Inhomogeneous Magnetic Field Research Articles

Optimal remote restoring of quantum states in communication lines via local magnetic field

Optimal state transport across spin chains, which are proposed as quantum wires for information transfer in solid state quantum architectures, is an important topic for quantum technologies. In this work, we study the remote restoring of a quantum state transferred along a spin chain. The structural state-restoring technique provides proportionality between the appropriate elements of the density matrices of the initial sender state and receiver state at some time instant. We develop a remote state-restoring protocol which uses an inhomogeneous magnetic field with step-wise time-dependent Larmor frequencies as the state-control tool. For simulating the multiparametric Hamiltonian we use two approximating models. First model is based on the Trotter-Suzuki method, while the second model is based on using short pulses of high intensity. In both cases we estimate the accuracy of the approximation and find the optimal restoring parameters (Larmor frequencies) of the protocol which maximize the coefficients in the proportionality for spin chains of various lengths.

Electron cyclotron resonance during plasma initiation

Electron-cyclotron resonance heating (ECRH) is the main heating mechanism in the Wendelstein 7-X (W7-X) stellarator. Although second-harmonic ECRH (X2) has been used routinely for plasma startup, startup at third harmonic (X3) is known to be much more difficult. In this work, we investigate the energy gain of particles during nonlinear wave–particle interaction for conditions relevant to second- and third-harmonic startups in W7-X. We take into account both the beam and the ambient magnetic field inhomogeneities. The latter is shown to significantly increase the mean energy gain resulting from a single wave–particle resonant interaction. In W7-X-like conditions, the improvement in maximum gained energy is up to 4 times the analogous uniform magnetic field case. However, this improvement is not enough to ensure X3 startup. The optimal magnetic field inhomogeneity length scale for average energy gain and start up in W7-X-like conditions is found to be in the range of $1$ to $3\ {\rm km}^{-1}$ . A possibility of using multiple beams with neighbouring resonances is also considered. A considerable enhancement of the energy gain is demonstrated.

Swimming polarity inversion in uncultured magnetotactic cocci.

Magnetotactic bacteria are microorganisms that produce intracellular magnetic nanoparticles organized in chains, conferring a magnetic moment to the bacterial body that allows it to swim following the geomagnetic field lines. Magnetotactic bacteria usually display two swimming polarities in environmental samples: the South-seeking (SS) polarity and the North-seeking (NS) polarity, characterized by the bacteria swimming antiparallel or parallel to the magnetic field lines, respectively. It has been observed that in the presence of inhomogeneous magnetic fields, NS magnetotactic bacteria can change their swimming polarity to SS or vice versa. The present study analyzes populations of NS cocci obtained from SS cocci isolated in the presence of a magnet. The aim was to study differences in the swimming characteristics and magnetic moment among both populations of cocci. For that, trajectories were recorded and the velocity and angle among the velocity and the applied magnetic field were calculated. In addition, micrographs from both SS and NS cocci were obtained and their magnetosomes were measured to analyze their length, width, aspect ratio and magnetic moment, to finally obtain the magnetic moment for each coccus. The results showed the following properties of NS relative to SS cocci: higher velocities, narrow bacterial magnetic moment distribution, higher dispersion in the distribution of angles among the velocity and the applied magnetic field and lower magnetic field sensibility. Those differences cannot be explained by the simple change in magnetic polarity of the magnetosome chain and can be related to the existence of an active magnetoreceptive process in magnetotactic bacteria.

Predicting dynamic, motion-related changes in B0 field inthe brain at a 7T MRI using a subject-specific fine-trainedU-net.

Subject movement during the MR examination is inevitable and causes not only image artifacts but also deteriorates the homogeneity of the main magnetic field (B0 ), which is a prerequisite for high quality data. Thus, characterization of changes to B0 , for example induced by patient movement, is important for MR applications that are prone to B0 inhomogeneities. We propose a deep learning based method to predict such changes within the brain from the change of the head position to facilitate retrospective or even real-time correction. A 3D U-net was trained on in vivo gradient-echo brain 7T MRI data. The input consisted of B0 maps and anatomical images at an initial position, and anatomical images at a different head position (obtained by applying a rigid-body transformation on the initial anatomical image). The output consisted of B0 maps at the new head positions. We further fine-trained the network weights to each subject by measuring a limited number of head positions of the given subject, and trained the U-net with these data. Our approach was compared to established dynamic B0 field mapping via interleaved navigators, which suffer from limited spatial resolution and the need for undesirable sequence modifications. Qualitative and quantitative comparison showed similar performance between an interleaved navigator-equivalent method and proposed method. It is feasible to predict B0 maps from rigid subject movement and, when combined with external tracking hardware, this information could be used to improve the quality of MR acquisitions without the use of navigators.

