Design of Power Supplies for the Pulsed High Magnetic Field Facility at HUST

Two types of pulsed power supply, a modular 12 MJ/25 kV capacitor bank and a 100 MVA flywheel pulsed generator, are under construction for the pulsed high magnetic field facility at the Huazhong University of Science and Technology (HUST) in Wuhan, China. The capacitor bank consists of 11 independent 1 MJ modules with a short circuit current of 40 kA each and 2 independent 0.5 MJ modules for 50 kA each. The bank is used to energize coils for magnetic fields in the 50–80 T range with pulse duration from 15 to 200 ms. The pulsed flywheel-alternator is used to energize a 50 T/100 ms long-pulse magnet via two 12-pulse power converter modules. Each converter module is designed to operate in the 95 to 66 Hz frequency operation range of the generator and can provide a no-load voltage of 4.6 kV and a full-load voltage of 3.4 kV at the rated current of 20 kA. In this paper the design of these two types of power supply is presented.     

The New Developed Components Tests for 1 MJ Capacitor Power Supply System in Wuhan High Magnetic Field Facility

A new 1 MJ, 25 kV, 40 kA pulsed capacitor power supply system for the Wuhan High Magnetic Field Facility (WHMFF) has been achieved. The desire for 70 or higher tesla magnetic field to support a lot of scientific researches based on it is just now beginning to be realized. The system consists of charger, capacitor bank, polarity changing switches, protective inductor, thyristor switch, crowbar, dump circuit and so on. In this paper, a series of tests for the new developed components such as high energy pulsed capacitor with 160 μF/25 kV/10 kA/10 ms/30% voltage reversal, thyristor switch (25 kV, 40 kA, 10 ms), polarity changing switch and ZnO linearly resistor disc for crowbar are introduced. The results show that all of new components are good or better than the old 1 MJ power supply system.     

Progress in the Development of the Wuhan High Magnetic Field Center

Since April 2008 the Wuhan High Magnetic Field Center (WHMFC) has been under development at the Huazhong University of Science and Technology (HUST) at Wuhan, China. It is funded by the Chinese National Development and Reformation Committee. Magnets with bore sizes from 12 to 34 mm and peak fields in the range of 50 to 80 T have been designed. The power supplies for these magnets are a capacitor bank with 12 modules of 1 MJ, 25 kV each and a 100 MVA/100 MJ flywheel pulse generator. The objective of the facility is to accommodate external users for extensive experiments in pulsed high magnetic fields. Up to seven measurement stations will be available at temperatures in the range from 50 mK to 400 K. The first prototype 1 MJ, 25 kV capacitor bank with thyristors, crowbar diodes and a mechanical switch has been developed and successfully tested. For the protection of the thyristor switch, a toroidal inductor is developed to limit the current at 40 kA. Five magnets have been wound with CuNb and copper wires and internal reinforcement by Zylon fiber; external reinforcement is a stainless steel shell encased by carbon fiber composite. Two Helium flow cryostats have been successfully tested and reached temperatures down to 4.2 K. Measurement stations for magneto-transport and magnetization are in operation. The design, construction and testing of the prototype system are presented.     

<Superscript>59</Superscript>Co NMR at Pulsed High Magnetic Fields

We report the ⁵⁹Co-NMR observation by spin-echo method at pulsed high magnetic fields up to 48 T. The 22 mm bore-resistive coil magnet with an inductance of 7.59 mH has a total time duration of 50 ms. After discharging the capacitor bank, NMR signals were observed near the maximum field. By repeatedly pulsing the RF sequence around the maximum field, spin echoes at different fields were recorded to give the NMR spectrum.     

