The high voltage power supply system for the pulsed high magnetic field facility at the Wuhan National High Magnetic Field Center (WHMFC) will be upgraded to a 167 MJ capacitor bank system comprising 73 modules. This system will serve 27 magnet experimental stations over the next five years. The capacitor bank system is located on the second floor of the Pulsed Building, while all experimental stations occupy the first floor; each floor covers approximately 2000 square meters. The 27 experimental stations are divided into four independent zones. Each zone is supplied by dedicated capacitor bank modules and features an independent grounding system. This configuration ensures that operators in unaffected zones are not exposed to hazards during high voltage or high magnetic field experiments conducted in another zone, requiring evacuation only from stations within the active zone. Consequently, this design significantly improves experimental efficiency and greatly enhances overall facility utilization.

Electromagnetic wiping offers the advantages of non-contact operation and ease of control compared to the gas wiping. However, the single-phase electromagnetic wiping technique predominantly generates an axially oriented magnetic flux, resulting in limited axial electromagnetic force and reduced wiping efficiency. This paper introduces a three-phase electromagnetic wiping (TPEW) method for hot-dip galvanizing pipes. Compared to single-phase coils, the three-phase coils in the TPEW create a traveling magnetic field along the pipe axis, generating stronger axial electromagnetic forces on the surface of the galvanized coating, thereby achieving more effective removal of excess liquid zinc. Furthermore, the frequency and amplitude of the TPEW coil currents can be easily adjusted, enabling precise modulation of the traveling magnetic field and the electromagnetic forces acting on the liquid zinc. This ultimately allows for accurate control over the thickness and uniformity of the coating. Experimental results show that at a current amplitude of 70 A and a frequency of 50 Hz or lower, the TPEW technique effectively reduces the average coating thickness to below 40 mu m. The modeling, simulation, and experimental results of the prototype demonstrate the feasibility of the TPEW approach, which effectively reduces the coating thickness and enhances its uniformity.

This study presents a power supply topology capable of generating a large current pulse with a long flat-top duration and a high output voltage. The proposed topology is based on the sequentially fired pulse forming network (SFPFN) and the active coupled inductor filter. The SFPFN generates the primary inaccurate current pulse, and the filter then shapes the current to achieve accurate output. In order to achieve the required accuracy, a novel active coupled inductor filter is proposed which consists of a switched-mode compensator, an auxiliary thyristor pair, a DC bias capacitor, and a coupled inductor. It is designed to deviate most of the voltage and current stress to the coupled inductor, the auxiliary thyristor pair, and the DC bias capacitor, thus reducing the semiconductor devices requirements of the switched-mode compensator. Experimental results based on a 335 A low-power prototype verified the capability of the proposed topology to produce high-precision current pulses and the potential to be generalized to high-power scenarios.

A novel topology, which consists of a sequentially fired pulse forming network (SFPFN) and a coupled inductor active filter, has been proposed to generate large current with a high-stability flat-top. To achieve high precision control during the flat-top phase when the circuit parameters change in a wide range, a control method based on model predictive algorithm is proposed in this article. First, the thermodynamic models of magnet and coupled inductor are established to update their internal resistance in real time, and the models of every circuit state of the topology are built to predict the future value of the state variable. Based on those models, the algorithm of the model predictive control (MPC) is constructed, in which the influence of circuit state transition on the optimal control action is considered. The discharge stages (rise time, flat-top, and fall time) are controlled by a state machine. At last, a full-scale system of 10 kV/20 kA is constructed, and the pulsed magnetic field of 40 T (20 kA) with the 10ms flat-top and the high-stability of 96 ppm are achieved.

