Magnitude Of Magnetic Field Research Articles

Plasma sputtering of biased electrodes in an oblique magnetic field

The surface erosion of biased electrodes immersed in a radio frequency (RF) plasma was investigated in oblique magnetic fields ranging from 0.1 T to 3.5 T. The plasma potential and density in the vicinity of the biased electrode have been measured using an RF-compensated cylindrical Langmuir probe moved by a three-dimensional motorised arm in the ALINE facility at 0.1 T. The erosion profiles were determined for different gases (argon and helium), magnetic field strength and plasma volume for the same electrode surface area at an angle of 5∘ with the magnetic field in three different experimental geometries. The radial electric field (perpendicular to the magnetic field) in the plasma column has been deduced from plasma potential measurements. This radial field makes the ions converge to the core of the plasma column at grazing angles (30∘) and is reversed at larger angles. The ion flux on the sample increases with the magnetic field magnitude leading to a strong erosion inhomogeneity. At lower plasma volume, the erosion rate is sensitively enhanced. Local redeposition was identified using x-ray photoelectron spectroscopy on the surfaces exhibiting preferential deposition directions. Finally, the asymmetric erosion patterns obtained from a molybdenum layer etching are explained by the similar asymmetric density maps obtained with the probe and by the drift and the local sheath acceleration.

Statistical Properties of Alfvén Ion Cyclotron Waves and Kinetic Alfvén Waves in the Inner Heliosphere

Alfvén ion cyclotron waves (ACWs) and kinetic Alfvén waves (KAWs) are found to exist at <0.3 au observed by Parker Solar Probe in Alfvénic slow solar winds. To examine the statistical properties of the background parameters for ACWs and KAWs and related wave disturbances, both wave events observed by Parker Solar Probe are selected and analyzed. The results show that there are obvious differences in the background and disturbance parameters between ACWs and KAWs. ACW events have a relatively higher occurrence rate but with a total duration slightly shorter than KAW events. The median background magnetic field magnitude and the related background solar wind speed of KAW events are larger than those of ACWs. The distributions of the relative disturbances of the proton velocity, proton temperature, the proton number density, and β cover wider ranges for ACW events than for KAW events. The results may be important for the understanding of the nature and characteristics of Alfvénic slow solar wind fluctuations at ion scales near the Sun, and provide the information of the background field and plasma parameters and the wave disturbances of ACWs and KAWs for further relevant theoretical modeling or numerical simulations.

Spin-dependent resonant Andreev tunneling in hybrid ferromagnetic metal–magnetic quantum dot–superconductor nanostructures

There exists a variety of theoretical proposals to transform states induced by magnetic nanoparticles inside a superconducting gap into Majorana fermion states. The main challenge in this route is a conclusive proof and undoubted distinguishing between topologically trivial subgap Andreev bound states and topologically nontrivial magnetically polarized Majorana bound states. This motivated us to investigate a nonequilibrium electrons tunneling through a ferromagnetic normal metal–magnetic quantum dot–s-wave superconductor (F-mQD-SC) nanostructure, where the mQD’s discrete levels are spin splitted. By using the Keldysh Green’s function method, the expressions for a tunnel current and probability of the Andreev reflection (AR) versus energy are derived and studied. We find that the system’s resonant ARs conductance exhibits different kinds of peaks depending on a spin splitting of the mQD levels, the spin polarization magnitude of the F-lead current, the gate voltage, and an external magnetic field magnitude. The nanostructure’s conductance versus a bias voltage exhibits extra peaks which at some combination of its parameters can mimic ones expected for Majorana modes in a topological superconducting state. The distinguishing transport characteristics of a F-mQD-SC nanoscale structure being in non-topological state are discussed. We suggest that the results obtained can provide helpful clarification for understanding recent experiments in superconductor–ferromagnet hybrid nanostructures with topologically protected excitations.

