Coil Current Research Articles (Page 1)

Abstract Frequent task in the numerical modelling of a superconducting magnet generating AC or pulsing fields is the evaluation of AC loss. Commonly, after solving the electromagnetic problem, the loss is calculated by integrating in time and volume the density of dissipated power, obtained locally as the product of electrical field and current density. However, the loss can be also determined from the product of current and voltage detected on the device terminations, in the way analogous to electrical measurement. Fortunately, this voltage signal can be easily determined in the frequently used T-A formulation. It can be further used for more detailed comparison with experiment, in particular the creation of magnetic hysteresis loops relating the flux linkage to the coil current. Methodology is illustrated on Benchmark #3 problem published by the HTS Modelling Workgroup.

MRI offers superior contrast to x-ray and CBCT that can play an important role in diagnosing dental pathologies. Current extraoral RF coils for MRI in dentistry provide only limited SNR, thus limiting spatial resolution. We propose an intraoral coil (IOC) array that can provide high SNR to achieve a 250 μm isotropic resolution and enable parallel imaging. A capacitively decoupled 2-channel IOC array with a buccal and a lingual element was placed on a bite form covered with silicon putty for subject-specific fixation. Phantom and in vivo measurements were performed at 3 T to compare the performance of the IOC array to an external single channel loop coil and a single-channel IOC in terms of sensitivity, image SNR, and g-factor for 2-fold acceleration. IOC array improves SNR by up to 20-fold compared to the tight-fit extraoral loop coil (Ø = 4 cm), provides more uniform sensitivity and allows parallel imaging with a g-factor of less than 1.07 for 2-fold acceleration. (250 μm)3 isotropic resolution of premolar and molar teeth could be realized using a T1-SPACE protocol within 2 min. Intraoral coil arrays are feasible and offer higher homogeneity and SNR compared to an extraoral loop coil. Moreover, they allow for parallel imaging, which significantly reduces total acquisition time, thereby improving diagnostic potential.

ABSTRACTMutual inductance serves as a critical factor governing the power transfer capacity and efficiency in wireless power transfer systems. Accurate calculation of mutual inductance is critical for system design. However, the problem of calculating mutual inductance for arbitrarily positioned circular coils with double‐sided bounded toroidal magnetic media has not yet been resolved. To tackle this problem, a fully analytical bilateral mirror method is introduced in this paper. In this approach, the influence of the magnetic medium on both the transmitter and receiver sides is replaced by three equivalent image current coils. By employing the criterion of magnetic flux uniqueness before and after the equivalence, the current coefficients of the image coils are individually determined, leading to an analytical formula for the mutual inductance when the receiver coil is in an arbitrary position. The mutual inductance calculation error between arbitrarily positioned coils was verified through finite element simulations and experimental platform testing to not exceed 4.46%; the effectiveness of the proposed method was thereby demonstrated. Moreover, this method was employed to design the optimal parameters of the toroidal magnetic medium.

The ultrahigh field magnetic resonance imaging (MRI) superconducting magnets require a high homogeneous magnetic field within the diameter of spherical volume (DSV) to generate high-quality images. Spherical harmonic-based B0 shimming relies significantly on the fitting process, which can be computationally demanding, particularly when managing multiple shim coils. The study presents an automatic room-temperature shimming approach that iteratively adjusts shim coil currents to enhance magnetic field homogeneity, using the full width at half maximum (FWHM) of the spectrum as a metric. The method efficiently identifies the optimal shim coil currents, enhancing spatial field homogeneity by minimizing the FWHM. Applying the method to the automatic shimming function of the system software, experimental validation conducted on a 7-T MRI superconducting magnet confirmed the efficacy of the proposed approach. Specifically, employing gradient coils and four shim coils, the automatic room-temperature shimming approach effectively improved the field homogeneity of a 100-mm DSV from 5.478 to 2.989 ppm (p-p) for imaging rat brains.

