High Magnetic Field Facility Research Articles

Concept Design of the Control System for the Upgrading Pulsed High Magnetic Field Facility

Concept Design of the Control System for the Upgrading Pulsed High Magnetic Field Facility

The relationship between deformation mechanisms and mechanical properties in nanocrystalline Cu/Ag-bilayer alloy

The nanocrystalline metallic bilayer structure can effectively enhance the strength of Cu alloy while maintaining excellent electrical conductivity. Based on the microstructure evolution of Cu/Ag alloy observed by transmission electron microscope (TEM), molecular dynamics (MD) simulations of Cu/Ag alloy with nanocrystalline metallic bilayer structure were established. The mechanical properties and deformation mechanisms of nanocrystalline Cu/Ag-bilayer alloys were investigated at different temperatures. A mixed Hall-Petch (H-P) relationship was observed between the ultimate stress and the increased layer thickness. In this paper, the deformation mechanism changes from dislocation accumulation at the Cu-Ag interface to dislocation through the Cu-Ag interface. In addition, the data analysis results of elastic modulus showed an approximately linear decrease trend with increasing temperature, and the deformation mechanism shifted from dislocation motion to a combination of dislocation motion and grain boundaries (GBs) diffusion. These findings provide guidance for the design of high magnetic field facility (HMFF) water-cooled magnets and very large-scale integration (VLSI) lead frames.

The Present Status and Progress of the CHMFL 40 T Hybrid Magnet

The development of new high magnetic field facilities in the Chinese High Magnet Field Laboratory (CHMFL) will soon be completed according to the present situation. For the construction of the 40 T hybrid magnet, which will be the highest magnetic field facility in China, great progress has been achieved so far, for example, the engineering design of the resistive insert composed of six Florida-Bitter-type coils has been completed and part of the Bitter disks has been punched in Shanghai, and significant R & D progress on the design and manufacture of the superconducting outsert has been made, and the other main components of the superconducting outsert, such as?cryostat, 80 K thermal shield, vacuum pumping units, busbars, a pair of 16 kA HTS leads, overpressure protection device and so on, have been manufactured. The recent development of the CHMFL 40 T hybrid magnet is introduced in detail.

Thermally stable quantum Hall effect in a gated ferroelectric-graphene heterostructure

The quantum Hall effect is widely used for the investigation of fundamental phenomena, ranging from topological phases to composite fermions. In particular, the discovery of a room temperature resistance quantum in graphene is significant for compact resistance standards that can operate above cryogenic temperatures. However, this requires large magnetic fields that are accessible only in a few high magnetic field facilities. Here, we report on the quantum Hall effect in graphene encapsulated by the ferroelectric insulator CuInP2S6. Electrostatic gating of the graphene channel enables the Fermi energy to be tuned so that electrons in the localized states of the insulator are in equilibrium with the current-carrying, delocalized states of graphene. Due to the presence of strongly bound states in this hybrid system, a quantum Hall plateau is observed over a wide range of temperatures in relatively modest magnetic fields.

Superconducting Magnetic Energy Storage for Pulsed Power Magnet Applications

As part of the exploration of energy efficient and versatile power sources for future pulsed field magnets of the National High Magnetic Field Laboratory-Pulsed Field Facility (NHMFL-PFF) at Los Alamos National Laboratory (LANL), the feasibility of superconducting magnetic energy storage (SMES) for pulsed-field magnets and other pulsed power loads is examined. Basic SMES parameters needed to power one of the coil groups of the large 100 T magnet were determined. A circuit topology for the power transfer between the SMES and the magnet was devised, and the basic performance of the topology was simulated to reproduce the pulse shape currently used in the 100 T magnet. The Finite element analysis (FEA) method was used to calculate the magnetic field distribution of several preferred coil configurations for effective SMES design. Magnetic field distribution and the field dependent critical current density of commercial high temperature superconducting (HTS) tapes were used to understand the conductor/cable requirements for the SMES.