Impact of weak radiofrequency and static magnetic fields on key signaling molecules, intracellular pH, membrane potential, and cell growth in HT-1080 fibrosarcoma cells

There are substantial concerns that extended exposures to weak radiofrequency (RF) fields can lead to adverse health effects. In this study, HT-1080 fibrosarcoma cells were simultaneously exposed to a static magnetic flux density between 10 mathrm{mu T} and 300 mathrm{mu T} and RF magnetic fields with amplitudes ranging from 1 nT to 1.5 μT in the frequency range from 1.8 to 7.2 MHz for four days. Cell growth rates, intracellular pH, hydrogen peroxide, peroxynitrite, membrane potential and mitochondrial calcium were measured. Results were dependent on carrier frequency and the magnitude of the RF magnetic field, modulation frequencies and the background static magnetic field (SMF). Iron sulphur (Fe-S) clusters are essential for the generation of reactive oxygen species and reactive nitrogen species (ROS and RNS). We believe the observed changes are associated with hyperfine couplings between the chemically active electrons and nuclear spins. Controlling external magnetic fields may have important clinical implications on aging, cancer, arthritis, and Alzheimer’s.

Grain-boundary topological superconductor

Majorana zero modes (MZMs) are of central importance for modern condensed matter physics and quantum information due to their non-Abelian nature, which thereby offers the possibility of realizing topological quantum bits. We here show that a grain boundary (GB) defect can host a topological superconductor (SC), with a pair of cohabitating MZMs at its end when immersed in a parent two-dimensional gapped topological SC with the Fermi surface enclosing a nonzero momentum. The essence of our proposal lies in the magnetic-field driven hybridization of the localized MZMs at the elementary blocks of the GB defect, the single lattice dislocations, due to the MZM spin being locked to the Burgers vector. Indeed, as we show through numerical and analytical calculations, the GB topological SC with two localized MZMs emerges in a finite range of both the angle and magnitude of the external magnetic field. Our work demonstrates the possibility of defect-based platforms for quantum information technology and opens up a route for their systematic search in future.

Method for control by orbital spacecraft magnetic cleanliness based on multiple magnetic dipole models with consideration of their uncertainty

Aim. Development of method for control by orbital spacecraft magnetic cleanliness based on multiple magnetic dipole models using compensation of the initial magnetic field with consideration of magnetic characteristics uncertainty. Methodology. Orbital spacecraft multiple magnetic dipole models calculated as solution of nonlinear minimax optimization problem based on near field measurements for prediction orbital spacecraft far magnetic field magnitude. Nonlinear objective function calculated as the weighted sum of squared residuals between the measured and predicted magnetic field. Weight matrix calculated as inverse covariance matrix of random errors vector. Values of magnetic moments and coordinates of placement of compensating magnetic dipoles for compensation of the orbital spacecraft initial magnetic field also calculated as solution of nonlinear minimax optimization problem. Both solutions of this nonlinear minimax optimization problems calculated based on particle swarm nonlinear optimization algorithms. Results. Results of prediction spacecraft far magnetic field magnitude based on orbital spacecraft multiple magnetic dipole models using near field measurements and compensation of the initial magnetic field with consideration of orbital spacecraft magnetic characteristics uncertainty for ensuring the orbital spacecraft magnetic cleanliness. Originality. The method for control by orbital spacecraft magnetic cleanliness based on multiple magnetic dipole models using compensation of the initial magnetic field with consideration of magnetic characteristics uncertainty is developed. Practical value. An important practical problem of ensuring orbital spacecraft magnetic cleanliness based on orbital spacecraft multiple magnetic dipole models using near field measurements and compensation of the initial magnetic field with consideration of orbital spacecraft magnetic characteristics uncertainty solved.

Dirac points, new photonic band gaps, and effect of magnetically induced transparency in dichroic cholesteric liquid crystals with wavelength-dependent magneto-optical activity parameter.

