Intense Pulsed Magnetic Fields Research Articles

Effect of high intensity pulsed magnetic field (30 T) on microstructure and tribological properties of Ni-based coatings

Pulsed magnetic fields can improve ferromagnetic and paramagnetic materials by improving their stress structure, domain variation, phase structure distribution and grain size of both solid and molten metals. Therefore, we strengthened the Ni-based wear-resistant coating by using the high-intensity (30 T) pulsed magnetic field equipment independently developed by our research group. The results show that the magnetic domains appeared as sheet domains and showed sinusoidal distribution after pulsed magnetic field intensification. The crystal structure is improved, the residual compressive stress is increased and the tribological coefficient is decreased. This study provides a new perspective on the design of high-strength metal base coatings for various applications.

Effect of sinusoidal and pulsed magnetic field exposure on the chronological aging and cellular stability of S. cerevisiae

Purpose: The aim of this study is to investigate the effects of low frequency and intensity sinusoidal magnetic field (SMF) and pulsed magnetic field (PMF) exposure on the chronological aging and cellular stability of Saccharomyces cerevisiae.Materials and methods: The S. cerevisiae wild type strain (WS8105-1C) was exposed to SMF (2.45 mT, 50 Hz, continuous) and PMF (1.5 mT, 25 Hz, 8 h/day). Chronological aging was evaluated during 40 days. Survival was assayed by clonogenic assay and drop test. Cellular stability was studied by spontaneous mutation count and the index of respiratory competence (IRC).Results: We found that exposure to PMF produces an acceleration of cellular chronological aging, not observed in the groups treated with SMF. A decrease in the spontaneous frequency of mitochondrial mutation during aging was observed in PMF-treated samples. However, no alterations in the IRC during aging were found for both, SMF and PMF, treatments.Conclusions: Exposure to PMF produces the acceleration of aging and an alteration in cellular stability.

Portable pulsed magnetic field generator for magnetized laser plasma experiments in low vacuum environments.

A portable pulsed magnetic field generator for magnetized laser plasma experiments in low vacuum environments is presented. It is based on a classical high-voltage discharge pulsed power system. A 95 kA peak current was delivered at a 65 kV discharge voltage, which generated a quasiuniform magnetic field of 12T in a Φ8 mm × 8 mm volume. A compact, sealed design was developed to avoid short-circuit breakdowns caused by an ambient low-pressure gas medium. Design improvements were made to the vacuum feedthrough, the transmission line, and the magnetic coil. The system worked well in a low vacuum environment for a laser plasma experiment using a gas target. But at intermediate ambient gas pressure, the ambient gas was ionized around the surface of the coil at first and then the ionized gas diffused inward and outward slowly, which affected the laser plasma image in the coil. Experiments and simulations indicated that the ambient gas was ionized by the induced electric field. We developed analytical models of the induced breakdown of the ambient gas to guide the experimental design of a gas target. The analysis can also be used in the experimental design of a solid target in an intense pulsed magnetic field of hundreds of tesla that the induced breakdown along solid's surface dominates the process.

Multiscale modeling of the elasto-plastic behavior of architectured and nanostructured Cu-Nb composite wires and comparison with neutron diffraction experiments

Nanostructured and architectured copper niobium composite wires are excellent candidates for the generation of intense pulsed magnetic fields (∼100T) as they combine both high strength and high electrical conductivity. Multi-scaled Cu-Nb wires are fabricated by accumulative drawing and bundling (a severe plastic deformation technique), leading to a multiscale, architectured, and nanostructured microstructure exhibiting a strong fiber crystallographic texture and elongated grain shape along the wire axis. This paper presents a comprehensive study of the effective elasto-plastic behavior of this composite material by using two different approaches to model the microstructural features: full-field finite elements and mean-field modeling. As the material exhibits several characteristic scales, an original hierarchical strategy is proposed based on iterative scale transition steps from the nanometric grain scale to the millimetric macro-scale. The best modeling strategy is selected to estimate reliably the effective elasto-plastic behavior of Cu-Nb wires with minimum computational time. Finally, for the first time, the models are confronted to tensile tests and in-situ neutron diffraction experimental data with a good agreement.

Electron acceleration by a radially polarized laser pulse in the presence of an intense pulsed magnetic field

An external pulsed magnetic field is applied to accelerate the electron by a radially polarized laser pulse in vacuum. The unique fields of radially polarized laser beams are utilized which leads to an improvement in trapping and acceleration of electrons so that an electron can be accelerated to a very high energy level. Moreover, a pulsed magnetic field is applied that further enhances the electron acceleration. The enhancement in electron energy is due to fact that the radial field vanishes on the axis and only the longitudinal field survives, which accelerates the electron axially. As time increases, the magnetic field plays a crucial role due to the resonance between the electrons and the electric field of the laser pulse at an optimum value. The combined role of radial polarization and a pulsed magnetic field can enhance the electron energy gain significantly.