Realisation of the reconfigurable pulsed high magnetic field facility and its scientific application at Wuhan National Pulsed High Magnetic Field Centre

AbstractTo generate arbitrary shape magnetic field waveforms for advanced scientific research, a reconfigurable pulsed high magnetic field facility (PHMFF) was developed at Wuhan National Pulsed High Magnetic Field Centre (WHMFC). First, the basic elements of PHMFF are introduced, and a ternary physical model composed of energy storage unit, magnet, transmission circuits and other auxiliary units is summarised to describe various magnetic field systems. Second, in order to realise the reconfiguration of magnetic field systems based on detailed elements, the control system with the ability of dynamic construction and control sequence reconfiguration is designed. On this basis, the PHMFF has been realised and various magnetic field systems are constructed to produce arbitrary shape magnetic field waveforms, such as half‐sine, ultra‐high, flat‐top and repetitive field pulses, which not only enhances the capability and efficiency of PHMFF, but also makes more scientific research possible in pulsed magnetic fields. So far, a peak magnetic field of 94.8 T, a flat‐top magnetic field of 64 T/10 ms and a repetitive magnetic field waveform of 20 T/60 Hz have been achieved, and some experiments and studies on the physical properties of materials have been carried out at WHMFC.

Analysis on the operation parameters of cooling water system in 45.22T hybrid magnet experiment

Chinese Steady High Magnetic Field Facility produced a steady field of 45.22 T by its hybrid magnet, which was the highest steady magnetic field in the world. The cooling water system was used to maintain the cool temperature environment for the insert resistive magnet coils and it was completed the upgrading in the year 2020 after ensuring the 40 T hybrid magnet experiment. The performance parameters and characteristics of the transformed cooling water system has been introduced. The variation trend of the magnet circulating water flow rate and the deionized water quality in 45.22 T hybrid magnet experiment has been analyzed, and also the heat exchange effect between the primary chilled water circuits and the secondary deionized water circuits were calculated. Some problems in cooling water system operation in this time hybrid magnet experiment have been pointed out.

The role of copper in the formation of the Nb3Sn superconducting phase

Nb3Sn has been widely used in high magnetic field facilities due to its excellent superconducting properties. Moreover, copper has become an indispensable constituent element in the fabrication of Nb3Sn superconductors. However, the role of copper in the formation of the Nb3Sn phase is still not thoroughly understood. In this work, Nb–Sn–Cu ternary samples with different molar ratios of copper were prepared by sintering elemental Nb, Sn and Cu mixed powders, and the effect of copper on the formation of the Nb3Sn phase was systematically investigated. It was found that the addition of copper had a significant effect on the formation of Nb3Sn. When the amount of added copper was small, the formation of the Nb3Sn phase was efficiently promoted with the aid of the liquid phase, and a high-purity sample of Nb3Sn could be formed by the transition from the Nb–Sn binary phases. However, at the same time, the bulk samples with a low ratio of copper possessed poor compactness due to the pressure build-up and tin burst generated by the liquid phase during heat treatment. With increasing copper content, the promotion effect became relatively weaker. More high melting temperature Cu–Sn phases were formed, and Nb3Sn was gradually formed by solid-state diffusion between Nb and the Cu–Sn matrix. Finally, it was found that the sample of Nb:Sn:Cu = 3:1:3 (mol. %) with a grain size of 70–120 nm possessed the highest critical current density due to its high phase purity and fine grain size of Nb3Sn.

Design and Study of a Series Active Filter for the 10MW-Level High Power and High Stability DC Power Supply

The output power of high stability dc power supply system, which drives the water-cooled magnet of Steady High Magnetic Field Facility (SHMFF), can reach up to tens of megawatt, so that the circuit usually adopts the realization scheme of Silicon-controlled rectifier plus LC filter. For the improvement of magnet current ripple, a novel series active filter (SAPF) is proposed, which adopts high-frequency switching technology and uses a switching power supply instead of a transistor or transformer in the traditional scheme in series at the output of the main power supply. The novel scheme has advantages of lower control complexity and less power loss, and thus higher engineering feasibility. In this paper, the system topology structure, operating principle and control policy are presented at first. Then the key part of the design is discussed, that is, how to accurately extract the output voltage ripple of the main power supply without delay. At last, a small prototype is made to verify the feasibility of the scheme.

