External Steady Magnetic Field Research Articles

GAS DISCHARGE IN PLASMA-METAL WAVEGUIDE WITH VARYING RADIUS OF METAL ENCLOSURE PARTIALLY FILLED BY RADIALLY NON-UNIFORM MAGNETIZED PLASMA

The article presents the results of theoretical study of phase and attenuation characteristics of the symmetric electromagnetic wave in long waveguide structure that partially filled by radially non-uniform plasma immersed in external steady magnetic field. The results of theoretical study of stationary gas discharge sustained by this wave in the considered waveguide structure with slightly varying radius of metal enclosure in the framework of electrodynamic model are presented as well. It was studied the influence of the effective plasma collision frequency on the phase and attenuation wave properties and on the plasma density axial distribution in gas discharge considered for different radial plasma density profiles.

Modulation of millimetre-wave and THz properties of IMPATT sources via external magnetic field

The modulation of millimetre-wave (mm-wave) and terahertz (THz) properties of impact avalanche transit time (IMPATT) sources under external steady magnetic field has been studied in this paper. The arrangement of magnetic field tuning of IMPATT oscillators by using external transverse steady magnetic field is referred to as magnetic field tunable avalanche transit time (MAGTATT) oscillators. The sensitivities of various static, large-signal and noise characteristics of silicon-based MAGTATT sources operating at mm-wave atmospheric window frequencies (94, 140 and 220 GHz) and two different THz frequencies (0.3 and 0.5 THz) have been studied. Comprehensive two-dimensional simulation models developed by the authors for evaluating static, large-signal and noise characteristics of MATATT diodes have been used for this purpose. The simulation results show that the above-mentioned magnetic field sensitivities of the device properties are significantly reduced with the increase of the operating frequency.

Influence of steady magnetic field on dynamic behavior mechanism in full penetration laser beam welding

To study influence from external static magnetic field on dynamic behavior interaction between laser beam and EH36 steel, four cases with different magnetic strength (0mT, 15mT, 25mT and 30mT) are designed to capture high-speed image series of full penetration laser welding through quartz glass. It can be observed that: (1) Part of laser welding energy is compacted in bottom of weld pool to increase penetration and bottom width of bead geometry; (2) Eruption cycle and intensity (height 2.125mm, width 1.75mm) of vapor plume are both weakened; (3) Inhomogeneity and fluctuation of energy distribution are prominently dropped off; (4) Cooling period is delayed to reduce thermal gradient, depression area of the final profile is also reduced. Meanwhile, a polynomial model is developed to reveal relationship between thermal density and distance along the weld center. Therefore, external steady magnetic field has influence on dynamic behavior mechanism (weld pool, vapor plume, energy homogeneity, cool down stage) and even the final morphology, while 15mT is an optimal value of the magnetic strength in these four cases. It can be concluded that selecting an appropriate magnetic field strength is helpful to stabilize laser process and improve welding quality.

Coupling of Helicon Antennas to Plasma near the Electron Cyclotron Resonance

Two inductive antennas, which are usually used for the excitation of a helicon discharge on the wave azimuthal modes m = 1 and m = 0, demonstrate unexpectedly different properties near the electron-cyclotron frequency wce. Though the alternating inductive electric field E produced by the antenna m = 1 is mainly parallel to the external steady magnetic field B0, nevertheless the absorption resonance at the frequency wce accompanied by an increase in the plasma density, takes place. For the m = 0 antenna, where these fields are mutually transverse and where the cyclotron resonance seems certainly must be present, it is absent. But the electron-cyclotron resonance (ECR) appears again provided the B0 field is turned up by the right angle around the same m = 0 antenna.

Excitation of the surface flute waves in electron cyclotron frequency range by internal rotating electron beam in a coaxial waveguide

The initial stage of interaction between a gyrating beam of electrons, which move along Larmor orbits in a narrow gap between a cylindrical plasma layer and an internal screen of a metal coaxial waveguide and electromagnetic eigen waves, is studied theoretically. These waves are extraordinary polarized ones; they propagate along the azimuthal angle across an axial external steady magnetic field in the electron cyclotron frequency range. The numerical analysis shows that the excitation process is stable enough in respect to changing plasma waveguide parameters. The wider the plasma layer, the broader the range of plasma waveguide parameters within which effective wave excitation takes place. The main influence on the excitation of these modes is performed by the applied axial magnetic field, namely: its increase leads to an increase of growth rate and a broadening of the range of the waveguide parameters within which wave excitation is effective.

Excitation of the Azimuthal Surface Waves in Electron Cyclotron Frequency Range by Rotating Electron Beam in a Coaxial Waveguide

The initial stage of interaction between gyrating beam of electrons, which move along Larmor orbits in a narrow gap between a cylindrical plasma layer and an external screen of a metal coaxial waveguide, and electromagnetic eigenwaves is studied theoretically. These waves are extraordinary polarized; they propagate along the azimuthal angle across an axial external steady magnetic field in the electron cyclotron frequency range. The numerical analysis shows that existence of internal metal conductor affects the magnitude of the growth rate weakly. It narrows the range of effective wavenumbers within which effective wave excitation takes place when compared with the case of absence of this conductor. Excitation of these modes is found to be impossible for resonators with relatively small external radii and low plasma densities when compared with a similar structure completely filled with plasma.

