Pulsed Magnetic Field Research Articles

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.

Experimental study of the mechanism of prepulse current on Z-pinch plasma using Faraday rotation diagnosis.

The prepulse current is an effective way to optimize the load structure and improve the implosion quality of the Z-pinch plasma. Investigating the strong coupling between the preconditioned plasma and pulsed magnetic field is essential for the design and improvement of prepulse current. In this study, the mechanism of the prepulse current on the Z-pinch plasma was revealed by determining the two-dimensional magnetic field distribution of preconditioned and nonpreconditioned single-wire Z-pinch plasma with a high-sensitivity Faraday rotation diagnosis. When the wire was nonpreconditioned, the current path was consistent with the plasma boundary. When the wire was preconditioned, the distributions of current and mass density presented good imploding axial uniformity, and the imploding speed of the current shell was higher than that of the mass shell. In addition, the mechanism of the prepulse current suppressing the magneto-Rayleigh-Taylor instability was revealed, which formed a sharp density profile of the imploding plasma and slowed the shock wave driven by the magnetic pressure. This discovery is essential and instructive for the design of preconditioned wire-array Z-pinch experiments.

Simultaneous measurement of specific heat and thermal conductivity in pulsed magnetic fields

We report an experimental setup for simultaneously measuring specific heat and thermal conductivity in feedback-controlled pulsed magnetic fields of 50ms duration at cryogenic temperatures. A stabilized magnetic field pulse obtained by the feedback control, which dramatically improves the thermal stability of the setup and sample, is used in combination with the flash method to obtain absolute values of thermal properties up to 37.2T in the 22-16K temperature range. We describe the experimental setup and demonstrate the performance of the present method with measurements on single-crystal samples of the geometrically frustrated quantum spin-dimer system SrCu2(BO3)2. Our proof-of-principle results show excellent agreement with data taken using a standard steady-state method, confirming the validity and convenience of the present approach.

Examination of Thickness Evaluation of Steel Plate Using DC Bias Magnetic Field by 3-D FEM Analysis Considering Minor Loop Magnetic Characteristics

Thickness evaluation of steel plates and large-diameter steel pipes in various plant structures is considered important for plant safety. In this paper, an electromagnetic inspection method that can evaluate this thickness using a pulsed magnetic field is investigated. When a steady square-wave pulse magnetic field with DC bias is applied from the surface of the steel plate, the relationship between the leakage flux on the steel plate and the plate thickness is investigated. The inspection principle is evaluated by electromagnetic field analysis considering eddy current and minor loop magnetic property of the steel plate and verification experiments. In addition, it is also confirmed that the calculation results considering the hysteresis curve in the steel plate are more useful than those considering only the initial magnetization curve.

Imaging and Mode Content Analysis of the Wave Beam From a Short-Pulse High-Power Gyrotron Using the Millimeter-Wave-Induced Gas Breakdown Initiated by a Metal–Dielectric Screen

The wave beam of a sub-terahertz (THz) gyrotron with a pulsed magnetic field was imaged in a single pulse using a microwave-induced gas breakdown initiated by a metal–dielectric (MD) screen. Images of sub-THz beams, which were recorded at the output of a quasi-optical mode converter, were compared with data obtained by numerical simulation of propagation and transformation of the wave beam from the gyrotron. The analysis of the waveguide mode content in the gyrotron was done. Based on experimental and simulation data, it was shown that the distortion of the sub-THz wave beam is caused by the deformation of the Teflon window at the gyrotron output. Based on the results of the study, the gyrotron was modified, and the quality of its wave beam was improved.

Molecular Mobility in Aqueous Systems of Primary Aliphatic Amino Alcohols

Self-diffusion coefficients (SDCs) of 3-amino-1-propanol (3AP), monoethanolamine (MEA), and water molecules are measured via 1H NMR using a pulsed magnetic field gradient and a stimulated echo sequence throughout a range of concentrations at temperatures of 293–333 K. It is found that the studied amino alcohols and water form a nearly tetrahedral three-dimensional network of hydrogen bonds between the molecules of the system. It is shown that this network is stable in the liquid phase, despite the mobility of the molecules that constitute the network. The mechanism of molecular mobility is studied. It is shown that the SDC of the molecules of the above amino alcohols and their aqueous solutions depends linearly on temperature. It is concluded that the molecular mobility mechanism has a pattern of activation. To verify this hypothesis and interpret the mechanism, the energies of activation are calculated for the self-diffusion of all the studied molecules in water–amino alcohol systems. The determined energies of activation for the mobility of amino alcohol molecules in aqueous systems have similar values, suggesting they undergo interactions that produce either mixed water–amino alcohol spatial networks or amino alcohol–water molecule associations in the liquid phase.

