Slow Electromagnetic Waves Research Articles

Generation and propagation of the ULF planetary-scale electromagnetic wavy structures in the ionosphere

In the present article, the results of theoretical investigation of the dynamics of generation and propagation of planetary (with wavelength 10 3 km and more) ultra-low frequency (ULF) electromagnetic wave structures in the dissipative ionosphere are given. The physical mechanism of generation of the planetary electromagnetic waves is proposed. It is established, that the global factor, acting permanently in the ionosphere—inhomogeneity (latitude variation) of the geomagnetic field and angular velocity of the earth's rotation—generates the fast and slow planetary ULF electromagnetic waves. The waves propagate along the parallels to the east as well as to the west. In E-region the fast waves have phase velocities (2–20) km s −1and frequencies (10 −1–10 −4) s −1; the slow waves propagate with local winds velocities and have frequencies (10 −4–10 −6) s −1. In F-region the fast ULF electromagnetic waves propagate with phase velocities tens–hundreds km s −1 and their frequencies are in the range of (10–10 −3) s −1. The slow mode is produced by the dynamoelectric field, it represents a generalization of the ordinary Rossby-type waves in the rotating ionosphere and is caused by the Hall effect in the E-layer. The fast disturbances are the new modes, which are associated with oscillations of the ionospheric electrons frozen in the geomagnetic field and are connected with the large-scale internal vortical electric field generation in the ionosphere. The large-scale waves are weakly damped. The features and the parameters of the theoretically investigated electromagnetic wave structures agree with those of large-scale ULF midlatitude long-period oscillations (MLO) and magnetoionospheric wave perturbations (MIWP), observed experimentally in the ionosphere. It is established, that because of relevance of Coriolis and electromagnetic forces, generation of slow planetary electromagnetic waves at the fixed latitude in the ionosphere can give rise to the reverse of local wind structures and to the direction change of general ionospheric circulation. It is considered one more class of the waves, called as the slow magnetohydrodinamic (MHD) waves, on which inhomogeneity of the Coriolis and Ampere forces do not influence. These waves appear as an admixture of the slow Alfven- and whistler-type perturbations. The waves generate the geomagnetic field from several tens to several hundreds nT and more. Nonlinear interaction of the considered waves with the local ionospheric zonal shear winds is studied. It is established, that planetary ULF electromagnetic waves, at their interaction with the local shear winds, can self-localize in the form of nonlinear solitary vortices, moving along the latitude circles westward as well as eastward with velocity, different from phase velocity of corresponding linear waves. The vortices are weakly damped and long lived. They cause the geomagnetic pulsations stronger than the linear waves by one order. The vortex structures transfer the trapped particles of medium and also energy and heat. That is why such nonlinear vortex structures can be the structural elements of strong macroturbulence of the ionosphere.

Theoretical Study of Surface Extraordinarily Polarized Waves on the Second Harmonic of the Ion Cyclotron Frequency in Nonuniform Plasma and their Application for Material Processing

Properties of slow electromagnetic surface waves propagating across an external magnetic field on the second harmonic of ion cyclotron frequency are studied here in the case of plasma with nonuniform density profile and weak spatial dispersion. These waves are eigen modes of the restricted wave guide structure consisting of semi bounded plasma region, dielectric layer (its thickness can be also equal to zero) and metal wall with conductivity that is much larger than that of the plasma. The structure is immersed into an external steady magnetic field oriented parallel to the plasma interface. Theoretical research into effect of transverse nonuniformity of plasma density on dispersion properties of these surface modes is carried out using a kinetic approach and a set of Maxwell equations for their field. To illustrate the ability of these modes to sustain a gas discharge, the flow of their wave power and the quantity of their power absorbed through collisional and collisionless mechanisms of the power transfer into the discharge are calculated. Comparison of the obtained results with the cases of surface cyclotron waves with other polarization is carried out as well.

Band structures of coupled electromagnetic slow waves

In this paper, a modified transfer matrix method is applied for the analysis of electromagnetic slow wave propagation in Kronig–Penny photonic crystals. Analytic expressions for Bloch wavenumbers in terms of normalized frequency are derived and the asymptotic behaviour of electromagnetic slow wave propagation in these structures is investigated at different regimes. The tight binding method is also used for the analysis of electromagnetic slow wave propagation in Kronig–Penny photonic crystals and analytic expressions are given. It has been shown that forbidden wavenumbers rather than forbidden frequencies can be observed under specific circumstances.