Fast-Field Cycling Nuclear Magnetic Resonance relaxometer's electromagnet with optimized homogeneity and reduced volume

In this article a Fast Field Cycling (FFC) Nuclear Magnetic Resonance (NMR) electromagnet with low power consumption (less than 200 W), high field homogeneity and reduced volume is projected and described. The electromagnet is iron and copper based, possessing a high permeability and allowing for good magnetic field homogeneity in the operating range of 0 to 0.33 T. With this solution, it is possible to increase 65% the maximum magnetic field keeping the magnetic field homogeneity in comparison with former similar FFC relaxometers. Electromagnet's experimental and simulation results evaluating the generated magnetic field, field homogeneity, heating effects and cooling requirements are also presented. In addition, some technical aspects of the required coupled systems such as the cooling, sample heating are assessed.

Reconstruction of Λ hyperons in an inhomogeneous magnetic field with a Kalman Filter based tracking algorithm

The high interaction rate, fixed target experiment HADES at GSI, located in Darmstadt, Germany, investigates collisions of heavy-ion, proton and secondary pion beams with a target material. Hyperons are one of the key observables for both heavy-ion and elementary collisions [1] [2]. The challenge is to detect displaced vertices with good accuracy without having a dedicated vertex detector, by employing state-of-the-art techniques. In this contribution we discuss a newly developed tracking algorithm that uses both a Kalman Filter (KF) and the high performance KF Particle package to further boost the reconstruction performance for hyperon decays with displaced vertices [3]. With the use of the covariance matrices, which take into account effects from multiple scattering and energy loss of the particles in the material, the reconstruction performance of the tracking algorithm can be significantly improved. The KF Particle utilises these covariance matrices together with its own internal KF to reconstruct primary and secondary decay vertices.

Micro-structural and optical properties of diamond-like carbon films grown by magnetic field-assisted laser deposition

Inhomogeneous magnetic field is introduced into pulsed laser deposition process, in order to find new properties of diamond-like carbon film grown under magnetic field, thereby offering the theoretical and experimental basis for further enhancing sp<sup>3</sup>-bond content in this film. Distribution of the magnetic strength and flux lines induced by a rectangular permanent magnet is calculated. And then, flying trace of the carbon ions in the magnetic field is also simulated by the iterative method, which indicates that the carbon ions cannot expand freely and they are confined and accumulate around the center region of the magnet source. Beside the surface interference, the measurement and the fitted results of ellipsometry parameters show that magnetic field exerts an important influence on layer-thickness distribution and optical constant of the pulsed laser deposition-grown diamond-like carbon film. Meanwhile, it is indicated that the inhomogeneity of the layer-thickness distribution and optical constant increase when the magnetic strength is higher. Micro-structure of diamond-like carbon film is affected seriously by magnetic field, which is indicated by Raman spectra. Magnetic field can enhance the local stress in the carbon matrix net, increasing the sp<sup>3</sup>-bond content. Theoretical research and experimental research both show that a suitable magnetic strength can excite micro-structure of diamond-like carbon film significantly, and the high-quality diamond-like carbon coating with practical application value will be obtained by technological adjustment.

New characteristic parameter of energy loss in permalloy

Characteristic parameters of energy storage and loss in soft magnetic materials (SMMs), product S of initial susceptibility and resonance frequency and product L of maximum and half width of imaginary part, were introduced in permalloy films. Expressions of characteristic parameters were derived from Landau–Lifshits–Gilbert equation with a general anisotropic free energy model. It was found S = L equals to intrinsic quantity of SMMs , where γ is the gyromagnetic ratio, is the saturation magnetization, and and are mutually orthogonal effective magnetic fields. In the presence of eddy current, it was found S remains equal to Q while L < Q results from inhomogeneity of microwave magnetic field caused by eddy current. Moreover, a linear scale of versus Gilbert damping factor α was found in permalloy films with different thicknesses. Hence, our findings provide a new perspective on energy storage and loss of SMMs.

