Electromagnetic Field Variations Research Articles

Enhanced propulsion performances under optimum parameters in closed drift accelerators

Parametric estimations of propulsion performances were conducted through numerical analysis and experiment in closed drift accelerators, the so-called hall thrusters. At high-voltage mode of DC regime which is ordinary operation region, the large-amplitude discharge current oscillation in the tens of kHz has been a serious problem that should be solved with a view to improving the stability of operation and the durability of thruster-in-itself. So the dependencies of propulsion performances, (thrust, specific impulse and thrust efficiency) including both amplitude and frequency of “low-frequency oscillation” on various parameters, (discharge voltage, neutral species temperature and magnetic field configuration) were investigated in the present study. Besides the following possibility was suggested: The operational conditions or the design providing the larger “average length of ionization-zone”, which we introduced as a new physical parameter, made it possible to operate with suppressing amplitude. In addition, the mechanisms of controlling amplitude were clarified from the spatio-temporal variations of plasma properties and electromagnetic field in the acceleration channel for single-cycle of discharge current oscillation. The knowledge obtained here would be useful for proposing ideal operation and design of hall thruster as a promising high-performance propulsion device in space missions requiring for high-reliance.

The feasibility of using decadal changes in the geoelectric field to probe Earth’s core

Electric field observations by using 1000 km scale submarine cables have been performed since early 1990s. One of the main purposes of the observations is to obtain observational constraints on the dynamics of Earth’s core such as the strength and the distribution of the toroidal magnetic field and its variation at the core mantle boundary. Several constraints have been obtained until present, but the electromagnetic plausibility of them have not been examined. In this paper, electromagnetic field variations generated by a simple spherical mean-field kinematic dynamo within an electrically conducting mantle are discussed. The field variations are assumed to be generated by perturbing a steady α 2 dynamo with torsional oscillation type zonal flows having period of 30 years. It is confirmed that the kinematic dynamo can generate the observed amplitude of electric voltage variation (∼100 mV) naturally. The amplitude of voltage variation is controlled mainly by the energy state of the dynamo, i.e., the magnetic Reynolds numbers, and the strength of the toroidal field variation at the CMB is determined by the magnetic Reynolds numbers and the conductance of the D″ layer. Potential obstacles for the detection of the 100 mV signal in 1000 km scale submarine cable voltages are the electric voltages induced by external magnetic field variations (magnetotelluric induction) and that induced by the ocean flow (motional induction). Although the magnetotelluric current with decadal time scales seems negligibly small, the motionally induced electric field variation can be as much as 100 mV for 1000 km scale. It is necessary to know the time variation of ocean flux in order to discuss the electric voltages generated in the deep interior of Earth correctly.

Analysis of optical SHG in photonic crystal consisting of centro-symmetric dielectric

Optical second harmonic generation (OSHG) in a two-dimension photonic crystal consisting of centro-symmetric dielectric is investigated. The calculation model and analyzing method for OSHG are discussed. Based on Finite Difference-Time Domain algorithm, the electromagnetic field distribution in the structure and the intensity of second harmonic generation along the waveguide are analyzed. The results show that the acute spatial variation of electro-magnetic field results in the radiation of OSHG, and the intensity of OSHG is proportional to the square of the waveguide length. When the beam intensity of the pumping wave with a wavelength of 10.6 microm is 1.3MW/mm2, the power conversion efficiency is 0.268% for a silicon photonic crystal with a length of 40 microm.

Analysis of Propagation Conditions of ELF Radio Waves on the “Zeus”–Transbaikalia Path

We consider the results of measurements of the absolute values of horizontal electric and magnetic components of the electromagnetic field of the “Zeus” ELF radio facility at frequencies 33, 44, 82, and 188 Hz, carried out in Transbaikalia. Electromagnetic-field variations during 17 semidiurnal sessions (about 204 hours of synchronous records) are analyzed. The length of the “Zeus”–Transbaikalia path is approximately 4000 km.

유전체 디스크가 삽입된 원통형 공동 공진기에서의 공진 모드 구분에 관한 연구

We described a method of resonant mode identification in dielectric-disc loaded cylindrical cavity resonators. The characteristic equations are solved using the ContourPlot graph of Mathematica. Contour graph method uses graphical method. It is comparable with numerical method. The numerical method is very difficult mode identification. The analysis is based on the approximated electromagnetic representation which is only concentrated on the calculation of resonant frequencies, and a mode identification of resonant frequencies has not been covered. However, It is possible to calculate precise resonant frequencies and to identify the mode of resonant frequencies using the contour graph method. The contour graph method is not a method using approximated representation of electromagnetic field variation at the outer area of dielectric in the resonators. It is a method using enact representation.