Negative refractive index for a surface magnetostatic wave propagating through the boundarybetween a ferrite and ferrite-insulator-metal media

Refraction of a slow surface electromagnetic wave (magnetostatic wave) at the boundary between ferrite and ferrite-insulator-metal media is investigated experimentally and theoretically. The boundary is created in an yttrium iron garnet film by placing a metal plate at a certain distance fromits surface. The refractive index is found to depend on the angle of incidence of the wave and can take on any positive or negative values. It is shown that in anisotropic media, in particular, inferromagnets, due to the noncollinearity of the wave vector and the group velocity vector, negative refraction can occur not only in the earlier predicted case where the incident wave is forward and the refracted wave is backward, but also in the case where both waves are forward.

Novel optical slow wave structure and surface electromagnetic wave coupler with conducting interfaces

Recently, a group of novel devices based on conducting interfaces has been proposed. These conducting interfaces can be implemented, for example, by using the inversion layer of MOS structures, trapped charges, or depletion layer charges. It has been shown that these structures can support surface electromagnetic waves. In this paper, the coupling of surface electromagnetic waves supported by conducting interfaces is first analysed. Next, by direct solution of Maxwell's equations and applying appropriate boundary conditions; exact analytical formulation of the dispersion equation has also been derived. Results driven by a coupled mode theory approach are justified by solving the exact transcendental dispersion equation derived from the second approach. A new type of optical modulator is proposed by demonstrating that the coupling length of this structure can be programmed by applying a transverse voltage. The possibility of optical slow wave propagation in dielectric slab waveguides in the presence of conducting interfaces is also explored.

Investigation of ion cyclotron range of frequencies mode conversion at the ion–ion hybrid layer in Alcator C-Mod

Mode conversion (MC) of long wavelength fast electromagnetic magnetosonic waves (fast wave, or FW) into shorter wavelength electrostatic (ion-Bernstein, or IBW) or slow electromagnetic (ion cyclotron, or ICW) waves is of great interest in laboratory, magnetic fusion and space physics experiments. Such processes are particularly important in multi-ion species plasmas. In this paper we report recent results from high power ion cyclotron range of frequencies (ICRF) heating experiments in the Alcator C-Mod tokamak. Mode converted waves near the He–H3 hybrid layer have been detected by means of phase contrast imaging in H(3He,D) plasmas [E. Nelson-Melby et al., Phys. Rev. Lett. 90, 155004 (2003)]. The measured wave k spectrum and spatial location are in agreement with theoretical predictions [F. W. Perkins, Nucl. Fusion 17, 1197 (1977)], which showed that in a sheared magnetic field, mode-conversion of FW into ICW may dominate over IBW for appropriate ion species (i.e., D–T, or equivalently, H–3He). Recent modeling with full wave codes, as well as solving the hot plasma dispersion equation in the presence of sheared magnetic fields, verifies the interpretation of such a mode conversion process. Thus, the geometry of the magnetic field, as well as the particular ion species mix, influences the physics of ICRF mode conversion. In this paper, we also report recent results on the study of mode conversion electron heating (MCEH) in D(H) plasmas [Y. Lin et al., Plasmas Phys. Controlled Fusion 45, 1013 (2003)]. By comparing the experimentally measured MCEH profile with modeling, the study shows that the MC ICW may make a significant contribution to the direct electron heating when the D–H hybrid layer is off axis on the high field side. Preliminary results of mode conversion poloidal plasma flow drive experiments in D(3He) are also reported.

Linear Theory of Plasma-Filled Coaxial Cylindrical Cherenkov Maser

Injection of background plasma into the beam-wave interaction region can greatly enhance the beam-wave interaction efficiency and the microwave output power of the device. In this paper, a new type of plasma-filled slow-wave structure, i.e., plasma-filled, dielectric-loaded coaxial cylindrical waveguide with a dielectric ring enclosing tightly the inner conductor, is developed. The Cherenkov radiation excited by the beam-wave interaction in the slow-wave structure is examined by use of the self-consistent linear field theory. The dispersion equation and the synchronized condition of the beam-wave interaction are derived. It's clearly shown that the Cherenkov radiation excited by the beam-wave interaction results from the coupling between the slow electromagnetic wave, TM-modes, propagated along the slow-wave structure and the negative-energy space-charge wave propagated along the relativistic electron beam. And the wave growth rate is solved, and the beam-wave energy exchange in the presence of the background plasma is discussed. Finally, the effects of the background plasma density on the dispersion characteristics, the distribution of the longitudinal fluctuating electric field, the wave growth rate and the beam-wave energy exchange are calculated and discussed.