Modality for estimating NMR relaxation time using perturbed angular correlation in double-photon emission nuclides

T2 relaxation time in magnetic resonance imaging (MRI), which is determined by magnetic dipole interactions, has been employed as a parameter for tumor detection. However, owing to the lack of MRI detection sensitivity, nuclear medicine imaging is currently the basic option for tracking low concentrations of chemical probes. Previous studies utilizing cascade radionuclides have focused on the relaxation due to electric quadrupole interactions. However, magnetic dipole interactions, which are crucial in MRI, remains to be elucidated. In this study, we determined the magnetic relaxation rate by using 111In, a cascade radionuclide used in clinical single-photon emission computed tomography (SPECT) scans. As the angle between the gamma rays from the nuclei is affected by the electrical and magnetic interactions acting on the nuclei, we measured the angular correlation ratio by using eight gadolinium gallium garnet (GAGG) multi-pixel photon counter (MPPC) 8 × 8 array detectors and extracted the magnetic relaxation rate. Consequently, we obtained a rate that increased with the Fe concentration, similar to the T2 relaxation rate, although it was influenced by the inhomogeneity of the external magnetic field. This study utilized low concentrations of the liquid-state radionuclide, which is commonly used in clinical nuclear medicine imaging scans and is expected to provide much higher sensitivity and more selective detection of tumors than conventional MRI.

KinKal: A Kinematic Kalman filter Track Fitting Package for the Mu2e Experiment

Many current physics experiments require precision reconstruction of low-energy particles. One example is the Mu2e experiment, which requires reconstructing an isolated 105 MeV electron with better than 500 KeV/c momentum resolution. Mu2e uses a low-mass straw tube tracker, and a CsI crystal calorimeter, to reconstruct tracks. In this paper, we present the design and performance of a track reconstruction algorithm optimized for Mu2e’s unusual requirements. The algorithm is based on the KinKal [1] kinematic Kalman filter track fit package. KinKal supports multiple track parameterizations, including one optimized for looping tracks, such as Mu2e signal tracks, and others optimized for straight or slightly-curved tracks, such as the high-momentum (&gt;1 GeV/c) cosmic ray muons used to calibrate and align the Mu2e detectors. All KinKal track parameterizations include the track origin time, to correctly model correlations arising from measurements that couple time and space, such as the straw drift time or the calorimeter cluster time. KinKal employs magnetic field inhomogeneity and material effect correction algorithms with 10−4 fractional precision. The Mu2e fit uses Artificial Neural Net functions to discriminate background hits from signal hits, and to resolve the straw tube hit left-right ambiguity, while iterating the extended Kalman filter. The efficiency, accuracy, and precision of the Mu2e track reconstruction, as tested on detailed simulations of Mu2e data, are presented.

Various facets of intermolecular transfer of phase coherence by nuclear dipolar fields.

It has long been recognized that dipolar fields can mediate intermolecular transfer of phase coherence from abundant solvent to sparse solute spins. Generally, the dipolar field has been considered while acting during prolonged free-precession delays. Recently, we have shown that transfer can also occur during suitable uninterrupted radio frequency pulse trains that are used for total correlation spectroscopy. Here, we will expand upon the latter work. First, analytical expressions for the evolution of the solvent magnetization under continuous irradiation and the influence of the dipolar field are derived. These expressions facilitate the simulations of the transfer process. Then, a pulse sequence for the retrieval of high-resolution spectra in inhomogeneous magnetic fields is described, along with another sequence to detect a transfer from an intermolecular double-quantum coherence. Finally, various schemes are discussed where the magnetization is modulated by a combination of multiple selective radio frequency pulses and pulsed field gradients in different directions. In these schemes, the magnetization is manipulated in such a way that the dipolar field, which originates from a single-spin species, can be decomposed into two components. Each component originates from a part of the magnetization that is modulated in a different direction. Both can independently, but simultaneously, mediate an intermolecular transfer of phase coherence.

Automated test apparatus for bench-testing the magnetic field homogeneity of NMR transceiver coils

We describe an automated hands-off bench testing method for measuring the magnetic field profile of transceiver coils for nuclear magnetic resonance (NMR). The scattering parameter (S-parameter) data is measured using a portable network analyzer, and the results are automatically exported to a computer for plotting and viewing. This assay dramatically reduces the time needed to measure the magnetic field (B1) homogeneity profile of a transceiver coil while also improving accuracy relative to manual operation. Here, we demonstrate the method on a saddle coil of a solution-state NMR probe in comparison to profiles obtained using NMR spectroscopy measurements. We also measure the axial homogeneity of a variable-pitch solenoid.

