Wave Magnetic Field Research Articles

About definition of modes and magnetosonic heating in a plasma's flow: Especial cases of perpendicular and nearly perpendicular wave vector and magnetic field

AbstractDynamics of hydrodynamic perturbations in a plasma depend strongly on an angle between the wave vector and equilibrium straight magnetic field. The case of perpendicular propagation is especial. There are only two (fast) magnetosonic modes since two (slow) ones degenerate into the stationary one with zero speed of propagation. This demands individual definition of wave modes by the links of hydrodynamic relations. These links are not limiting case of the relations in the case of non‐zero angle. The nonlinear excitation of the entropy mode in the field of intense magnetosonic perturbations is also unusual. Bulk and shear viscosity and thermal conduction are considered as the damping mechanisms in a weakly nonlinear flow. The leading‐order dynamic equation is derived which governs perturbation of density in the entropy mode. The links of magnetosonic perturbations and magnetosonic heating may be indicators of plasma‐, geometry of a flow, damping coefficients and type of wave motion. The “almost resonant” character of magnetosonic heating excited by the slow magnetosonic wave in the course of nearly perpendicular wave propagation, is discussed.

Optimization of bifurcating channel cooling system for double inclined conductive panel system under inclined magnetic field

A novel cooling system with wavy branching channels is proposed considering nano-enhanced magnetic field effects for thermal management of double inclined conductive panels. Thermal performance assessment is conducted by varying Reynolds number (250≤Re≤1000), Hartmann number (0≤Ha≤400), magnetic field inclination (250≤γ≤1000), amplitude (0≤Af≤0.4) and wave number (1≤Nf≤12). As the cooling fluid, water with Ag–MgO hybrid nanoparticles is considered. Temperature drops of 4.5 °C and 2.6 °C are obtained with the highest Re for left inclined panel (p1) and right inclined panel (p2). As the vortex distribution is highly affected for the wavy branching channels by the magnetic field strength, its impact on the cooling performance for p1 and p2 are different. It shows a favorable impact for panel p2 while average Nusselt number (Nu) increments become 10% and 6.3% when using flat and wavy branching channels at the highest magnetic field strength. For panel p1, varying inclination of magnetic field results in average surface temperature drop of 1.6 °C for wavy channel. The optimum value of wave number in the corrugated branching channel is Nf=2 for achieving the highest cooling performance while higher amplitudes of corrugation has favorable impacts on the cooling for each of the panels. As compared to un-cooled panel configuration, utilization of flat branching channel with nano-enhanced magnetic field results in 47.4 °C and 48.9 °C surface temperature drops for panels p1 and p2. Optimization based on COBYLA is utilized to achieve additional temperature drops as compared to parametric computational fluid dynamics. The optimum values of (Ha, γ, Af) are obtained as (40, 89, 0.04) at Re=100 and (40, 60.8, 0.0038) at Re=1000. The proposed single cooling method with wavy branching channel under nano-enhanced magnetic field can be used and further developed for effectively cooling of photo-voltaics with inclined arrangement, electronic cooling and many other heat transfer devices.

A study of the propagation of magnetoacoustic waves in small-scale magnetic fields using solar photospheric and chromospheric Dopplergrams: HMI/SDO and MAST observations

In this work, we present a study of the propagation of low-frequency magneto-acoustic waves into the solar chromosphere within small-scale inclined magnetic fields over a quiet-magnetic network region utilizing near-simultaneous photospheric and chromospheric Dopplergrams obtained from the HMI instrument onboard SDO spacecraft and the Multi-Application Solar Telescope (MAST) operational at the Udaipur Solar Observatory, respectively. Acoustic waves are stochastically excited inside the convection zone of the Sun and intermittently interact with the background magnetic fields resulting into episodic signals. In order to detect these episodic signals, we apply the wavelet transform technique to the photospheric and chromospheric velocity oscillations in magnetic network regions. The wavelet power spectrum over photospheric and chromospheric velocity signals show a one-to-one correspondence between the presence of power in the 2.5–4 mHz band. Further, we notice that power in the 2.5–4 mHz band is not consistently present in the chromospheric wavelet power spectrum despite its presence in the photospheric wavelet power spectrum. This indicates that leakage of photospheric oscillations (2.5–4 mHz band) into the higher atmosphere is not a continuous process. The average phase and coherence spectra estimated from these photospheric and chromospheric velocity oscillations illustrate the propagation of photospheric oscillations (2.5–4 mHz) into the solar chromosphere along the inclined magnetic fields. Additionally, chromospheric power maps estimated from the MAST Dopplergrams also show the presence of high-frequency acoustic halos around relatively high magnetic concentrations, depicting the refraction of high-frequency fast mode waves around vA≈vs layer in the solar atmosphere.

