External Steady Magnetic Field Research Articles

Stability of surface waves at magnetized plasma – metal interface

AbstractThe stability of high‐frequency potential surface waves at a dense magnetized plasma – metal interface with respect to a low‐frequency plasma density modulation is studied in the point of view of the surface waves control. The discussion is addressed to the situation, when an external steady magnetic field is directed perpendicularly to the interface. The nonlinear interaction process of the high‐frequency surface wave, its satellites and the low‐frequency plasma density perturbation is investigated. It is shown that the low‐frequency plasma density perturbation can be represented as a superposition of forced waves of surface and volume types and can lead to an additional attenuation of the surface waves. This attenuation arises when the surface wave amplitude exceeds the threshold value. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of steady magnetic field on laser-induced breakdown spectroscopy.

Effects of a steady magnetic field on the laser-induced breakdown spectroscopy of certain elements (Mn, Mg, Cr, and Ti) in aqueous solution were studied, in which the plasma plume expanded across an external steady magnetic field (approximately 6 kilogauss). Nearly 1.6 times enhancement in the line emission intensity was observed in the presence of the magnetic field. The temporal evolution of the line emission showed a significant enhancement in plasma emission between 2- and 7- micro(s) gate delays for Mg in the presence of the magnetic field (5-30 micro(s) for Mn). This enhancement in the emission is attributed to an increase in the rate of recombination because of an increase in plasma density due to a magnetic confinement after cooling the plasma. The increase in the optical line emission due to magnetic confinement was absent when the plasma was hot with a dominant background (continuum) emission. The limits of detection of Mg and Mn were reduced by a factor of two in the presence of a steady magnetic field of 5 kilogauss.

Excitation of surface cyclotron O modes by charged-particle beams

A theoretical investigation of the interaction between a charged-particle beam and ordinarily polarized surface waves at the first two harmonics of ion and electron cyclotron frequencies propagating across an external steady magnetic field is carried out. The case of weak plasma spatial dispersion when the Larmor radii of plasma particles are much less than the penetration depth of these waves into the plasma is considered. The indicated waves are eigenmodes of the planar plasma–vacuum–metal waveguide structure, which is exposed to a steady magnetic field oriented parallel to the plasma surface. It is supposed that a cold charged- particle beam propagates over the plasma surface in the vacuum region. The beam density is less than the plasma density. Excitation of these O modes at the first and second harmonics of electron and ion cyclotron frequencies caused by the both resonant beam and dissipative instabilities is studied analytically. The dependence of their growth rates on parameters of the considered waveguide structures is also examined.

Application of Electron Cyclotron Surface Modes to Solids Processing

A theoretical model of stationary microwave gas discharge sustained by ordinarily polarized surface cyclotron modes in a planar metal chamber with a dielectric coating is presented. Cyclotron surface O-modes are eigenmodes of this discharge structure. They possess eigenfrequencies at harmonics of the electron cyclotron frequency and propagate across an external steady magnetic field that is oriented parallel to the discharge chamber wall. The problem is studied using a kinetic description for plasma particles, Maxwells equations for electromagnetic fields of the indicated modes and a wave power balance equation for a description of the energy transfer process. The effect of external magnetic field and the geometry of the discharge chamber on the discharge properties is examined. A comparative analysis of gas discharge parameters for the cases of surface cyclotron modes with different polarizations is carried out as well.

Microwave Gas Discharge Sustained by the Azimuthal Surface Waves

A theoretical model of plasma source based on azimuthal surface waves (ASW) propagation in a plasma filled cylindrical metal waveguide is presented. The ASW propagate across an external axial steady magnetic field and posses the eigenfrequencies in the range between upper hybrid frequency and the cut-off frequency for HF bulk wave. The problem is studied using a local hydrodynamic approach and taking into consideration a collisional wave damping. Spatial distributions of the ASW fields and produced plasma density are examined both analytically and numerically.

Propagation of the surface cyclotron O-modes at harmonics of ion andelectron cyclotron frequencies

Theoretical studies of ordinarily polarized surface waves at the first andsecond harmonics of the ion and electron cyclotron frequencies propagatingacross an external steady magnetic field are carried out in the case of a weakplasma spatial dispersion along the normal direction towards the plasmainterface when the penetration depths of these waves are much greater than theLarmor radii of plasma particles. These waves are eigenmodes of the planarplasma-dielectric layer-metal waveguide structure which is placed into asteady magnetic field oriented parallel to the plasma surface. Theireigenfrequencies can be either greater than or less than the correspondingharmonics of the ion or electron cyclotron frequencies under differentconditions in the waveguide considered. The dependence of their damping ratescaused both by collisions between plasma particles and the resonantplasma-wave interaction on the waveguide structure parameters is alsostudied. A comparison of the collisional damping with the collisionlessdamping is carried out for these modes. To illustrate the possibility ofplasma periphery heating by these modes, the flow of their wave power andthe quantity of the absorbed wave power are calculated.