We investigated the properties of cholesteric liquid crystals (CLCs) being in an external static magnetic field directed along the helix axis. We considered a dichroic CLC, that is, CLC with parameters ReΔ=Reɛ_{1}-Reɛ_{2}/2=0 and ImΔ=Imɛ_{1}-Imɛ_{2}/2≠0, where ɛ_{1,2} are the principal values of the local dielectric permittivity tensor. We have shown that in the case of the wavelength dependence of the magneto-optic activity parameter, new features appear in the optics of dichroic CLCs, in particular, in this case new Dirac points appear. Dirac points are points where there is an intersection of any two wave vector curves (they degenerate) and a linear law of the wave vector dependence on the frequency near these points. And moreover, at some Dirac points photonic band gaps (PBGs) appear; at others, lines of magnetically induced transparency (MIT), that is, a full transmission band appears, in an absorbing medium. In this case a polarization-sensitive transmission band appears too. At certain values of the helix pitch of the CLC and of the magnitude of the external magnetic field, three PBGs of different nature appear: a transmittance band, two narrow lines of MIT, and at others a broadband MIT, etc. This system is nonreciprocal, and the nonreciprocity changes over a wide range. It is observed both for reflection and transmittance and for absorption. The soft-matter nature of CLCs and their response to external influences lead to easily tunable multifunctional devices that can find a variety of applications. They can be applied as tunable narrow-band or broadband filters and mirrors, a highly tunable broad/narrow-band coherent perfect absorber, transmitter, ideal optical diode, and in other devices.

Bloch–Siegert Effect for Surface Nuclear Magnetic Resonance Sounding Experiments in the Unsaturated Zone

The Bloch–Siegert effect is relevant for NMR experiments where components of the excitation pulse other than the circularly polarized component have an influence on the evolution of the magnetization of the spin system under consideration. For linearly polarized excitation fields this happens at amplitudes higher than roughly one tenth of the magnitude of the static magnetic field. Since surface nuclear magnetic resonance (SNMR) experiments, also called magnetic-resonance-soundings (MRS), are conducted in the relatively low local field of the earth, the Bloch–Siegert effect can quickly become relevant. This is especially the case for SNMR experiments in the unsaturated zone, where due to short relaxation times fast pulses of high intensity must be used. To describe the Bloch–Siegert effect, we use the average Hamiltonian approximation obtained by the Magnus expansion of up to fifth order, as well as the solution of the Bloch equations. The results of these approximations are tested against the Bloch simulations and it is shown that they are only valid for limited ranges of the excitation field amplitude. The influence of the Bloch–Siegert effect on sensitivity kernels is described and verified with experimental data obtained with a small scale SNMR sensor on water containers.

Direct thrust measurements of 2U-sized bi-directional wave plasma thruster

The results of direct thrust measurements of the thruster with multiple thrust vectoring capability utilizing Kr are presented. The thruster is a 2U size system. The tested bi-directional plasma thruster consists of the thruster head, inbuilt rf generator creating 9 MHz current applied to the antenna, inbuilt power supply for the set of electromagnets, and thruster control system. The thruster head consists of the set of electromagnets, open-ended gas discharge chamber, and antenna. During thrust measurements, the magnitude and configuration of the external static magnetic field, the propellant flow rate, and the power modes of the rf generator are changed. The magnitude of the magnetic field in current units is adjusted in the range of 3…5 A. The propellant flow rate is adjusted in the range of 2…100 sccm. The power modes of the rf generator are adjusted in the range of 50…250 where the value 250 corresponds to a power of 100 W. The dynamic background pressure in the vacuum chamber is 0.1 Pa at 100 sccm. Two specific thrust modes are defined: the high thrust mode (∼7 mN) and the high specific impulse mode (∼900 s).

Magnetic Discontinuities in the Inner Heliosphere: Do Intermediate Shocks Exist?

Magnetic discontinuities are fundamental structures in space and laboratory plasmas where the changes in magnetic and velocity fields are constrained by Rankine–Hugoniot relations. Due to the absence of precise measurements for particles, some issues therein are hardly investigated. The nature of discontinuities driven by the magnetohydrodynamics (MHD) turbulence, and the intermediate shock are two puzzles to be solved. The MHD turbulence generates numerous discontinuities with both small normal magnetic fields and nearly constant magnetic field magnitudes in statistics. By utilizing the data from the Parker Solar Probe, we identify among the turbulence-driven discontinuities two components that exhibit diverse statistical characteristics of the plasma density, and reveal that these discontinuities comprise 80.2% rotational and 19.8% tangential discontinuities. Then, we note a special class of discontinuities within 0.35 au that have jump conditions similar to that of the rotational discontinuity and the shock simultaneously, including (1) positively correlated jumps in the plasma density and temperature, (2) a small change in the magnetic field magnitude, and (3) opposite tangential magnetic fields on two sides. These features conform to the theoretical intermediate shock, which previous studies have found to not practically exist due to the breakdown of the evolutionary condition. By the conservation law of the mass flux across a boundary, we calculate their propagation speeds and find three intermediate shock candidates with super-Alfvénic upstream and sub-Alfvénic downstream flows. This work can improve our understanding of plasma intermittencies and suggests reassessing conclusions based on ideal MHD Rankine–Hugoniot relations.

