Generation Of High Magnetic Fields Research Articles

Well balanced pick-up assembly for double pulsed magnetic field apparatus

The generation of high magnetic pulsed fields involves several technological challenges. State-of-the-art field peak intensities can be achieved by means of double-coil systems and, as for other configurations, a special pick-up system is required to clean the signal from spurious components and artifacts. However, the design of a well-balanced pick-up for double-coil systems is not a trivial task because of the different mutual inductance of the two field coils. In general the pick-up can be optimized for one coil only, but not for both. Here we present a new pick-up concept specifically aimed at solving this problem, based on an active compensation bridge and a special compensating coil located outside field-generating coils. Besides yielding a good balance of the signal over all pulse duration, a further advantage is an additional increase in the signal-to-noise ratio.

Technical Overview of Superconducting Magnets

Superconducting magnets are most used in MRI systems. The features of superconducting magnets are high magnetic field generation and highly stable magnetic field. Superconducting magnets are also energy-saving devices for electromagnets. In this paper, I described the basics of superconductivity, introduced the superconducting wires used in magnets, and explained cryogenic heat insulation technology, superconducting connection technology, and design method for a highly uniform magnetic field as technologies used in superconducting magnets. Then, I introduced development trends in helium saving magnets and high temperature superconducting magnets that do not use liquid helium to solve the recent helium problem.

Predicting electrical conductivity in Cu/Nb composites: A combined model-experiment study

The generation of high magnetic fields requires materials with high electric conductivity and good strength properties. Cu/Nb composites are considered to be good candidates for this purpose. In this work, we aim to predict, from theory, the dependence of electric conductivity on the microstructure, most notably on the layer thickness and grain sizes. We also conducted experiments to calibrate and validate our simulations. Bimetal interfaces and grain boundaries are confirmed to have the largest impact on conductivity in this composite material. In this approach, a distribution of the layer thickness is accounted for in order to better model the experimentally observed microstructure. Because layer thicknesses below the mean free path of Cu significantly degrade the conductivity, an average layer thickness larger than expected may be needed to meet conductivity requirements in order to minimize these smaller layers in the distribution. We also investigate the effect of variations in volume fraction of Nb and temperature on the material’s conductivity.

Sensitive Fiber Optic Sensor for Rapid Hot-Spot Detection at Cryogenic Temperatures

The incredible current density and high magnetic field generation possible with high-temperature superconductors (HTS) have the potential to revolutionize energy generation, e.g. high-power generators, and compact fusion energy devices. However, an open issue that limits the applications of this class of superconductors is the challenge of rapidly detecting a hot spot which can lead to a quench. Owing to the inherent advantages of fibre optic sensors, they are promising candidates to be integrated in HTS magnets for hot-spot detection. In this paper, closely spaced fibre Bragg gratings (FBG) with the same Bragg wavelength are used to establish an ultra-long FBG (ULFBG) for distributed hot-spot monitoring. We investigate the capability of a 10m ULFBG to detect a small temperature rise at the end of the sensor. The results show that a 10 m long ULFBG can rapidly detect a small hot spot within 1 K temperature rise at 80 K. It is expected that ULFBG can be wavelength-division multiplexed and integrated to superconducting coils to achieve long-distance hot-spot monitoring with extremely high spatial resolution and fast response.

High Magnetic Field as a Tool for Discovery in Condensed Matter Physics

The Journal of the Physical Society of Japan highlights in this special topic recent advances in modern physics that have been realized with the generation of pulsed high magnetic fields.