This study presents the design progress of the equilibrium configuration for the China Fusion Engineering Demo Reactor (CFEDR). A new equilibrium was developed using the TEQ code, incorporating both zero-dimensional physical parameters and the engineering specifications of the magnetic coils. Through iterative optimization of the divertor and blanket structures, the first viable single-null divertor (SND) plasma configuration was achieved. The METIS code was further used to efficiently calculate current and pressure profiles during the ramp-up and flattop phases, thereby validating the design of the poloidal field (PF) coils. Results indicate that the current PF coil system meets the requirements for the SND configuration but faces challenges in maintaining the quasi-snowflake plus shape.

Abstract Extremely low‐frequency (below 10 Hz) current‐induced magnetic field detection has significant applications in high‐voltage DC systems, lithium‐ion battery diagnostics, and industrial process monitoring. Nitrogen‐vacancy (NV) ensembles magnetometry typically employs flux concentrators to enhance magnetic detection sensitivity, but this enhancement comes at the cost of introducing more low‐frequency magnetic noise, such as the thermal magnetization noise of ferromagnetic materials, directly limiting their potential at low frequencies. Here, the enhancement of the signal‐to‐noise ratio (SNR) in extremely low‐frequency magnetic field detection within NV magnetometry, achieved via nonlinear response, is experimentally demonstrated. The approach enables the extension of the magnetic field detection bandwidth to the Hz range while simultaneously enhancing magnetic field sensitivity by using a magnetic flux concentrator. The magnetic field from the coil current, enhanced by the flux concentrator, drives NV ensembles into the nonlinear response region of the differential spectrum of the optically detected magnetic resonance (ODMR). Within this regime, nonlinear effects generate signal‐frequency mixing and 1/f noise suppression. By pre‐modulating the target signal at the driving frequency, its recovery through frequency mixing retains 1/f noise suppression, consequently enhancing SNR. For the 0.5 Hz signal, experimental results demonstrate up to a 2.6‐fold enhancement in SNR. This approach offers a new strategy for utilizing NV ensembles in extremely low‐frequency magnetic field detection.

Abstract The Grad–Shafranov (GS) equation is a nonlinear elliptic partial differential equation that governs the ideal magnetohydrodynamic equilibrium of a tokamak plasma. Previous studies have demonstrated the existence of multiple solutions to the GS equation when solved in idealistic geometries with simplified plasma current density profiles and boundary conditions. Until now, the question of whether multiple equilibria might exist in real-world tokamak geometries with more complex current density profiles and integral free-boundary conditions (commonly used in production-level equilibrium codes) has remained unanswered. In this work, we discover multiple solutions to the static forward free-boundary GS problem in the MAST-U tokamak geometry using the validated evolutive equilibrium solver FreeGSNKE and the deflated continuation algorithm. By varying the plasma current, current density profile coefficients, or coil currents in the GS equation, we identify and characterise distinct equilibrium solutions, including both deeply and more shallowly confined plasma states. We suggest that the existence of even more equilibria is likely prohibited by the restrictive nature of the integral free-boundary condition, which globally couples poloidal fluxes on the computational boundary with those on the interior. We conclude by discussing the implications of these findings for wider equilibrium modelling and emphasise the need to explore whether multiple solutions are present in other equilibrium codes and tokamaks, as well as their potential impact on downstream simulations that rely on GS equilibria.

Abstract Flexible and precise current control of high temperature superconducting (HTS) loads based on flux pump is critical in many applications, which stabilizes both the generated magnetic field and operating current. For HTS loads with small inductances, such as small coils and single cables, it is difficult to stabilize the load current at a specific value without a current controller. Existing works have rarely studied methods to control such currents in HTS loads, prohibiting flux pumps from being used in high precision applications. This paper proposes a fuzzy proportional-integral-derivative (PID) control strategy to regulate the closed-loop load current of a small HTS coil and an HTS single cable, by controlling the DC bias field of a linear-motor type flux pump. The proposed control method enables stabilization of the load current at a preset level in HTS load with small inductance. The experimental results validate the effectiveness and robustness of the proposed control method, which enables the HTS flux pump to be potentially used for highly stable HTS magnets, or as a testbed current source for HTS cables, such as CORC®, etc.