Effect of Wide-Spectrum Pulsed Magnetic Field on Solidification Structure of Pure Al at Constant Flow Velocity

The electromagnetic force generated by a pulsed magnetic field within a metal melt leads to changes in the internal temperature and flow fields of the molten metal, thus improving the solidification of the metal structure. Using the combination of a solidification test, experimental simulation and theoretical analysis, this study simulated the distribution of both electromagnetic force and the flow field in a metal melt under wide-spectrum pulse conditions, and studied the influence of a wide-spectrum pulsed magnetic field on the solidification structure of pure aluminium with a constant flow velocity. The results of this study show that the structural refinement of the solidification of pure aluminium can be different, in spite of equal flow velocity. Furthermore, this study shows that an applied time-averaged electromagnetic force causes crystal nuclei to pass through the solid–liquid interface boundary layer and promotes the growth of crystal grains. These grains flowed with the melt flow field to achieve both refinement and homogenization of the solidified structure.

Modulating the magnetization dynamic properties of zigzag magnetic nanowires by the four-fold magnetic anisotropy

The magnetization dynamic properties of zigzag magnetic nanowires with varied fourfold magnetic anisotropy, which modulated novel microwave responses without any external magnetic field, were investigated. The microwave properties associated with two different remanent magnetic states were found to be highly sensitive to fourfold magnetic anisotropy. A large frequency shift between the two remanent magnetic states was observed when fourfold magnetic anisotropy was added at a particular direction. The results are valuable for the realization of bias field-free microwave applications. In addition, the microwave properties demonstrated by two different remanent magnetic states could be transformed using a nanosecond pulse magnetic field, and fast switching in the system could be achieved with the fourfold magnetic anisotropy.

Microstructure evolution, diffusion behavior, and mechanical properties of a Cu/AlCoCrFeNi2.1 composite under pulsed magnetic field

A Cu/AlCoCrFeNi2.1 composite was fabricated via solid-liquid method. In order to acquire the good interface bonding, the pulsed magnetic field (PMF) treatment was applied during the preparation of the Cu/AlCoCrFeNi2.1 composite. The effects of different processes and parameters, including pulse frequency on the interface microstructure, element distribution, diffusion thickness, and mechanical properties of the composite were investigated. The results demonstrated that PMF treatment effectively decreased the diffusion layer thickness of the composite, and improved mechanical properties of the Cu side. The diffusion thickness of the composite reduced from 31.22 μm to 6.20 μm after applying PMF. The action mechanism of PMF during preparation was revealed. The ultimate tensile strength, yield strength, and elongation of the Cu/AlCoCrFeNi2.1 composite via PMF were 192.6 MPa, 121.7 MPa, and 43.8%, respectively, which were higher than that of the composite without PMF. The maximum shear strengths of the composites with and without PFM were 120.2 MP and 137.4 MPa, respectively. When the pulse frequency was 2 Hz, the macro-segregation was eliminated to form the high-quality interface. This work paves a way for the performance improvement and complex parts preparation of layer composite by using PMF.

Predicting the effect of different magnetic fields on the solute segregation during direct chill casting of large-size magnesium alloy slab

PurposeThe purpose of this paper is to reveal the solute segregation behavior in the molten and solidified regions during direct chill (DC) casting of a large-size magnesium alloy slab under no magnetic field (NMF), harmonic magnetic field (HMF), pulsed magnetic field (PMF) and two types of out-of-phase pulsed magnetic field (OPMF).Design/methodology/approachA 3-D multiphysical coupling mathematical model is used to evaluate the corresponding physical fields. The coupling issue is addressed using the method of separating step and result inheritance.FindingsThe results suggest that the solute deficiency tends to occur in the central part, while the solute-enriched area appears near the fillet in the molten and solidified regions. Applying magnetic field could greatly homogenize the solute field in the two-phase region. The variance of relative segregation level in the solidified cross-section under NMF is 38.1%, while it is 21.9%, 18.6%, 16.4% and 12.4% under OPMF2 (the current phase in the upper coil is ahead of the lower coil), HMF, PMF and OPMF1 (the current phase in the upper coil lags behind the lower coil), respectively, indicating that OPMF1 is more effective to reduce the macrosegregation level.Originality/valueThere are few reports on the solute segregation degree in rectangle slab under magnetic field, especially for magnesium alloy slab. This paper can act a reference to make clear the solute transport behavior and help reduce the macrosegregation level during DC casting.