Proposal of defect inspection method of steel plate by full-wave rectified magnetic field

The large-diameter steel pipes are often used in petrochemical plants. In this large-diameter steel pipe, there are many cases where corrosion in the steel pipe is inspected from the outside of the steel pipe. In particular, there is a demand for a method for detecting defects inside or outside the steel pipe from the outer side of the steel pipe at high speed. Therefore, the electromagnetic inspection method is useful for detecting these defects. In the electromagnetic inspection method, using both static (DC) magnetic field and alternating (AC) magnetic field is proposed for inspecting inner side defects as well as outside defects. On the other hand, the Fourier series expansion of the full-wave rectified wave of the stationary AC magnetic field shows that it is a composite of the DC component and the AC component due to the cosine wave. Therefore, in this research, an inspection method using full-wave rectified AC magnetic field is proposed for inspecting inner side defects as well as surface defects. In this paper, the usefulness of the proposed method is demonstrated by electromagnetic field analysis using the “play model” that takes into account minor loop magnetic properties. In addition, a verification experiment is also carried out.

Колебания геомагнитного поля в диапазоне 2.5–12 Гц в F-слое ионосферы по данным спутников SWARM

We have analyzed geomagnetic variations in the 2.5–12 Hz frequency range in the ionospheric F layer above the electron density maximum, using data from two SWARM satellites. The analysis is based on the data obtained under weak and moderate magnetic activity for 12 days in September and December 2016. To separate spatial inhomogeneities from time variations of the magnetic field, we analyzed signal waveforms and cross-spectra in a 2.56 s sliding window. A maximum in the occurrence and power spectral density of the variations was found at latitudes above the polar boundary of the auroral oval, which correspond to the magnetospheric input layers and dayside polar cusp/cleft. Typical waveforms of the high-latitude variations are the wave packets lasting for 5–10 periods, recorded with a short time delay by two satellites spaced by 40–100 km. These variations might be the ionospheric manifestation of the electromagnetic ion-cyclotron waves generated at the non-equatorial magnetosphere near the polar cusp. The waveforms and cross-spectra of the variations are examined in more details for two cases with different spatial distributions of the magnetic field in the ionosphere. For the ionospheric conditions corresponding to event 1 (September 17, 80° geomagnetic latitude, afternoon sector), spatial distributions of wave magnetic field in the ionosphere and on Earth are estimated using a model of Alfvén beam with a finite radius incident on the ionosphere [Fedorov et al., 2018].

Колебания геомагнитного поля в диапазоне 2.5–12 Гц в F-слое ионосферы по данным спутников SWARM

We have analyzed geomagnetic variations in the 2.5–12 Hz frequency range in the ionospheric F layer above the electron density maximum, using data from two SWARM satellites. The analysis is based on the data obtained under weak and moderate magnetic activity for 12 days in September and December 2016. To separate spatial inhomogeneities from time variations of the magnetic field, we analyzed signal waveforms and cross-spectra in a 2.56 s sliding window. A maximum in the occurrence and power spectral density of the variations was found at latitudes above the polar boundary of the auroral oval, which correspond to the magnetospheric input layers and dayside polar cusp/cleft. Typical waveforms of the high-latitude variations are the wave packets lasting for 5–10 periods, recorded with a short time delay by two satellites spaced by 40–100 km. These variations might be the ionospheric manifestation of the electromagnetic ion-cyclotron waves generated at the non-equatorial magnetosphere near the polar cusp. The waveforms and cross-spectra of the variations are examined in more details for two cases with different spatial distributions of the magnetic field in the ionosphere. For the ionospheric conditions corresponding to event 1 (September 17, 80° geomagnetic latitude, afternoon sector), spatial distributions of wave magnetic field in the ionosphere and on Earth are estimated using a model of Alfvén beam with a finite radius incident on the ionosphere [Fedorov et al., 2018].

