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In the Tokamak discharge experiment, obtaining the largest possible null field region is a necessary condition for the smooth breakdown of the plasma, and adjusting the poloidal field coil current is key to achieving a better null field region. This paper, based on the Sino-Thai Tokamak cooperation project Thailand Tokamak-1 (TT-1) device, employs an exponentially decreasing Particle Swarm Optimization (PSO) algorithm to optimize the poloidal field coil current to create the desired null field region in the vacuum chamber area. First, a calculation model for the mutual inductance coefficient and the null field region is established according to the characteristics and magnetic structure of the TT-1 device, enabling the calculation of the null field region. Then, an optimization model for the poloidal field coil current is established, aiming to create a sufficiently large null field region (less than 10 Gauss) to facilitate breakdown. The optimization is carried out using both a typical linearly decreasing PSO algorithm and an improved PSO algorithm to determine the optimal poloidal field coil current. Compared to the unmodified PSO algorithm, the improved PSO algorithm reduces the root mean square error by 31.80%. The results show that the improved PSO algorithm is more suitable for the optimization of the poloidal field coil, has stronger optimization capabilities, and can effectively create the desired null field region, providing an important reference for the smooth breakdown of plasma in the TT-1 device.

The first plasma of the JT-60SA was obtained, and the plasma current reached 1.2 MA in 2023. During the commissioning of the superconducting magnets, a nominal current of 25.7 kA was achieved for the toroidal field coils, and the operating current reached half of the nominal current of 20 kA for the central solenoid and equilibrium field coils during individual energization tests. All coils were successfully energized simultaneously, and operated stably under repeated plasma operations at 15-20-minute intervals. Improvements to mitigate the large noise in the quench detection system are ongoing for the next plasma operation.

The two leading concepts for confining high-temperature fusion plasmas are the tokamak and the stellarator. Tokamaks are rotationally symmetric and use a large plasma current to achieve confinement, whereas stellarators are non-axisymmetric and employ three-dimensionally shaped magnetic field coils to twist the field and confine the plasma. As a result, the magnetic field of a stellarator needs to be carefully designed to minimize the collisional transport arising from poorly confined particle orbits, which would otherwise cause excessive power losses at high plasma temperatures. In addition, this type of transport leads to the appearance of a net toroidal plasma current, the so-called bootstrap current. Here, we analyse results from the first experimental campaign of the Wendelstein 7-X stellarator, showing that its magnetic-field design allows good control of bootstrap currents and collisional transport. The energy confinement time is among the best ever achieved in stellarators, both in absolute figures (τE > 100 ms) and relative to the stellarator confinement scaling. The bootstrap current responds as predicted to changes in the magnetic mirror ratio. These initial experiments confirm several theoretically predicted properties of Wendelstein 7-X plasmas, and already indicate consistency with optimization measures.

Nuclear magnetic resonance (NMR) spectroscopy, based on its extremely high backfield, can be used for the imaging and analysis of matter, which has given mankind a clearer perception of the composition of matter. The homogeneity of the magnet is the key to imaging. This paper analyzes the characteristics of various novel materials with active homogeneous fields regarding critical temperature, critical magnetic field, critical current and stress structure. The results show that YBCO and Bi-2223 strip structures cannot be wound when making coils, and with the change of rotation angle, the stronger the electromagnetic force on the strip, the greater the strain, which makes it difficult to fabricate uniform-field coils with high precision. In contrast, the feasibility of Bi-2212 in superconducting uniform-field coils is basically satisfied, and it has better performance.

The Hybrid Excitation Flux Switching Generator (HEFSG) has gained significant popularity in recent times owing to its relatively simple remarkably efficient topology. To optimize the performance of the generator, recent advancements and emerging patterns in mathematical modeling and software simulation, along with the utilization of optimization techniques, have facilitated the development of a novel methodology for electrical machine design. This study investigates the configuration and optimization of a Hybrid Excitation Flux Switching Generator, focusing on the rotor, armature coil, and field excitation. The optimization process involves multiple sequences for each component, employing the Local Optimization Method as an iterative approach to determine the optimal sequence that yields the highest output efficiency. Through the investigation of six rotor sequences, two armature coil sequences, and two field excitation coil sequences, a detailed optimization process was conducted. Consequently, the final output voltage of the HEFSG gains a 1.10% increment of voltage compared to the initial outcomes. Several sequences have influenced the output voltage performance of the generator during the optimization process. Therefore, modifications to the design of the arrangement contribute to the expansion of the operational range of the generator.

Liquid hydrogen (LH2) is a potential coolant of high-temperature superconducting (HTS) devices. However, owing to the high flammability of hydrogen and the risk of hydrogen embrittlement in materials, studies on LH2-cooled superconducting devices are rare. We developed an LH2 test apparatus to analyze the basic characteristics of LH2 as a coolant and evaluate the energizing characteristics of LH2-cooled superconducting wires. A REBCO external field coil was designed and manufactured for conducting cooling stability tests on various HTS coils cooled by LH2. The field coil, comprising eight single pancake coils of 4 mm wide REBCO wires, with inner diameter 106 mm and outer diameter 250 mm was divided into upper and lower sections. The test coil was placed in the central space. A magnetic field perpendicular to the test coil’s wire surface was generated by running currents in opposite directions through the upper and lower sections. Each double pancake coil was securely placed in a stainless-steel housing to withstand repulsive electromagnetic forces. The manufactured field coil was cooled using LH2, energized to 150 A, and successfully generated the intended magnetic field of 1.75 T. No increase in voltage was observed in any of the double pancake coils, and there was no mechanical degradation due to electromagnetic forces. Subsequently, we initiated thermal runaway tests on various HTS coils using the manufactured field coil to assess the cooling stability of LH2-cooled HTS coils. The study will facilitate the development of explosion-proof designs and safety technologies for LH2-cooled superconducting devices and cooling systems.