Cognitive improvement via a modulated rhythmic pulsed magnetic field in D-galactose-induced accelerated aging mice

Rhythmic physical stimulations have emerged as effective noninvasive intervention strategies in the treatment of pathological cognitive deficits. Transcranial magnetic stimulation (TMS) can regulate neural firing and improve the learning and memory abilities of rodents or patients with cognitive deterioration. However, the effects of elaborate magnetic stimulation with low intensity during aging or other neurological disordering processes on cognitive decline remain unclear. In this study, we developed an elaborate modulated pulsed magnetic field (PMF) stimulation with a complex pattern in the theta repeated frequency and gamma carrier frequency and then determined the effects of this rhythmic PMF on the cognitive function of accelerated aging mice established by chronic subcutaneous injection of D-galactose (D-gal). The results of the Morris water maze (MWM) test showed that mice treated with modulated PMF displayed shorter swimming distance and latency time in the spatial exploration acquisition trial and exhibited a significant preference in the target presumptive platform area in the probe trial, all of which indicated the enhancement in spatial learning and memory abilities upon PMF stimulation of the accelerated aging mice. The novel object recognition (NOR) test results showed a similar tendency as the MWM results although without statistical significance. Further determination of histological structures demonstrated that the cognitive function-related hippocampal CA3 neurons degenerated upon D-gal injection, which could also be partially rescued by PMF application. In comparison with the high-intensity TMS approach, low-intensity magnetic stimulation could be much safer and allow deeper penetration without adverse effects such as seizure. In summary, modulated PMF, even with low intensity, could effectively improve rodent cognitive functions impaired by D-gal-induced accelerated aging, which might provide a new safe therapeutic strategy for cognitive deficits as well as other neurological disorders.

Field-induced spin level crossings within a quasi- XY antiferromagnetic state in Ba2FeSi2O7

We present a high-field study of the strongly anisotropic easy-plane square lattice $S=2$ quantum magnet ${\mathrm{Ba}}_{2}{\mathrm{FeSi}}_{2}{\mathrm{O}}_{7}$. This compound is a rare high-spin antiferromagnetic system with very strong easy-plane anisotropy, such that the interplay between spin level crossings and antiferromagnetic order can be studied. We observe a magnetic field-induced spin level crossing occurring within an ordered state. This spin level crossing appears to preserve the magnetic symmetry while producing a nonmonotonic dependence of the order parameter magnitude. The resulting temperature--magnetic field phase diagram exhibits two dome-shaped regions of magnetic order overlapping around 30 T. The ground state of the lower-field dome is predominantly a linear combination of $|{S}^{z}=0\ensuremath{\rangle}$ and $|{S}^{z}=1\ensuremath{\rangle}$ states, while the ground state of the higher-field dome can be approximated by a linear combination of $|{S}^{z}=1\ensuremath{\rangle}$ and $|{S}^{z}=2\ensuremath{\rangle}$ states. At 30 T, where the spin levels cross, the magnetization exhibits a slanted plateau, the magnetocaloric effect shows a broad hump, and the electric polarization shows a weak slope change. We determined the detailed magnetic phase boundaries and the spin level crossings using measurements of magnetization, electric polarization, and the magnetocaloric effect in pulsed magnetic fields to 60 T. We calculate these properties using a mean-field theory based on direct products of SU(5) coherent states and find good agreement. Finally, we measure and calculate the magnetically induced electric polarization that reflects magnetic ordering and spin level crossings. This multiferroic behavior provides another avenue for detecting phase boundaries and symmetry changes.