Orbital and thermal modelling of a 3U CubeSat equipped with a high-temperature superconducting coil

High-temperature superconductor (HTS) based devices have the potential to be useful technologies for space applications, allowing very high current transfer and magnetic field generation. However, HTS technology requires cryogenic temperatures (<90 K) to operate, and it is not well understood if and how this can be achieved for HTS devices integrated into space vehicles. In this study, the thermal and power performance of a hypothetical 3U CubeSat equipped with an HTS magnetic coil is explored over a range of orbits around the Earth. After eliminating the possibility of passive cooling this close to a planetary body, a cryocooler was deemed necessary to maintain the required temperatures and was included in the simulations. The results show that the best strategy for maintaining the cryogenic operating environment is to maximise the power availability to the cryocooler from solar panels. This approach increases the volume-averaged temperature of the satellite, but the benefits of increased power outweigh the cost of a decreased cryocooler efficiency. This work demonstrates that a 1 T magnetic field can be generated with an HTS electromagnet in a space environment on a small satellite, enabling the use of HTS for space applications such as electric propulsion and energy storage.

Heat Load Calculations on an HTS Coil Integrated into a Small Satellite during a Sun-Synchronous Low Earth Orbit

High-temperature superconductivity (HTS) has the potential to be a useful technology for space applications, allowing for high current densities and magnetic field generation in compact devices. However, HTS requires cryogenic temperatures and it is not well understood how this can best be achieved in a space environment. Using a modelling approach, the expected heat load on a hypothetical 3U CubeSat with an HTS coil during a sun-synchronous low Earth orbit was predicted. The direction and magnitude of solar, albedo and infrared incident radiation toward the satellite was calculated for each orbital position of a circular 732 km, Ω = 0° longitude of ascending node orbit. Using a finite element approach, the surface radiosity and temperature of the CubeSat was predicted and validated. Finally, the instantaneous heat load on the HTS magnet, which generates a 1T magnetic field, was calculated as a function of orbital position. This study provides technical information about the characteristics of the refrigeration device required to maintain cryogenic temperatures for an HTS coil on a space faring vessel, such as a portable cryocooler. Selection and design of a satellite cooling system must be optimised according to the calculated heat load and available solar power.

High fidelity triangular sweep of the magnetic field for millisecond scan EPR imaging

Linearity of the magnetic field sweep is important for high resolution continuous wave EPR imaging. Driving the field with triangular wave function is the most efficient way to scan EPR projections. However, the magnetic field sweep profile can be significantly distorted during fast millisecond projection scan. In this work, we introduce a method to generate highly linear and properly symmetrical triangular sweeps of the magnetic field using calibrated harmonics of the triangular wave function. First, the frequency response function of the EPR magnet and its power circuitry was obtained. For this, the field sweeping coil was driven with sinusoidal signals of different frequencies and the actual magnetic field inside the magnet was recorded. To cover wide range of frequencies, the measurements were carried out independently using gaussmeter, Hall-effect linear sensor integrated circuit, and an inductance coil. For each frequency, the system gain and the phase delay were determined. These data were used to adjust the amplitudes and the phases of individual harmonics of the triangular wave function. After the calibration, the maximum deviation of the magnetic field from the linear function was 0.05% of sweep width for 4 ms scan. The maximum discrepancy between the forward and the reverse scan was less than 0.04%. Sweep overhead time for changing the scan direction was 5%. The proposed approach allows generation of high fidelity triangular magnetic field sweeps with accuracy better than 0.1% for the range of the magnetic field sweep widths up to 48 G and scan duration from 10 s down to 1 ms.

Modeling superconducting transition temperature of doped MgB2 superconductor from structural distortion and ambient temperature resistivity measurement using hybrid intelligent approach