Geoelectrical structure across the Bohemian Massif and the transition zone to the West Carpathians

Geoelectrical methods of magnetotelluric (MT) and geomagnetic deep soundings (GDS) were employed to infer the electrical conductivity structure at depths of specific regions of the Bohemian Massif (BM) and in the transition zone between the BM and the West Carpathians (WCP). Transfer functions between components of temporal variations of the natural electromagnetic field induced in the Earth by external sources were estimated and converted to electrical conductivity (resistivity) profiles. While the results from other regions of the BM are noted in references, the emphasis here is placed on the new analysis of MT/GDS data at field stations along the regional almost 500-km long Deep Seismic Sounding profile No. VI traversing the country from NW to SE. Inversion of its results suggests a complex geoelectrical structure, characteristic for each geological unit, with layers of increased electrical conductivity at crustal and uppermost mantle depths. The results also indicate strong fields of anomalous induction marking geoelectrical inhomogeneities at the eastern margin of the BM and in the foreland of the WCP.

Coseismic piezoelectric effects due to a dislocation: 1. An analytic far and early-time field solution in a homogeneous whole space

Piezoelectricity is a property that arises from the crystal anisotropy of substances. Piezoelectric substances generate electromagnetic (EM) field variations related to the temporal variations of the stress field. Since piezoelectric substances are abundant in the earth’s crust, the presence of a coseismic piezoelectric EM phenomenon in the real earth is a reasonable expectation. This paper examines the fundamental characteristics and detectability of coseismic EM signals relating to the piezoelectricity of crustal substances. Combining the fundamental equations of EM fields and the motion of an elastic medium, we derived analytical expressions of EM fields related to the variation of the stress field caused by slip of a point dislocation in a uniform whole space filled with an elastic, conductive, and piezoelectric substance. Numerical calculations, with physical parameters permissible for crustal rocks and a unit step function substituted as the source time function, show that the initial phase of EM signals, amounting to 1 nT and 10 2 mV/km, are observable at a 10 km distance from the slip about 0.01 s after slip occurs, when the seismic moment magnitude is around 7–8. This result suggests difficulty in detecting such piezoelectric EM signals related to earthquakes. However, it is shown that if the observations are succeeded due to a dense observation network installed around the epicenter, information on piezoelectric property relating to the direction of the symmetry axis in the deep seismogeneic zone can be obtained.

3D eddy current formulation for moving conductors with variable velocity of coordinate system using edge finite elements

A general formulation for moving conductors using 3D edge finite elements is introduced. In the formulation, the velocity of the coordinate system can be selected arbitrarily. A proper gauge condition for this formulation is also indicated. The optimal velocities of the coordinate system are investigated by numerical experiments. It is clarified that the accuracy of the analysis depends on the time variation of electromagnetic fields, which are observed differently in each coordinate system. From this point of view, we introduce a novel method that uses several different coordinate systems in one conductive region.

Manipulation of nonlinear optical response via nanoscale spatial structure of resonant internal field

By means of nonlocal theory, a peculiar signal enhancement is discussed for the nonlinear response due to resonant behavior of a particular spatial pattern of the internal field in an ultrathin film. Also, a theory of transient nonlinear pulse response of confined excitons is presented, and a numerical result is demonstrated for a particular model. The microscopic variation of the internal electromagnetic field is fully treated in this method, and a nanoscale spatial variation of the internal field in an ultrathin film is found even in the response to a very short pulse.

Faraday rotation in a cold, inhomogeneous magnetoplasma: A numerical comparison of ray and full wave analyses

A numerical full wave analysis is used to determine the spatial variation of electromagnetic fields of a radio wave in a stratified ionosphere. It is shown that the Faraday rotation may be accumulated as the analysis proceeds by breaking the electric field into constituent characteristic modes and accumulating phase. This has been achieved for vertical, oblique, reflective, and transionospheric propagation. Comparison of the full wave analysis with simpler methods of calculating the rotation, such as ray tracing and very high frequency approximations, permits the determination of the conditions under which these simpler methods break down. It is found that ray tracing agrees very closely with the full wave analysis in most situations and always so for transionospheric propagation. Some discrepancy between these methods appears when reflecting from severe vertical gradients where the full wave analysis is known to be required in accurately estimating the transmission coefficients. For reflective propagation at oblique incidence, small departures in the methods are also evident. Both methods converge to the high‐frequency approximation as the radio frequency increases above the peak plasma frequency.

