Measurement Of Magnetic Field Distribution Research Articles

Application of multipole moments and magnetic techniques for determination of tokamak plasma shift

AbstractIn this contribution, we presented approaches for the determination of tokamak plasma column shift based on multipole moments and magnetic techniques. First, we presented analytical details for using this technique. Then, the principle of different models based on this technique for the design and fabrication of six coils will be presented: four modified Rogowski coils (two cosine coils and two sine coils) and two saddle coils (saddle sine coil and saddle cosine coil). Also, to compare the results, the flux loops technique is used. Because of continuous measurements of magnetic field distribution around the tokamak plasma using multipole coils, this technique gives us more reliable information about the plasma current displacement. Moreover, we deduced the plasma current and plasma boundary centers shift using the two semi-empirical techniques in the IR-T1 tokamak. First, the plasma current center is calculated from the vertical field coil characteristics. The calculation is made focusing on the vertical field coil current and voltage changes due to a horizontal displacement of the plasma column. Also, the plasma boundary center shift was measured from the external magnetic coils. The results from these two techniques are compared and discussed.

New approaches on application of multipole moments for determination of toroidal plasma shift

An application of multipole moments for the determination of toroidal plasma column shift is presented. First, we present analytical details for using this technique. Then, the principle of different models based on this technique for design and fabrication of a six coils will be presented: four modified Rogowski coils (two cosine coils and two sine coils) and two saddle coils (saddle sine coil and saddle cosine coil). As continuous measurements of magnetic field distribution around the toroidal plasma can be made using these coils, this technique is a good method for the determination of toroidal plasma column shift.

Asymmetric spin echo sequence and requirements on static magnetic field of NMR scanner

The article describes studies with two NMR sequences frequently used for static magnetic field distribution measurement. The gradient echo sequence is suitable for such measurements, it has good sensitivity and fast measurements are possible. The asymmetric spin echo sequence is also suitable for inhomogeneity measurements, but the time taken for measurement is longer. The purpose of the studies was the comparison of the features and the quality of results of both sequences under conditions of an imperfect static magnetic field. The imperfection deliberately was inserted into the static magnetic field of a low-field NMR scanner. Two common measurements were used for comparison, nevertheless due to the low-field NMR scanner the processing of the measured data was not entirely standard and processing using optimisation was required. The experiments revealed that the asymmetric spin echo sequence can provide images of a good quality and also under interference from a static magnetic field where measurement using the gradient echo sequence is not able to provide useable images.

Remote Measurement of Magnetic Field Distribution in the Solenoid

This paper presented an innovative approach to implement physics experiment by remote measurement system. In the experiment of magnetic field distribution in the solenoid, a two channel programmable current source was adopted, one channel of the programmable current source was used to incentive the solenoid to produce magnetic field and the other was used for the Hall probe to generate Hall voltage. The Hall probe was controlled by a step motor to different positions of the solenoid. The Hall voltage and the position curve were obtained by the measurement system showed the magnetic field distribution of the solenoid. The entire experiment was done via the internet to realize the remote experiment.

RETRACTED ARTICLE: Multipole Moments Based Study on Determination of Toroidal Plasma Equilibrium Position and Shift

The multipole moments based technique studied for the determination of toroidal plasma column shift. First, we presented analytical details for using this technique. Then, principle of two different models based on this technique for design and fabrication of a modified Rogowski coil (MRC) and Saddle Sine coil (SSC) will be presented. Because of continuous measurements of magnetic field distribution around the toroidal plasma using the MRC and SSC, this technique is the good method for the determination of toroidal plasma column shift.

Répartition du flux magnétique dans une structure anisotrope à joints de type step-lap. Mesures, modélisation 2D et simulation 3D

This article, which deals with grain oriented steel sheets (GO), has a dual purpose. The first goal is to understand how the magnetic field sets up in a magnetic circuit with step-lap joints. Then, the importance of magnetic field components normal to the sheet plane is pointed out with an experimental instrumentation and a 3D finite element simulation (FE). Because of the difficulties for modeling 3D magnetic circuits with anisotropic sheets, a method of homogenization is proposed. The principle is to substitute a 3D anisotropic structure by a magnetically equivalent 2D model. Results of the magnetic field distribution measurements are compared with the results of 3D and equivalent 2D simulations.