Oscillating magnetic field current drive in a spherical plasmadevice

The continuous steady-state current drive in a spherical argon plasma bytransverse oscillating magnetic field (OMF) is investigated. The experimentalresults reveal that a rotating magnetic field is generated, and its amplitudedepends linearly on the external steady vertical magnetic field. It has beenshown that steady toroidal currents of up to about 400 A can be driven by a490 kHz OMF with an input power of 1.4 kW. The generation of steady toroidalmagnetic fields directed oppositely in the upper and lower hemispheres havebeen recorded. The measurements of time-varying magnetic fields unveil astrong nonlinear effect of the frequency-doubled field harmonics generation.The electron number density and temperature of up to 6.2×1018 m-3 and 12 eV have been obtained. The observed effects validate theexisting theory of the OMF current drive in spherical plasmas.

Electron Heating During Microwave Gas Discharge Sustained by Surface Cyclotron Waves

Theoretical analysis of electron heating in microwave gas discharge sustained by surface cyclotron waves (SCW) is presented. A discharge chamber with planar geometry immersed into a steady magnetic field that is oriented perpendicularly to the plasma interface is considered. The plasma is assumed to be bounded by a planar dielectric sheath. The SCW are the eigenmodes of this structure. Their eigenfrequencies belong to the ranges between the harmonics of the electron cyclotron frequency. SCW propagate across the external steady magnetic field. Plasma particle motion is examined using a kinetic approach. A model of particle mirror reflection from the interface of the plasma is utilized. Spatial distribution of the SCW electromagnetic fields, SCW power flow and their energy absorption by plasma particles under both collisional and collisionless regimes are studied analytically. The presented results can be interesting for plasma technologies on processing of solids.

Parametrical Instability of Surface Type X‐modes Immersed into a Nonmonochromatic Pumping Electric Field

AbstractParametrical excitation of surface type X‐modes (STXM) at the second harmonic of electron cyclotron frequency by nonmonochromatic external alternating electric field is under consideration. STXM are the eigenmodes of a planar magnetoactive plasma waveguide structure consisting of a metal wall with dielectric coating and uniform plasma filling. An external steady magnetic field is applied along the plasma interface, so it is perpendicular to the group velocity of the considered extraordinarily polarized waves. Influence of the plasma waveguide parameters on the parametrical instability of the STXM is studied. External alternating electric field is assumed to consist of two fields with different amplitudes and frequencies. A theoretical investigation is carried out using kinetic equation for plasma particles under the conditions of weak plasma spatial dispersion and small amplitudes of external electric fields. The obtained results can be useful for research in branch of edge plasma physics.

Theoretical Model of a Stationary Low-pressure Plasma Sourcebased on Surface Type X-mode

A theoretical model of a stationary low-pressure gas dischargesustained by the surface type X-mode (STXM) in a planar metalwaveguide with a dielectric coating is presented. The STXM areeigenmodes of this discharge structure, they possess eigenfrequenciesin the range between the second and the third electron cyclotronharmonic, propagate across an external steady magnetic field orientedparallel to the plasma–dielectric interface. The problem isstudied using a kinetic description for plasma particles motion andmodel of their diffuse reflection from the dielectric interface. Thespatial distributions of the sustained plasma and the STXMelectromagnetic fields, as well as the effect of external magneticfield and electrodynamic characteristics of the discharge chamber onthe discharge parameters are studied analytically.

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.

Unusual magnetic properties of UGa 3 single crystals

The magnetic behaviour of single-crystalline UGa 3 has been studied by means of DC- and AC-magnetic susceptibility and thermal conductivity measurements. As many as three pronounced singularities have been found in both, the χ(T) and κ(T) variations. The features at T N = 65K are associated with an antiferromagnetic phase transition while those at T 1 = 40K and T 2 = 8K have an unknown origin. At low temperatures a significant diamagnetic response is observed in χ′(T) accompanied by a rapid rise in χ″(T). This behaviour of the AC-susceptibility is strongly dependent on the frequency of the alternating magnetic field and on the strength of the external steady magnetic field.