Highly efficient induction heating units for metallurgy and machine construction

Induction heating units are being used increasingly widely in metallurgy and machine construction in all industrially developed nations: in metalhurgy—to refine ferrous, nonferrous, and noble metals, including in vacuums; in machine construction—for quenching, soldering, annealing, stamping, hard-facing, and other operations. The reason is the possibility of moving products at high speeds in such furnaces within a precisely prescribed heating zone thanks to the formation of eddy currents induced in the material to a certain depth by the variable electromagnetic field of the induction coil.

The latest aspects of telluric and electromagnetic variations associated with shallow and intermediate depth earthquakes in the South Aegean

Recent observations of telluric and electromagnetic field variations (radioemissions) assocuated with shallow and intermediate depth earthquakes in the South Aegean are presented. A telemetric system, installed on Crete Island, which continuously records the telluric and electromagnetic field variations is described. In the field stations of the system we measure both the telluric variations (using an appropriate electric dipole configuration) and the horizontal electric component of the electromagnetic field in 3 kHz, 10 hKz, 41 MHz and 53 MHz (using tuned and l/2 antennas respectively. Furthermore, a theoretical model is given on the generation and the form of preseismic telluric variations based on the charge dislocation model.

REVIEW OF ELECTRIC AND MAGNETIC FIELDS ACCOMPANYING SEISMIC AND VOLCANIC ACTIVITY

New observations of magnetic, electric and electromagnetic field variations, possibly related to recent volcanic and seismic events, have been obtained on Mt. Unzen in Japan, Reunion Island in Indian Ocean, the Long Valley volcanic caldera in California, and for faults in China and Russia, California and several other locations. For volcanic events, contributions from different physical processes can be identified during the various eruption stages. Slow processes (weeks to months) include near-surface thermal demagnetization effects, piezomagnetic effects, and effects from rotation/displacement of magnetized material. Rapid processes (seconds to days) include piezomagnetic effects from instantaneous stress redistribution with explosive eruptions and electrokinetic effects from rupture of high pressure fluid compartments commonly encountered in volcanic regions. For seismic events, the observed coseismic offsets are instantaneous, provided care has been taken to ensure sensors are insensitive to seismic shaking and are in regions of low magnetic field gradient. Simple piezomagnetic dislocation models based on geodetically and seismically determined fault parameters generally match the observed signals in size and sign. Electrokinetic effects resulting from rupture of fluid filled compartments at hydrostatic to lithostatic pore pressures can generate transient signals in the frequency band 100 Hz to 0.01 Hz. However, large-scale fluid driven processes are not evident in near-field measurements in the epicentral region minutes to weeks before large earthquakes. The subset of ionospheric disturbances generated by trapped atmospheric pressure waves (also termed gravity waves and/or acoustic waves, traveling ionospheric disturbances or TID's) that are excited by earthquakes and volcanic eruptions are common and propagate to great distances. These are known and expected consequences of earthquakes, volcanic explosions (and other atmospheric disturbances), that must be identified and their effects removed from VLF/ULF electromagnetic field records before associating new observations of ionospheric disturbances with earthquake activity.

Theory of resonant SNOM (scanning near-field optical microscopy): breakdown of the electric dipole selection rule in the reflection mode

A theoretical study is reported about SNOM with the use of light in resonance with the quantized levels of a mesoscopic sample. The microscopic variation of electromagnetic field and the coherence of matter state are properly treated by solving the microscopic Maxwell equations and Schrödinger equation self consistently. A remarkable effect, i.e., the breakdown of the dipole selection rule, is shown in the reflection mode where a probe tip is used for both illumination of the sample and collection of the signal. Namely, both dipole-active and higher-multipole-active levels give comparable signal intensities for appropriate probe tip positions.