Analysis and design of in-vessel magnetic compression coil system for HFRC

A field-reversed configuration (FRC) experiment facility HUST-FRC (HFRC) is being built at Huazhong University of Science and Technology, where the magnetic compression of FRC will be investigated. To generate a pulsed compression magnetic field, a compression coil system is under development, consisting of in-vessel compression coils, a pulsed power supply, and feedthroughs. Energized by the pulsed power supply, a large current peaking ∼110 kA within 50 μs is transferred to in-vessel compression coils across the feedthroughs. This article presents the analysis and design of the compression coil system. At first, field ripple optimizations are performed to reduce the axial and toroidal ripples within 5%, resulting in an optimized coil arrangement and an improved coil conductor structure. In addition, the power supply circuits are quite complex due to the strong electromagnetic couplings among the coils and between each coil and the metal chamber wall. To rapidly and accurately design the electrical parameters of the pulsed power supply for achieving the target coil currents, a decoupled optimization method based on a circuit-electromagnetic model and a decoupled equivalent circuit model is proposed. The errors of the coil currents and the magnetic field are within 1%. Lastly, a feedthrough design and an optimized feeder scheme are proposed to achieve the structural stability of the feedthroughs since they are subjected to large electromagnetic forces.

Development of a phased array flexible Rayleigh-wave electromagnetic acoustic transducer for pipe inspection

In this paper, a novel Phased Array fully Flexible Rayleigh-wave EMAT (PAFR-EMAT) suitable for inspection of curved surface based on flexible coil bias field magnet EMAT is proposed. The PAFR-EMAT consists of a flexible racetrack coil generating long pulsed bias magnetic field instead of the conventional permanent magnets, and flexible meander coils triggered in sequence to induce transient eddy current for exciting enhanced Rayleigh wave of MHz frequency. Based on the Lorentz force mechanism, pulsed electromagnetic fields and the generated ultrasonic waves of the proposed new EMAT are studied through numerical simulation at first. Experiments are conducted then to check the practical performance of the PAFR-EMAT for pipe inspection. Results show that the PAFR-EMAT has good performance in Rayleigh wave generation for inspection of the curved surface of metallic pipe and is capable to detect surface crack of small depth.

Studying the Thermoelastic Waves Induced by Pulsed Lasers Due to the Interaction between Electrons and Holes on Semiconductor Materials under the Hall Current Effect

In the present work, the interaction between electrons and holes in semiconductor materials is investigated. According to the excitation process, the optical-elastic-thermal-diffusion (OETD) process is considered when the medium is exposed to a strong magnetic field and laser pulses. Photo-elastic and photo-electronics deformations are taken into account when the Hall current impact appears due to the magnetic field pressure on the semiconductor medium. Due to the complexity of the model, the governing equations that describe the system in one dimension (1D) are studied. Mathematical transformations (Laplace transform) were used to simplify the equations to obtain the physical quantities under study which were affected by laser pulses. To obtain complete solutions, some conditions were obtained from the free surface as well as from a mechanical ramp type and pulse heat flux, and then numerical transformations were applied using the inverse Laplace transform. Under the influence of several variables in this question, the results were explained graphically for silicon (Si) material and the results were analyzed in terms of their physical significance.

The CHIMERA facility development programme

The CHIMERA fusion technology facility will enable testing of large in-vessel component modules under reactor-like conditions of combined in-vacuum thermal power density and magnetic field. With an integral large superconducting magnet and a PWR-like water loop, CHIMERA is also ideally placed for experiments on liquid metal breeding blanket prototypes. Facility construction is underway at the UKAEA site in South Yorkshire. The superconducting magnet is fully wound and terminated, and the bespoke pulsed magnet power supply has been delivered. Even before construction and commissioning is complete, a parallel and supporting research and development programme is in progress and is reported here. A bespoke infrared heating system has been developed, capable of applying 0.5 MW/m2 to component surfaces up to the size of the ITER test blanket module first wall. The modules of this heater are highly specialised and designed to endure the high magnetic forces from the CHIMERA static and pulsed magnets. CHIMERA will feature a range of diagnostics, including load cells to measure static and pulsed magnetic forces, and induced current sensors, all of which have been tested to confirm acceptable operation in the pulsed magnetic field. Manufacture of the test mock-up to be used for facility commissioning is underway. Testing will be enhanced with simulation ‘digital twin’ capability, and a development project is now producing first virtual test results, informing commissioning of the CHIMERA device.