Multiscale modeling of the anisotropic electrical conductivity of architectured and nanostructured Cu-Nb composite wires and experimental comparison

Nanostructured and architectured copper niobium composite wires are excellent candidates for the generation of intense pulsed magnetic fields (> 90T) as they combine both high electrical conductivity and high strength. Multi-scaled Cu-Nb wires can be fabricated by accumulative drawing and bundling (a severe plastic deformation technique), leading to a multiscale, architectured and nanostructured microstructure providing a unique set of properties. This work presents a comprehensive multiscale study to predict the anisotropic effective electrical conductivity based on material nanostructure and architecture. Two homogenization methods are applied: a mean-field theory and a full-field approach. The size effect associated with the microstructure refinement is taken into account in the definition of the conductivity of each component in the composites. The multiscale character of the material is then accounted for through an iterative process. Both methods show excellent agreement with each other. The results are further compared, for the first time, with experimental data obtained by the four-point probe technique, and also show excellent agreement. Finally, the qualitative and quantitative understanding provided by these models demonstrates that the microstructure of Cu-Nb wires has a significant effect on the electrical conductivity.

Multiscale modeling of the elastic behavior of architectured and nanostructured Cu–Nb composite wires

Nanostructured and architectured copper niobium composite wires are excellent candidates for the generation of intense pulsed magnetic fields (> 90T) as they combine both high strength and high electrical conductivity. Multi-scaled Cu–Nb wires are fabricated by accumulative drawing and bundling (a severe plastic deformation technique), leading to a multiscale, architectured, and nanostructured microstructure exhibiting a strong fiber crystallographic texture and elongated grain shapes along the wire axis. This paper presents a comprehensive study of the effective elastic behavior of this composite material by three multi-scale models accounting for different microstructural contents: two mean-field models and a full-field finite element model. As the specimens exhibit many characteristic scales, several scale transition steps are carried out iteratively from the grain scale to the macro-scale. The general agreement among the model responses allows suggesting the best strategy to estimate the effective behavior of Cu–Nb wires and save computational time. The importance of crystallographical and morphological textures in various cases is discussed. Finally, the models are validated by available experimental data with a good agreement.

Three-dimensional critical phase diagram of the Ising antiferromagnet CeRh2Si2 under intense magnetic field and pressure

Using novel instrumentation to combine extreme conditions of intense pulsed magnetic field up to 60 T and high pressure up to 4 GPa, we have established the three-dimensional (3D) magnetic field-pressure-temperature phase diagram of a pure stoichiometric heavy-fermion antiferromagnet (${\mathrm{CeRh}}_{2}{\mathrm{Si}}_{2}$). We find a temperature- and pressure-dependent decoupling of the critical and pseudometamagnetic fields at the borderlines of antiferromagnetism and strongly-correlated paramagnetism. This 3D phase diagram is representative of a class of heavy-fermion Ising antiferromagnets, where long-range magnetic ordering is decoupled from a maximum in the magnetic susceptibility. The combination of extreme conditions enabled us to characterize different quantum phase transitions, where peculiar quantum critical properties are revealed. The interest to couple the effects of magnetic field and pressure on quantum-critical correlated-electron systems is stressed.

In vivo pulsed magneto-motive ultrasound imaging using high-performance magnetoactive contrast nanoagents.

Previously, pulsed magneto-motive ultrasound (pMMUS) imaging has been introduced as a contrast-agent-assisted ultrasound-based imaging modality capable of visualizing biological events at the cellular and molecular level. In pMMUS imaging, a high intensity pulsed magnetic field is used to excite cells or tissue labeled with magnetic nanoparticles. Then, ultrasound (US) imaging is used to monitor the mechanical response of the tissue to an externally applied magnetic field (i.e., tissue displacement). Signal to noise ratio (SNR) in pMMUS imaging can be improved by using superparamagnetic nanoparticles with larger saturation magnetization. Metal-doped magnetic nanoparticles with enhanced tunable nanomagnetism are suitable candidates to improve the SNR and, therefore, sensitivity of pMMUS imaging, which is essential for in vivo pMMUS imaging. In this study, we demonstrate the capability of pMMUS imaging to identify the presence and distribution of zinc-doped iron oxide nanoparticles in live nude mice bearing A431 (human epithelial carcinoma) xenograft tumors.

