. 5 (2021) 8400405.

Acknowledgment

This presentation is based on results obtained from a project, JPNP14004, subsidized by the New Energy and Industrial Technology Development Organization (NEDO).

Figure 1. Compression test results (a) for the initial configuration, (b) after providing the gas vent paths.

Keywords: High-temperature superconducting coil, REBCO, Compressive stress

Abstract Body

High-T_c superconducting power supplies are devices which can deliver kA+ currents into superconducting circuits without introducing any heat pathways from the ambient laboratory environment. Experimental results from a prototype optically switched, high-T_c superconducting half-wave transformer rectifier submerged in liquid nitrogen are presented. The entire secondary side of the rectifier is comprised of commercially manufactured coated conductors. This includes the transformer secondary, the bridge, and an HTS double pancake load coil. The switch is opened by applying nanosecond bursts of infrared light which transition the bridge into a resistive state. The frequency of the transformer primary is 1 Hz and the bridge is switched using optical radiation from a benchtop Nd:YAG laser with a wavelength of 1.064 μm. The pulse repetition rate is 35 kHz with pulse duration’s of 200 nanoseconds. Using this configuration, 100 A is injected into 220 μH load coil in approximately 60 seconds. The voltage measured over the bridge exceeds 100 mV and lasts approximately 3 ms each cycle or a duty cycle of 0.3%. The measured resistance is several milliohms, significantly higher than is measured using other switching mechanisms such as dynamic resistance or J_c(B,θ). Increasing the primary frequency dramatically increases the charging speed of the device.

Acknowledgment

This work was supported by a faculty research establishment grant from Victoria University of Wellington and in part by the New Zealand Ministry of Business, Innovation and Employment under the Advanced Energy Technology Platform program “High power electric motors for large scale transport” contract number RTVU2004

Keywords: High-T_c Superconductors, Optical Switching, Power Electronics, Transformer Rectifier

Abstract Body

In the semiconductor manufacturing process, there is a robot for moving wafers safely and efficiently. The current situation with this robot is that the moving parts of the robot cause friction and dust which contaminate wafers. Therefore, we have focused on superconductive-assisted machine (SUAM) which makes it possible to levitate wafers and transport them without contact and dust with moving parts. To transport wafers, a stable and sufficient repulsive force and a stable restoring force to withstand lateral movement are required. In our previous work [1][2], SUAM with superconducting tapes performed well as SUAM with superconducting bulks. Therefore, we considered that it is necessary to evaluate the performance of SUAM using superconducting tapes, and it can improve the repulsive force by adding ribs.

 In this study, we used the application, JMAG-Designer 22.1, for the finite element method (FEM) to analyze basic electromagnetic field. We created two different models with 6 sheets in one layer, 72 mm long, 12 mm wide, 2 µm thick, and with the ribs, 65 mm long, 12 mm wide, 2 µm thick. Here, rib, shown in Fig.1(a) inset figure, is the tape structure placed perpendicularly to flat tapes to obtain larger repulsive force. We analyzed 1, 3, and 5 layers which is placed at 12 mm below the 4-pole magnet. Fig. 1(a) shows the calculation of repulsive force and Fig. 1(b) shows the restoring force for two models with 1, 3 and 5 layers of superconducting tapes with ribs and without ribs. Wafers can be levitated with a repulsive force of 5 – 10 N. Since there is no sudden movement, a restoring force of 0.2 N is enough to transport it. From the result, the SUAM can be used to transport wafers because it has sufficient repulsive force and restoring force to withstand lateral movement.

[1] Kinoshita Y, Zhang R, Otabe E S, Suzuki K, Tanaka Y, Nakashima H, Nakasaki T 2020 J. Phys.: Conf. Ser. 1590 012023

[2] Iwasaki S, Kinoshita Y, Ishii H, Otabe E S, Suzuki K, Nakasaki T 2022 J. Phys.: Conf. Ser. 2323 012025

Fig. 1 (a) Repulsive force and (b) Restoring force when the magnetized distance is 12 mm for with ribs and without ribs for 1, 3, and 5 tape layers.

Abstract Body

High performance electron cyclotron resonance (ECR) ion source requires superconducting magnets to produce high magnetic fields for confining the plasma. A Nb 3 Sn superconducting magnet is under development at Lawrence Berkeley National Laboratory (LBNL) aiming to produce 2T sextupole field and 3T / 0.5T / 2T mirror fields at the plasma chamber. The magnet is preloaded with the technology of “bladder and key” to secure the enough mechanical contact between the pole and winding. Unlike to NbTi magnet, Nb 3 Sn is a brittle and strain sensitive material, the peak stress during the room temperature assembly and after cool-down must be lower than ~100MPa and ~150MPa. The peak stress criteria must be taken into account for the room temperature assembly. In this presentation, we investigate the mechanical properties at each step at coil winding, bladder and key operation, cool-down and energization for the magnet with 3D mechanical analysis. The results show that the stress concentrates at the coil end, and less clearance for the key insertion. To avoid the damage on the Nb 3 Sn during the room temperature assembly, we optimize the structure to keep the coil stress less than 100MPa without any reduction of the clearance for the key insertion.

Abstract Body

Superconductor cables consisting of coated conductors wound spirally on metal core in multiple layers, such as the CORC^® cable, are attracting interests because of their large current carrying capacities. Another advantage of such cables is current sharing among coated conductors improving robustness against local defects in coated conductors: the current can bypass the local defect in a coated conductor through others, and, then, the fatal blockage of current in the coated conductor can be prevented. Such bypassing currents are speculated, but their experimental observations were quite limited, and, the reported ones were not clear. Furthermore, even if there were not defect in all coated conductors composing a cable, the current distribution among coated conductors could be far from uniform because of imbalanced connecting resistances at terminals of the cable and/or imbalanced inductances among coated conductors. In such backgrounds, the current distribution measurements in such cables are very important to clarify their current transport characteristics.