Connection Between Chorus Wave Amplitude and Background Magnetic Field Inhomogeneity: A Parametric Study

AbstractWhistler mode chorus waves frequently appear as discrete, repetitive, and quasi‐monochromatic emissions with frequency chirping. With different wave amplitude and frequency chirping rate, chorus waves have been observed not only in the magnetosphere of the Earth but also in the magnetospheres of other planets, such as Saturn and Jupiter. Motivated by understanding different properties of chorus waves at these planets using the recently proposed “Trap‐Release‐Amplify” (TaRA) model, we perform a parametric study using Particle‐In‐Cell simulations by varying background magnetic field inhomogeneity and the corresponding threshold hot electron number density. We show the consistency between simulation results and theoretical predictions for threshold hot electron number density, chorus chirping rate, and wave amplitude. Our results suggest the significant role of the background magnetic field inhomogeneity in affecting chorus wave properties, including its amplitude at different planets as predicted by the TaRA model.

Method of liquid consumption measuring in nuclear magnetic flowmeters-relaxometers

The need to expand the functionality of systems for monitoring the parameters of the flow of liquid media is substantiated. The advantages of using meters based on the phenomenon of nuclear magnetic resonance to control the parameters of the flow of liquid media are noted. Let us consider the problems that arise during the operation of nuclear magnetic flowmeters-relaxometers operating in two measurement modes (pulse and with periodic modulation of the magnetic field in the nuclear magnetic resonance signal recording system - modulation technique). It is noted that the main problem in the operation of these devices is associated with an increase in the error in measuring liquid flow or the termination of its measurement process with rapid changes in liquid flow. The use of a magnetic tag mode, which allows us to solve this problem, significantly limits the possibilities of using nuclear magnetic resonance flowmeters-relaxometers when used to monitor the parameters of other liquids or with a large increase in the temperature of the flowing medium. A method for creating a magnetic mark at the noise level for measuring liquid flow is proposed. In the method, changing the composition of the flowing medium (including the liquid itself) does not have a significant effect on the formation of a magnetic mark at the noise level in a strong inhomogeneous magnetic field. The results of experimental studies of the nutation line from changes in magnetic field inhomogeneity are presented. A mathematical model has been developed based on the modified Bloch equations and relationships between the magnetic field parameters have been established to implement the magnetic mark mode in the nuclear magnetic resonance signal with magnetization inversion at the noise level. The use of a method makes it possible to make the influence of rapid changes in the value of liquid flow (by a factor of 10 or more) on the flow measurement error insignificant.

Developing a novel quasi-3D movable water phantom for radiation therapy workable in the magnetic resonance environment.

The use of magnetic resonance linear accelerators (MR-LINACs) for clinical treatment has opened up new possibilities and challenges in the field of radiation oncology. However, annual quality assurance (QA) is relatively understudied due to practical considerations. Thus, to overcome the difficulty of measuring the dose with a small water phantom for TRS-398 or TG-51 in all external beam radiation treatment unit environments, such as MR compatibility, we designed a remote phantom with a three-axis changeable capacity for QA. The designed water phantom was tested under an MR environment. The water phantom system comprised of three parts: a phantom box, a dose measurement tool, and a PMD401 drive system. The UNIDOSE universal dosimeter was used to collect beam data. The manufacturer's developer tools were utilized to position the measurement. To ensure magnetic field homogeneity, a distortion phantom was prepared using sixty fish oil capsules aligned radially to distinguish the oil and free air. The phantom was scanned in both the MR simulator and computed tomography (CT), and the acquired images were analyzed to determine the position shift. The dimensions of the device are 30 cm in the X-axis, 20 cm in the Y-axis, and 17 cm in the Z-axis. Total cost of materials was no more than $10,000 US dollars. Our results indicate that the device can function normally in a regular 1.5 T MR environment without interference from the magnetic field. The water phantom's traveling speed was found to be approximately 5 mm/s with a position difference confined within 6 cm intervals during normal use. The distortion test results showed that the prepared MR environment has uniform magnetic field homogeneity. In this study, we constructed a prototype water phantom device that can function in an MR simulator without interference between the magnetic field and electronic components. Compared to other commercially available MR-LINAC water phantoms, our device offers a more cost-effective solution for routine monthly QA. It can shorten the duration of QA tests and relieve the burden on medical physicists.