Design and Performance of the First Dual-Coil Magnet at the Wuhan National High Magnetic Field Center

The first 80 T dual-coil magnet was manufactured and tested at the Wuhan National High Magnetic Field Center (WHMFC). The inner coil consists of 8 layers of 2.8 mm × 4.3 mm CuNb microcomposite wire developed in China; the bore diameter is 14 mm and the outer diameter 135 mm. The outer coil was wound directly on the inner coil with 12 layers of 3 mm × 6 mm soft copper. Each conductor layer of both coils was reinforced by Zylon/epoxy composite. The inner and outer coil were driven by a 1.6 MJ/5.12 mF capacitor bank and by eight 1 MJ/3.2 mF modules, respectively. At the voltage of 14.3 kV for the inner coil and 22 kV for the outer coil, the inner and outer coils produced peak fields of 48.5 T and 34.5 T respectively, which gave a total field of 83 T. This was the first combined operation of the new capacitor banks installed at the WHMFC. We present details of the design, manufacture and test of the dual-coil magnet and discuss crucial material properties. Based on this experience, a second dual-coil magnet will be designed; the enhanced design will be discussed. With the total energy of 12.6 MJ, peak field up to 90 T is expected.     

The Design and Tests of Battery Power Supply System for Pulsed Flat-Top Magnets in WHMFC

A capacitor bank power supply of 14.8 MJ is built in Wuhan National Pulsed High Magnetic Field Center (WHMFC). Another pulse generator power supply of 100 MJ/100 MVA is expected to be finished by the end of August, 2012. These power supplies can drive pulsed magnets with a magnetic field of 50 T to 80 T and a pulse duration of 15 ms to 1000 ms (Li et al. in IEEE Trans. Appl. Supercond. 18:596, 2008). In addition to that, a new battery bank power supply system is also designed. This system can output a maximum voltage of 1000 V, a maximum current of 40 kA and a pulse duration of 2 s to feed pulsed flat-top magnets of 40 T/2 s. This power supply consists of battery bank and its charger, thyristor DC switch and its forced commutation, DC breaker, control system, Crowbar, PWM controller and magnet. The battery bank uses 945 lead-acid batteries and its modular design makes it easy to modify the voltage and current of the power supply by changing the connections of the batteries based on the requirement of single-coil, double-coil and triple-coil magnets. The design and primary tests of the battery power supply system will be introduced in this paper (Schillig et al. in IEEE Trans. Appl. Supercond. 10:526, 2000).     

Design of a 60 T Quasi-continuous Magnetic Field System with a Hybrid Capacitor/Rectifier Power Supply

At the Wuhan National High Magnetic Field Center, a 135 MW rectifier power supply is being installed nearby a 11 MJ capacitor bank power supply. By combining the two power supplies, a 60 T / 100 ms quasi-continuous magnetic field can be achieved in a monolithic copper coil magnet with a 22 mm diameter bore. Comsol Multiphysics 3.5a and Matlab 7.11.0 were adopted to verify the performance of the magnet and the hybrid power supply system. Details of the designed magnet, the power supply and the simulation results are presented.     

Magnet-Technology Development at the Dresden High Magnetic Field Laboratory

The Dresden High Magnetic Field Laboratory (HLD) is a user facility which provides scientists with the possibility to perform a broad range of experiments in pulsed magnetic fields. Recent progress in the magnet-technology development at the HLD has led to significant advances in achieving non-destructive pulsed magnetic fields close to the megagauss mark. Using 9.5 MJ dual-coil magnets with 16 mm bore, in 2011 a world-record field of 91.4 T has been achieved. Later 94.2 T have been reached. We report on the magnet design and performance of these magnets as well as on the design for the next generation of dual-coil magnets characterized by interchangeable inner sub-coils and improved control of the axial preload.     

Generation and measurement of multi megagauss fields in inertial magnets

We present here the development of a facility to generate high (multi megagauss) magnetic field of 4 to 5μs rise time, using inertial magnets. The facility includes a low inductance, high current capacitor bank (280 kJ/40 kV) and an inertial magnet, which is a copper disk machined to have a keyhole in it. As the high current from the capacitor bank is discharged through the copper disk, a high magnetic field is produced along its axis, before it is destroyed by the combined effect of the dynamic loading and skin effect. A maximum peak magnetic field of 257 T is realized, when the magnet with 3.6mm inner diameter, 35mm outer diameter and 5mmlength, is powered by the capacitor bank charged to 28 kV (134 kJ). The transient magnetic field is measured using a B dot probe with an error of ±25 T. The probe in most of high field shots (> 200 T) got destroyed before recording the peak field and the trailing edge of the magnetic field. Experimental evidence of enhancement of the probe survival for longer time in copper disks using spatial non-uniform conductivity with 1mm thick SS brazed to the inner wall of the inertial magnet is also reported.     