Geoeffectiveness of Interplanetary Alfvén Waves. II. Spectral Characteristics and Geomagnetic Responses

Using multipoint observations over 10 yr near 1 au, we investigate the spectra (5 minutes to 2 hr) of interplanetary Alfvén waves and the responses in the geomagnetic activities. We compute the two-point correlations of the wave magnetic field between the ACE and the THEMIS spacecraft, which are separated by ∼200 Earth radius (R E) in the solar wind. Alfvén waves associated with high two-point correlations exhibit steep spectra (spectra index ∼−1.63). Such Alfvén waves occur mostly in slow-speed streams. By contrast, Alfvén waves with low two-point correlations exhibit flatter spectra (spectra index ∼−1.51) with a relative enhancement of power above 2 × 10−4 Hz. The occurrence of Alfvén waves with low two-point correlations is more equally distributed between high-speed and low-speed streams. In general, interplanetary Alfvén waves show correlations with moderate geomagnetic responses in symmetric ring-current intensity, SuperMAG electrojet (SME), and Kp indices. Statistical analyses indicate that the Alfvén waves with flat spectra correspond to stronger responses in the geomagnetic indices than those with steep spectra, suggesting the importance of the tens of minutes (30–90 minutes) Alfvénic power spectra in the generation of SME/Auroral Electrojets. These observations may shed light on the response of the magnetosphere to fluctuating interplanetary magnetic field B z .

Wave number and magnetic field effects on the boundary layer flow over an accelerating vertical surface with zero-time periodic boundaries

The problem of the wave number and magnetic field effects on a boundary layer flow over an accelerating vertical surface in the presence of heat generation and reacting species, and zero-time periodic boundaries is examined. We assumed the fluid is Newtonian, chemically reactive and of order one, and magnetically susceptible. The governing non-linear partial differential equations of the Bousinesq form are solved using the Homotopy Perturbation Method. Expressions for the concentration, temperature, and velocity are obtained, computed, and presented graphically. The analysis of results shows that the increase in the: Wave number increases the concentration, temperature, velocity, Sherwood, Nusselt number, and stress on the wall; Magnetic field increases the concentration, temperature, and velocity in the range of 0 < M < 1.5; Dufour number increases the concentration, temperature, and velocity of the fluid.

The effect of wave frequency drift on the electron nonlinear resonant interaction with whistler-mode waves

Electron resonant interaction with electromagnetic whistler-mode waves plays a crucial role for electron flux dynamics in planetary magnetospheres. One of the most intense types of whistler-mode waves consists of chorus waves generated via nonlinear resonant interaction with hot anisotropic electrons and propagating with time-varying (drifting) wave frequency. Electron nonlinear resonant interactions with such waves in a dipole magnetic field are well described analytically within the Hamiltonian approach under the approximation of monochromatic waves (of constant frequency). This paper aims to generalize this description to waves with drifting frequency. We show how frequency drift modifies two main nonlinear resonant effects: phase trapping and phase bunching. The obtained results contribute to the development of the Hamiltonian approach for wave–particle resonant interactions.

Effect of Deceleration Mode of Traveling Wave Magnetic Field on the Liquid Steel Transportation Behavior in the Mold of Slab Casting

Effect of Deceleration Mode of Traveling Wave Magnetic Field on the Liquid Steel Transportation Behavior in the Mold of Slab Casting

Simulation of a Transverse Flux Linear Induction Motor to Determine an Equivalent Circuit Using 3D Finite Element