Evaluation of the Effect of the Magnetic Field Therapy on Motor Unit Action Potentials and Balance of Healthy Subjects

[Purpose] The aim of this study was to investigate the effect of the magnetic field therapy on the motor unit action potentials from the muscles of the sole of the foot and balance of healthy subjects. [Subjects] Twentyfour volunteer students from Yeditepe University Department of Physical Therapy and Rehabilitation participated in this study. [Method] The feet region received 60-Gauss intensity pulsed magnetic field therapy for 20 minutes using a 30-cm solenoid electrode. Motor unit action potentials of the muscles of the sole were evaluated in both the dominant and non-dominant legs before and after the application of magnetic field therapy. One leg standing balance tests under the eyes open and eyes closed conditions in the static and dynamic forms were also evaluated in both the dominant and non-dominant legs before and after the application of magnetic field therapy. [Results] Motor unit action potential values and balance tests results showed statistically significant improvements in the post-treatment period in comparison to the pre-treatment observations. A strongly significant positive correlation was found between the motor unit action potentials and eyes open static balance on the non-dominant side. [Conclusions] Magnetic field therapy improves the activities of muscles and balance of healthy subjects.

Performance of Trapped Magnetic Field in Superconducting Bulk Magnets Activated by Pulsed Field Magnetization

Melt-textured large grain high temperature superconducting materials have a characteristic feature so as to trap the magnetic fields applied from outside, and act as quasi- permanent magnets yielding intense magnetic fields which reach values of several T in the open space above the sample surface. The performance of the magnets has been precisely investigated when intense pulsed magnetic fields generated by feeding currents up to 9.12 kA to the pulse coil settled around a cylindrical bulk magnet. In the experiment a condenser bank with large capacitances of 40-120 mF has been adapted to apply the magnetic fields up to 8.44 T to the Gd-Ba-Cu-O-based bulk magnet with the size of 30 mm in diameter. The trapped field has reached 3.28 T on the sample surface. The magnetic fields successively penetrating the sample in the process called the IMRA method have been investigated with respect to the behavior of the magnetic flux in the sample.

Magnetic separation technique for groundwater by five HTS melt-processed bulk magnets arranged in a line

A magnetic separation study for groundwater purification has been practically conducted by using the multi-pole magnet system. The magnetic pole was composed of 10 open magnetic spaces by arranging five HTS melt-processed bulk magnets in a line in a vacuum sheath. The individual bulk magnets were activated by feeding intense pulsed magnetic fields up to 6T. The magnetic field distribution was estimated with respect to various pole arrangements. The actual groundwater samples of Sanjo City were processed so as to form large precipitates by adding the coagulant and pH controlling. The maximum separation ratio of the iron-bearing precipitates has exceeded over 70% when slurry water was exposed to 10 magnetic poles of up to 2.5T at a flowing rate of less than 4.8l/min. An obvious attraction of flocks to the magnetic poles was observed even when the water contains no magnetite powder at the flow rate of 1.01l/min. This implies the validity of the multi-pole magnet system with respect to the actual application to water purification.

An improved approach to calibrating high magnetic field gradients for pulsed field gradient experiments

Probes capable of generating short high intensity pulsed magnetic field gradients are commonly used in diffusion studies of systems with very short T 2. Traditional methods of calibrating magnetic field gradients present unique challenges at ultrahigh field strengths and are often inapplicable. Currently the most accurate method of determining magnetic gradient strength is to use the known diffusion coefficient of a standard sample and determine gradient strength from the echo attenuation plot of a diffusion experiment, however, there are problems with finding suitable standards for high intensity gradients. Here, we show that molecules containing at least two receptive nuclei (i.e. one with high and one with low gyromagnetic ratios) are excellent systems for calibrating high intensity gradients.

Pulse-echo ultrasound in pulsed magnetic fields

As the technology of high-speed data acquisition evolves along with the ability to record multi-megabyte continuous streams of data, the application of pulse-echo ultrasound to transient measurements have become possible. I will discuss a system that has been developed at the National High Magnetic Field Laboratory for measurements of sound speed and attenuation in materials subjected to intense pulsed magnetic fields. The magnetic field pulses have millisecond durations and can only be repeated a few times a day. We are able to process from a single magnetic pulse, a record of sound speed that reveals structural changes as a function of magnetic field. We are not alone in this effort; at least two other groups at other high magnetic field laboratories are using similar techniques [C. Proust et al., Lab. National des Champs Magnetiques Pulses, Toulouse France, UMR 5147CNRS-INSA-UPS; Wolf et al., ‘‘New Experimental Techniques for Pulsed Magnetic Fields-ESR and Ultrasonics,’’ Physica B 294–295, 612–17 (2001)]. This presentation is intended to acquaint the audience with the techniques of setting up a pulse-echo ultrasound system by taking advantage of modern digitizing systems available and computer based post processing using commercially available application software. I will present data from experiments that we have carried out and discuss the precision with which the sound speeds can be determined.