Collisional drift fluid equations and implications for drift waves

The usual theoretical description of drift-wave turbulence (considered to be one possible cause of anomalous transport in a plasma), e.g. the Hasegawa - Wakatani theory, makes use of various approximations, the effects of which are extremely difficult to assess. This concerns in particular the conservation laws for energy and momentum. The latter law is important in relation to charge separation and the resulting electric fields, which are possibly related to the L - H transition. Energy conservation is crucial to the stability behaviour; it will be discussed by means of an example. New collisional multi-species drift-fluid equations were derived by a new method which yields, in a transparent way, conservation of energy and total angular momentum and the law for energy dissipation. Both electrostatic and electromagnetic field variations are considered. The only restriction involved is the validity of the drift approximation; in particular, there are no assumptions restricting the geometry of the system. The method is based primarily on a Lagrangian for dissipationless fluids in the drift approximation with isotropic pressures. The dissipative terms are introduced by adding corresponding terms to the ideal equations of motion and of the pressures. The equations of motion, of course, no longer result from a Lagrangian via Hamilton's principle. However, their relation to the ideal equations also implies a relation to the ideal Lagrangian, which can be used to advantage. Instead of introducing heat conduction one can also assume isothermal behaviour, e.g. = constant. Assumptions of this kind are often made in the literature. The new method of introducing dissipation is not restricted to the present kind of theory; it can equally well be applied to theories such as multi-fluid theories without using the drift approximation of the present paper. Linear instability is investigated by means of energy considerations and the implications of taking ohmic resistivity into account are discussed. A feature of the results is that for purely electrostatic perturbations the second spatial derivative of the density profile plays a role, in contrast to the usual approximations. For a class of systems with , it is shown that linear instability can only occur when the resistivity is sufficiently large, while the Hasegawa - Wakatani theory predicts instability for arbitrarily small non-vanishing resistivity. It is shown that, for essentially electrostatic instabilities, magnetic perturbations in resistive systems may not be negligible even for . An example which will be treated in a future paper indicates in addition that, in systems with vanishing ion temperature, electron temperature profiles should strongly influence the stability via resistive effects. This is in addition to effects leading to -modes. It also demonstrates that, in general, it is not possible to perform an expansion with respect to the resistivity near . The new formalism is interesting not only from a theoretical point of view, but also, in particular, as a useful tool for numerical calculations.

Generation of massive neutrinos by variable fields with allowance for mixing and radiative effects

The probabilities of the processesF → v i V j γ andFB → v i V j of generation of massive neutrinos by a variable electromagnetic field, due to the contribution of four-particle peaks in the one-loop approximation with allowance for mixing, are obtained. A comparative analysis is made of the quantities considered here and of generation mechanisms discussed earlier (F → v i V j ) in the case of vacuum neutrino synchrotron emission.

Plasma Generation and Beam Extraction on Reentrant-Cavity-Type Electron Cyclotron Resonance Ion Source

An electron cyclotron resonance (ECR) ion source 8 cm in diameter using a reentrant coaxial cavity and a ring cusp magnetic field was developed to improve plasma uniformity and operational reliability. The reentrant coaxial cavity is utilized to achieve electrical breakdown easily, to tune in variable electromagnetic fields and to introduce microwaves into plasma from an annular window of a discharge chamber sidewall. Microwaves are resonantly absorbed by the ECR magnetic field. Above 10 sccm flow rate for Ar, uniform and overdense plasmas were obtained in an area 4 cm in diameter from the center axis. The maximum plasma density of 1.26×1011 cm-3 was achieved on the center axis at 20 sccm. However, plasma densities for N2 and O2 were lower than the cutoff density. The maximum ion beam current density of 1.26 mA/cm2 was obtained at a forward power of 304 W for Ar.

Electromagnetic fields near metal surfaces

Electromagnetic field variation at the surface region of nearly free electron metal (Al), noble metal (Ag) and transition metals (Cr, Rh, Pd and Mo) are studied with respect to the incident photon energy. The electromagnetic field used is the one calculated by Bagchi and Kar using the local frequency dependent dielectric response function. The results so obtained may be of significance in the photoemission scattering cross-section calculations in understanding electronic structure and properties of these metals.

HADRON FORM FACTORS IN QCD

We consider the QCD sum rules approach for hadron form factors in infrared region 0≤Q2<1 GeV2. The QCD sum rules in external variable field are formulated. As an example this method is used to calculate proton and nucleon magnetic form factors. The detailed calculation of the nucleon polarization operator in external variable electromagnetic field is done. The obtained form factors (proton and neutron) are in a good agreement with experimental ones.

Electromagnetic field variations in the activation of bone cell synthesis: Gary Ketcherside Loma Linda, California: Loma Linda University, 1988

Electromagnetic field variations in the activation of bone cell synthesis: Gary Ketcherside Loma Linda, California: Loma Linda University, 1988