Vilnius High Magnetic Field Centre Facilities

A brief overview of the high-field facilities at the Vilnius High Magnetic Field Centre (VMC) is presented in this paper. We highlight the main activity of the VMC, which lies in studying the effects of pulsed magnetic and electrical fields on material properties, and give a short description of the pulsed magnets. A new method for generating nanosecond duration strong electric field pulse in conjunction with a magnetic field pulse is presented. The possibility of modulating electric field pulses by pulsed magnetic fields is discussed. Here, we also report on our investigations of the colossal magnetoresistance (CMR) effect in thin polycrystalline La-Sr-MnO films, which are of special interest for the design of new B-scalar magnetic field sensors used for magnetic field distribution measurements during railgun operation and other applications.

Performance evaluation of short-wavelength FIR laser polarimeter with dual silicon photoelastic modulators

Measurement of an internal magnetic field distribution in magnetically confined fusion devices is indispensable for both understanding the plasma physics and controlling plasmas. A polari-interferometer based on the Faraday effect has been used for such a purpose. This paper describes performance evaluations of a part of the polarimeter with photoelastic modulators (PEMs) of the short-wavelength far-infrared (FIR) laser polari-interferometer. The wavelengths of the light source are 57.2 and 47.7 μ m, which are suitable for a high-density operation and large fusion devices. The PEM for the FIR region is newly developed with high-resistive silicon in which absorption of the FIR laser is small. The polarization angle is successfully measured and an angle resolution of 0.01° with a time resolution of 1 ms is achieved. A drift of the baseline of about 0.1° for 1000 s is observed and is found to be caused by changes in the room temperature.

Modeling And Measurement System For Magnetic Field Distributions In Biological Structures

Abstract In this paper we develop a system for modeling and measurement of magnetic field distributions in biological structures caused by the externally applied electromagnetic field. We describe an effective and versatile approach for three-dimensional reconstruction of the field distributions from two-dimensional visualization the measured magnetic field data. The finite element model for magnetic field calculation is built. The magnetic fields of very thin slices of the 3D object are determined and visualized. Using these 2D images as slices of 3D image and based on the field theory and image processing techniques we developed a reconstruction approach for 3D visualization of magnetic field. This approach combines new technologies of 3D visualizations and characterizes with flexibility, simplicity and portability. The proposed approach was successfully applied for 3D reconstruction and visualization of magnetic field and current distributions in biological structures. The virtual microscope is developed for investigations of magnetic field distributions in biological structures during magnetic stimulation. Anisotropic Magneto-Resistive (AMR) sensors are applied for magnetic field measurements. AMR sensors are combined in array probes in order to increase productivity of measurement process and improving the performance of probes.

Simple and accurate unwrapping phase of MR data

A new method for unwrapping phase of MR data, acquired using a double gradient-echo measurement, is introduced. The method not only removes artifacts due to gradients or hardware imperfections but also simultaneously shortens the effective echo time of the measuring sequence to unwrap the phase. The acquisition is repeated twice using different echo times and the ratio of both acquired and Fourier transformed data matrices is calculated. The state of unwrapping depends on the difference of the echo times and can be very high without any distortion. Influence on the signal-to-noise of the resulting field map is the same as for the unwrapped data. This method is applicable on all MR scanners and is very suitable for magnetic field distribution measurements.

Elimination of Distortions in Static Magnetic Field Distribution Measurements

A new method for magnetic field distribution measurement distortions elimination using gradient-echo double measurement is introduced. To exclude phase distortion unwrapping algorithms or methods are used shortening the echo time of the measuring sequence. In the article the measurement acquisition was double repeated with different echo times and ratio of the both acquired and Fourier transformed data matrices was performed. The distortion due to phase periodicity was suppressed and also distortion due to background influence was eliminated. Method is applicable for all NMR scanners and is suitable for magnetic field distribution measurements. Ill. 3, bibl. 13 (in English; summaries in English, Russian and Lithuanian).