This paper presents a Transverse Flux Linear Induction Motor prototype simulated with a 3D Finite Element tool. The main objective of the paper is to obtain an accurate method to construct an equivalent circuit that simulates the motor, using some specific parameters. The method has three steps. In the first step, we simulate two indirect tests to represent rotating induction machines, standstill and locked rotor tests. Using the test results, we define an equations system that incorporates the longitudinal end-effect. The system allows us to select specific parameters needed to build the equivalent circuit using six different configurations. In the second step, we classify the parameters in two groups: parameters from the primary and secondary parts. We test the primary part parameters defining the magnetizing inductance as a combination of the longitudinal and the transversal magnetizing inductance. To this end, the method analyses the first harmonic of the magnetic field wave along the air gap, which is located above the central teeth. Thus, it is possible to establish a difference between transversal and longitudinal components of the magnetic field density. The parameters of the secondary part will be compared using 2D Field Theory with a linear induction motor that operates with a transverse flux configuration. In the third step, the method analyses the selected parameters using a goodness factor, a dimensionless key performance indicator, specifically used to evaluate the behavior of linear induction motors and the specific parameters estimated for the equivalent circuit.

MRI Findings In Patients With Headache And Vertigo

BACKGROUND:A headache is a condition of pain in the head. In Medical nomenclature, it is known as cephalgia.Primary and secondary headaches are the two forms of headaches. The first type of headache is primary headache, which includes migraine, cluster headaches, and tension headaches. They are non-aggressive in nature. Primary headaches are usually chronic in character and are caused by no underlying functional illness. The second type of headache is secondary headache, which is always brought on by major organic disorders. It can range from benign cranial conditions like sinusitis or mastoiditis to life-threatening intracranial pathologies like subarachnoid haemorrhage or brain tumours. Vertigo is a perception of motion or spinning that is often represented as dizziness. Vertigo is not the same as being featherbrained. People with vertigo tone as though they are actually handicraft or moving, or that the world is spinning around them. Vertigo is frequently caused by issues with certain regions of the brain. Vertigo can be caused by a variety of factors, including benign paroxysmal positional vertigo (BPPV), which occurs when certain head motions cause vertigo. Migraines are a type of severe headache. Mostly the patients with vertigo and headache normally do not require a brain MRI. For Secondary reason of headache,some patients need an brain MRI. MRI is best Diagnostic modality for the diagnosis and management of secondary headache and vertigo. CONCLUSION: Magnetic resonance imaging (MRI) is a finest diagnostic modality that creates detailed images of the organs and tissues in your body using a magnetic field and computer-generated radio waves. It is considered as the best diagnostic method for the diagnosis and therapy of secondary headache and vertigo. A modest percentage of medical institution fundamental positive findings in neuroimaging are seen in MRI of patients with headache. In these patients, the cost-effectiveness of MRI as a screening tool is of limited benefit.

Effects of Field‐Aligned Cold Plasma Density Filaments on the Fine Structure of Chorus

AbstractThe whistler‐mode chorus emission, a major driver of radiation belt electron energization and precipitation, exhibits significant amplitude modulations on millisecond timescales. These subpacket modulations are accompanied by fast changes in the wave normal angle. Understanding the evolution of wave propagation properties inside chorus elements is essential for modeling nonlinear chorus‐electron interactions, but the origin of these rapid changes is unclear. We propose that the variations come from propagation inside thin, field‐aligned cold plasma enhancements (density ducts), which produce differing modulations in parallel and perpendicular wave magnetic field components. We show that a full‐wave simulation on a filamented density background predicts wave vector and amplitude evolution similar to Van Allen Probes spacecraft observations. We further demonstrate that the commonly assumed wide density ducts, in which wave propagation can be studied with ray tracing methods, cannot explain the observed behavior. This indirectly proves the existence of wavelength‐scale field‐aligned density fluctuations.

Analysis of the Magnetic Field Magnetoinductive Wave Characteristics of a Wireless Power Transfer System.