Effect of an external alternating electric field non-monochromaticity on parametric excitation of surface ion cyclotron X-modes

The application of an external alternating electric field in the range of ion cyclotron frequencies is a well-known method for the excitation of surface electromagnetic waves. The present paper is devoted to the development of a kinetic theory of parametric excitation of these eigenwaves propagating across an external steady magnetic field along the plasma boundary at the second harmonic of the ion cyclotron frequency. Unlike previous papers on this subject, parametric excitation of surface ion cyclotron X-modes is studied here under the condition of non-monochromaticity of an external alternating electric field. Non-monochromaticity of the external alternating electric field is modeled by the superposition of two uniform and monochromatic electric fields with different amplitudes and frequencies. The nonlinear boundary condition is formulated for a tangential magnetic field of the studied surface waves. An infinite set of equations for the harmonics of a tangential electric field is solved using the approximation of the wave packet consisting of the main harmonic and two nearest satellite harmonics. Two different regimes of instability have been considered. If one of the applied generators has an operation frequency that is close to the ion cyclotron frequency, then changing the amplitude of the second generator allows one to enhance the growth rate of the parametric instability or to diminish it. But if the operation frequencies of the both generators are not close to the ion cyclotron frequency, then changing the amplitudes of their fields allows one to decrease the growth rate of the instability and even to suppress its development. The problem is studied both analytically and numerically.

Excitation of azimuthal surface modes by annular electron beams in the electron cyclotron frequency range

Excitation of extraordinarily polarized azimuthal surface eigenwaves is shown to be possible in the electron cyclotron frequency range in waveguides with metal walls that are partially filled with cold magnetoactive plasma. Interaction of these waves with electron beams, which rotate around the plasma column in a narrow layer separating the plasma from the wall of the waveguide, is studied. Dependences of the beam instability growth rate on the waveguide parameters (plasma and beam density; value of the external steady axial magnetic field; radius of the plasma cylinder and width of the vacuum layer; magnitude and sign of azimuthal wave number) are studied numerically. Two regimes of beam instability are demonstrated: separate resonance and resonance overlapping.

Parametric excitation of surface ion cyclotron extraordinary polarized waves by an external alternating electric field

An external alternating electric field in the range of ion–cyclotron frequencies is shown to excite extraordinary polarized surface electromagnetic waves at the second harmonic of ion–cyclotron frequencies. The kinetic model of a uniform semi-bounded plasma is applied. Plasma electrodynamical properties are described by using the Vlasov–Boltzmann kinetic equation in the approach of weak spatial plasma dispersion. Two components of these modes’ wave vector, which are oriented across an external steady magnetic field, are taken into account. Fields of these ion–cyclotron modes are described by Maxwell equations. Their phase velocity is assumed to be much lower than light velocity. The external alternating electric field is assumed to be uniform and monochromatic. The nonlinear boundary condition is formulated for the tangential magnetic field of the studied surface waves (SW). An infinite set of equations is derived for the values of tangential electric field harmonics on the plasma interface. This set is solved using the approach to the wave packet consisting of the main harmonic and two nearest satellite harmonics. Simple analytical expressions for the growth rates of parametric instability of these SW are derived. The influence of plasma parameters on their parametric excitation is numerically analyzed.

Nuclear Spin Relaxation in Glass States of 3He-A in Stretched Aerogel

We present results of pulse NMR investigations of superfluid A-like phase of 3He in stretched aerogel. In this case we have anisotropic orbital glass (OG) with two possible types of ordering in spin space—ordered spin nematic (OG-SN) or disordered spin glass (OG-SG) states. It was found that longitudinal relaxation of magnetization is non-exponential in both states and depends on temperature and on inhomogeneity of external steady magnetic field. At the same conditions the relaxation in OG-SG state is more rapid than in OG-SN state. For transverse orientation of the magnetic field relative to anisotropy axis the duration of free induction decay signal was longer than in normal phase. It may be explained by formation of coherently precessing spin state.

Coupled Vibration Analysis of Magnetizable Plate in Steady Magnetic Field With Considering Geometric Nonlinearity

The magnetizable materials such as SUS316 are expected as substances of the composition apparatus of a nuclear fusion reactor. Then, it is important to establish the electromagnetic and structural coupled analysis method and to clarify the resonance characteristics of ferromagnetic material for an earthquake-resistance design. This paper describes the electromagnetic and structural coupled analysis considering geometric nonlinearity for magnetizable material. Analysis results show the increment of the natural frequency of a magnetizable cantilever plate located under an external steady magnetic field.