Fast Capacitor Bank for Pulsed Magnetic-Field Studies

The design of a 20 kV, 60 , ?F, 12-kJ capacitor bank for pulsed magnetic-field studies is reported in detail. In particular, a parallel-plate discharge circuit is described which results in a total bank inductance of 120 nH. Initial experiments with a flux concentrator magnet coil yielded a magnetic field of 250 kG in a volume of 2.41 cm3 at a bank voltage of 14 kV.     

Test and Operation of the WHMFC 12.6 MJ Capacitor Bank Power Supply System

The 12.6 MJ capacitor bank power supply system of the Wuhan National High Magnetic Field Center (WHMFC) at Huazhong University of Science and Technology (HUST) consists of 11 independent 1 MJ modules and 2 independent 0.8 MJ modules; it was tested and put into operation in October 2010. The capacitor bank power supply system connects to 8 measurement cells through three current collectors and four selectors. A number of nondestructive magnets for different bore sizes and peak fields have been energized by this system, including an 83 T dual stage magnet. The results of tests and operation are presented in this paper.     

Milestones and Highlights in the Design and Use of Pulsed Magnets

The development and use of pulsed magnets is reviewed, tracing it back to the beginning 85 years ago: the original work of P. Kapitsa with his great optimism and cheerful acceptance of coil explosions, and the first use of a capacitor bank by T.F. Wall in the same period. Later milestones were the introduction of a new type of strong “micro-composite” wire by S. Foner in 1986, boosting the field level to 68 T, and subsequently the development of coils with optimised internal reinforcement by fibre composites at K.U. Leuven. Recent highlights are the establishment of very large dedicated pulsed field laboratories, notably at Los Alamos (NHMFL) with a flywheel-generator and at Dresden (HLD) with a 50 MJ capacitor bank, both in pursuit of developing a 100 T user magnet. Finally, destructive techniques beyond 100 T are reviewed.     

Developments of Multi-extreme High Field ESR in Kobe

Recent developments of “multi-extreme” high magnetic field electron spin resonance (ESR) in Kobe will be reviewed. Our high magnetic field ESR covers the frequency region between 0.03 and 7 THz and the temperature region between 1.8 and 300 K. With this high magnetic field ESR system we can apply the magnetic field up to 55 T using a Cu-Ag pulsed magnet and a 300 kJ (10 kV) capacitor bank. Under this high magnetic field we can also apply the high pressure up to 1.4 GPa. As we can make the measurement under low temperature, high magnetic field and high pressure simultaneously, we name it as “multi-extreme” ESR. Moreover, in order to gain the sensitivity of our high magnetic field ESR, we have developed a micro-cantilever ESR system using a torque method, which enables the ESR measurement of micrometer size single crystal at low temperature. At the moment we are in the process of extending the magnetic field region of micro-cantilever ESR. Recently we have succeeded in making the measurement up to 369 GHz and the achieved sensitivity is about 10¹⁰ spins/G, which is much higher than that using the conventional transmission method. Finally our development of magnetization detected ESR using SQUID magnetometer (SQUID ESR) will be also presented.     

The performance of new, redesigned ignitron tubes in axial magneticfields

The test results from two special ignitron tubes exposed to axial magnetic fields are described. The experiments were made using a capacitor bank with 2.56 mF total capacitance and 128 kJ maximum energy at 10 kV. To study the effects of axial magnetic fields on the switching characteristics, including the self-breakdown voltage of the tubes, the test specimens were mounted inside four high-power, water-cooled electromagnets. The highest magnetic field which can be generated by this arrangement is 0.7 T for conduction tests and 1.0 T for high-voltage tests. The test results include voltage and current measurements along with optical diagnostics performed on a special tube which provides optical access to the discharge volume. The ignitron tubes tested were a small, glass-walled tube and one experimental size-D tube with stainless steel walls. Particular attention is given to the failure of the glass tube and the change in holdoff ability with and without magnetic field for both the metal and glass ignitrons     

Irreversible Magnetic Properties of Ceramic Hgba2Ca2Cu3O8 at Very High Pulsed Magnetic Fields

The magnetic properties of ceramic HgBa₂Ca₂Cu₃O₈ have been investigated using pulsed magnetic fields up to 50 tesla. The irreversibility line H _irr (T) and the magnetic critical current J _c,m (H,T) have been extracted from the high field hysteresis loops. Irreversibility fields exceed available fields at temperatures below 15 K. The magnetic critical current J _c,m is strongly dependent on the granular structure of the ceramic superconductor. This is reflected in the moderate value of the critical current density and its significant field dependence.     