Reliability Analysis of a Pulsed High Magnetic Field Facility at WHMFC

To accurately evaluate the reliability of Pulsed High Magnetic Field Facility (PHMFF) at the Wuhan National Pulsed High Magnetic Field Centre (WHMFC), a reliability analysis method based on a Markov chain is introduced in this paper. Because PHMFF is developed to generate a pulsed high magnetic field for scientific experiments by dynamically constructing diversified magnetic field systems, the reliability of PHMFF is in fact determined by the actual operating magnetic field system. Considering that all magnetic field systems are composed of pulsed power modules, magnets, control modules and experimental test systems, in this paper, the reliability of these critical modules is first discussed. In the analysis of modules, the failure mode and effect analysis (FMEA) method is used to determine the main failure modes, and then a Markov chain is established to analyze and calculate the reliability of the modules. Finally, based on the reliability of critical modules, the reliability of two typical magnetic field systems was estimated according to the reliability block diagram. The calculation results show that the reliability of all modules is above 95%, and although in complex magnetic field systems, the reliability still meets the experimental requirements.

Test of 10 kA-Class HTS WISE Conductor in High Magnetic Field Facility

Test of 10 kA-Class HTS WISE Conductor in High Magnetic Field Facility

Transverse Stress Applying Technology for High-Current Superconducting Conductors Testing

High-current superconducting conductors are widely used in fusion magnets, high energy accelerators and high magnetic field facilities. It's urgent to carry out experimental research on DC performance of new conductors to meet the development needs of these magnets. A new test facility with maximum background magnetic field of 6 T and maximum sample current of 30 kA is developed. For the purpose of preventing the sample conductors from premature quenches due to mechanical disturbance under the magnetic field, it is necessary to apply a certain transverse stress to the sample through sample support. In this paper, two different kinds of transverse stress applying technologies, active method and passive method, are developed. The general design of these two kinds of sample supports, the influence of cooling and powering process on sample transverse stress with active sample support, the assembly gap analysis of passive sample support are described in detail. The used sample supports respectively for Nb-Ti Rutherford cable, MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cable-in-conduit Conductors (CICC) and Bi-2212 sub-cable testing are presented. Comprehensively considering the stability margin of conductor sample and the influence of transverse stress on performance of the sample, the selection basis of transverse stress applying at room temperature is also summarized.

Crystal growth and magnetic properties of quantum spin liquid candidate KErTe2 * *Project supported by the National Key Research and Development Program of China (Grant Nos. 2017YFA0302904 and 2016YFA0300504), the National Natural Science Foundation of China (Grant Nos. U1932215 and 11774419), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB33010100), and Postdoctoral Science Foundation of

Recently rare-earth chalcogenides have been revealed as a family of quantum spin liquid (QSL) candidates hosting a large number of members. In this paper we report the crystal growth and magnetic measurements of KErTe2, which is the first member of telluride in the family. Compared to its cousins of oxides, sulfides and selenides, KErTe2 retains the high symmetry of and Er3+ ions still sit on a perfect triangular lattice. The separation between adjacent magnetic layers is expectedly increased, which further enhances the two dimensionality of the spin system. Specific heat and magnetic susceptibility measurements on KErTe2 single crystals reveal no structural and magnetic transition down to 1.8 K. Most interestingly, the absorption spectrum shows that the charge gap of KErTe2 is roughly 0.93±0.35 eV, which is the smallest among all the reported members in the family. This immediately invokes the interest towards metallization even superconductivity using the compound.

