Wave Magnetic Field Research Articles

Electromagnetic fields of time-dependent magnetic monopole

Dirac-Maxwell's equations, retained for magnetic monopoles, are generalized by introducing magnetic scale field. It allows the magnetic monopoles to be time-dependent and the potentials to be Lorentz gauge free. The non-conserved part or the time-dependent part of the magnetic charge density is responsible to produce the magnetic scalar field which further contributes to the magnetic and electric vector fields. This contribution makes possible to create an ideal square wave magnetic field from an exponentially rising and decaying magnetic charge. The Maxwell-Heaviside equations prescribe both open dissipative systems having coefficient of performance (COP) > 1 and equilibrium systems having COP 1, by functioning as open dissipative systems freely receiving and using excess energy from the active vacuum. To study the open dissipative systems the potentials are to be made Lorentz gauge free. While studying such systems, Anastasovski et al (2) obtained equations for vacuum current density and vacuum charge density and proposed to pick up by a receiver and use to generate huge electrical energy. Similar results have been deduced by Lehnert (3-6) and Lehnert and Scheffel (7) from the condition of a nonzero charge density from vacuum fluctuations in combination with the requirement of Lorentz invariance. By another approach Teli and Jadhav (8) removed the Lorentz condiction on potentials by introducing scalar potentials in the Generalized Dirac- Maxwell's equations which made the electrical charges time varying in nature. These charges then did not satisfy the continuity equation. The non-conserved part of the charge density was accommodated in terms of a scalar field. They obtained electromagnetic fields of non-conserving electric charged particle. However, magnetic monopoles, elementary particles with a net magnetic charge, have been a curiosity for physicists and many believe they ought to exist. Our attempt is to find out the fields of non-conserving magnetic monopoles

Sound wave excitation of spin current

The kinetics of conduction electrons interacting with the field of sound waves in a constant magnetic field is studied. Macroscopic balance equations for macroscopic spin components are derived to describe nonlinear acoustic resonance regime. It is shown that such an interaction may give rise to a spin current.

Detecting Larmor Precession of a Single Spin with a Spin-Polarized Tunneling Current

Detection and manipulation of a single spin is essential for spin-based quantum information and computation. We propose an experimental method to detect the Larmor precession of a single spin with a spin-polarized tunneling current. The calculation demonstrates that the modulation of the tunneling current is significantly increased as compared with the non-spin-polarized current. The signal-to-noise ratio in the current power spectrum will be dramatically improved by this method. The longitudinal relaxation time can be measured by temporal control of spin orientation with pulses of magnetic field or radio frequency electromagnetic wave, while the transverse relaxation time can be derived by analyzing the resonant peak profile with a spectrum analyzer. Such ability in characterizing spin relaxation is of particular interest in providing insights into the coherence/decoherence of a single spin.

Electron acceleration by Z-mode waves associated with cyclotron maser instability

We demonstrate by a particle simulation that Z-mode waves generated by the cyclotron maser instability can lead to a significant acceleration of energetic electrons. In the particle simulation, the initial electron ring distribution leads to the growth of Z-mode waves, which then accelerate and decelerate the energetic ring electrons. The initial ring distribution evolves into an X-like pattern in momentum space, which can be related to the electron diffusion curves. The peak kinetic energy of accelerated electrons can reach 3 to 6 times the initial kinetic energy. We further show that the acceleration process is related to the “nonlinear resonant trapping” in phase space, and the test-particle calculations indicate that the maximum electron energy gain Δεmax is proportional to Bw0.57, where Bw is the wave magnetic field.

Densification of MnZn Ferrite Sintered under Multi-Physical Field Coupling

This work provides a novel idea of fabricating MnZn bulk ferrite materials. MnZn ferrite powders with a composition of Zn0.8Mn0.2Fe2O4 (wt%) are sintered to form cylindrical bulk ferrite with diameters of 1.0mm, and heights of 1.0mm under multi-physical field coupling with Gleeble-1500D thermal simulation instrument. The results show that sintered ferrite has a spinel structure, and that some magnetic properties like maximum energy product and remanence of the Multi-physical Field Coupling sintered sample are better than that obtained by conventional sintering. Densification process and solid phase reaction are promoted by alternating magnetic field and high frequency wave generated by AC current.