Hole-doping dependence of the magnetic penetration depth and vortex core size inYBa2Cu3Oy: Evidence for stripe correlations near18hole doping

We report on muon spin rotation measurements of the internal magnetic field distribution $n(B)$ in the vortex solid phase of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{y}$ (YBCO) single crystals, from which we have simultaneously determined the hole-doping dependences of the in-plane Ginzburg-Landau (GL) length scales in the underdoped regime. We find that ${T}_{c}$ has a sublinear dependence on $1∕{\ensuremath{\lambda}}_{ab}^{2}$, where ${\ensuremath{\lambda}}_{ab}$ is the in-plane magnetic penetration depth in the extrapolated limits $T\ensuremath{\rightarrow}0$ and $H\ensuremath{\rightarrow}0$. The power coefficient of the sublinear dependence is close to that determined in severely underdoped YBCO thin films, indicating that the same relationship between ${T}_{c}$ and the superfluid density is maintained throughout the underdoped regime. The GL coherence length ${\ensuremath{\xi}}_{ab}$ (vortex core size) is found to increase with decreasing hole-doping concentration and to exhibit a field dependence that is explained by proximity-induced superconductivity on the CuO chains. Both ${\ensuremath{\lambda}}_{ab}$ and ${\ensuremath{\xi}}_{ab}$ are enhanced near $\frac{1}{8}$ hole doping, supporting the belief by some that stripe correlations are a universal property of high-${T}_{c}$ cuprates.

Stacking procedure for noise reduction in magneto-optical imaging

Magneto-optical effects are exploited for direct visualization of the magnetic field distribution in solid-state physics, in chemistry and in astrophysics. In this paper, we present a procedure for increasing the signal-to-noise ratio ( S/ N) in microscopic magneto-optical imaging of magnetic materials. The procedure consists of the repetitive measurement of the bi-dimensional magnetic field distribution and of custom routines for assembling the data. These routines use morphological operators for the alignment and the sum of the collected frames (stacking) and for discharging measurements affected by artefacts. The stacked image gains a S/ N improvement equal to the square root of the number of selected frames. Also the pixel depth is increased by the same factor. The proposed stacking procedure is applied to the measurement of static magnetic field distributions of domain walls and magnetic vortices in garnet films.

A levitation force and magnetic field distribution measurement system in three dimensions

A levitation force and magnetic field distribution measurement system in three dimension has been designed and constructed, which can be used for the levitation force measurement between a superconductor and a magnet, or magnet to magnet in three dimensions; and for the measurement of magnetic field distribution in three dimensions according to your need in space. It can also give out the dynamical changing result of magnetic field density with time during levitation force measurement. If we change the sensor of the detector of the measurement system, it also can be used for other kinds of measurement of physical properties. It is a good device for the measurement of magnetic properties of materials. In addition the device can also be used to work at carving in three dimensions.

Measurement and visualization of three-dimensional radial and vectored magnetic field distribution by use of the magnetic CT method

The measurement and visualization of three-dimensional radial and vectored magnetic field distribution based on the magnetic computed tomography (CT) method have been reported. Applying the method, it is possible to measure a surrounding magnetic field such as a spherical region by using a simple probe, which is not limited to the measurement of two-dimensional magnetic field distribution. It has been shown that the magnetic field distribution of a spherical surface covering a sample object can be visualized from the measured and calculated results with a spherical CT probe and CT reconstruction algorithm.

