Hall Probe Measurements Research Articles

Navigation of superparamagnetic particles with a pre-magnetized high-temperature superconducting bulk in a weak background field

Abstract Recent research has shown significant progress towards a full body magnetic drug delivery (MDD) system for use in targeted cancer treatments. Although many different MDD systems have been proposed to generate strong remote forces capable of rapidly changing directions at distances greater than 10 cm, current state-of-the-art technologies lack in force strength and/or degrees of freedom. Knowing that high temperature superconducting (HTS) bulks can achieve trapped fields an order of magnitude larger than ferromagnets, this work aims at numerically and experimentally evaluating the forces that can be produced by HTS bulks in a uniform magnetic field. We first use Hall probe measurements and finite element simulations to determine the magnetic field generated by an HTS pellet and show that both results are in good agreement. Using a combination of simulations and experiments, we then show that for a 14 × 6 mm YBa2Cu3O 7 − x pellet magnetized at 2 T, remote forces on superparamagnetic microparticles are maximized at background fields of ∼50 mT. In addition, the direction of the magnetic forces can be flipped by changing the direction of the applied field relative to the HTS’s magnetization. The HTS bulk was successfully used to navigate magnetic microparticles in a glass bifurcation mimicking the hepatic artery of the human liver. Finally, we show by simulation that a large HTS pellet magnetized at 5 T in a field of ∼250 mT can generate stronger forces with more degrees of freedom than the strongest forces achievable in current MDD technologies.

Modeling Geomagnetically Induced Currents in the Alberta Power Network: Comparison and Validation Using Hall Probe Measurements During a Magnetic Storm

AbstractDuring space weather events, geomagnetic disturbances (GMDs) induce geoelectric fields which drive geomagnetically induced currents (GICs) through electrically‐grounded power transmission lines. Alberta, Canada—located near the auroral zone and thus prone to large GMDs—has a dense network of magnetometer stations and surface impedance measurements to better characterize the GMD and ground conductivity, respectively. GIC monitoring devices were recently installed at five substation transformer neutrals, providing a unique opportunity to compare data to modeled GICs. GICs are modeled across the >240 kV provincial power transmission network during a moderate GMD event on 24 April 2023. GIC monitoring devices measured larger neutral‐to‐ground currents than expected up to 117 Amps during peak storm time, providing unequivocal evidence linking network GICs with GMDs. The model performs reasonably well (correlation coefficients >0.5; performance parameter >0.15) at four of five substations, but generally underestimates peak GIC values (sometimes by a factor >2), suggesting that the present model underrepresents overall network risk. The model performs poorly at one of the five substations (correlation = 0.46; performance parameter = 0.10), the reasons for which may be due to simplifications and/or unknowns in network parameters. Despite these underestimates, during this GMD, the model predicts the largest GIC at substations located in the northeastern part of the province (240 kV) or around Edmonton (500 kV)—regions which have significant electrical and industrial infrastructure. Further refinement of the network model with transformer resistances, more line and earthing resistances, and/or including lower voltage levels is necessary to improve data fit.

Novel correction procedure for compensating thermal contraction errors in the measurement of the magnetic field of superconducting undulator coils in a liquid helium cryostat.

Superconducting undulators (SCUs) can offer a much higher on-axis undulator field than state-of-the-art cryogenic permanent-magnet undulators with the same period and vacuum gap. The development of shorter-period and high-field SCUs would allow the free-electron laser and synchrotron radiation source community to reduce both the length of undulators and the dimensions of the accelerator. Magnetic measurements are essential for characterizing the magnetic field quality of undulators for operation in a modern light source. Hall probe scanning is so far the most mature technique for local field characterization of undulators. This article focuses on the systematic error caused by thermal contraction that influences Hall probe measurements carried out in a liquid helium cryostat. A novel procedure, based on the redundant measurement of the magnetic field using multiple Hall probes at known relative distance, is introduced for the correction of such systematic error.