Effective model for rare-earth Kitaev materials and its classical Monte Carlo simulation* *Project supported by the National Key Research and Development Program of China (Grant Nos. 2017YFA0302904 and 2016YFA0300504), the National Natural Science Foundation of China (Grant Nos. U1932215, 11774419, 11574392, and 11974421), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB33010100), the Fundamental Research

Recently, the family of rare-earth chalcohalides were proposed as candidate compounds to realize the Kitaev spin liquid (KSL) [Chin. Phys. Lett. 38 047502 (2021)]. In the present work, we firstly propose an effective spin Hamiltonian consistent with the symmetry group of the crystal structure. Then we apply classical Monte Carlo simulations to preliminarily study the model and establish a phase diagram. When approaching to the low temperature limit, several magnetic long range orders are observed, including the stripe, the zigzag, the antiferromagnetic (AFM), the ferromagnetic (FM), the incommensurate spiral (IS), the multi- Q , and the 120° ones. We further calculate the thermodynamic properties of the system, such as the temperature dependence of the magnetic susceptibility and the heat capacity. The ordering transition temperatures reflected in the two quantities agree with each other. For most interaction regions, the system is magnetically more susceptible in the ab-plane than in the c-direction. The stripe phase is special, where the susceptibility is fairly isotropic in the whole temperature region. These features provide useful information to understand the magnetic properties of related materials.

High action gas switches.

High action, high voltage closing switches are the key components of pulsed power systems based on high energy capacitor banks, primarily used for high power lasers, electromagnetic accelerators, high pulsed magnetic field facilities, crushing materials, and electromagnetic compatibility tests. There are several options for closing switches, including ignitrons, vacuum switches, pseudo-spark switches, solid-state switches, and high pressure gas switches (spark gaps). Spark switches are currently the most used due to their relatively simple design, reliability, and ease of maintenance and repair. The main disadvantage of spark gaps is a limited lifetime, which is directly or indirectly related to the erosion of the electrodes. To prevent erosion of the electrodes, multichannel switches and switches with movement of the discharge channel were proposed. In this Review, both types of switches are considered.

Diffuser design and experimental research of a large-scale chilled water storage system

ABSTRACT Naturally stratified technology is the most economical and effective method in chilled water storage technique and its core is the design of water diffuser. The better the performance of diffuser and the higher the efficiency of chilled water storage is. With the development of science and technology, many large-scale scientific facilities come into being, most of which need to be equipped with large-scale water storage system and run in the extreme operating conditions. If these water storage systems adopt the naturally stratified technology, it is necessary to optimize the design of the diffuser to achieve an ideal storage efficiency, which can not only save energy but also guarantee the operation of the facilities. The water storage system of Steady High Magnetic Field Facilities is one of the representative water storage systems with large flow rate and large temperature difference. By establishing the discrete equation of heat conduction, the results show that the convection doping related to the design of the diffuser is the primary factor affecting the thickness of thermocline. It was also verified by experiments that the large-scale chilled water storage device with well-designed octagonal diffuser and uniform flow orifice can achieve ideal storage efficiency under the operation conditions of large flow rate and large temperature difference.

A pulsed high magnetic field facility for electric polarization measurements

&lt;sec&gt;Multiferroic materials, which exhibit the coexistence of ferromagnetic, ferroelectric, or ferroelastic orders, are of particular interest for not only fundamental physics but also potential applications. An important physical property of multiferroic materials, especially those with magnetically driven ferroelectricity, is known as a strong magnetoelectric coupling between the magnetic order and the ferroelectric order. The external magnetic fields can directly interact with spins or magnetic moments of the materials and lead the spontaneous ferroelectricity to be suppressed, and in some cases result in field-induced ferroelectricity in a higher field. Depending on the exchange interactions, these ferroelectric phase transitions may take place in a critical magnetic field as high as several tens of tesla. The standard electric-polarization measurement based on a commercial PPMS system is limited by the strength of the static field consequently. As an extremely experimental condition, pulsed magnetic fields can be used to reveal new physical phenomena in multiferroic materials. Due to the short pulse duration and the effect of eddy current, this measurement technique under pulsed high magnetic fields is still a challenge to date although a few laboratories have developed it in recent years.&lt;/sec&gt;&lt;sec&gt;Wuhan National High Magnetic Field Center (WHMFC) of China is a newly built pulsed-field laboratory. This experimental station is equipped with the many measuring instruments such as for measuring electric transport, magnetization, electron spin resonance, magneto-optics, and high pressure, which were established after the national assessment at the end of 2014. Recently, using a pyroelectric technique we successfully constructed an electric-polarization measurement system based on the large-scaled facility at the WHMFC. The nondestructive magnet driven by discharging a 1.25 MJ capacitor bank can generate a pulsed field up to 60 T. By tuning the charging energy and voltages, the pulse duration time can be modulated from 4.3 ms to 10.8 ms. A helium-3 cryogenic system equipped on this facility can achieve a lowest temperature down to 0.5 K. A high-precision rotation probe is designed and fabricated with angle varying from –5° to 185° for an angular-dependent study. The pyroelectric current is detected by a shunt resistor of 10 kΩ and the electric polarization is derived by integrating the pyroelectric current over the time. The resulting data have a good accuracy and quality which are helpful in detecting weak ferroelectric phase transitions induced by pulsed fields with a fast field sweep rate. In this paper, we introduce this measurement system in detail including the method, principle and its advantages in comparison with those in static fields. Recent study and progress of magnetoelectric multiferroic materials under high magnetic fields are also reported.&lt;/sec&gt;