Generating steep, pulsed heavy currents with a high stability flat-top on a highly inductive load is a challenging task. This is due to the voltage of the current rising tens of times higher than that of the stable current, and the load resistance undergoing nonlinear changes caused by Joule heat. Hence a hybrid power supply, which includes the cooperative discharge of capacitor-battery and a novel flat-top regulation bypass circuit, is proposed in this article. The high voltage of capacitor source (CAPS) makes the magnet current rise fast. The stable output of battery voltage can maintain high current output and the bypass circuit with IGBTs operating in the active region (IGBTs-AR) regulates the magnet current accurately during the flat-top. A unit of RC with semiconductor switch is in series with the IGBTs-AR to suppress the power dissipation of IGBTs-AR. An isolation valve set of 28 kV/ 22 kA and a bypass circuit of 4 kA/ 100 ms are developed to implement isolation and automatic commutation between the battery source and CAPS, and to regulate the magnet current, respectively. Finally, the detailed tests are performed and the magnetic fields of 20.058 T/10 ms/ 200 ppm and 10.747 T/ 45 ms/ 450 ppm are realized.

Electromagnetic wiping has the advantages of non-contact and easy control compared to traditional gas wiping. However, electromagnetic wiping devices available are primarily designed for cylindrical workpieces such as steel wire and pipes, leading to low efficiency when applied to steel strips. This paper presents a three-phase electromagnetic wiping device for hot-dip galvanizing of steel strips. Based on the traveling magnetic field of the linear motor, the device allows precise control over coating thickness by adjusting the frequency and amplitude of the current. A Multiphysics model of the electromagnetic field and fluid field is established to study the body force of the coating in a hot-dip galvanizing process. Simulation results show that the proposed wiping device can effectively remove the excess zinc liquid and reduce coating thickness.

The flat-top pulsed magnetic field has the dual advantages of high field strength and high stability, which is an important extreme experimental condition in frontier basic science research. It is difficult to study a pulse power supply with both high instantaneous power and high average power to generate high current of ten thousand of amperes with steep edge, long flat top duration and high stability on the load of large inductive pulse magnet. Therefore, this paper proposes a capacitor-battery cooperative pulsed power supply scheme, and analyzes the process of the cooperative power supply by complex frequency domain method, as well as verifies its superiority by simulation. At last, a prototype is developed and the tests of the current commutating between capacitor and battery are carried out.

Many vacuum electronic devices require a power supply to drive magnets to generate a flat top pulsed magnetic field in their cavities. However, there is a thick copper plating layer in cavities, resulting in serious eddy current hysteresis. In this paper, a control algorithm based on variable-step model predictive control is proposed for the eddy current compensation of high-power gyrotron terahertz wave sources. Compared to traditional flat top pulse current sources, the proposed algorithm generates a controlled current overshoot in the magnet, increasing the magnetic field stabilization speed by approximately 50%. The control algorithm has multiple operating states, and can achieve computational load balancing by adjusting the sampling time and prediction step length under different states, while generating a more stable flat top pulse current than traditional methods.

The closed-loop fluxgate current transducer (CFCT) is the only current sensor whose measurement accuracy can reach a level of the parts per million (ppm) at present. However, the false balance, which makes the CFCT unable to work, caused by an excessive offset current is the inherent flaw of the CFCT. The high di/dt (rate of current change) of the primary current is the main factor resulting in the offset current overload. Therefore, the CFCT is currently only applied for steady-state direct-current measurements. In this article, an approach is proposed to eliminate the false balance of the CFCT in the dynamic process by adding a feedforward branch, which provides a follow-up bias point for the CFCT to make the CFCT always work in a small-signal range, where a risk of magnetic saturation does not arise. The zero-flux state of the CFCT still only depends on the feedback branch, so its high measurement accuracy is maintained. The experiments prove that the CFCT can measure a flat-top pulsed current with an accuracy of the ppm level by this method.

Pulse gyrotrons have lingered at the short-pulse operation below 1 ms because of the rapid changes in magnetic field strength. This article is aiming to incorporate the Flat-Top Pulse Magnetic Field (FTPMF) into the pulse-magnet gyrotron, which means there will be the first chance to make a pulse-magnet gyrotron available to generate radiation up to 10 ms or above. In such a long pulse width, many scientific experiments, Namely, ESR or DNP-NMR, can be carried out. This article will propose a suitable FTPMF facility for pulse gyrotrons. The topology, principle, and simulation result will be given.