Numerical Evaluation on Current Behavior of No-Insulation Coils With Parallel HTS Tapes

No-insulation coil (NIC) has been proposed for improvement of thermal stability. NIC can reduce heat generation due to a current distribution that bypass the defect when a local hot-spot is formed. However, a charge delay because of no turn-to-turn insulation is one of the important characteristics of NICs. To decrease the charge delay of NIC, a winding technique with parallel HTS tapes without insulation between layers has been proposed. However, the increase of the number of parallel layers causes the significant current imbalance between parallel tapes. In this paper, the relationship between the number of parallel tapes and the effect on charge delay reduction is investigated. In addition, the effect on the thermal stability and magnitude of central magnetic field and thermal stability due to the current imbalance is also verified. Both analyses are carried out for both NIC with and without defects. The analysis results show that charge delay of NICs is reduced according to increase of number of parallel tapes. Current imbalance between layers increases in accordance with the increase of the number of parallel tapes. However, the analysis results also show that thermal stability and central magnetic field are not degraded by this imbalance current. In terms of NIC with the defect, thermal stability and fluctuation of central magnetic field are most improved by the effect of current sharing between parallel tapes when the number of parallel tapes is largest.

Whistler‐Mode Waves in Magnetic Ducts

AbstractObservations from the NASA Magnetospheric Multiscale (MMS) satellites show packages of extremely low frequency (ELF) whistler‐mode waves localized inside the small‐scale irregularities of the magnetic field. These irregularities are formed by the narrow field‐aligned channels where the magnitude of the background magnetic field inside the channel is greater or less than outside. By analogy with the classical density ducts, we introduce the high‐B duct, where the magnitude of the field inside the channel is greater than the outside, and the low‐B duct, where the magnitude of the field inside the channel is less than the outside. We investigate the guiding of the ELF whistler‐mode waves by high‐B and low‐B ducts. We derive the analytical criteria for the wave ducting by these ducts and confirm them with two‐dimension, time‐dependent simulations of the electron‐MHD model. Also, we model ELF whistler‐mode waves observed inside the high‐B and low‐B ducts by MMS satellites.

Generation of Giant Magnetic Fields in a Hollow Mesoscale Sphere

The superresonance effect for a hollow dielectric sphere is numerically simulated with the Mie theory. It is shown for the first time that weakly dissipative mesoscale spheres with an air-filled cavity exhibit a high-order Fano resonance related to internal Mie modes. Superresonance in a hollow sphere is achieved by the accurate choice of the cavity radius, while for a monolithic dielectric sphere, it is ensured by the accurate choice of the outer diameter of the particle under study. In this case, the relative intensities of the resonance peaks in the optical range for both magnetic and electric fields near the sphere poles can have enormous values of 106−107, if the magnetic field magnitude exceeds that of the electric field by a factor larger than 15 for the hollow sphere with a Mie size parameter about 40.

Strain sensitivity and microscopic deformation mechanism of graphene foam containing active nanoparticles under magnetic fields

Magnetic aerogels have attracted many practical applications in recent years, which requisites a comprehensive understanding on basic mechanics of this hybrid composite system. In this paper, the microscopic deformation mechanism and strain variation (εΔ) of such a hybrid material under external magnetic field (Ef) is systematically studied by the coarse-grained molecular dynamics simulation method. The major factors like layer thickness, magnitude of external magnetic field and crosslinks effects are mainly considered. The recovery behavior is also studied under cyclic Ef. Interestingly, the εΔ of such a hybrid material is much affected by the graphene sheet thickness, magnitude of applied Ef and crosslinks, due to their direct influences on the microstructural evolution. The εΔ of non-bonded hybrid composite with single layer thick graphene sheet (εΔ⁓0.19) is four times higher relative to eight layers thick system (εΔ⁓0.045). With the increase of graphene sheet thickness, the microstructural evolution of nanoparticles will change from wrapping of single layer sheets around them to flow and jump from one thick sheet to other. We also found the critical value of Ef, i.e., 200 nN for single layer thick graphene sheet hybrid systems beyond which the εΔ tend to decrease, however, εΔ for eight layers system continue to increase as a function of Ef magnitude. The addition of crosslinks remarkably enhances the εΔ (⁓0.74) and recovery (⁓90%) of hybrid composite system. The bonded nanoparticles initiate the folding and unfolding mechanism of graphene sheets during cyclic Ef. The results clarify the micro mechanism and basic mechanics of magnetic aerogels that will be helpful to the design the future devices and advanced sensors.