Obliquely propagating ion-acoustic double layers in magnetized electron-positron-ion plasma

Ion–acoustic double layers has been studied in magnetized electron-positron-ion plasma. The modified Korteweg-de Vries (m-KdV) is derived using reductive perturbation method. It is found that for the selected set of parameters, the system supports rarefactive (compressive) double layers depending upon the values of cold electron concentration (μ). It is also found that the magnetization affects only the width of the double layer. For a given set of parameter values, as we increases the magnetization, the width of the double layer increases and an increases in the obliqueness θ, where θ is the angle between wave vector and magnetic field, the width of the double layer also increases. The angle of obliqueness θ does not affects the amplitude of the double layer. It is also investigated that for the given set of parameter values, on increasing the positron concentration the amplitude of the rarefactive (compressive) double layer decreases (increases), and the width of the rarefactive (compressive) double layer increases (decreases). The effect of the temperature ratios of ions and positron on the amplitude and width of the double layers are discussed.

Fast acceleration of inner magnetospheric hydrogen and oxygen ions by shock induced ULF waves

The interaction between interplanetary shocks and the Earth's magnetosphere manifests in many important space physics phenomena including particle acceleration. We investigated the response of the inner magnetospheric hydrogen and oxygen ions to a strong interplanetary shock impinging on the Earth's magnetosphere. Both hydrogen and oxygen ions are found to be heated/accelerated significantly with their temperature enhanced by a factor of two and three immediately after ∼1 min and ∼12 min of the shock arrival respectively. Multiple energy dispersion signatures of ions were found in the parallel and anti‐parallel direction to the magnetic field immediately after the interplanetary shock impact. The energy dispersions in the anti‐parallel direction preceded those in the parallel direction. Multiple dispersion signatures can be explained by the flux modulations of local ions (rather than the ions from the Earth's ionosphere) by ULF waves. It is found that the energy spectrum from 10 eV to ∼40 keV are highly correlated with the cross product of observed ULF wave electric and magnetic field (V = (E × B)/B2), which indicate that both cold plasmaspheric plasma and hot thermal ions (10 eV to ∼40 keV) are accelerated and decelerated with the various phases of ULF wave electric field. We then demonstrate that ion acceleration due to the interplanetary shock compression on the Earth's magnetic field is rather limited, whereas the major contribution to acceleration comes from the electric field carried by ULF waves via drift‐bounce resonance for both the hydrogen and oxygen ions. The integrated hydrogen and oxygen ion flux with the poloidal mode ULF waves are highly coherent (>0.9) whereas the coherence with the toroidal mode ULF waves is negligible, implying that the poloidal mode ULF waves are much more efficient in accelerating hydrogen and oxygen ions in the inner magnetosphere than the toroidal mode ULF waves. The duration of high coherence for oxygen ions with the poloidal mode ULF wave is longer than that for hydrogen ions, indicating that oxygen ions can be heated/accelerated more efficiently by the poloidal mode ULF wave induced by the interplanetary shock.

Surface Acoustic Wave Magnetic Sensor using Galfenol Thin Film

The performance of a surface acoustic wave (SAW) magnetic field sensor using galfenol (FeGa) thin film is investigated in this effort. We measure the change in the SAW velocity as a function of an externally applied magnetic field for galfenol films of varying thicknesses. A maximum change of 0.64%, greater than results reported for similar sensors, is obtained with a 500 nm thick film.

On the electrodynamics in time-dependent linear media

In this work we study the classical electrodynamics in homogeneous conducting and nonconducting time-dependent linear media in the absence of charge sources. Surprisingly, we find that the time dependence of the permittivity gives rise to an additional term in the Ampere-Maxwell equation and an asymmetry between the electric and magnetic field wave equations. As special cases we consider a linear and an exponential growth of the permittivity, as well as a sinusoidal time-dependent permittivity.