Self-organization of planetary electromagnetic waves in the E-region of the ionosphere

A physical mechanism for the generation of slow and fast electromagnetic-type planetary waves due to standing factor—latitude variation of geomagnetic field—in the dissipative E-region of the ionosphere is suggested. It has been shown that slow waves are generated due to the dynamo-field in the ionosphere, and fast waves by the vortical electric field. The slow electromagnetic wave is analog to the Rossby planetary wave; the fast electromagnetic wave is a new mode of natural oscillations of the E-region of the ionosphere. Linear waves propagate along the parallel west and east directions in the dynamo-region of the ionosphere against a background of the mean zonal flow. Phase velocity of the fast waves is a few km s −1 , oscillation frequencies are in the frequency band of 10 −2– 10 −4 s −1 and the wavelength is of the order of 10 3 km and higher. Phase velocities of the slow waves and local winds are at the same order of magnitude, the frequency band is 10 −4– 10 −5 s −1 and wavelength is of 10 3 km and higher order. Fast waves generate intense magnetic fields in order of a few hundred nanotesla (nT); slow waves—a few tens of nT. In this paper the nonlinear theory of both fast and slow planetary electromagnetic waves in the E-region of the ionosphere is investigated for the first time. It was established that these perturbations are self-localized as nonlinear solitary vortical structures in the dynamo-region of the ionosphere move to the west (fast) and to the east (slow) against a background of the mean zonal flow. The nonlinear structure consists of cyclone–anticyclone-type mutual counter-clockwise-rotating vortices, which capture medium particles. Energy and enstrophy of these large-scale vortices are weakly attenuated and are long-lived. Vortical structures generate magnetic fields, which are an order of magnitude larger than those generated by the corresponding linear waves. Features and parameters of electromagnetic wavy structures are theoretically investigated and are in good agreement with the experimental data of large-scale ULF wavy perturbations observable in the ionosphere.

A simplistic plasma dust removal model employing radiation pressure

A simple heuristic model is developed to examine the feasibility of using radiation pressure as a means to transport plasma dust out of the path of the forthcoming electron or photon beam. A slow electromagnetic surface wave coupled to a planar target or substrate exerts the required pressure in the removal process. The model is examined using data and parameters from single-shot radiography experiments. Optimal source requirements are identified for a typical radiography experiment. Source energies and powers are a minimum over an optimum band of frequencies where both conduction and plasma oscillation effects are mutually significant. Above the band of frequencies, dissipative losses in the surface supporting the surface wave increases exponentially with frequency. Below the optimal band, the energy concentration over the plume at the surface structure decreases significantly with frequency, thereby requiring higher source energies/powers for plasma removal.

On the Interaction between an Electron Beam and a Slow Electromagnetic Wave in an O -Type Oscillator

On the Interaction between an Electron Beam and a Slow Electromagnetic Wave in an O -Type Oscillator

The electromagnetic field in the plasma jet of a microwave plasmatron

A coaxial microwave plasmatron operating at a frequency of 10 GHz is investigated. The microwave field distribution in the plasma jet of the plasmatron is studied using a vibrating string as a small perturbation source. The phase structure of the microwave field inside the plasma is found to differ from that on the outer side of the plasma jet boundary. A slow surface electromagnetic wave propagating along the plasma jet is observed.

Slow electromagneticw waves in tangentially magnetized ferromagnetic films

Dispersion and energy characteristics of slow volume electromagnetic waves in tangentially magnetized ferromagnetic films are computed in a rigorous manner. For a wave that experiences anomalous dispersion and propagates with the external magnetostatic field, distinguishing features of the energy-flux velocity and the ratio of the electric to the magnetic energy density as functions of the wave number are noted. A marked contrast between these results and those obtained within the magnetostatic approximation is revealed for a wide range of wave numbers.

Ion surface cyclotron waves at plasma-metal interfaces

The dispersion properties of slow electromagnetic surface waves propagating across a constant external magnetic field and along a plane plasma-metal interface at harmonics of the ion cyclotron frequency are studied. The motion of the plasma particles is described by a Vlasov-Boltzmann kinetic equation. The effects of the plasma size, the dielectric permittivity of the transition region between the plasma and metal, and the magnitude of the constant external magnetic field on the dispersion characteristics of ion surface cyclotron waves are studied.

Circuit theory of video delay lines

Electromagnetic slow waves guided by single-layer coils and video delay lines are studied from the point of view of circuit theory. The main idea is to introduce into the model the mutual inductance that exists between nearby coil turns. This concept leads to finite-difference, finite-sum equations which pass in the limit into a partial differential equation and an integro-differential equation. The capacitance between adjacent wire turns is taken into account. The decrease of inductance at high frequencies, as computed from the integro-differential equations, is compared with prior computations based on electromagnetic field theory. In this respect agreement between the two theories is complete. A comparison with experiment is made, from which a novel parameter of the coil, termed the series capacitance parameter and measured in Fm, is determined.