Jets and Mirror Mode Waves in Earth's Magnetosheath.

Magnetosheath jets are localized plasma structures with high dynamic pressure which are frequently observed downstream of the Earth's bow shock. In this work we analyze Magnetospheric MultiScale magnetic field and plasma data and show that jets can be found in the quasi-perpendicular magnetosheath in regions permeated by Mirror mode waves (MMWs). We show that structures identified as jets by their enhanced dynamic pressure can have very different internal structure, with variable signatures in magnetic field magnitude and components, velocity, and density and can be associated to ion distribution functions of various types. This suggests that jets observed in the quasi-perpendicular magnetosheath are generated by different mechanisms. We find that jets can be related to traveling foreshocks, flux transfer events, and some have MMWs inside them. Our results suggest that some jets have a local source and their formation does not depend on upstream structures. We find that different types of ion distributions can exist inside the jets, while in some cases anisotropic distributions are present, in others counterstreaming distributions exist. We also show that for jets with MMWs inside them, ion distributions can be modulated. This highlights the importance of using ion distributions to identify and classify different types of jets.

Effects of optimisation parameters on data-driven magnetofrictional modelling of active regions

Context. The solar magnetic field plays an essential role in the formation, evolution, and dynamics of large-scale eruptive structures in the corona. The estimation of the coronal magnetic field, the ultimate driver of space weather, particularly in the ‘low’ and ‘middle’ corona, is presently limited due to practical difficulties. Data-driven time-dependent magnetofrictional modelling (TMFM) of active region magnetic fields has been proven to be a useful tool to study the corona. The input to the model is the photospheric electric field that is inverted from a time series of the photospheric magnetic field. Constraining the complete electric field, that is, including the non-inductive component, is critical for capturing the eruption dynamics. We present a detailed study of the effects of optimisation of the non-inductive electric field on the TMFM of AR 12473. Aims. We aim to study the effects of varying the non-inductive electric field on the data-driven coronal simulations, for two alternative parametrisations. By varying parameters controlling the strength of the non-inductive electric field, we wish to explore the changes in flux rope formation and their early evolution and other parameters, for instance, axial flux and magnetic field magnitude. Methods. We used the high temporal and spatial resolution cadence vector magnetograms from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). The non-inductive electric field component in the photosphere is critical for energising and introducing twist to the coronal magnetic field, thereby allowing unstable configurations to be formed. We estimated this component using an approach based on optimising the injection of magnetic energy. Results. Our data show that flux ropes are formed in all of the simulations except for those with the lower values of these optimised parameters. However, the flux rope formation, evolution and eruption time varies depending on the values of the optimisation parameters. The flux rope is formed and has overall similar evolution and properties with a large range of non-inductive electric fields needed to determine the non-inductive electric field component that is critical for energising and introducing twist to the coronal magnetic field. Conclusions. This study shows that irrespective of non-inductive electric field values, flux ropes are formed and erupted, which indicates that data-driven TMFM can be used to estimate flux rope properties early in their evolution without needing to employ a lengthy optimisation process.