Unidirectionally Solidified Al-Cu Eutectic Alloy under High Intensity Pulsed Magnetic Field

The pulsed electric current produced by discharging of capacitors pass through the double solenoids with ferrosilicon core, the instant strong pulsed magnetic field with the oscillating and declining characters was made between two ferrosilicon cores. The effect of high-pulsed magnetic field on the unidirectionally solidified Al-Cu eutectic microstructure with 10µm/s withdrawn velocity was investigated. Under the high intensive pulsed magnetic field, the Al-Cu eutectic solidified morphology experience three evolution stages that are regular columnar structure to breaking off fine grain, coarsening dendrite to newly regularization columnar structure with increasing of 0～15.5J charge energy. It is found that rich copper phase evidently come out inter eutectic cells and the eutectic spacing decrease in newly regularization specimen. The induced electric field caused by high pulsed magnetic field in metallic melt brought into oscillating solute electro-migration in front of solidification interface, which has the effect of promoting solute diffusion and reducing the constitutionally supercooling region.

Generation and Application of Ultra-High-Intensity Magnetic Field Gradient Pulses for NMR Spectroscopy

Two different concepts of gradient current power supplies are introduced, which are suitable for the generation of ultra-high intensity pulsed magnetic field gradients of alternating polarity. The first system consists of a directly binary coded current source (DBCCS). It yields current pulses of up to ±120 A and a maximum voltage across the gradient coil of ±400 V. The second system consists of two TECHRON 8606 power supplies in push–pull configuration (PSPPC). It yields current pulses of up to ±100 A and a maximum voltage across the gradient coil of ±300 V. In combination with actively shielded anti-Helmholtz gradient coils, both systems are used routinely in NMR diffusion studies with unipolar pulsed field gradients of up to 35 T/m. Until now, alternating pulsed field gradient experiments were successfully performed with gradient intensities of up to ±25 T/m (DBCCS) and ±35 T/m (PSPPC), respectively. Based on the observation of the NMR spin echo in the presence of a small read gradient, procedures to test the stability and the matching of such ultra-high pulsed field gradient intensities as well as an automated routine for the compensation of possible mismatches are introduced. The results of these procedures are reported for the PSPPC system.

MICROWAVE PULSED FIELD EFFECTS ON DYNAMICS OF FLUXONS IN THE CRITICAL STATE

We report experimental results on microwave second harmonic emission in different superconductors in the critical state, exposed to intense pulsed mw magnetic fields. We show that the second order response of some superconducting samples shows a magnetic hysteretic behavior. We suggest that this behavior is related to non-equilibrium phenomena induced by the mw pulses. In particular, it may be ascribed to the different time response of the fluxons in the reverse and direct critical state.

Prospects for performing neutron scattering in intense pulsed magnetic fields (invited)

Present dc split-pair superconducting magnets designed for neutron scattering studies can reach fields up to 14.5 T. Prospects for achieving pulsed magnetic fields up to 30 T in conjunction with spallation neutron sources are reviewed, along with a number of scientific questions that can be addressed with such a capability.

スプレードライ造粒粉末を用いてパルス磁場中成形したＮｄ‐Ｆｅ‐Ｂ系焼結磁石の磁気特性

Nd-Fe-B alloy powder was granulated by a spray drying method using an organic binder in order to improve the powder flowability during feeding and compacting. In this experiment, whether or not the degree of magnetic orientation of primary particles in granulated powders is raised by applying high intensity pulsed magnetic field in compacting was studied, in order to improve magnetic properties of sintered magnets. It was found that the orientation of particles (remanences) was improved remarkably by applying high intensity pulsed magnetic field in initial process of compaction of granulated powders, so that magnetic properties of magnets are superior to those of magnets when applying only static magnetic field in compacting. The observation of granulated powders after applying magnetic field shows that granulated powders were destructed more easily by such high intensity pulsed field. The orientation of primary particles in granulated powders depends strongly on the apparent density of powders when applying pulsed field. It was very effective for improving magnetic properties of magnets using granulated powders to apply pulsed field when powders fed in die cavity are free for orientation. By means of controlling the binding strength of binder and timing of pulsed magnetic field, magnetic characteristics of magnets using granulated powders became almost equal to that of magnet using raw powder.

Resonant tunneling in double-quantum-well triple-barrier heterostructures.

We present a low-temperature (mK) magnetotransport study, using intense pulsed magnetic fields to 50 T, of two double GaAs quantum well, triple AlAs barrier resonant tunneling structures, which demonstrates the critical influence of the second quantum well on the tunneling behavior. We show that charge accumulation in the first well, and thus the overall tunneling characteristic, is controlled by the position of the lowest bound state in the second well, and identify tunneling transitions that are unique to triple-barrier structures. We also demonstrate that the tunneling current is sensitive to integer and fractional quantum Hall effect states, and find that the voltage-tunable accumulation of charge in one of the samples provides an unusual environment for the study of ground states of a two-dimensional electron system. \textcopyright{} 1996 The American Physical Society.