In gyrotrons operating in high-order modes, during the startup process, the shadowing of the operating mode by two sidebands may take place. By “shadowing,” we mean the situation when, during the voltage rise, one of the parasitic modes is excited first, and this excitation prevents the excitation of the desired mode. Then, the oscillations of the first parasitic mode, whose frequency is higher than the frequency of the desired operating mode, can be replaced by excitation of the second parasitic mode, whose frequency is lower than the operating one. As a result, the desired mode remains in the “shadow” of these parasitic modes and is never excited. This paper describes such effect in gyrotrons with diode-type electron guns. This paper consists of two parts. First, the problem is studied in a generalized approach, which means that the results are valid to gyrotrons operating at arbitrary voltages and in any modes. By using this approach, it is possible to determine the critical density of the mode spectrum, above which the shadowing occurs. This study is carried out for the cases when the interaction between modes is synchronous and when it is nonsynchronous. Second, this paper contains the analysis of a typical Megawatt-class gyrotron with a diode-type electron gun. It is studied whether the moving of this gyrotron to operating in higher-order modes will lead to the shadowing of the desired mode or other, more complicated, dynamic, and/or stochastic processes will take place.

The operation of gyrotrons highly depends on the alignment between the magnet and the tube, which will cause instability problems or degrade the output efficiency, especially for high-frequency gyrotrons with a small cavity size. In this letter, the influence of misalignment, including parallel shift, arbitrary tilt, and their co-existence, on the behavior of the electron beam was studied. A prototype of an 800 GHz gyrotron with a sapphire window was developed to study the correlation between the misalignment and the beam trajectory. A method to determine the tilt angle and shift distance was proposed. The feasibility of the misalignment correction method was verified in the experiment.

The Wuhan National High Magnetic Field Center is incorporating the flat-top pulsed magnetic field (FTPMF) into pulse gyrotrons. It will be the first chance to make a pulse-magnet gyrotron available for generating a long-pulse radiation of 100 ms or above without affecting its high operating frequency and high radiation power. However, unlike continuous wave gyrotrons, pulse gyrotrons in long-term operation have their own challenges, namely, misalignment caused by concussions, much stronger low-frequency electromagnetic interference from the pulse magnet, and inevitable explosion. This article will focus on the difficulties faced by pulse gyrotrons in years of operation, discuss the protection and restoration from failures, and, consequently, propose a fully redundant, explosion-proof, and quickly recoverable auxiliary system for long-term operation of pulse gyrotrons. This system integrates the control unit of traditional pulsed magnets and superconducting magnets so that it can be compatible with any form of gyrotron facilities. Therefore, once the FTPMF or the superconducting magnet is available, the long-pulse radiation will be obtained. Several experimental results, including the most recent explosion, show the reliability of the proposed system.

国家脉冲强磁场实验装置的脉冲电容器型电源是产生最高90 T以上超强脉冲磁场的关键设备,其充电采用整流、高频逆变、整流的高精度恒流充电机,多台充电机同时工作时对实验室1 MVA的小型配电网产生较大冲击,特别是充电过程中产生的间谐波,给其他高端精密的科学测量仪器等用电设备造成干扰,严重影响前沿基础科学实验的高精度数据采集.在此首先进行串联谐振恒流充电机的原理分析,通过建立系统仿真模型,开展间谐波发射特性的研究,最后在装置上进行了间谐波测试,仿真结果和实验数据吻合,验证了理论和仿真分析的正确性,为下一步间谐波治理方案设计提供了重要的基础.

The compression of the electron beam and the efficiency of the gyrotron are strongly dependent on the magnetic field. Especially for gyrotrons using pulsed magnets, the pulsed magnet provides a strong magnetic field to the gyrotron but also brings some new problems in magnet design and testing. In this article, we take the pulsed magnet design and test of an 800-GHz gyrotron as an example. Considering the needs of working at room temperature and withstanding severe electromagnetic forces, the treatment of magnet strength in design and fabrication is introduced in detail. The design and measurement of the magnetic field distribution are also presented. Finally, a pulsed magnet that can generate a 30-T magnetic field and can be repeatedly discharged is designed and experimentally verified.