INVESTIGATION OF THE MAGNETIC FIELD FROM OBSERVATIONS OF THE OH MASER IN THE G10.624–0.385 STAR FORMATION REGION

The results of a study of the variability of maser emission in OH lines in the 18 cm range in the G10.624–0.385 star formation region from monitoring data performed at the Large Radio Telescope in Nançay (France) in 2008–2023 are presented. It is obtained that for a Zeeman pair in line 1667 MHz splitting (about 1.96 km/s) and, consequently, the magnitude of the longitudinal magnetic field have been stable for more than 25 years. In the satellite lines of 1612 and 1720 MHz, broadband absorption and emission are observed, respectively. Mirrored The profiles of the OH 1612 and 1720 MHz satellite lines indicate that the levels of the corresponding transitions are pumped by IR radiation from a source immersed in a magnetized molecular cloud around the OH maser. Spatial identification of details in both main lines is carried out. It is found that the transverse magnetic field is directed mainly along some organized structure in the form of an arc.

Attitude-Independent Magnetometer Calibration Using Nonlinear Least Squares

This paper presents a new formulation for attitude-independent calibration of three-axis magnetometers. The proposed solution employs a Non-Linear Least Squares (NLLS) estimator that uses the non-linear sensor model proposed by Foster and Elkaim in the well-known Extended Two-Step (ETS) algorithm. Our solution has several advantages over ETS and is more straightforward to implement than many subsequent algorithms. It enables the calculation of the calibration parameters’ uncertainties and does not require the assumption that all magnetometer measurements have a constant magnetic field magnitude. The former is essential for evaluating calibration quality, while the latter may be required for on-orbit magnetometer calibration. However, the NLLS has the drawback of requiring an initial parameter estimation to ensure convergence. Therefore, our work presents a new technique to calculate the scale factors and offsets for initializing the NLLS. Simulations and practical implementations demonstrate that our method performs similarly to a recently computed analytical solution of the ETS. Furthermore, a Monte Carlo simulation shows that the NLLS algorithm provides a slightly better estimation of the scale factors than the ETS, in addition to the abovementioned advantages.

Interplanetary Shocks between 0.3 and 1.0 au: Helios 1 and 2 Observations

The Helios 1 (H1) and Helios 2 (H2) spacecraft measured the solar winds at a distance between ∼0.3 and 1.0 au from the Sun. With increasing heliocentric distance (r h), the plasma speed is found to increase at ∼34–40 km s−1 au−1 and the density exhibits a sharper fall () compared to the magnetic field magnitude () and the temperature (). Using all available solar wind plasma and magnetic field measurements, we identified 68 and 39 fast interplanetary shocks encountered by H1 and H2, respectively. The overwhelming majority (85%) of the shocks are found to be driven by interplanetary coronal mass ejections (ICMEs). While the two spacecraft encountered more than 73 solar wind high-speed streams (HSSs), only ∼22% had shocks at the boundaries of corotating interaction regions (CIRs) formed by the HSSs. All of the ICME shocks were found to be fast forward (FF) shocks; only four of the CIR shocks were fast reverse shocks. Among all ICME FF shocks (CIR FF shocks), 60% (75%) are quasi-perpendicular with shock normal angles (θ Bn) ≥ 45° relative to the upstream ambient magnetic field, and 40% (25%) are quasi-parallel (θ Bn < 45°). No radial dependences were found in FF shock normal angle and speed. The FF shock Mach number (M ms), magnetic field, and plasma compression ratios are found to increase with increasing r h at the rates of 0.72, 0.89, and 0.98 au−1, respectively. On average, ICME FF shocks are found to be considerably faster (∼20%) and stronger (with ∼28% higher M ms) than CIR FF shocks.

Overlapping of linear optical spectra in metallic carbon nanotubes, Controlled by applied axial magnetic field and uniaxial strain

The excitons and absorption spectra of M11 and M22 transitions in metallic carbon nanotubes were calculated by the tight-binding model, under the combined effect of axial magnetic field and uniaxial strain. It is interesting to find that the separated absorption peaks induced by axial magnetic field will meet each other when the uniaxial strain is applied. At the same axial magnetic field, the first overlapping point is appeared for Mii−−2 and Mii+−1 exciton with small uniaxial strain, and the biggest uniaxial strain is needed for Mii−−1 and Mii+−2 exciton. When we change the magnitude of the axial magnetic field, the overlapping point displays different variation trend for four separate excitons. This overlapping phenomenon is also occurred for other metallic tubes: with bigger diameter, smaller uniaxial strain is needed. More important is that an useful tool is offered to regulate the optical properties of carbon nanotubes by applying simultaneously the axial magnetic field and uniaxial strain.