Excitation of Slow Electromagnetic Waves in a Dielectric-Lined Waveguide Having a Thin Annular Plasma Sheet

Excitation of slow electromagnetic waves for a configuration, in which a thin annular relativistic electron beam (TAREB) propagates through a cylindrical, dielectric-lined waveguide having a thin, annular plasma sheet at the same radial position as the TAREB, is studied in the presence of an infinite longitudinal guide magnetic field. Determinant dispersion equation is derived and directly numerically solved. The operation frequency and the growth rate of the waves are obtained and discussed.

Propagation and Parametric Excitation of Surface CyclotronWaves

Properties of slow electromagnetic surface waves propagating acrossan external magnetic field in planar plasma waveguides on theharmonics of ion and electron cyclotron frequencies are studied in thepaper. The considered waveguide structures consist of metal plateswith dielectric coating and plasma filling. The external steadymagnetic field is supposed to be oriented perpendicularly to theplasma interface. The analytical research is carried out using akinetic description for plasma particles, the mirror reflection modelfor the interaction between particles and plasma boundary. Parametricexcitation of surface cyclotron waves (SCW) are investigated as well.Effects of the waveguide parameters on the SCW dispersion andparametric instability increments are studied both analytically andnumerically.

Radiation of slow electromagnetic waves in an isotropic medium with spatial dispersion

This paper discusses the distinctive features of radiation of electromagnetic waves with anomalously large values of the wave vector and small phase velocity that exist near narrow absorption lines. The distribution of radiated energy with respect to angle and frequency is calculated for Cerenkov radiation and bremsstrahlung of the slow waves. It is shown that the angular distribution of the slow-wave bremsstrahlung exhibits a characteristic maximum in the direction perpendicular to the plane of motion of the particles.

Slow electromagnetic waves in asymmetric SISIS′ junctions

Splitting of the Swihart velocity in the asymmetric SISIS′ devices (where S is a superconductor and I is an insulator) has been investigated. Analysis based on the existing models of the dynamic state of the stacked junctions shows that if one of the external electrodes, S′, has a considerably lower critical temperature T′ c than the other two electrodes, and the temperature of the system approaches T′ c but T< T′ c, then the velocities c + and c − approach their limit values: c + → c 0, and c − → 0 (here c 0 is the Swihart velocity in the single SIS junction). Experimentally, both asymmetric Nb/AlAlO x Nb/AlAlO x Ta/Nb and symmetric Nb/AlAlO x Nb/AlAlO x Nb two-terminal devices have been investigated. The values c − = (1.47 ± 0.04) × 10 6 m/s and c − = (1.7 ± 0.1) × 10 6 m/s have been obtained for the devices of the first and second type, respectively. Although, as expected, the value of c − is lower in the first case, the difference between the c − values for the two types of devices is rather small. This is in agreement with the theory, because in the first case the influence of the thickness of the middle electrode on the value of c − predominates the same effect arising from the reduced superconductivity of the Ta/Nb electrode.

Effect of the zero spatial harmonic in a slow electromagnetic wave on operation of relativistic backward-wave oscillators

A linear theory of resonant backward-wave oscillators (BWOs) that takes into account the zero spatial harmonic is developed. It is shown that, depending on the phase shift, this harmonic can either increase or decrease the starting current of the device. The nonlinear theory shows the same effect of the phase shift on the maximum efficiency of the BWO. The numerical analysis of nonstationary processes has also demonstrated the effect of the phase shift on the range of beam current values in which the BWO operates in a steady-state single-frequency regime. The effect of boundary conditions at the cathode end of the slow-wave structure on the phase shift between harmonics is also analyzed.

Surface waves on the harmonics of the electron cyclotron frequency propagating along a plasma - metal interface

Dispersion properties of slow electromagnetic surface waves propagating on the harmonics of the electron cyclotron frequency across the external steady magnetic field are studied in the case when the magnetic field is parallel to the plasma - metal interface. Theoretical investigation of these surface modes is carried out using the kinetic description under the condition of weak plasma spatial dispersion, when the radii of the charged plasma particles' Larmor rotation are much less than the spatial scale of the considered wave perturbation. The effect of the plasma density transverse inhomogeneity, of plasma particles' concentration and of the external magnetic field value on the dispersion properties of the surface waves on electron cyclotron harmonics (SWCH) is researched.