Surface cyclotron waves in a nonuniform plasma filled metal waveguide with dielectrical coating

The problem concerning the dispersion properties of the slow extraordinary polarized electromagnetic surface waves on the harmonics of ion and electron cyclotron frequencies (SWCH) in magnetoactive plasma is studied. An external steady magnetic field is applied parallel to the plasma interfaces, rectangular with respect to the group velocity of the considered waves. The influences of the transverse plasma density nonuniformity, the plasma particle concentration, the external magnetic field value and the dielectric coating of the waveguide metal walls on the dispersion properties are considered. A theoretical investigation is carried out under the condition of weak plasma spatial dispersion using a kinetic plasma model. The obtained results can be used in branches of plasma electronics and plasma edge physics.

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.

Parametric Instability of Surface Waves on the Second Harmonic of Electron Cyclotron Frequency in a Plasma Layer

AbstractThe parametric instability of surface waves on the second harmonic of electron cyclotron frequency (SWCF) in a plasma filled dielectric wave guide is examined in a kinetic approximation. The studied surface waves are extraordinary polarized modes and propagate across the external steady magnetic field. The amplitude of the electrical pump wave is assumed to be small. Simple expressions for increments of the parametric instability of the SWCF are calculated. The otained results can be used in controlled fusion researches in order to avoid undesirable regimes of plasma periphery heating in that fusion devices which use the resonance electron cyclotron heating method.

Electron Surface Cyclotron Waves in the Metallic Waveguide Structures with Two‐Component Filling

AbstractThe dispersion properties of the slow electromagnetic surface waves propagating across external magnetic field in planar metallic waveguides with plasma and dielectric filling on the harmonics of the electron cyclotron frequency are studied in this paper. The external steady magnetic field is supposed to be directed perpendicularly to the waveguide wall. Dielectric layer separates semibounded plasma from the metallic wall. The analytical research is carried out using the kinetic description for plasma particles, the mirror reflection model for the interaction between particles and plasma boundary. Skin depth of the surface cyclotron waves (SCW) is much greater than electron Larmor radius. Effect of the following parameters of the waveguide structures: dielectric constant and thickness of the dielectric layer, plasma density value and number of the cyclotron harmonics, on the SCW dispersion is examined both analytically and numerically.

Magnetized Fiber Orientation Control in Solidifying Composites: Numerical Simulation

This work deals with the development of a numerical algorithm for the prediction of magnetic force lines inside a flowing solidifying melt with the ultimate purpose of simulating and controlling alignment of short nickel-coated fibers during the curing process in composites. A complete mathematical model and an accompanying computer program have been developed for the simulation of a steady laminar flow of an incompressible fluid with strong heat transfer (involving solidification) and a strong superimposed magnetic field. An extended form of the Boussinesq approximation allowing for temperature-dependent physical properties of the fluid and the solid including latent heat of phase change was incorporated. This formulation simultaneously predicts detailed velocity, pressure, and temperature fields in the moving fluid while capturing the forming solid phase by using a single computer code. The same code can simulate the reverse process of thawing or melting of the solid phase. The computed sample configurations involve a two-dimensional closed container, a straight and a U-shaped channel, and a passage of an arbitrary shape. It was found that the presence of an external steady magnetic field: (a) diminishes flow field vorticity, (b) causes higher velocity gradients within the boundary layers, (c) is able to orient magnetized fibers along the lines of local magnetic lines of forces.

The two-dimensional uncoupled problem of magnetothermoelasticity for a magnetically hard layer

We propose a method for approximate solution of the problem of finding the thermally stressed state of a magnetically hard layer that is subject to the action of an external steady magnetic field. We obtain the general solution of the temperature fields and displacements for the two-dimensional problem. Bibliography: 5 titles.

The effect of a steady azimuthal field on rotating magnetic field current drive

The method of generating steady azimuthal currents in a cylindrical plasma column by means of a rotating magnetic field is investigated numerically and analytically for the case where an external steady azimuthal magnetic field is applied to the plasma. For a plasma of low resistivity, the effect of imposing a strong azimuthal field is a substantial reduction in the amount of current that can be driven. For a resistive plasma the effect is more complicated. In some cases the azimuthal field enhances current drive as has been observed in recent experiments.

Effect of gravity and the Earth's rotation on the spin precession of neutrons

The authors examine in detail the effect of the gravitational field of the Earth and its rotation in the spin precession of neutrons moving in an external steady magnetic field. It is shown that the effect is significant for slow neutrons diffracting in the single crystal and for cold neutrons. Extensive numerical examples are given.