Intensification of dayside diffuse auroral precipitation: contribution of dayside Whistler-mode chorus waves in realistic magnetic fields

Abstract. Compared to the recently improved understanding of nightside diffuse aurora, the mechanism(s) responsible for dayside diffuse aurora remains poorly understood. While dayside chorus has been thought as a potential major contributor to dayside diffuse auroral precipitation, quantitative analyses of the role of chorus wave scattering have not been carefully performed. In this study we investigate a dayside diffuse auroral intensification event observed by the Chinese Arctic Yellow River Station (YRS) all-sky imagers (ASI) on 7 January 2005 and capture a substantial increase in diffuse auroral intensity at the 557.7 nm wavelength that occurred over almost the entire ASI field-of-view near 09:24 UT, i.e., ~12:24 MLT. Computation of bounce-averaged resonant scattering rates by dayside chorus emissions using realistic magnetic field models demonstrates that dayside chorus scattering can produce intense precipitation losses of plasma sheet electrons on timescales of hours (even approaching the strong diffusion limit) over a broad range of both energy and pitch angle, specifically, from ~1 keV to 50 keV with equatorial pitch angles from the loss cone to up to ~85° depending on electron energy. Subsequent estimate of loss cone filling index indicates that the loss cone can be substantially filled, due to dayside chorus driven pitch angle scattering, at a rate of ≥0.8 for electrons from ~500 eV to 50 keV that exactly covers the precipitating electrons for the excitation of green-line diffuse aurora. Estimate of electron precipitation flux at different energy levels, based on loss cone filling index profile and typical dayside electron distribution observed by THEMIS spacecraft under similar conditions, gives a total precipitation electron energy flux of the order of 0.1 erg cm−2 s−1 with ~1 keV characteristic energy (especially when using T01s), which can be very likely to cause intense green-line diffuse aurora activity on the dayside. Therefore, dayside chorus scattering in the realistic magnetic field can greatly contribute to the YRS ASI observed intensification of dayside green-line aurora. Besides wave induced scattering and changes in the ambient magnetic field, variations in associated electron flux can also contribute to enhanced diffuse aurora emissions, the possibility of which we cannot exactly rule out due to lack of simultaneous observations of magnetospheric particles. Since the geomagnetic activity level was rather low during the period of interest, it is reasonable to infer that changes in the associated electron flux in the magnetosphere should be small, and consequently its contribution to the observed enhanced diffuse auroral activity should be small as well. Our results support the scenario that dayside chorus could play a major role in the production of dayside diffuse aurora, and also demonstrate that changes in magnetospheric magnetic field should be considered to reasonably interpret observations of dayside diffuse aurora.

Nonlinear spatiotemporal evolution of whistler mode chorus waves in Earth's inner magnetosphere

We analyze the nonlinear evolution of whistler mode chorus waves propagating along a magnetic field line from their equatorial source. We solve wave evolution equations off the equator for the wave magnetic field amplitude and wave frequency, subject to boundary conditions at the equator comprising model “chorus equations” that describe the generation of a seed chorus element. The electron distribution function is assumed to evolve adiabatically along a field line. The wave profiles exhibit nonlinear convective growth followed by saturation. Convective growth is due to nonlinear wave trapping, and the saturation process is partly due to a combination of adiabatic effects and a decreasing resonant current with latitude. Notwithstanding computationally expensive full‐scale kinetic simulations, our study appears to be the first to analyze the nonlinear evolution and saturation of whistler mode waves off the equator.

Propagation of charged particle waves in a uniform magnetic field

This paper considers the probability density and current distributions generated by a point-like, isotropic source of monoenergetic charges embedded into a uniform magnetic field environment. Electron sources of this kind have been realized in recent photodetachment microscopy experiments. Unlike the total photocurrent cross section, which is largely understood, the spatial profiles of charge and current emitted by the source display an unexpected hierarchy of complex patterns, even though the distributions, apart from scaling, depend only on a single physical parameter. We examine the electron dynamics both by solving the quantum problem, i. e., finding the energy Green function, and from a semiclassical perspective based on the simple cyclotron orbits followed by the electron. Simulations suggest that the semiclassical method, which involves here interference between an infinite set of paths, faithfully reproduces the features observed in the quantum solution, even in extreme circumstances, and lends itself to an interpretation of some (though not all) of the rich structure exhibited in this simple problem.