This study analyzes the magnetic field wave characteristics of a wireless power transfer (WPT) system from a time-varying view in the nonradiative near field. Phenomena of both forward and backward traveling waves were found. These wave phenomena refer to magnetoinductive waves (MIWs) according to the findings in this study and MIW theory and characteristics. A traditional MIW only appears in the MIW waveguide, which is always constructed by many parallel coils. However, this study analyzed MIWs in a two-coil WPT system, proving that MIWs exist not only in a multi-coil system but also in a basic two-coil system. The velocity of MIWs, a kind of a phase velocity, was calculated. An approximate equation for evaluating wave velocity is proposed. Furthermore, the MIWs in the two-coil WPT system were extended into a more general situation. In this general situation, two separated standing waves were set, and a traveling wave was generated by those two standing waves. The result explains the mechanisms of MIWs in a general situation from a time-varying view. Lastly, a simulation was conducted to verify the accuracy of the study. The results demonstrated that MIWs exist, and the approximate equation is correct. This study presents a novel view on the mechanisms of the WPT system from a wave view.

Anomalous resonance between low-energy particles and electromagnetic plasma waves

Cyclotron resonance between plasma waves and charged particles is a fundamental and ubiquitous process in the plasma universe, during which the particle’s gyromotion has a constant phase in the wave field to enable a sustained energy exchange. In this classical picture, however, the particle’s angular velocity is determined only by the background magnetic field. Here, we show that the classical condition of cyclotron resonance fails to describe the observations of low-energy particles in resonance with large-amplitude waves, which highlights the roles of the wave field in nonlinearly modifying the resonant picture. The revised scenario of anomalous resonance is then validated by the agreement between test-particle simulations and ultrafast spacecraft measurements, which present in-phase and/or antiphase relationships between the wave magnetic field and ion flux oscillations at energy and pitch-angle ranges incompatible with the classical resonance condition. This revision could significantly affect the wave-particle energy exchange and wave evolution processes.

Making the invisible visible-ultrashort echo time magnetic resonance imaging: Technical developments and applications.

Magnetic resonance imaging (MRI) uses a large magnetic field and radio waves to generate images of tissues in the body. Conventional MRI techniques have been developed to image and quantify tissues and fluids with long transverse relaxation times (T2s), such as muscle, cartilage, liver, white matter, gray matter, spinal cord, and cerebrospinal fluid. However, the body also contains many tissues and tissue components such as the osteochondral junction, menisci, ligaments, tendons, bone, lung parenchyma, and myelin, which have short or ultrashort T2s. After radio frequency excitation, their transverse magnetizations typically decay to zero or near zero before the receiving mode is enabled for spatial encoding with conventional MR imaging. As a result, these tissues appear dark, and their MR properties are inaccessible. However, when ultrashort echo times (UTEs) are used, signals can be detected from these tissues before they decay to zero. This review summarizes recent technical developments in UTE MRI of tissues with short and ultrashort T2 relaxation times. A series of UTE MRI techniques for high-resolution morphological and quantitative imaging of these short-T2 tissues are discussed. Applications of UTE imaging in the musculoskeletal, nervous, respiratory, gastrointestinal, and cardiovascular systems of the body are included.

Wave propagation and power deposition in blue-core helicon plasma

The wave propagation and power deposition inside and outside the blue-core helicon plasma are computed, together with their transitional behaviours prior to and after the blue-core formation. Computations refer to the experiments on the CSDX (controlled shear decorrelation experiment) (Thakur et al., Plasma Sources Science and Technology 23: 044,006, 2014 and Thakur et al., IEEE Transactions on Plasma Science 43: 2754–2759, 2015). It is found that the radial profile of wave electric field peaks off-axis during the blue-core formation, and the location of this peak is very close to that of particle transport barrier observed in experiment; the radial profile of wave magnetic field shows multiple radial modes inside the blue-core column, which is consistent with the experimental observation of coherent high m modes through Bessel function. The axial profiles of wave field indicate that the decay length shortens for increased external field strength, especially when the blue-core mode has been achieved, and this length is relatively longer inside the core than that outside. The wave energy density is overall lower in two orders after blue-core formation than that prior to, and the energy distribution shows a periodic boundary layer near the edge of blue-core column. The dispersion relation inside the blue-core column suggests the presence of two radial modes, while outside the blue-core column it shows no variation, i.e. constant wave number with changed frequency. The power deposition appears to be off-axis in the radial direction, forming a hollow profile, and when the blue-core mode has been formed it shows periodic structure in the axial direction. Analyses based on the step-like function theory and introduced blue-core constant provide consistent results and more physics understanding. These details of wave propagation and power deposition during the blue-core formation are presented for the first time, and helpful for understanding the mechanism of blue-core phenomenon. The equivalence of blue-core plasma column to optical fiber for electromagnetic communication is also explored, and preliminary calculation shows that total reflection can indeed occur if the incident angle is larger than a threshold value. This may inspire a novel application of helicon plasma, and is one of the most interesting findings of present work.