An in-vacuum measurement system for CPMUs at Diamond Light Source

An in-vacuum Hall probe measurement system was designed, built, and used to measure four Cryogenic Permanent Magnet Undulators (CPMUs) at Diamond Light Source. The devices were tuned to correct the phase error at cold temperatures based on the measurements from the in-vacuum system. The in-vacuum system consists of a stretched wire system supplied by Danfysik and an in-house built Hall probe system. The Hall probe system has gone through two iterations: the first beam was prone to deforming with temperature changes; the second was made thicker following design changes to the magnet holders and girders of the CPMUs which allowed more space for the beam inside the vacuum vessel. The design and commissioning of the measurement system will be presented, along with some measurements of the CPMUs at room temperature and at 77 K. Details such as triggering of the Hall probe measurements, height compensation, and temperature compensation will be covered.

Diode type unidirectional conduction in Hall measurement of magnetic honeycomb lattice

Artificial magnetic honeycomb lattice is emerging as a new platform for spintronics research applications, as evidenced from recent findings of magnetic diode effect and collective magnetic switching phenomena in different lattice geometries. In this report, we present Hall measurements on thermally tunable artificial magnetic honeycomb lattice. Experimental investigation using detailed Hall probe measurements reveals diode-type unidirectional conduction in both longitudinal and Hall resistances. The unidirectional conduction persists to low temperature but remains unaffected to modest application of perpendicular magnetic field. The behavior can be understood in terms of topological magnetic charges that arise on the vertices of honeycomb lattice and affect electrical transport properties. The experimental finding can be utilized for the design of spintronic logic devices.

Hall probe magnetic measurements of the superconducting undulator

The superconducting undulator with 15.6 mm period and 1.2 T magnetic field described in this article has 8 mm magnetic gap. The magnetic measurements system in such conditions required using of special tube (ante-chamber) inside of undulator magnetic gap. The thermal insulation between cold magnet and this measurement tube does not allow to have stable temperature along this tube length. The temperature range into this tube is 70–300 K. Hall probe measurements in this case are a rather complicated problem. The features of the method of measurement and processing of results are described.

A flexible approach on pulsed wire magnetic measurement method

The Pulsed Wire (PW) method offers a promising solution for performing local magnetic field measurements in undulators that have limited access that restricts traditional Hall-Probe (HP) measurements. With this technology, undulators can be designed with a closed frame structure, becoming more compact and cost effective.At the same time, the PW method suffers from intrinsic error sources which can impact the quality of the magnetic field measurements and therefore losing confidence in its results. This paper provides a flexible framework for calculating the magnetic field, correcting for the dispersion effect and the pulse shape. This framework is used to correct experimentally collected pulsed wire data and compare them against Hall-probe measurements for the same magnetic field.

Flux Creep in a Bi-2212 Rutherford Cable for Particle Accelerator Applications

Bi-2212 superconducting cables are being considered for use in the high field magnets needed for the next generation of particle accelerators. Magnetization in these cables and the decay of that magnetization lead to field error and field-error drift, respectively, which need to be compensated. To study this, a segment of the winding pack was extracted from a racetrack coil made from Bi-2212 Rutherford cable. Using a Hall probe measurement technique, we measured the response of the cable's magnetization and its magnetization decay to changes in the applied magnetic field. The effect of adjustments to the cycling of the magnetic field was studied, intended to simulate the preinjection cycles of an accelerator magnet. Three <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> vs. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> loops were constructed by sweeping the magnetic field applied to the sample from 0 to 2.5 T, then to a preinjection field “x” (where x = 0, 0.25, 0.75 T), and finally up to 1 T. The applied field was then held at 1 T for 1500 s, and the magnetization decay was measured. The decay was found to vary from 8% to 14% after 1500 s, depending on the preinjection field cycle.