Improvement of superconducting properties of MgB2 superconductor becomes necessary in several medium and large scale commercial practical applications where generation of high magnetic field is of significant interest. High power cables, energy storage devices, wind turbines and magnetic resonance imaging are the potential areas of application where MgB2 superconductor with improved property is indispensable. In order to facilitate quick determination of transition temperature of MgB2 superconductor and to determine the conditions at which this superconducting property is optimal for the desired application, this present contribution hybridizes genetic algorithm (HGA) with support vector regression (SVR) machine learning to model the transition temperature of doped MgB2 superconductor using ambient room temperature resistivity (RTR), residual resistivity ratio (RRR) and structural lattice distortion (SLD) due to the incorporated dopants as descriptors. The developed HGA-SVR-RTR model that utilizes RTR as descriptor shows better performance than the proposed HGA-SVR-RRR model (that employs RRR as descriptor) and HGA-SVR-SLD model (that implements SLD as descriptors) with improvement in performance by 88.45% and 71.41%, respectively using mean absolute error (MAE) as a parameter that evaluates the model performance. The developed HGA-SVR-RTR model also outperforms the existing models such as GPR-prediction (2020), STTE model (2016) and STTE model (2014) with performance improvement of 74.85%, 74.76% and 92.96%, respectively using MAE as a yardstick for performance comparison. The developed HGA-SVR-RRR model performs better than HGA-SVR-SLD model with percentage improvement of 59.6% on the basis of MAE. The performance of the developed models would definitely facilitate cost effective search for doped MgB2 superconductor for desired application without experimental stress.

Oscillatory magnetic fields for neutron resonance spin-echo spectroscopy

The generation of high frequency oscillatory magnetic fields represents a fundamental component underlying the successful implementation of neutron resonant spin-echo spectrometers, a class of instrumentation critical for the high-resolution extraction of dynamical excitations (structural and magnetic) in materials. In this paper, the setup of the resonant circuits at the longitudinal resonant spin-echo spectrometer RESEDA is described in comprehensive technical detail. We demonstrate that these circuits are capable of functioning at frequencies up to 3.6 MHz and over a broad bandwidth down to 35 kHz using a combination of signal generators, amplifiers, impedance matching transformers, and a carefully designed cascade of tunable capacitors and customized coils.

Analysis of Effective Parameters on Magnetizer Using Finite Element Method

Permanent magnets due to their high energy production are widely used in a variety of electromagnetic devices. Such devices can be found in marine, aerospace, and robotic applications which require the minimization of weight and volume of the electro- magnetic devices. The coercively of some permanent magnets are high so the magnetizer is used for high magnetic field generation. Different parameters such as core shape, core material, turn number, cross section of the air gap, magnet type, etc have been known to affect the magnetizer operation. The amplitude and waveform of fixture current is obtained from PSPICE simulations and also experimental measurement. A 2D finite element analysis is developed to simulate magnetic fields and mechanical forces. The main parameters affecting optimal design of the magnetizer are discussed. Simulation results show that the core structure, air gap width, and turn numbers are the most important parameters when designing such a device.

Time-domain terahertz spectroscopy in high magnetic fields.

There are a variety of elementary and collective terahertz-frequency excitations in condensed matter whose magnetic field dependence contains significant insight into the states and dynamics of the electrons involved. Often, determining the frequency, temperature, and magnetic field dependence of the optical conductivity tensor, especially in high magnetic fields, can clarify the microscopic physics behind complex many-body behaviors of solids. While there are advanced terahertz spectroscopy techniques as well as high magnetic field generation techniques available, a combination of the two has only been realized relatively recently. Here, we review the current state of terahertz time-domain spectroscopy (THz-TDS) experiments in high magnetic fields. We start with an overview of time-domain terahertz detection schemes with a special focus on how they have been incorporated into optically accessible high-field magnets. Advantages and disadvantages of different types of magnets in performing THz-TDS experiments are also discussed. Finally, we highlight some of the new fascinating physical phenomena that have been revealed by THz-TDS in high magnetic fields.