In this study, we introduce two measurement methods of a two-layer spiral coated conductors. A sample used in experiments is shown schematically in Fig. 1. Each layer consists of two coated conductors wound spirally on a metal core. The first measurement method is by using the Hall sensors. The difference between the winding directions as well as the winding pitches of the two layers are utilized: the two layers generate different longitudinal magnetic fields along the core of the cable. The generated longitudinal magnetic field can be measured by the Hall sensors installed in the hallow core, then the currents in the two layers can be calculated. The second method is by using the pick-up coil wound around the cable, which can also measure the longitudinal magnetic field. We will compare the two method and discuss their advantages and their disadvantages.

This work was supported by JST-ALCA-Next Program Grant Number JPMJAN24G1, Japan.

Abstract Body

High temperature superconductors (HTS) are excellent technology for creating high field magnets of 10 T or greater, however they are rarely used to create magnets that must also ramp the magnetic field at high rates. This is due to transient loss mechanisms under changing magnetic fields that are a characteristic of high temperature superconductors.

A critical application for high ramping magnetic fields is in the characterization of new rare-earth permanent magnet materials, which are essential for reducing the cost, improving the supply chain security for electric transportation and industry, and reducing CO2 emission. Our hypothesis is that, using HTS wires, we can develop high-field, fast-cycling, large -bore, and small fringe-field magnets as test instruments for industry usage. Target magnet specifications will be:

1. High field: ~ 10 T

2. Rapid-cycling: 1 minute for full-cycle (40 T/min), 80 times faster than LTS magnets

3. Large sample bore: > 35 mm, suitable for industry usage

4. Low fringe fields by using high permeability carbon steel: no interference in surrounding instruments

We have a three-year project to design 10 T fast-ramping HTS magnets for characterizing new rare-earth permanent magnet materials. In this talk, the detailed project plan will be introduced and some initial numerical and experimental results on AC loss of a sub-scale coil winding will be presented.

Acknowledgment

This work was supported in “Fast-ramping superconducting magnets” funded by US Office of Naval Research under Grant award No. N629092412037.

Keywords: Fast ramping magnet, AC loss, rare-earth materials

Abstract Body

On January 13, 2021, the high-temperature superconducting (HTS) magnetic levitation (maglev) engineering prototype vehicle was launched in Chengdu, China. This actual head car symbolizes the beginning of engineering application for HTS pinning maglev transportation technology. To address the problem in monitoring and recognizing the complex operating conditions of HTS maglev system, it is crucial to develop intelligent state recognition theories and experimental platforms. The core component of HTS maglev vehicle is the superconducting levitator, where HTS bulks interact with magnetic field provided by permanent magnet guideway to achieve levitation and guidance. Extreme conditions such as uneven magnetic field, insufficient liquid nitrogen, and vacuum failure can lead to significant temperature rise inside the HTS bulks. If temperature rise is not effectively controlled and exceed safety thresholds [1], it would lead to substantial degradation or failure of levitation performance. Existing temperature monitoring methods for HTS bulks are inadequate for high-speed transport safety requirements [2]. Therefore, a multi-sensor monitoring platform for superconducting levitator was established, integrating information from various sensors. Experiments were conducted to study the evolution of multiple parameters under different operating speeds (3.6 km/h, 7.2 km/h, 10.8 km/h), varying loads (ranging from 74 N to 222 N), and different liquid nitrogen content (100%, 40%, 20%). Results showed that at speeds of 3.6 km/h, 7.2 km/h, and 10.8 km/h, the temperature rises of the HTS bulk were 0.2 K, 0.5 K, and 0.6 K, respectively. Under loads of 74 N, 111 N, 148 N, 185 N, and 222 N, the temperature rises were 1.1 K, 1.2 K, 1.1 K, 0.9 K, and 1.6 K, respectively. With liquid nitrogen contents of 100%, 40%, and 20% at the speed of 7.2 km/h, the maximum temperature rises were 0.6 K, 2.2 K, and 3.5 K, respectively. Due to length limitation in the experimental track, data augmentation techniques were used to expand the dataset of operating states [3]. Vibration acceleration was analyzed through time-domain, frequency-domain, and time-frequency domain feature extraction, 20 features were extracted. Moreover, the combination of HTS technology and AI technology is already an innovative research direction [4]. Therefore, various artificial intelligence algorithms were then employed to recognize the temperature states of the HTS bulks. The convolutional neural network (CNN) achieved the highest accuracy in state recognition, with 83.33% for varying liquid nitrogen contents and speeds, and 92.66% for different loads, highlighting the effectiveness of the multi-sensor fusion method for superconducting levitator state recognition and ensuring efficient HTS maglev vehicle monitoring.

References

[1] J Zheng, P Pang, P Wen. Measurement, 2023, 220: 113364.
[2] P Pang, J Zheng, Y H Zhao, et al. Superconductor Science and Technology, 2024, 37: 025011.
[3] H Q Ge, C Q Shen, X H Lin, et al.Measurement Science and Technology, 2024, 35:086141.
[4] M Yazdani-Asrami, A Sadeghi, W Song, et al. Superconductor Science and Technology. 2022, 35:123001.

Acknowledgment

This work was partially supported by the National Natural Science Foundation of China (52375132) and the Sichuan Science and Technology Program (24RCYJ0137).

Figure 1. (a) Multi-sensor integrated superconducting levitator, (b) Wireless data receiving platform.

Keywords: High-temperature superconductor (HTS), Magnetic levitation (maglev), Multi-sensor monitoring, HTS temperature rise, Time-frequency domain features, Convolutional neural network (CNN) model