Pulsed-wire system for magnetic-field measurements on an in-vacuum undulator at NSRRC

Pulsed-wire measurement of a magnetic field has been developed by many groups. A pulsed-wire system has been set up and used to measure an in-vacuum undulator magnetic field at NSRRC. A copper zirconium wire (length 4 m, diameter 100 μm) has been selected. The pulse current is generated with an in-house power supply. A high-resolution and fast-feedback laser-photodiode system served to detect the displacement of the wire. Construction of an in-vacuum NdFeB-permanent-magnet undulator (period 22 mm, magnetic length 2 m) has been completed for Taiwan Photon Source. In this work, we applied a highly stiff, thin copper zirconium wire to diminish the maximum sag during measurement of a long undulator. We also demonstrate that the distance between the location of a wire dispersion sensor and a fixed point of the wire is an important issue to separate the main and weak reflection signals in pulsed-wire measurement. From the results of the undulator measurement, we obtained the magnetic field performed with the pulsed wire and Hall probe measurements, which are compared.

Quantification of the Effect of an External Magnetic Field on Water Oxidation with Cobalt Oxide Anodes.

Here, we quantify the effect of an external magnetic field (β) on the oxygen evolution reaction (OER) for a cobalt oxide|fluorine-doped tin oxide coated glass (CoOx|FTO) anode. A bespoke apparatus enables us to precisely determine the relationship between magnetic flux density (β) and OER activity at the surface of a CoOx|FTO anode. The apparatus includes a strong NdFeB magnet (βmax = 450 ± 1 mT) capable of producing a magnetic field of 371 ± 1 mT at the surface of the anode. The distance between the magnet and the anode surface is controlled by a linear actuator, enabling submillimeter distance positioning of the magnet relative to the anode surface. We couple this apparatus with a finite element analysis magnetic model that was validated by Hall probe measurements to determine the value of β at the anode surface. At the largest tested magnetic field strength of β = 371 ± 1 mT, a 4.7% increase in current at 1.5 V vs the normal hydrogen electrode (NHE) and a change in the Tafel slope of 14.5 mV/dec were observed. We demonstrate through a series of OER measurements at sequential values of β that the enhancement consists of two distinct regions. The possible use of this effect to improve the energy efficiency of commercial water electrolyzers is discussed, and major challenges pertaining to the accurate measurement of the phenomenon are demonstrated.

(Gd,Y,Er)Ba2Cu3Oy bulk superconducting system processed via infiltration growth

Ternary bulk REBa2Cu3Oy superconductors processed via oxygen-controlled melt growth (OCMG) have exhibited superior superconducting properties with respect to binary and single systems. However, the OCMG process is rather complicated, expensive, and difficult to scale-up into industrial level. To overcome these issues, we have studied the yet unexplored ternary bulk (Gd,Y,Er)Ba2Cu3Oy “(Gd,Y,Er)-123″ system, fabricated via trendy infiltration growth (IG) process. We studied the effect of varying Y-211 and Er-211 ratio (Gd: Y: Er = 0.33: 0.33-x: 0.33+x, where x = 0, 0.05, 0.1, 0.15 and 0.2) in the preform on the final superconducting properties and microstructure. We succeeded to fabricate (Gd,Y,Er)-123 single-grain bulks (diameter – 20 mm). The critical current density (Jc) and trapped field increased proportionally with the increased amount of Er-211 in the preform. Hall-probe measurements showed that the best bulk (x = 0.2) exhibited trapped field of 0.53 T at 77 K (applied field of 1 T) and self-field Jc values of 238 and 63 kA/cm2 at 50 and 77 K, respectively. FE-SEM micrographs revealed formation of two different types of secondary phases in the matrix (small and large). EDX analysis showed that the smaller 211 particles were Er-rich, while the larger ones were an irregular mixture of three RE-211 phases.

Axisymmetric magnetically enhanced discharges described in terms of flux coordinates

Magnetically enhanced glow discharges and arcs are widely used in materials processing and other branches of plasma technology. An important class—including, for example, circular magnetrons, Hall thrusters, and certain ion sources—is axisymmetric devices with a poloidal magnetic field. This paper discusses the representation of such fields using the so-called flux coordinates (ψ,θ,s), a system of field aligned spatial coordinates which include the flux label ψ of a magnetic field line, the azimuth angle θ, and the arc length s. After reviewing the formalism—which finds widespread use in fusion research and plasma astrophysics—a number of special amendments are introduced to make it suitable for technological plasmas. Focus is put on the description of internal and external domain boundaries (separatrices and walls). The flux coordinates are numerically constructed for the confinement region of a circular magnetron using an analytical field model that was obtained in earlier investigations by fitting a physically plausible ansatz to Hall probe measurements. As a first application, the dynamics of the energetic electron component in a high power impulse magnetron sputtering discharge is investigated on the basis of a linear kinetic model and the corresponding confinement is calculated by solving an eigenvalue problem.