Electromagnetic, Thermal, and Mechanical Quench Simulation of NI REBCO Pancake Coils for High Magnetic Field Generation

The no-insulation (NI) winding technique drastically enhances the thermal stability of REBa 2 Cu 3 O y (REBCO) coils. Even if a larger current than a critical current is carried in NI REBCO pancake coils, the coils would not burn out. So far, many NI REBCO pancake coils showed a “self-protecting” characteristic in experiments. However, most of these experiments have been done under a low magnetic field or cooled by liquid nitrogen. Under these conditions, a huge electromagnetic force does not occur after an NI REBCO pancake coil transitions into a normal state. Recently, the NI winding technique has been applied to high-field magnets, such as NMR and accelerators. Under a high magnetic field (> 20 T), a huge hoop stress is generated after one NI REBCO pancake coil constituting a high-field magnet by stacking reaches to quench. The huge hoop stress causes the delamination of REBCO-coated conductors. That is, the quench protection condition of high-field NI REBCO magnets is decided according to the mechanical condition, even though the magnets show a high thermal stability. In this paper, three simulation models for NI REBCO pancake coils are compared, and then the mechanical condition is discussed for a quench protection through an electromagnetic, thermal, and mechanical simulation of multistacked NI REBCO pancake coils for high field generation.

Magnetizing Performance Evaluation of HTS Bulk Magnet Using a 12 K Refrigerator With High Cooling Capacity

We study a high magnetic field generation using HTS bulk magnets activated by pulsed-field magnetization with the goal of their industrial application. In our previous study, a single-stage GM-type refrigerator and a two-stage GM-type refrigerator with an air-cooled-type compressor and a Stirling refrigerator were used for cooling an HTS bulk aiming at simplifying the bulk magnet system. Now, we developed a new bulk magnet system using a two-stage GM-type refrigerator with a high cooling capacity of 12 W at 20 K aiming to enhance a trapped field by improving the cooling ability. When a GdBCO bulk 60 mm in diameter and 20 mm thick was cooled from the room temperature to the lowest, the lowest temperature was 13.3 K at the sample stage and 45.5 K at the bulk surface for 3.5 h. When a single pulsed field was applied with varying the amplitude and temperature, the maximum flux densities of 3.59 T on the bulk surface and 2.34 T at the pole surface, and the total magnetic flux of 2.48 mWb were achieved at 20 K.

Electromagnetic 2D Scanning Micromirror for High Definition Laser Projection Displays

We present the design, fabrication, and analysis of an electromagnetic biaxial scanning micromirror for a high definition laser pico-projection display system. The device consists of a microfabricated double gimbaled structure for mechanical amplification of horizontal scan angle and a set of uniquely designed permanent magnets for high magnetic field generation in a small volume. With the fabricated 1.2-mm-diameter micromirror, the maximum scan angle of 52° at 28.9 kHz and 33° at 60 Hz have been obtained for horizontal and vertical scans, respectively. The effective volume of the packaged micromirror measures 0.34 cm3. A prototype full-color pico-projection display system has been fabricated with micromirror package and laser sources integrated into a 3.7 cm3 volume.

Formation of periodic magnetic field structures in overdense plasmas

AbstractThe role played by the angle of incidence of a short pulse laser in the generation of magnetic field via Weibel instability from overdense plasmas is investigated with the help of three-dimensional particle-in-cell simulations. The simulations have been done for different cases by varying the angle of incidence. When the laser pulse is incident normally (θ = 0°), it gets self-focused at a very short distance and the axial intensity rises up to several times the fundamental laser intensity. Strong current filamentation is observed, which causes the generation of high magnetic fields across the current filament. When the laser is incident obliquely at θ = 30° and 60°, periodic density ripple-like structures are formed on the plasma surface which is due to emission of energetic electron jets caused by vacuum heating. The periodic structures carry forward and return currents, which results in the formation of periodic magnetic field structures having strong magnetic fields. At θ = 60°, the inter spacing distance coincides with the incident laser wavelength. The magnetic energy is found to be highest in case of normal incidence, which is due to strong current filamentation. The filamentation becomes weaker as the angle of incidence is increased.