Local-gauge finite-element method for electron waves in magnetic fields

The finite-element method (FEM) has already been extended to analyze transport properties of electron waves of two-dimensional electron systems in magnetic fields. Although many researchers have created new formulations or improvements to this method, few have analyzed how this method is applied to realistic systems. The present paper suggests that conventional formulations of the FEM do not give accurate results for large systems or for strong magnetic fields; in addition, it suggests that the selected gauge significantly influences the numerical results. Furthermore, this paper proposes a conceptually different formulation of the FEM that solves the poor convergence problem. This formulation is simple: matrix elements are multiplied by the Peierls phase in the absence of a magnetic field. To show the advantages of this formulation, numerical examples are presented.

The quantum acoustomagnetoelectric field in a quantum well with a parabolic potential

The acoustomagnetoelectric (AME) field in a quantum well with a parabolic potential (QWPP) has been studied in the presence of an external magnetic field. The analytic expression for the AME field in the QWPP is obtained by using the quantum kinetic equation for the distribution function of electrons interacting with external phonons. The dependence of the AME field on the temperature T of the system, the wavenumber q of the acoustic wave and external magnetic field B for the specific AlAs/GaAs/AlAs is achieved by using a numerical method. The problem is considered for both cases: The weak magnetic field region and the quantized magnetic field region. The results are compared with those for normal bulk semiconductor and superlattices to show the differences, and we use the quantum theory to calculate the AME field in the QWPP.

Electron magneto-hydrodynamic waves bounded by magnetic bubble

The propagation of electron magneto-hydrodynamic (EMHD) waves is studied experimentally in a 3-dimensional region of low magnetic field surrounded by stronger magnetic field at its boundaries. We report observations where bounded left hand polarized Helicon like EMHD waves are excited, localized in the region of low magnetic field due to the boundary effects generated by growing strengths of the ambient magnetic field rather than a conducting or dielectric material boundary. An analytical model is developed to include the effects of radially nonuniform magnetic field in the wave propagation. The bounded solutions are compared with the experimentally obtained radial wave magnetic field profiles explaining the observed localized propagation of waves.

A computational and theoretical analysis of falling frequency VLF emissions

Recently much progress has been made in the simulation and theoretical understanding of rising frequency triggered emissions and rising chorus. Both PIC and Vlasov VHS codes produce risers in the region downstream from the equator toward which the VLF waves are traveling. The VHS code only produces fallers or downward hooks with difficulty due to the coherent nature of wave particle interaction across the equator. With the VHS code we now confine the interaction region to be the region upstream from the equator, where inhomogeneity factor S is positive. This suppresses correlated wave particle interaction effects across the equator and the tendency of the code to trigger risers, and permits the formation of a proper falling tone generation region. The VHS code now easily and reproducibly triggers falling tones. The evolution of resonant particle current JE in space and time shows a generation point at −5224 km and the wavefield undergoes amplification of some 25 dB in traversing the nonlinear generation region. The current component parallel to wave magnetic field (JB) is positive, whereas it is negative for risers. The resonant particle trap shows an enhanced distribution function or ‘hill’, whereas risers have a ‘hole’. According to recent theory (Omura et al., 2008, 2009) sweeping frequency is due primarily to the advective term. The nonlinear frequency shift term is now negative (∼−12 Hz) and the sweep rate of −800 Hz/s is approximately nonlinear frequency shift divided by TN, the transition time, of the order of a trapping time.

Spatio-temporal structure of Alfvén waves excited by a sudden impulse localized on an L-shell

Abstract. This paper is concerned with the spatial structure and temporal evolution of the azimuthally small scale Alfvén wave generated by a sudden impulse concentrated on a given magnetic shell. At the outset, both poloidal and toroidal components are present in the wave's magnetic field. The oscillation in the poloidal component on a given magnetic shell is a superposition of two monochromatic oscillations, one with the local resonance frequency on this shell, and the other with the frequency corresponding to the resonance frequency on the source surface. The superposition of these two oscillations leads to beating. Due to phase mixing, the poloidal component of the oscillation decreases with time down to zero, transferring its energy to the toroidal component. Beating in the toroidal component is less pronounced. As time elapses, energy concentration near the source magnetic shell occurs with the frequency of the oscillation corresponding to the Alfvénic resonance frequency on this surface. Outside this thin region wave amplitudes become rather small at oscillation frequencies corresponding to the local resonance frequency of the respective magnetic shell.