Differential Magnetometer Measurements of Geomagnetically Induced Currents in a Complex High Voltage Network

AbstractSpace weather poses a hazard to grounded electrical infrastructure such as high voltage (HV) transformers, through the induction of geomagnetically induced currents (GICs). Modeling GICs requires knowledge of the source magnetic field and the Earth's electrical conductivity structure, in order to calculate the geoelectric fields generated during magnetic storms, as well as knowledge of the topology of the HV network. Direct measurement of GICs at the ground neutral in substations is possible with a Hall effect probe, but such data are not widely available. To validate our HV network model, we use the differential magnetometer method (DMM) to measure GICs in the 400 kV grid of Great Britain. We present DMM measurements for the 26 August 2018 storm at a site in eastern Scotland with up to 20 A recorded. The line GIC correlates well with Hall probe measurements at a local transformer, though they differ in amplitude by an order of magnitude (a maximum of 2 A). We deployed a long‐period magnetotelluric (MT) instrument to derive the local impedance tensor which can be used to predict the geoelectric field from the recorded magnetic field. Using the MT‐derived electric field estimates, we model GICs within the network, accounting for the difference in magnitude between the DMM‐measured line currents and earth currents at the local substation. We find that the measured line and earth GICs match the expected GICs from our network model, confirming that detailed knowledge of the complex network topology and its resistance parameters is essential for accurately computing GICs.

Field Measurements of a Cryogenic Permanent Magnet Undulator at the TPS

A PrFeB-based cryogenic permanent-magnet undulator (CPMU) with a period length of 15 mm (CU15) is being constructed to provide high brilliant X-rays for the Taiwan Photon Source (TPS) nano-probe beamline. Field measurements of this undulator will be performed with a Hall probe in a vacuum environment. The in-situ Hall probe measurement system (Yang et al. , 2014) was improved (Yang et al. , 2016) to allow measurement and tuning of the CU15 magnetic field. A field strength and temperature dependent calibration of the Hall probe was done to obtain realistic field distributions. By tuning the differential adjusters and spring modules, we can correct magnetic field errors caused by assembly tolerances and temperature gradients along the magnetic arrays, thus lowering phase errors to reach our design goals. This paper describes details of improvements in the measurement system, field tuning methods, and measurement results at cryogenic temperatures.

Magnetic measurements and analysis of trajectory straightness of 20 mm period hybrid undulator

The U20 is a prototype NdFeB-cobalt steel hybrid device of 20 mm period length with twenty five periods and designed to provide a magnetic flux density from 2400 G (rms) to 500 G (rms) in the 10 mm–20 mm gap range. The electron trajectory and the field harmonics are analyzed on the basis of the Hall probe measurements on U20. The electron trajectory of the U20 undulator lacks straightness. The trajectory straightness is done by locally manipulating the magnetic field strengths at select locations. It is demonstrated that improvement of the phase error and field harmonics are achieved through trajectory straightness.

Visualization and quantification of inhomogeneous and anisotropic magnetic fields by polarized neutron grating interferometry

The intrinsic magnetic moment of a neutron, combined with its charge neutrality, is a unique property which allows the investigation of magnetic phenomena in matter. Here we present how the utilization of a cold polarized neutron beam in neutron grating interferometry enables the visualization and characterization of magnetic properties on a microscopic scale in macroscopic samples. The measured signal originates from the phase shift induced by the magnetic potential. Our method enables the detection of previously inaccessible magnetic field gradients, in the order of T cm−1, extending the probed range by an order of magnitude. We visualize and quantify the phase shift induced by a well-defined square shaped uniaxial magnetic field and validate our experimental findings with theoretical calculations based on Hall probe measurements of the magnetic field distribution. This allows us to further extend our studies to investigations of inhomogeneous and anisotropic magnetic field distribution.