The global demand for aircraft is currently increasing, paralleled by a growing emphasis on decarbonization through the replacement of fossil fuel engines with electric propulsion. In response to this trend, we have developed a superconducting motor distinguished by its high efficiency, output, and low weight. Our focus centers on two critical aspects. Firstly, we addressed the issue of the field coil’s shape. The widely used REBCO wire in high-temperature superconductivity is tape-shaped, making a racetrack coil the most straightforward method for winding the wire. However, this configuration necessitates dividing the motor shaft as it comes in contact with the field coil, raising concerns about the mechanical durability of motors. To overcome this challenge, we introduce a saddle-type coil and design a coil shape that achieves a single continuous through-axis. Utilizing the Frenet-Serre formula, we created a 3D model of the coil’s end without applying load to the wire. This method, previously employed in accelerators, enhances durability, potentially leading to increased output due to higher rotation speeds and reduces weight through part savings. Secondly, introducing a saddle coil presents challenges in forming an ideal magnetic field distribution. In a rotating-field-type motor using an iron core, the winding can be directly wound around it, resulting in multiple coils forming similar magnetic fields that can be superimposed to create one large magnetic pole. However, with a saddle coil, coils are arranged along the circumference, and the magnetic field distribution and an anticipated decrease in output. To address this, we aimed to optimize the magnetic field distribution and increase output through a parameter survey. Specifically, we conducted an analysis under fixed armature conditions (current, number of turns, and shape) in three cases. In Case1, with a fixed total number of turns for the field coil, we compared magnetic field distributions and output by varying the number and arrangement of coils. In Case2, building on the findings of Case1, we aimed to enhance output by fixing the coil arrangement and increasing the number of turns. Finally, in Case 3, we examined the change in motor size with fixed coil parameters while altering the coil arrangement and pitch.

A single-field-period quasi-isodynamic stellarator configuration is presented. This configuration, which resembles a twisted strip, is obtained by the method of direct construction, that is, it is found via an expansion in the distance from the magnetic axis. Its discovery, however, relied on an additional step involving numerical optimization, performed within the space of near-axis configurations defined by a set of adjustable magnetic field parameters. This optimization, completed in 30 s on a single CPU core using the SIMSOPT code, yields a solution with excellent confinement, as measured by the conventional figure of merit for neoclassical transport, effective ripple, at a modest aspect ratio of eight. The optimization parameters that led to this configuration are described, its confinement properties are assessed and a set of magnetic field coils is found. The resulting transport at low collisionality is much smaller than that of W7-X, and the device needs significantly fewer coils because of the reduced number of field periods.

Magnetic reconnection rapidly converts magnetic energy into some combination of plasma flow energy, thermal energy and non-thermal energetic particles. Various reconnection acceleration mechanisms have been theoretically proposed and numerically studied in different collisionless and low-β environments, where β refers to the plasma-to-magnetic pressure ratio. These mechanisms include Fermi acceleration, betatron acceleration, parallel electric field acceleration along magnetic fields and direct acceleration by the reconnection electric field. However, none of them have been experimentally confirmed, as the direct observation of non-thermal particle acceleration in laboratory experiments has been difficult due to short Debye lengths for in situ measurements and short mean free paths for ex situ measurements. Here we report the direct measurement of accelerated non-thermal electrons from magnetically driven reconnection at low β in experiments using a laser-powered capacitor coil platform. We use kilojoule lasers to drive parallel currents to reconnect megagauss-level magnetic fields in a quasi-axisymmetric geometry. The angular dependence of the measured electron energy spectrum and the resulting accelerated energies, supported by particle-in-cell simulations, indicate that the mechanism of direct electric field acceleration by the out-of-plane reconnection electric field is at work. Scaled energies using this mechanism show direct relevance to astrophysical observations.Laboratory experiments demonstrate that electrons are accelerated to high energies by the reconnection electric field in magnetically driven reconnection. This mechanism is expected to be relevant for many astrophysical environments.

The highly uniform magnetic field coil is one of the most important components of miniaturized atomic inertial sensors. However, the development of the magnetic field model of coils in magnetic shielding with irregular shapes is difficult in practice. In this study, an optimization method for the design of coil structure parameters based on hybrid modelling with the finite element method and the SNOPT algorithm was proposed. The finite element method was used to characterize the geometric structure of the magnetic shield accurately and incorporate the characteristic B-H parameters of the material into the optimization model to improve the design accuracy. The three-dimensional model was reduced to two dimensions, and the parameters of the coil structure were optimized by an intelligent algorithm, which improved the solution efficiency. The effectiveness of the proposed approach was demonstrated by optimizing the design of a solenoid coil inside the cylindrical magnetic shielding with holes and stovepipes, which reduced the design error caused by the magnetic leakage flux.