A linear bypass circuit was developed to realize the high stability flat-top pulsed magnetic field (FTMPF) powered by battery-bank at the Wuhan National High Magnetic Field Center (WHMFC) in 2018. It mainly consists of the insulated-gate bipolar transistors (IGBTs) operating in the active region and a power resistor connected in series with the IGBTs. However, the terminal voltage of the IGBTs is high due to the operation in active region, which limits their through-current capability. In this paper, an approach for injecting current to the power resistor is proposed to reduce the terminal voltage of the IGBTs. Compared with the original technology, the through-current capability of the IGBTs will be enhanced greatly and the regulation scope of the FTPMF system will be expanded with the same number of IGBT. The method is discussed in detail and the number of IGBT is reduced from 35 to 8 in achieving an FTPMF of 40 T.

A high-stability flat-top pulsed magnetic field (FTPMF) is strongly needed for some scientific studies, such as nuclear magnetic resonance and specific heat measurement. This paper presents a new linear flat-top regulation bypass circuit to generate a high-stability FTPMF based on a battery bank power supply. The bypass circuit consists of insulated-gate bipolar transistors (IGBTs) in parallel that operate in the active region and are free of switch ripples. To achieve precise control of the IGBT current, the influence of the Miller effect and the nonlinearity of the IGBT's transfer characteristic are studied in detail. Then, a dual-feedback loop is designed and analyzed. A prototype consisting of a 1000 V/30 kA battery bank and a bypass circuit of 1700 V/3600 A IGBTs is developed. An FTPMF with a field/duration of 23.370 T/100 ms and a stability of 64.2 ppm has been achieved.

A higher magnetic field can provide more opportunities to reveal new phenomena in a scientific research. Aiming to achieve a higher magnetic field, Wuhan National High Magnetic Field Center (WHMFC), Wuhan, China has designed a a power supply system for 100 T magnetic field under existing power supply conditions in April 2015. The 100 T magnet consisting of three coils is energized by a multipower supply system. The outer coil is energized by a pulsed generator-rectifier connected to battery bank in series. The middle coil and the inner coil are energized by two capacitor bank, respectively. To ensure safety and reliable operation, control sequence as well as protection system for the power system is designed and developed. A test system including the prototype of three-coil magnet is established at WHMFC. A series of tests are carried out on hybrid power supply systems. 73.3 T peak field has been achieved as the highest magnetic field in the test. The test results presented in this paper show the hybrid power supply system is feasible and operable.

In Wuhan National High Magnetic Field Center (WHMFC), a new DC breaker based on the pulsed electromagnetic forming (EMF) technology is developed. The breaker is intended to interrupt the current in the battery power supply and protect the long pulsed magnet. The breaker consists of a pulsed magnet (EMF coil), aluminum tube (the main contact of the DC breaker) and supports. The aluminum tube is designed to break due to the electromagnetic repulsion produced by the induced eddy currents, which is activated in the results of the pulsed magnet powered by a capacitor. Firstly, the aluminum wire electrical explosive DC breaker and the EMF technology are combined. Then, the model based on the Maxwell's equations is constructed using the COMSOL Multiphysics™. The magnetic flux distribution, magnetic force, tube deformation and their interactions are studied in simulations. Both simulations and primary experimental results show that the design of the proposed DC breaker with compact volume and easy maintenance is feasible. In addition to the pulsed high magnetic field facility applications, the breaker can also be applied to numerical potential industrial fields.

Wuhan National High Magnetic Field Center (WHMFC) at Huazhong University of Science and Technology is one of the top-class research centers in the world, which can offer pulsed fields up to 90.6 T with different field waveforms for scientific research and has passed the final evaluation of the Chinese government in 2014. This paper will give a brief introduction of the facility and the development status of pulsed magnetic fields research at WHMFC. In addition, it will describe the application development of pulsed magnetic fields in both scientific and industrial research.