Optical Chiral Induced Spin Selectivity XMCD Study.

The chiral induced spin selectivity (CISS) effect in which selective transport of electron spins through helical chiral molecules occurs, has attracted a lot of attention in recent years. This effect was used to magnetize ferromagnetic (FM) samples by utilizing adsorbed chiral molecules. The electron transfer through the molecules was generated optically or electrically. In the optical configuration, circularly polarized light induced efficient magnetization by spin torque transfer (STT), using a hybrid of quantum dots (QDs) and chiral molecule self-assembled monolayer (SAM). Here, we use X-ray magnetic chiral dichroism (XMCD) spectroscopy in order to probe the optically induced magnetization on thin FM films. The results show differences in the FM magnetization depending on the optical circular polarization, matching previous non-local Hall probe measurements.

100 keV H+ ion irradiation of as‐deposited Al‐doped ZnO thin films: An interest in tailoring surface morphology for sensor applications

We report the influence of 100 keV H+ ion beam irradiation on the surface morphology, crystalline structure, and transport properties of as‐deposited Al‐doped ZnO (Al:ZnO) thin films. The films were deposited on silicon (Si) substrate by using DC sputtering technique. The ion irradiation was carried out at various fluences ranging from 1.0 × 1012 to 3.0 × 1014 ions/cm2. The virgin and ion‐irradiated films were characterized by X‐ray diffraction, Raman spectroscopy, atomic force microscopy, and Hall probe measurements. Using X‐ray diffraction spectra, 5 points Williamson‐Hall plots were drawn to deduce the crystallite site and strain in Al:ZnO films. The analysis of the measurements shows that the films are almost radiation resistant in the structural deformation under chosen irradiation conditions. With beam irradiation, the transport properties of the films are also preserved (do not vary orders of magnitude). However, the surface roughness and the crystallite size, which are crucial parameters of the ZnO film as a gas sensor, are at variation with the ion fluence. As ion fluence increases, the root‐mean‐square surface roughness oscillates and the surface undergoes for smoothening with irradiation at chosen highest fluence. The crystallite size decreases initially, increases for intermediate fluences, and drops almost to the value of the pristine film at highest fluence. In the paper, these interesting experimental results are discussed in correlations with ion‐matter interactions especially energy losses by the ion beam in the material.

Reconstruction of the static magnetic field of a magnetron

The simulation of magnetron discharges requires a quantitatively correct mathematical model of the magnetic field structure. This study presents a method to construct such a model on the basis of a spatially restricted set of experimental data and a plausible a priori assumption on the magnetic field configuration. The example in focus is that of a planar circular magnetron. The experimental data are Hall probe measurements of the magnetic flux density in an accessible region above the magnetron plane [P. D. Machura et al., Plasma Sources Sci. Technol. 23, 065043 (2014)]. The a priori assumption reflects the actual design of the device, and it takes the magnetic field emerging from a center magnet of strength mC and vertical position dC and a ring magnet of strength mR, vertical position dR, and radius R. An analytical representation of the assumed field configuration can be formulated in terms of generalized hypergeometric functions. Fitting the ansatz to the experimental data with a least square method results in a fully specified analytical field model that agrees well with the data inside the accessible region and, moreover, is physically plausible in the regions outside of it. The outcome proves superior to the result of an alternative approach which starts from a multimode solution of the vacuum field problem formulated in terms of polar Bessel functions and vertical exponentials. As a first application of the obtained field model, typical electron and ion Larmor radii and the gradient and curvature drift velocities of the electron guiding center are calculated.

Design of Cone Magnets and Shielding to Align and Calibrate Hall Probe Measurement System

To measure the magnetic fields with a Hall probe, accurate alignment needs to be considered. Therefore, we present improvements to the Hall probe measurement system, including cone magnets and a zero-field shield as simulated by the OPERA. The design of the cone magnets of the North-face-North type is greatly helpful to monitor the magnet alignment. The accurate location of the Hall probe doping area should be determined before doing any measurements. In addition, a zero-field shielding tube is used to reset the probe to zero. The results of simulations are reported in this paper.