Effect of structural steel ion plasma nitriding on material durability in pulsed high magnetic fields

The work was aimed to study the influence of plasma nitriding on electrical and mechanical properties of structural steels and their durability in pulsed high magnetic field. The plates and cylindrical magnetic flux concentrators were made of several steel grades (30KhGS, 40Kh, 50KhGA, 38Kh2MYuA, and U8A), heat-treated, and subjected to the low-temperature (400, 500°C) plasma nitriding. Electrical and mechanical properties of materials, phase composition of steel surface layer, microstructure and microhardness profiles were investigated on the plates before and after plasma treatment. Microstructure and microhardness profiles across the subsurface layer of plasma treated and untreated concentrators applied for high magnetic field generation were also studied. Magnetic field of 50 T under tens of microseconds in duration inside the flux concentrators was generated by long-life outer coil.

JOULE HEATING EFFECT REDUCTION OF AN ELECTROMAGNET SYSTEM UTILIZING ON-CHIP MAGNETIC CORE

Joule heating effect is substantial in an electromagnet system due to high density current from current-carrying conductor for high magnetic field generation. In Lab-on-chip (LoC) Magnetically Activated Cell Sorting (MACS) device, Joule heating effect generating high temperature and affecting the biological cells viability is investigated. The temperature rise of the integrated system was measured using resistance temperature detector, RTD Pt100. Three temperature rise conditions which are from the bare spiral-shaped magnet wire, the combination of magnet wire and on-chip magnetic core and combination of magnet wire, on-chip magnetic core and 150 mm polydimethylsiloxane (PDMS) layer have been investigated. The combination of electromagnet of spiral-shaped magnet wire coil and on-chip magnetic core has reduced the temperature significantly which are, ~ 38 % and ~ 26 % with magnet wire winding, N = 10 (IDC = 3.0 A, t = 210 s) and N = 20 (IDC = 2.5 A, t = 210 s) respectively. The reduced Joule heating effect is expected due to silicon chip of high thermal conductivity material enable fast heat dissipation to the surrounding. Therefore, the integration of electromagnet system and on-chip magnetic core has the potential to be used as part of LoC MACS system provided the optimum operating conditions are determined

Critical current density and current distribution in field cooled superconducting disks

Applications of bulk superconductors concern superconducting motors and generators, the levitation of vehicles, the generation of high magnetic fields with small size cryo-magnets, the shielding of magnetic fields and other applications. For all of them, it is essential to determine the critical current density, and to understand the effect of the shape and size of the bulks on the properties of interest. In this contribution, we show how the combination of levitation force and trapped field measurements allow one to determine the characteristics and the potential performances of superconducting disks using analytical modeling. As examples of applications we detail the effects of the magnetizing field and of the bulk sheet critical current density on the levitation force. An important result of the reported measurements is that in field-cooled samples, the shielding currents possibly do not flow along the whole thickness of the disks.

INTEGRATED HIGH MAGNETIC GRADIENT SYSTEM FOR TRAPPING NANOPARTICLES

Lab-on-chip (LoC) magnetic separator is important in clinical diagnostics and biological studies where different types of biological cells need to be isolated from its heterogeneous population. In this work, a novel design of on-chip V-shaped magnetic core generating high magnetic gradient and force for trapping magnetically labelled bioparticles is presented. The integrated magnetic system consisted of a spiral-shaped planar microcoils and a V-shaped permalloy (Ni80Fe20) magnetic core structure, which was designed to be part of LoC separator system. The effects of V-shaped magnetic core tip area, the current injection to the microcoils on the magnetic field, as well as its gradient and force on magnetic nanoparticles were simulated and analyzed. Finite element analysis (FEA) simulation using two dimensional (2D) axial symmetry model and steady state analysis of the DC magnetostatics module confirmed the effect of V-shaped magnetic core tip on the high magnetic field generation. The smallest V-shaped magnetic core tip area and the highest current injected to the magnetic coils had significantly amplified the magnetic flux density, its gradient, and the magnetic force generated on a magnetic nanoparticles. Functional test results justified the proportional relationship between DC applied and the trapping area of the magnetic nanoparticles. Effective separation of biological cells tagged with magnetic nanoparticles in LoC system was expected with integration of this high gradient on-chip magnetic system.