Solid-state flexible energy storage devices hold the key to realizing portable and flexible electronic devices. Achieving fully flexible energy storage devices requires that all of the essential components (i.e., electrodes, separator, and electrolyte) with specific electrochemical and interfacial properties are integrated into a single solid-state and mechanically flexible unit. In this study, we describe the fabrication of solid-state flexible asymmetric supercapacitors based on an ionic liquid functionalized-chemically modified graphene (IL-CMG) film (as the negative electrode) and a hydrous RuO₂–IL-CMG composite film (as the positive electrode), separated with polyvinyl alcohol–H₂SO₄ electrolyte. The highly ordered macroscopic layer structures of these films arising through direct flow self-assembly make them simultaneously excellent electrical conductors and mechanical supports, allowing them to serve as flexible electrodes and current collectors in supercapacitor devices. Our asymmetric supercapacitors have been optimized with a maximum cell voltage up to 1.8 V and deliver a high energy density (19.7 W h kg⁻¹) and power density (6.8 kW g⁻¹), higher than those of symmetric supercapacitors based on IL-CMG films. They can operate even under an extremely high rate of 10 A g⁻¹ with 79.4% retention of specific capacitance. Their superior flexibility and cycling stability are evident in their good performance stability over 2000 cycles under harsh mechanical conditions including twisted and bent states. These solid-state flexible asymmetric supercapacitors with their simple cell configuration could offer new design and fabrication opportunities for flexible energy storage devices that can combine high energy and power densities, high rate capability, and long-term cycling stability.

This paper reports the effects of thermal energy on reducing the overshoot of the current sweep cycle method to reduce the screening current-induced field (SCF) in a 2G high temperature superconducting (HTS) coil. A disadvantage of the current sweep cycle method is the necessity for large overshoot in the coil current. For a 2G HTS coil, excessive overshooting of the coil current is undesirable (Yanagisawa et al 2012 AIP Conf. Proc. 1434 1373–8 ). In an effort to circumvent this overshooting problem, the thermal energy effect was investigated in combination with the current sweep cycle method based on experiments in this study. The experimental results show that greater SCF reduction in the HTS coil was obtained upon increasing thermal energy by heater current.

In order to achieve a persistent current mode opera-tion with high temperature superconducting (HTS) coils, we have been trying to improve the concept of a joint-less HTS coil. The coil has a perfect closed loop without any joints in a coil, and we have proven that a persistent current can be induced in the coil by sev-eral charge up method such as PCS, flux pump, or field cooling with a background magnet. In this paper, based on the previous experiment which showed partially successful results [10], we de-signed and fabricated a small solenoid type joint-less HTS magnet with 100-m long ReBCO wide conductor and tested it in liquid ni-trogen bath. After the persistent current mode operation of fifteen hours, we tried to measure temporal and spatial homogeneity by a field mapper we developed under the DSV of 10 mm.

In this paper, a new method is presented for sensitive quench detection in high-temperature superconductor (HTS) rotating machinery. The normal zone propagation velocity of an HTS is about 1000 times slower than that of a low-temperature superconductor. Therefore, the propagation of normal zone resistance, which occurs when the HTS transits from the superconducting state to the normal state, is also slower. Thus, it is difficult to detect the abnormal signals by voltage measurement using voltage taps. Moreover, the monitoring signal includes noise generated by interaction between the HTS rotating machinery and the industrial environment. Therefore, when quenching occurs in the HTS rotating machinery, a thermal runaway occurs in the hot spot. Furthermore, the magnetic energy stored in the HTS coil can damage the machinery. For these reasons, a new method is proposed for sensitive quench detection that reduces the noise generated from the power supply and from the HTS rotating machinery, using both an RLC resonance circuit and fast Fourier transform analysis.

We present a recently developed shimming method that uses a system of room-temperature (RT) orthogonal shimming coils to improve the spatial field homogeneity of high-resolution nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) superconducting magnets. Conventional RT shimming methods require recursive routines of field mapping and RT shim coil current adjustments, which lead to a less effective and time-consuming process. In this paper, we introduce a new RT shimming method that utilizes a process of gradual and automatic search to find an optimal operating point with a genetic algorithm (GA), a type of optimization technique. The proposed algorithm is capable of determining the optimal set of currents for a system of shimming coils to create the best spatial field homogeneity by minimizing the NMR spectral linewidth. We used a commercial 600-MHz NMR magnet with a full NMR spectral linewidth at half maximum (FWHM) of 2.2 ppm, as determined by an NMR test sample contained in a cylindrical glass tube with a diameter of 5 mm to demonstrate that the shimming method can improve the FWHM to 0.15 ppm. The results demonstrate the strong potential of the proposed RT shimming methodology for the auto-shimming process of NMR/MRI applications.

Given that REBCO wire is typically manufactured as a tape, it is possible for REBCO magnets to exhibit a relatively larger screening current-induced field (SCF). It is well known that the SCF in an REBCO magnet can be effectively reduced by the so-called current sweep method. However, it requires an overshooting in the magnet current, often close to the magnet's critical current, to effectively suppress the SCF, which may not be favored in terms of operation reliability. In this study, we experimentally validated an alternative approach which mitigates the SCF using thermal cycling together with the current sweep reversal. Well known is the fact that the large load factor, defined as the ratio of operating current to critical current of an REBCO magnet, deteriorates the SCF impact on field uniformity. The key idea is to increase the magnet temperature to increase the effective load factor of the magnet close to its quench limit momentarily, minimize the SCF, and then return back to the nominal operating condition. The combined approach of the thermal cycling and the current sweep may be effective when attempting to eliminate the SCF without ramping an REBCO magnet to a current that may be dangerously high, especially when the magnet is operated at a high operating current. This paper presents the test results of the combined approach in the conduction-cooled REBCO magnet, and the results demonstrate the potential of the approach for more safe and effective elimination of the SCF.