The Use of Steady Electromagnetic Fields to Control the Columnar Solidification of Binary-Metal Alloys

This article considers the nondirectional solidification of a binary-metal alloy in a cylindrical cavity, which is cooled along its outer vertical wall and the bottom. To study the influence of convection within the liquid phase on the final segregation, three cases are examined: the purely buoyancy-driven convection (case 0), the impact of an external steady axial magnetic field on the melt flow during solidification (case 1), and the effect of the combination of an external magnetic field with a steady electrical current (DC) applied directly to the melt (case 2). The results show that convection in the form of multivortices caused by the thermosolutal buoyancy leads to macrosegregations in the form of V-channels. The application of an external axial magnetic field alone suppresses the multivortex structure and, thus, the macrosegregation. By contrast, the parallel use of an additional voltage of 10−3 V leads to an increase in final macrosegregation.

Large magnetoresistance in magnetoimpedance of Co 68Fe 5Nb 12B 15 ribbons

The magnetoinductance (mi), AC magnetoresistance (ACMR) and magnetoimpedance (MI) in as cast Co 68Fe 5Nb 12B 15 ribbons of length from 1 to 5 cm were studied. The mi, ACMR and MI are large for 5 cm long ribbons. At a frequency of 13 MHz, large value of ACMR (67%) compared with the mi and MI is observed. This is explained as due to the decrease of the skin depth with increase of frequency. With the application of the external steady magnetic field the skin depth increases resulting in a large ACMR. The larger values of mi, ACMR and MI ratios for 5 cm long ribbons compared to those in the smaller ribbons may be due to smaller demagnetizing fields.

Effect of annealing on magnetoimpedance of Co 68Fe 4Zr 10Cu 2B 16 ribbons

Magnetoimpedance (MI) in Co 68Fe 4Zr 10Cu 2B 16 alloy has been investigated in the frequency range 500 kHz–5 MHz and with the application of external steady magnetic field in the longitudinal direction, up to 100 Oe. MI measurements were carried out on as-cast ribbons and also on conventionally annealed and Joule-annealed ribbons. In as cast ribbons, the maximum MI observed is 13% at a frequency of 500 kHz and it decreases to 5% and 4% with conventional annealing at 100 °C and 150 °C, respectively. On the other hand, MI decreases to 8% and 6% with Joule annealing employing currents of 100 mA and 200 mA, respectively. However, Joule annealing with the application of a magnetic field of 5–10 Oe in the transverse direction causes the MI to decrease to 12% and 11% for currents of 100 mA and 200 mA, respectively. In the as-cast ribbons, double peak behavior is observed in all the frequencies whereas, in the annealed ribbons, double peak behavior in general is observed only at high frequencies.

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.

Influence of dynamic structure on the microstructure formation of a steel surface in the electrolyte in a steady magnetic field

The periodic microfabrication effect of metal element surfaces in an electrolyte solution in an external steady magnetic field was investigated. Authors have shown that corrosion velocity and periodic microstructure formation on the metal element surface can be controlled by magnetic field application. Geometric configuration of periodic microstructure depends on metal element characteristics, electrolyte solution, treatment time, magnetic field magnitude and other parameters. Investigation results have shown possibility of magnetic field influence on hydrodynamic conditions and metal surface structure under its etching in the nitric acid solution. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magneto-modified catalyst on the base of nanocrystalline CuO

Abstract The weakly oxidized nanocrystalline copper powders of different sizes (average particle size of 30 and 100 nm) were used as the reactants at copper phthalocyanine (PcCu) formation. The nanocrystalline cupric oxide located at the particles surface serves as a heterogeneous magneto-controlled catalyst. A new effect of acceleration of chemical reaction rate controlled by low external steady magnetic field (∼2 kOe) at room temperature was revealed and investigated on an example of formation of a coordination compound of PcCu. The rate of PcCu formation accelerated by 7–8 times after applying of a magnetic field.

Surface Wave Control under Plasma–Metal Processing

The nonlinear interaction of high-frequency potential surface waves at a dense magnetized plasma–metal interface with a low-frequency plasma density modulation is considered in the point of view of the surface waves control. An external steady magnetic field is directed perpendicularly to the interface. The influence of external magnetic field strength and plasma parameters on temporal dynamics of the waves is studied.

Surface Waves at a Dusty Plasma-Metal Interface

The theory of electrostatic surface wave propagation along the plain interface between a low-temperature nonisothermal dusty plasma and a metal wall is presented. The discussion is addressed to the situation, when the plasma contains massive negatively charged impurity or dust particles and is immersed in an external steady magnetic field, which is directed perpendicularly to the plasma-metal interface. It is found that charged dust grains can significantly affect the propagation and damping of the high-frequency surface waves and can lead under certain conditions to low-frequency surface waves.

Effect of magnetic field on the thermal nonlinearity of surface waves in plasma-metal structures

A study is made into the effect of the nonlinear mechanism of plasma electron heating on the dispersion properties of potential surface waves propagating along the interface between a metal and finite-pressure magnetoactive plasma. An external steady magnetic field is directed normally to the interface. Different mechanisms of electron energy loss are treated in a weak heating approximation. The energy balance equation is used to determine the spatial distribution of the plasma electron temperature under conditions of nonlocal heating. The effect of the plasma parameters on the nonlinear shift of the wavenumber and on the spatial damping factor of surface waves is investigated. The results obtained are valid for both semiconductor and gaseous plasmas.