Abstract Modeling of DIII-D plasmas spanning shapes from single to double-null (DN) reveals new insights into the nature of resonant magnetic perturbation (RMP) conditions necessary for edge-localized mode (ELM) suppression. The suppression of ELMs with RMPs has proven difficult in DN configurations, where no device has thus far reported any hints of suppression. Modeling using the GPEC code finds a reduced high-field side response closer to DN shaping. The resulting synthetic diagnostic measurements are consistent with what has been observed in experiments on DIII-D, validating the plasma response model in this regime. While common metrics for suppression do not illustrate a clear distinction between single-null (SN) and DN cases, the pedestal top resonant field does show a ∼20% decrease at DN shaping in modeling. Field penetration is assessed using linear tearing theory, which demonstrates a lack of sufficient pedestal top resonant flux in the DN shape, requiring at least 1.5 × greater RMP coil currents than what was used in experiment. Analysis from drift kinetic simulations further indicate up to 2 × larger critical island widths are required at the pedestal top for tearing mode growth compared to SN cases. Effective island widths inferred from 3D ideal MHD are also analyzed, where maximum widths in lab coordinates indicate a threshold of ∼18–24× the ion gyroradius for sufficient profile flattening for ELM suppression. These results suggest that ELM suppression may be possible in DN with sufficiently large RMP coil amplitude. Future prospects of achieving RMP ELM suppression in the DN configuration may involve going to lower triangularity, which is also highlighted in this work.

In the context of increasing the complexity and intelligence of modern power systems, traditional maintenance approaches for circuit breakers have shown limitations in meeting both reliability and economic requirements. This paper proposes a multi-sensor data fusion fault detection method based on the RF-Adaboost algorithm for spring-operated circuit breakers. By integrating pressure, speed, coil current, and energy storage motor sensors into the mechanism, multi-source operational data are acquired and processed via denoising and feature extraction techniques. A fault detection model is then constructed using the RF-Adaboost classifier. The experimental results demonstrate that the proposed method achieves over 96% accuracy in identifying typical fault states such as coil voltage deviation, reset spring fatigue, and closing spring degradation, outperforming conventional approaches. These results validate the model’s effectiveness and robustness in diagnosing complex mechanical failures in circuit breakers.

The compression effect of compact torus (CT) plasma in gradient magnetic field is investigated in this work. A magnetic compression platform is built which can generate a variable axial magnetic field (1.0, 0.8, 0.6, 0.4, 0.2, 0.1 T) with different coil currents (146.0, 116.8, 87.6, 58.4, 29.2, 14.6 A). Five magnetic pickup coils are arranged which are used to display the time-spatial revolution of CT plasma during the penetration process, and they are located at the positions of 0, 200, 400, 600, and 800 mm in the axial direction, respectively. These experiments are carried out on the Experimental Advanced Superconducting Tokamak (EAST)-Compact Torus Injector (CTI) system, and the results show that the velocity of CT plasma was reduced significantly in places with large magnetic field gradients, as well as the full width at half maximum of the CT plasma. In addition, the magnetic field strength increases initially and then rapidly decreases during the compression process, or even reverses at the end, which may be related to the squeezing of the magnetic field lines and reconnection of the magnetic platform.

Abstract We introduce a methodology to calibrate in situ a set of coils generating bi- or tri-axial magnetic fields, at frequencies where a calibration performed under static conditions would be inaccurate. The methodology uses harmonic analysis of one component of the magnetization of an atomic sample whose spins adiabatically follow an ad hoc applied time-dependent field. The procedure enables the identification of phases and amplitudes of the coil currents required to produce a dynamic magnetic field with the assigned polarization. This determines coil constants that can be subsequently used to produce arbitrary three-dimensional time-dependent fields.