AlScN-Based SAW Magnetic Field Sensor for Isolated Closed-Loop Hysteretic Current Control of Switched-Mode Power Converters

This letter uses a surface acoustic wave magnetic field sensor for measurement and closed-loop current control of the inductor current in a GaN-based dc-dc power converter. The sensor is based on aluminium scandium nitride thin films with relatively high Sc concentration of 32% and fabricated on low-cost 8-in silicon substrate, with a magnetostrictive FeCoSiB film on top of a SAW delay line. The device has dc and bidirectional current measurement capability (derived from the magnetic flux density around a current trace) and is operated electrically isolated above the current trace. With permanent magnets as magnetic bias, the setup has a usable bidirectional current range of ±5 A. A phase detector IC measures the phase shift between the 296 MHz, 19 dBm input, and 35 dB attenuated output signal of the delay line sensor. The active sensor area has a distance of 2.5 mm from the current trace. In a 1.2 mT bias, the sensor is operated with a sensitivity of 18.28°/mT and bipolar current range of up to ±5 A. The sensor signal is enhanced by an analog filter to compensate the over 1 µs delay from the delay line and readout circuit. Finally, the sensor is used as the input of an analog hysteretic current control loop. The closed-loop current control operation is demonstrated using a 48 V GaN-based half-bridge dc-dc converter with 16 kHz triangular inductor current.

Numerical analysis of the spatial structure of Alfvén waves in a finite pressure plasma in a dipole magnetosphere

We have carried out a numerical analysis of the spatial structure of Alfvén waves in a finite pressure inhomogeneous plasma in a dipole model of the magnetosphere. We have considered three magnetosphere models differing in maximum plasma pressure and pressure gradient. The problem of wave eigenfrequencies was addressed. We have established that the poloidal frequency can be either greater or less than the toroidal frequency, depending on plasma pressure and its gradient. The problem of radial wave vector component eigenvalues was considered. We have found points of Alfvén wave reflection in various magnetosphere models. The wave propagation region in the cold plasma model is shown to be significantly narrower than that in models with finite plasma pressure. We have investigated the structure of the main Alfvén wave harmonic when its polarization changes in three magnetosphere models. A numerical study into the effect of plasma pressure on the structure of behavior of all Alfvén wave electric and magnetic field components has been carried out. We have established that for certain parameters of the magnetosphere model the magnetic field can have three nodes, whereas in the cold plasma model there is only one. Moreover, the longitudinal magnetic field component changes sign twice along the magnetic field line.

Численный анализ пространственной структуры альфвеновских волн в плазме конечного давления в дипольной магнитосфере

We have carried out a numerical analysis of the spatial structure of Alfvén waves in a finite pressure inhomogeneous plasma in a dipole model of the magnetosphere. We have considered three magnetosphere models differing in maximum plasma pressure and pressure gradient. The problem of wave eigenfrequencies was addressed. We have established that the poloidal frequency can be either greater or less than the toroidal frequency, depending on plasma pressure and its gradient. The problem of radial wave vector component eigenvalues was considered. We have found points of Alfvén wave reflection in various magnetosphere models. The wave propagation region in the cold plasma model is shown to be significantly narrower than that in models with finite plasma pressure. We have investigated the structure of the main Alfvén wave harmonic when its polarization changes in three magnetosphere models. A numerical study into the effect of plasma pressure on the structure of behavior of all Alfvén wave electric and magnetic field components has been carried out. We have established that for certain parameters of the magnetosphere model the magnetic field can have three nodes, whereas in the cold plasma model there is only one. Moreover, the longitudinal magnetic field component changes sign twice along the magnetic field line.