COMPARISON OF CARDIAC MAGNETIC FIELD DISTRIBUTIONS DURING DEPOLARIZATION AND REPOLARIZATION

Multichannel magnetocardiography measures the magnetic field distribution of the human heart noninvasively from many sites over the body surface. Multichannel magnetocardiogram (MCG) analysis enables regional temporal differences in the distribution of cardiac magnetic field strength during depolarization and repolarization to be identified, allowing estimation of the global and local inhomogeneity of the cardiac activation process. The aim of this study was to compare the spatial distribution of cardiac magnetic field strength during ventricular depolarization and repolarization in both normal subjects and patients with cardiac abnormalities, obtaining amplitude measurements by magnetocardiography. MCGs were recorded at 49 sites over the heart from three normal subjects and two patients with inverted T-wave conditions. The magnetic field intensity during depolarization and repolarization was measured automatically for each channel and displayed spatially as contour maps. A Pearson correlation was used to determine the spatial relationship between the variables. For normal subjects, magnetic field strength maps during depolarization (R-wave) showed two asymmetric regions of magnetic field strength with a high positive value in the lower half of the chest and a high negative value above this. The regions of high R-wave amplitude corresponded spatially to concentrated asymmetric regions of high magnetic field strength during repolarization (T-wave). Pearson-r correlation coefficients of 0.7 (p<0.01), 0.8 (p<0.01) and 0.9 (p<0.01) were obtained from this analysis for the three normal subjects. A negative correlation coefficient of -0.7 (p<0.01) was obtained for one of the subjects with inverted T-wave abnormalities, suggesting similar but inverted magnetic field and current distributions to normal subjects. Even with the high correlation values in these four subjects, the MCG was able to identify differences in the distribution of magnetic field strength, with a shift in the T-wave relative to the R-wave. The measurement of cardiac magnetic field distribution during depolarization and repolarization of normal subjects and patients with clinical abnormalities should enable the improvement of theoretical models for the explanation of the cardiac depolarization and repolarization processes.

Paramagnetic vortex state in Pr2$minus;xCexCuO4 single crystals

Transverse-field muon spin rotation (TF-μSR) measurements of the internal magnetic field distribution of Pr2−xCexCuO4 single crystals reveal a large increase in the magnitude of the average field in the vortex state under field-cooling conditions. The observed increase in the average internal magnetic field measured by μSR is discussed in the context of the paramagnetic Meissner effect.

Modeling of Electromagnetic Environment Inside a Factory Building via Finite Difference Time Domain Method

Increased use of factory automation (FA) apparatus raises concern over electromagnetic interference among electronic devices at the industrial sites. The purpose of the present paper is to discuss modeling of electromagnetic environment inside a factory building via Finite Difference Time Domain (FDTD) method. The principal noise frequency radiated by an inverter-motor system in the building is between 1MHz and 10MHz. Three-dimensional simulation code is verified against measurement of magnetic field distribution inside a simulated building and a laboratory. Effect of wire reinforced concrete wall on the numerical modeling is discussed. As long as the noise source is far away from the wall, the reinforced concrete wall can be modeled as a simple metallic wall reflecting the electromagnetic wave of the frequencies between 1MHz and 10 MHz. When the noise source is embedded inside the wall, however, each reinforcing wire must be modeled.

Evidence for static magnetism in the vortex cores of ortho-II YBa2Cu3O6.50.

Evidence for static alternating magnetic fields in the vortex cores of underdoped YBa2Cu3O6+x is reported. Muon spin rotation measurements of the internal magnetic field distribution of the vortex state of YBa2Cu3O6.50 in applied fields of H = 1 T and H = 4 T reveal a feature in the high-field tail of the field distribution which is not present in optimally doped YBa2Cu3O6.95 and which fits well to a model with static magnetic fields in the vortex cores. The magnitude of the fields is estimated to be 18(2) G and decreases above T = 10 K. We discuss possible origins of the additional vortex core magnetism within the context of existing theories.

Measurement of the Gradient between the Bending Field and the Vertical Line at the SR Magnet

We developed SR compact superconducting magnets which are used for X ray lithography. If the vertical axis of the superconducting coil of SR magnet is out of the vertical line the horizontal field Bx will be appeared. The electron beam is kicked toward vertical direction by this field and this causes a large electron beam orbit distortion in the horizontal coordinate. From the beam optics, the gradient of the coil axis needs to be less than 1 mrad. We developed a magnetic field distribution measurement system of the horizontal magnetic field Bx(s) in the high bending magnetic field By0 which is 3.5T at the center of the SR (Synchrotron Radiation) magnet and measured the distribution of Bx(s) . Where, s is the beam direction. From the horizontal magnetic field Bx(s) and vertical dipole field By0(=3.5T), we can evaluate the gradient of bending field from the vertical direction. The average gradient along S direction was 0.55mrad. This value satisfies our requirement which is less than 1mrad.