Helmholtz coils are widely used to generate controlled magnetic fields in magnetometer calibration, electromagnetic system testing, material property research experiments, and biotesting. Existing limitations in the homogeneity region of magnetic fields create difficulties in implementing experimental studies. Using multilevel generators with adjustable currents in coils allows generating gradient fields, which speeds up biotesting and increases its accuracy. This work is devoted to modeling gradient hypomagnetic fields using square Helmholtz coils. In COMSOL Multiphysics 6.1, a finite element model has been developed for analyzing magnetic fields generated by DC coils interacting with the Earth’s external magnetic field. The patterns of field formation for different coil orientations relative to the declination and inclination angles of the magnetic field vector have been studied. The study of the formation patterns of gradient hypomagnetic fields in the space between square Helmholtz coils placed in the external magnetic field of the Earth was carried out using finite element modeling in the COMSOL Multiphysics software environment. The effect of currents in the coils on the distribution of the hypomagnetic field intensity in space and along the axis was investigated. Dependences of the informative parameters of the gradient curve of the hypomagnetic field intensity on the value of currents in the coils were obtained, allowing one to construct control functions for currents in square Helmholtz coils to form multi-level fields with an adjustable attenuation coefficient. The results of numerical modeling performed for cases of uniform and gradient distribution of magnetic fields were experimentally confirmed. The conducted full-scale experiments made it possible to compare the calculated data with actual measurements, which indicates a high reliability of the developed model.

ABSTRACTIn this paper, a model‐aided state parameter inversion identification method based on the coil current (CC) of electromagnetic trip device (ETD) is proposed to realise the state parameter inversion online and the quantitative description of defects. Firstly, the inductance calculation model (ICM) considering flux saturation is established based on the magnetic circuit model, and the electromagnetic dynamic coupling model of ETD is constructed and the models are verified by experiments. Subsequently, the state parameter vector space, which can be used to describe the typical defect types is constructed, and the corresponding dataset is created by the electromagnetic dynamics model. Afterwards, the parameter inversion model with CC features as input and state parameter vector as output is obtained by the convolutional neural network (CNN). The accuracy of the parameter inversion model and the validity of the inversion method are verified. Compared with the traditional state classification method based on CC features, the state parameter inversion method proposed can realise the physical quantitative description of the mechanical state, has more explicit physical interpretability and provides a new way to conduct state evaluation and defect diagnosis.

Abstract High-temperature superconducting (HTS) no-insulation (NI) coils provide enhanced thermal stability against local overheating but exhibit complex inductive behaviour due to turn-to-turn bypass currents. Furthermore, coil magnetization induces screening currents that generate non-uniform current density distributions and a screening current-dependent inductance (SCDI). This SCDI further complicates the inductive behaviour of HTS NI coils, while the inductive behaviour itself also influences current evolution and screening current profiles. A comprehensive electromagnetic model that accounts for the bidirectional coupling between inductive behaviour and the screening current effect is essential. In this study, we propose a precision electromagnetic model that integrates an equivalent circuit model with a J-model, emphasizing their bidirectional coupling. The model was validated using an NI magnet constructed from 12 single pancake coils, which was charged to a series of target currents spanning low to high self-field conditions. The results demonstrate that the model accurately reproduces the screening current evolution, the SCDI matrix of all pancake coils, magnetic flux density, coil voltage, and the screening current–induced field (SCIF). Additionally, the observed lower coil voltage compared to the expected value from a normal inductance is in agreement with experimental results. A larger SCIF was observed due to advanced and delayed current evolution in different SP coils caused by the SCDI. Field-dependent dynamics arising from variations in critical current and magnetic flux penetration are also effectively captured. The proposed model provides a robust framework for accurately estimating the coupled inductive and screening current dynamics in large-scale high-field HTS NI magnets, thereby offering critical insights for magnet design and operational safety.

In order to solve the problem that the system parameters will be offset during the detection process of the pulsed eddy current receiving coil, this paper first analyzes the response signal of the receiving system and the deconvolution process of the response signal, and discusses the influence of various system parameters on the deconvolution accuracy. A method is proposed to change the system response characteristics and apply a step signal through the excitation coil to realize parameter identification through the response of the receiving coil system. The error of feature extraction under the change in each parameter is discussed, and the influence of increasing the matching resistance and switching the capacitor in parallel on the identification accuracy is analyzed and compared. It is proposed to realize the accurate identification of the receiving system through the Newton method. It is proved from both simulation and experiment that the method proposed in this paper can realize the identification of the receiving coil parameters efficiently, conveniently, and accurately, and can improve the inversion accuracy of the pulsed eddy current detection signal and improve the detection accuracy.