Analysis of charging characteristics of a 500 MHz HTS-LTS series NMR magnet with an intra-layer no-insulation HTS layer-wound coil structure

The intra-layer no-insulation (LNI) layer-wound coil has the advantages of high spatial magnetic field homogeneity and a smaller number of joints, as well as the ability of self-protection during quench, which has great potential in making MRI or NMR superconducting magnet. In this paper, a 500 MHz NMR magnet connected in series by a high temperature superconducting (HTS) magnet and a low temperature superconducting (LTS) magnet was designed, fabricated, and tested at a low field for homogeneity, in which the HTS magnet is an LNI layer-wound coil structure. And a helical equivalent circuit model of the 500 MHz HTS-LTS NMR magnet coupled with the stacked homogenization T-A and mechanical model is established, which agrees with the experimental results. This paper provides a sufficient numerical analysis of the charging characteristics of the HTS-LTS series magnet, including magnetic field homogeneity, current distribution, loss distribution, screening current induced stress, etc. And this paper provides valuable insights into the ramping behavior of the HTS-LTS series magnet, which can be useful for practical charging experiments.

Наночастицы магнетита увеличивают проводимость азолектинового бислоя в неоднородном магнитном поле

In the magnetofection method, magnetic fields and magnetic nanoparticles are used to increase the efficiency of gene delivery into cells. Magnefection enhances the introduction into cells of gene vectors with which magnetic nanoparticles are associated, due to the action of a magnetic field that holds the nanoparticles in the area of their application. It is believed that the magnetic field itself does not change the mechanism of absorption (endocytosis) of nanoparticles. Both the beneficial effect of magnetofection - delivery of the vector into the cell, and its side effect - cytotoxicity are associated with the interaction of particles with cell membranes and, in particular, with lipid bilayers. In our work, we investigated the effect of an applied stationary inhomogeneous magnetic field and spherical superparamagnetic magnetite nanoparticles with a diameter of about 4 nm on the conductivity of azolectin bilayer lipid membranes. The membranes were formed in a stationary magnetic field with a magnetic induction of up to 26 mT. The magnetic field had no effect on the conductivity of the membrane. After monitoring the membrane conductivity, magnetic nanoparticles were added to the solution surrounding the membrane. The addition was carried out on one side of the membrane so that the magnetic field attracted nanoparticles to the membrane surface. After adding nanoparticles in a magnetic field, the conductivity of the membranes increased by one to two orders of magnitude. This effect was observed for all membranes. A smooth increase in conductivity was accompanied in a number of cases (for 25% of the membranes) by the appearance of current jumps, which can be associated with the formation of through conducting pores with a radius of about 0.5 nm. The conductivity increased with increasing magnetic field gradient.

Thermal QCD in a non-uniform magnetic background

Off-central heavy-ion collisions are known to feature magnetic fields with magnitudes and characteristic gradients corresponding to the scale of the strong interactions. In this work, we employ equilibrium lattice simulations of the underlying theory, QCD, involving similar inhomogeneous magnetic field profiles to achieve a better understanding of this system. We simulate three flavors of dynamical staggered quarks with physical masses at a range of magnetic fields and temperatures, and extrapolate the results to the continuum limit. Analyzing the impact of the field on the quark condensate and the Polyakov loop, we find non-trivial spatial features that render the QCD medium qualitatively different as in the homogeneous setup, especially at temperatures around the transition. In addition, we construct leading-order chiral perturbation theory for the inhomogeneous background and compare its prediction to our lattice results at low temperature. Our findings will be useful to benchmark effective theories and low-energy models of QCD for a better description of peripheral heavy-ion collisions.

Quantum steering vs entanglement and extracting work in an anisotropic two-qubit Heisenberg model in presence of external magnetic fields with DM and KSEA interactions

We examine the Dzyaloshinski-Moriya (DM) and Kaplan-Shekhtman-Entin-Wohlman-Aharony (KSEA) interactions in thermal equilibrium submitted to the anisotropic Heisenberg two-qubit model in an inhomogeneous magnetic field. The steerability between the two qubits is evaluated using quantum steering. The concurrence serves as a witness to quantum entanglement. Both the extracted work and the ideal efficiency of the two qubits are quantified. We discuss how quantum correlations behave in relation to the bath's temperature, the Kaplan-Shekhtman-Entin-Wohlman-Aharony coupling parameter and DM coupling. We find that the nonclassical correlations in a two-qubit Heisenberg XYZ Model are fragile under thermal effects. Nevertheless, the results indicate that the concurrence is stronger than quantum steering under thermal effects in the presence of DM and KSEA. We obtained that an extraction of work is comparable with the bare energies.

Experimental implementation of laser cooling of trapped ions in strongly inhomogeneous magnetic fields

Experimental implementation of laser cooling of trapped ions in strongly inhomogeneous magnetic fields