Evaluation and measurement of magnetic field exposure at a typical high-voltage substation and its power lines

This study presents a survey of magnetic field measurements including those resulting from 380/154 kV power substations, which play a vital role in human body biological studies. The survey was carried out in the main power substation of Antalya, Turkey, located at the suburban region of the city, under actual loads. The paper also presents the actual magnetic field strength measured near the 380/154 kV substation and power transmission lines (380 and 154 kV) connecting to the substation. Since most part of these lines pass through a residential area, they have been included in the study, and the actual magnetic field variation around them has been investigated by comparative analysis of measured data. For the occupants working at substations, occupational exposure has been analysed with actual magnetic fields at operating locations. Induced internal electric fields and current densities in the occupants' body due to exposure to external magnetic fields produced by a conventional 380/154 kV power substation have been investigated.     

Design of Non-destructive Pulsed Magnets at the HLD

In this paper, we consider several aspects of the design and construction of non-destructive pulsed magnets on the basis of work which is under way at the Dresden High Magnetic Field Laboratory (HLD). A number of pulsed magnets including 60 T/1.5 MJ and 70 T/8.5 MJ mono-coils have been successfully tested and are ready for operation. Some perspectives of the pulsed-magnet development are discussed. A way to achieve 100 T in non-destructive pulsed magnets and the role of various factors and challenges are addressed. Results of the finite element analysis (FEA) of the designed coils are presented.      

25kV/2A谐振式恒流充电电源

为 1MJ 电容器储能系统研制了一台输出电压 25kV,输出电流2A的恒流充电电源。该电源采用零电流切换非连续全波谐振原理。串联 LC 谐振电路由接成全桥形式的4只大功率 IGBT 驱动,谐振频率固定为 80kHz,开关工作频率 30-65kHz 可调。谐振产生的非连续正弦形电流经匝比为 1:50 的高压变压器升压至 25kV,经快恢复高压二极管串组成的全桥电路整形为一系列非连续的半正弦状电流脉冲,给 10000μF 高压电容器组充电。最终充电电压和充电电流的大小由微处理器控制,前者正比于充电电流脉冲的总个数,后者则正比于开关工作频率。     

Research in High Magnetic Fields: The Installation at the University of Nijmegen

For research in the highest continuous and pulsed magnetic fields large, complex and powerful installations are needed. This paper describes the new 20 MW installation for continuous high magnetic fields that has been built at the University of Nijmegen. The ultra-low ripple power converter provides the capability to perform experiments up to 33 T with resistive magnets (up to 40 T with the hybrid magnet system under construction) and will be of great value for investigations in physics, chemistry and biology at the forefront of fundamental and applied research. Typically during experiments, the magnetic field is slowly varied or held constant for a period lasting from a few minutes to an hour. The cooling installation is designed to allow uninterrupted operation at maximum power for 3 hours, and when the magnetic field is being swept between zero and full field the cooling plant does not pose limits to the operation. When much higher fields are required, there is the option to go to pulsed magnetic fields with duration in the tens of milliseconds.     

Microminiature Hall Probes for Applications at Pulsed Magnetic Fields up to 87 Tesla

Microminiature Hall probes (MHP) may be used as magnetic field transducers, with virtually no change of sensitivity with temperature, for applications at room and cryogenic temperatures. The probes have a nominal active sensing area from 90×90 μm down to 20×20 μm and are based on Sn-doped n-InSb/i-GaAs MBE-grown heterostructures. MHPs were intensively tested in static (up to 14 T) and pulsed magnetic fields and shown to be appropriate for various applications in the temperature range 2–300 K and in pulsed magnetic fields up to 87 T. The latest version of these probes, with overall cross-section thickness-width dimensions of 150×750 μm, are the smallest encapsulated Hall probes currently available and can be placed in areas not previously accessible to commercial packaged or unpackaged sensors.