Mercurial magnetic field waves measured by orbiting satellite

Researchers working with NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging ( MESSENGER) spacecraft report the frequent detections of Kelvin‐Helmholtz (KH) waves at the edge of the innermost planet's magnetosphere. In six different sets of magnetic field measurements made by the orbiter as it passed through Mercury's magnetopause, the boundary that separates the planet's magnetosphere from the solar wind plasma in the magnetosheath, Sundberg et al. detected the magnetic field oscillations characteristic of fully developed KH waves. These waves form when fuids of different speeds travel alongside each other—in this case, the magnetosphere and magnetosheath plasmas—and promote mixing of the plasmas on larger spatial, and shorter time, scales than diffusive transport. The observations, which span the frst 88 days of MESSENGER's time in orbit, bring Mercury alongside Earth, Saturn, and Venus as planets for which such KH waves are of importance.

Streamline generation code for particle dynamics description in numerical models of turbulence

Streamline Version 4 is a versatile Fortran 77 & C++ program for calculating charged test particle trajectories or field-lines for user-specified fields using the test-particle method. The user has the freedom to specify any type of field (analytical, tabulated in files, time dependent, etc.) and maintains complete control over initial conditions of trajectories/field-lines and boundary conditions of specified fields. The structure of Streamline was redesigned from previous versions in order to know not only particle or field-lines positions and velocities at each step of the simulations, but also the instantaneous field values as seen by particles. This was made to compute the instantaneous value of the particle’s magnetic moment, but other applications are possible too. Accuracy tests of the code are shown for different cases, i.e., particles moving in constant magnetic field, magnetic plus constant electric field and wave field. In addition in the last part of the paper we concentrate our discussion on the study of velocity space diffusion of charged particles in turbulent slab fields, paying attention to the discretization of the fields and the temporal discretization of the dynamical equations. The diffusion of charged particles is a very common topic in plasma physics and astrophysics since it plays an important role in many different phenomena such as stochastic particle acceleration, diffusive shock acceleration, solar energetic particle propagation, and the scattering required for the solar modulation of galactic cosmic rays.

Evolution of the plasma sheet electron pitch angle distribution by whistler-mode chorus waves in non-dipole magnetic fields

Abstract. We present a detailed numerical study on the effects of a non-dipole magnetic field on the Earth's plasma sheet electron distribution and its implication for diffuse auroral precipitation. Use of the modified bounce-averaged Fokker-Planck equation developed in the companion paper by Ni et al. (2012) for 2-D non-dipole magnetic fields suggests that we can adopt a numerical scheme similar to that used for a dipole field, but should evaluate bounce-averaged diffusion coefficients and bounce period related terms in non-dipole magnetic fields. Focusing on nightside whistler-mode chorus waves at L = 6, and using various Dungey magnetic models, we calculate and compare of the bounce-averaged diffusion coefficients in each case. Using the Alternative Direction Implicit (ADI) scheme to numerically solve the 2-D Fokker-Planck diffusion equation, we demonstrate that chorus driven resonant scattering causes plasma sheet electrons to be scattered much faster into loss cone in a non-dipole field than a dipole. The electrons subject to such scattering extends to lower energies and higher equatorial pitch angles when the southward interplanetary magnetic field (IMF) increases in the Dungey magnetic model. Furthermore, we find that changes in the diffusion coefficients are the dominant factor responsible for variations in the modeled temporal evolution of plasma sheet electron distribution. Our study demonstrates that the effects of realistic ambient magnetic fields need to be incorporated into both the evaluation of resonant diffusion coefficients and the calculation of Fokker-Planck diffusion equation to understand quantitatively the evolution of plasma sheet electron distribution and the occurrence of diffuse aurora, in particular at L > 5 during geomagnetically disturbed periods when the ambient magnetic field considerably deviates from a magnetic dipole.