Abstract This large database study of resonant magnetic perturbation (RMP) edge localized mode (ELM) suppression thresholds in the AUG, DIII-D, EAST, and KSTAR tokamaks details the key strengths and weaknesses of RMP metrics. The RMP ELM suppression database used for this work contains plasma information at the time of transition from ELMing to ELM suppressed states where a clear experimental threshold is identified. The experimental threshold distributions are compared for five metrics: (1) the island overlap width, (2) pedestal top Chirikov overlap, (3) peeling edge displacement, (4) pedestal top resonant drive, and (5) edge dominant mode overlap. The distributions, the regularity of the dependence on RMP coil currents, and the sensitivities of a given metric to equilibrium reconstruction details are compared. The overlap metric proves to be a good compromise between including the appropriate plasma response physics and maintaining a numerical robustness. This quantity does not exhibit clear power-law scalings for projection, but machine learning can assist in predicting thresholds within the existing parameter ranges and providing uncertainty quantification of those predictions. Two new first-principles models, one utilizing a threshold from the non-linear Modified Rutherford equation evaluated at the pedestal top and one utilizing the SLAYER code to calculate the linear tearing threshold from torque balance, offer possible paths to extrapolation beyond the existing database parameter space.

The use of oil–water rings has become an emerging, effective, and energy-saving method of transporting heavy oil. Maintaining the shape of the oil–water ring and preventing rupture during the transport of heavy oil are of great scientific significance in oil–water annular flow transportation. To ensure the oil–water ring passes smoothly through the elbow without rupture, this article proposes an asymmetrical magnetohydrodynamic (MHD) propulsion method to utilize the significant difference between the conductivity of heavy oil and electrolyte solution to achieve an accelerating effect on the outer water ring. The magnetohydrodynamic device designed by this method can generate a magnetic field and provide Lorentzian magnetic force to achieve the asymmetric acceleration of the oil and water rings, to homogenize the water ring velocity on the inner and outer elbows, to push the deviated oil core back to the center of the pipeline, and to repair the rupture of the water film. The flow state of the oil–water ring in the bend pipe under the joint action of the electric field and magnetic field is simulated by a differential MHD thick oil simulation flow model, which confirms that the device can realize the repair of the oil–water ring flow at the bend pipe and ensure that the oil–water ring flow passes through the bend pipe stably. Meanwhile, the effects of coil current, electrode plate voltage, and the conductivity of electrolyte solution on the morphology and velocity of the oil–water ring in the elbow are investigated. In addition, the role of the device in maintaining the morphology under different gravitational conditions is investigated. These results provide a reference design for related devices and offer a new approach to heavy oil transportation.

Electron beam ion traps (EBITs) are compact devices optimized for producing ions in high charge states for spectroscopic studies or as extracted beams. Key characteristics, such as current density and electron-ion overlap, govern ionization and excitation rates. Using visible and X-ray imaging of emissions from highly charged ions, the spatial distributions of the electron beam and ion cloud in the Smithsonian Astrophysical Observatory (SAO) EBIT were measured, enabling the determination of the effective electron density. The nominal electron beam full width at half maximum (FWHM) was determined to be 92.0 ± 9.7 μm, while the ion cloud FWHM was 410.5 ± 16.5 μm, indicating an effective electron density roughly an order of magnitude lower than determined geometrically. The effects of magnetic fields on the electron beam size were also investigated, demonstrating sensitivity to the focusing magnet and bucking coil currents. These findings emphasize the need for simultaneous measurement of the effective electron density to improve the accuracy of density-sensitive studies in EBIT systems.

A new mode of operation of a so-called dipolar magnetic confinement apparatus and a novel approach to stationary magnetic plasma confinement with co-axial current coils, which can be suitable for fusion applications, are suggested.