Energy Efficient Control of Parallel Variable-Frequency Pumps in Magnetic Water-Cooling System

Abstract This paper presents an optimal control method for the prediction of parallel centrifugal variable frequency pump performance in any conditions to maximize the total efficiency of the pump system, thereby minimizing energy consumption. First, a theoretical model of parallel water pumping set was established, after which the shaft power model was setup specifically for the off-rating conditions. By combining the typical polynomial fitting method of the efficiency and the shaft power model we brought up, a new optimized control method was proposed. Using this method, the complex optimization task was solved with the optimal control of the operating number selection and speed ratios for parallel variable speed pumps based on the decision-making. The proposed method was subsequently applied to the pumping set of the water-cooling system in High Magnetic Field Facility. The practical testing results of the proposed method showed its superiority over both the primitive and the previous optimal methods, by considerably lowering the power consumption and accurately calculating the performance parameters in any conditions. The method has universality and simplicity for online implementation, which provides a reference for the control methods of parallel centrifugal pumps in variable flow systems with a differential pressure control strategy.

Numerical simulation of spark channel dynamics in railgun switches

Discharge of a capacitive storage on a load with unipolar pulse is employed for pumping of powerful lasers and also for feeding of electromagnetic launchers, and pulsed high magnetic field facilities. Spark gaps are often used to commute energy on a load. In some applications unipolar pulse is not feasible and oscillatory regime (underdamped sinusoidal) has to be realized for the capacitor bank discharge. Spark gaps, developed for unipolar discharge, cannot directly be employed in under-damped (oscillatory) regime, because at current transition through zero the arc channel could stop motion and ignite at initial place on the following half period. Two main objectives were pursued in this work: 1. develop and test simulation model of a the spark channel motion in linear rail geometry for the oscillatory regime of capacitor bank discharge; 2. Investigate arc motion and electrodes heating depending on the current and charge transfer in wide operation range.

Prospect for a 60 GHz multicharged ECR ion source.

The conceptual design of a fourth generation hybrid electron cyclotron resonance (ECR) ion source operated at 60 GHz is proposed. The axial magnetic mirror is generated with a set of three Nb3Sn coils, while the hexapole is made with room temperature (RT) copper coils. The motivations for such a hybrid development are to study further the ECR plasma physics and the intense multicharged ion beams' production and transport at a time when a superconducting (SC) hexapole appears unrealistic at 60 GHz. The RT hexapole coil designed is an evolution of the polyhelix technology developed at the French High Magnetic Field Facility. The axial magnetic field is generated by means of 3 Nb3Sn SC coils operated with a maximum current density of 350 A/mm2 and a maximum coil load line factor of 81%. The ECR plasma chamber resulting from the design features an inner radius of 94 mm and a length of 500 mm. The radial magnetic intensity is 4.1 T at the wall. Characteristic axial mirror peaks are 8 and 4.5 T, with 1.45 T minimum in between.