The potential of pulsed magnetic field to achieve microbial inactivation and enzymatic stability in foods: A concise critical review

Pulsed magnetic field (PMF) is an emerging nonthermal technique being explored in recent times for its ability to ensure adequate microbial and enzymatic inactivation in food products. The major process parameters in PMF pasteurization or sterilization of food matrices are the magnetic field intensity and the number of pulses. Biosystems such as microbes and enzymes contain several charged particles which undergo drifting under the influence of Lorentz force in the magnetic field. This leads to the formation of induced currents, leading to the inactivation of microbes and enzymes. Magnetoporation induced by PMF leads to a loss of cytosol and nucleic acid content; along with an increase in intracellular Ca2+ content, leading to microbial death. The loss of enzyme activity after PMF treatment can be majorly attributed to the unfolding of the tertiary structure. The inactivation trends reported in literature indicated towards the presence of “window effect” which comprised of two effects, namely the “intensity window” and “time window” to which the biosystem, (the microbe or the enzyme) specifically responded to. The coupling of hurdle technologies with PMF can be an attractive strategy to ensure the same. The review aims to critically review the potential of PMF as a sustainable nonthermal treatment in ensuring microbial safety and enzymatic stability in food products, prompting more research in this area.

The increase in c-fos expression in epileptic seizures is inhibited by magnetic field application, but not KCa1.1 channel expression

ABSTRACT The aim of this study was to understand the expression of big potassium (BK, KCa1.1) channels in epileptic seizures under magnetic field application. Forty Wistar albino adult male rats were divided into five groups (n = 8). First group rats were control group. Pentylenetetrazole (PTZ) administrated to second group rats to induce the seizures with 35 mg/kg intraperitoneally injection every two days. Levetiracetam (LEV) i.p. at a dose of 108 mg/kg was given to third group rats as positive control group (PC) before 20 minutes PTZ administration. Pulsed magnetic field with 1.5 mT was exposed to the fourth group rats for 3 hours a day for 1 month as magnetic field (MF) group. 1.5 mT pulsed magnetic field was exposed to the fifth group rats for 3 hours a day for 1 month in addition to PTZ administration (PTZ+MF). KCa1.1 not changed in hippocampus of PTZ rats while increased in frontal cortex and pons for PTZ group but not changed with magnetic field exposure. KCa1.1 increased in heart of PTZ animals and turned back to mean control values with magnetic field exposure. Suppressing the expected increase of c-fos protein expression in seizures with magnetic field application but not being able to change the KCa1.1 expression shows that new studies can be done by increasing the frequency of 1.5 mT magnetic field.

Magnetocaloric Effect in the Laves Phase of GdNi2 in Strong Magnetic Fields

Experimental studies of the magnetic and magnetocaloric properties of the Laves phase of GdNi2 have been carried out in external static up to 3 T and pulsed up to 50 T magnetic fields. It has been found that in a magnetic field of 3 T the change in the magnetic entropy of the alloy reaches its maximum value ΔSm = −8 J/(kg K) in the vicinity of the Curie temperature TC = 73.6 K. The corresponding adiabatic temperature change in this case, calculated by an indirect method, is ΔTad ≈ 3 K. The maximum value of the adiabatic temperature change measured by the direct method in a pulsed magnetic field of 50 T at T0 = 77 K, was equal to ΔTad = 15 K, which agrees well with theoretical predictions.

Pulsed magnetic field increases the effect of ultraviolet C radiation and thermal shock in aged yeasts

The study of the effects of the magnetic field (MF) on living matter continues to be a dilemma. Until now, the interaction mechanisms of MF with living matter that explain the observed phenomena are unknown. Despite the existing literature and the multiple effects described to date, there are few published articles that study the combined effect of MF with other physical agents during the cellular aging process. In this sense, the aim of this work is to study whether low frequency and intensity pulsed and sinusoidal MF exposure produce alterations in the cell killing effect of ultraviolet C (UVC) radiation and thermal shock during the chronological aging of S. cerevisiae. Yeast cells were exposed to 2.45 mT (50 Hz) sinusoidal MF and 1.5 mT (25 Hz) pulsed MF, during 40 days of aging, in combination with UVC radiation (50 J/m2) and/or thermal shock (52°C). Cell survival was evaluated by clonogenic assay. The exposure of yeast to pulsed MF produces an acceleration of aging, which is not observed in cells exposed to sinusoidal MF. The pulsed MF modifies the cellular response to damaging agents only in aged S. cerevisiae cells. In this sense, the pulsed MF applied increases the damage induced by UVC radiation and by thermal shock. In contrast, the sinusoidal MF used has no effect.