Superposition Of Magnetic Field Research Articles

Influence of Microstructure on the DC-Bias-Superposition Characteristics of NiZn Ferrites

The influence of microstructure on the magnetic properties, especially the dc-bias-superposition characteristics, of NiZn ferrites has been investigated. The value of saturation magnetic flux density ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ) first increased and then changed little with variation of the sintered density, and showed little relation to the microstructure. Coercivity ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) decreased continuously with increasing average grain size. Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> -remanence) first increased with increasing average grain size, but then gradually decreased when abnormal grain growth prevailed. The incremental permeability (permeability with magnetic field superposition) was influenced by both Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> . A sample with higher Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> favored the attainment of a higher incremental permeability. The <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -factor was mainly determined by the sintered density and microstructure. To sum up, a uniform and dense microstructure with relatively small average grain size is favorable for obtaining better dc-bias-superposition characteristics, including permeability and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -factor.

Self-Magnetic Field Calculation in Modeling the Current-Carrying Electrode System With Plasma Jet and Cathode Spot Motion in a Vacuum Arc

The method of magnetic field calculation and its influence on simulating the motion of cathode spots (CSs) in a vacuum arc were investigated in this paper. A method based on coordinate transformation and magnetic field superposition principle was proposed. In this method, the influence of current passing through an electrode rod and a contact plate was taken into account. Comparison was made between the proposed method and two simplified methods which were on the basis of the Biot–Savart law. Moreover, simulation results of CS motion with magnetic field calculated by different methods were shown and compared. Investigation results indicated that current passing through the contact plate and electrode rod could significantly influence the magnetic field and thus influence the simulation results of CS motion. Furthermore, it was shown that the proposed magnetic field calculation method had higher calculation accuracy with acceptable consumption of calculation time.

Effects of Co-substitution on DC-bias-superposition characteristic of the NiCuZn ferrites

Low-temperature-fired Ni 0.5− x Cu 0.2Zn 0.3Co x Fe 1.95O 4 (0.00≤ x≤0.10, with 0.02 intervals) ferrites were produced by the conventional ceramic technique. Both microstructure and sintering density changed little in samples sintered at 900 °C. Saturation magnetic flux density gradually increased with increase in Co-substitution content. Coercive force first decreased with x value and obtained the minimum with x=0.04, then it continuously increased with x value. Permeability presented a fully opposite variation trend compared with coercive force. Furthermore, coercive force had a more important influence on DC-bias-superposition characteristic than that of saturation magnetic flux density. The sample with 0.04 Co-substitution favored to obtain a higher incremental permeability (permeability with magnetic field superposition) under a relatively low superposition magnetic field. And the sample with 0.08 Co-substitution favored to obtain a steady incremental permeability under different superposition magnetic fields.

Electrocrystallisation of metallic films under the influence of an external homogeneous magnetic field—Early stages of the layer growth

The effects of a uniform magnetic field on the early stages of Ag, Fe and CoFe alloys electrocrystallisation have been investigated. It was found for Fe and CoFe alloys, irrespective of the applied parameters, that early stages of the layer growth can be characterised by a nucleation and 3D diffusion controlled growth. The influence of the deposition parameters on the nucleation behaviour was studied on the basis of the Sharifker–Mostany (SM) model. A modification to the existing model has been proposed in order to model alloy systems. It is reported that a magnetic field superposed parallel to the electrode surface has a significant influence on the early stages of Fe and CoFe alloys growth. The growth of the nuclei is enhanced by the Lorentz-force-driven convection, while the nucleation processes remain unaffected. The hydrodynamic origin of these phenomena is confirmed by independent rotating disk electrode (RDE) investigations. Moreover, the proposed mechanism of a magnetic field influence on the 3D diffusion controlled growth is supported by a microscopic investigation of Ag deposits. It was found that Ag deposits obtained without a magnetic field superposition are characterised by a relatively large number of small 3D growth centres, whereas the deposits obtained in a field show fewer 3D centres but their size is greatly increased.

Transport AC loss characteristics of a nine strand YBCO Roebel cable

Transport AC loss in a short length of 9/2 YBCO Roebel cable (nine 2 mm wide strands) ismeasured. The AC loss data are compared with those in a 5/2 YBCO Roebel cable (five 2 mmwide strands) as well as that in a single strand. All the strands composing the cables andthe single strand are insulated and cut from the same stock material. The validity of themeasurement method was reconfirmed by results at a range of frequencies. At a wide range ofIt/Ic, the normalized AC losses in the Roebel cable were around 6.2–6.7 times of those in the singlestrand. This is less than the nine times predicted for a tight bundle of nine conductors. Thenormalized transport AC losses in the 5/2 Roebel cable are much smaller than those in the 9/2Roebel. This should be due to larger superposition of magnetic field in the 9/2 Roebel. TheIc of the 9/2 and 5/2 Roebel cables is determined by serial connection of the strands. Thiseliminates the effect where differing resistances in the current terminations causeuneven current sharing between strands when the strands are connected in parallel.

Motion of plasma-dust structures and gas in a magnetic field

Numerous studies have revealed that the superposition of magnetic field causes plasma-dust structures to rotate in the plane normal to the field. The only explanation for this rotation found in the literature is that the plasma-dust structures are acted upon by the forces of ion entrainment (ion drag forces) from ions moving under the effect of the magnetic field in the azimuthal direction. However, this study demonstrates that the experimentally observed motion of plasma-dust structures cannot be explained by the forces of ion entrainment alone. We show that the observed motion of plasma-dust structures is further affected by their entrainment by gas rotating under the effect of the moment of force IxB , which exists in regions of discharge with nonuniform magnetic field in the vicinity of solenoid end faces, as well as at the narrowing of cross section of the discharge channel. An eddy electric current exists in a discharge with strata in a uniform magnetic field; this current causes the rotation of gas and is associated with the noncollinearity of the gradients of plasma density and temperature. Estimates are provided for the density of this current and for its impact on the rotation of gas in a magnetic field. Recent experimental data by Karasev [Phys. Rev. E 74, 066403 (2003)] are discussed.

The dynamical mechanism of A-B effect and its testing scheme

The dynamical mechanism of A-B effect is discussed in detail. It is found that A-B effect is due to the superposition of the magnetic field produced by the moving charges with that in the solenoid, rathor than the existence of vector potential A. If such a magnetic field superposition can be prevented, the A-B effect will disappear, even though the vector potential A still exists in space. To verify this conclusion, a new experimental scheme is suggested.

An MHD-based treatment of electrolysis in magnetic fields generated inside a solenoid

The effect of magnetic field superposition on electrolysis carried out in magnetic fields generated inside a solenoid is analysed using the theory of magnetohydrodynamics. It is shown that induced field inhomogeneity is responsible for the creation of local vortex motion which enhances ionic mass transport rates. A detailed vorticity analysis of two laboratory-scale, and a pilot plant-scale experimental magnetoelectrolytic cell serves for illustration.

Impact of magnetic fields on the spatial relaxation of electrons

The spatial relaxation of the electrons in weakly ionized plasmas of atomic and molecular gases acted upon by spatially homogeneous electric fields has been the subject of detailed kinetic studies in recent years. In particular, the relaxation behavior of the electron velocity distribution and of relevant macroscopic transport and dissipation properties of the electrons, initiated by different disturbances, have been systematically investigated and its basic mechanisms analyzed. These studies have revealed that, particularly in atomic plasmas, the electrons generally respond to disturbances with weakly damped, spatially periodic relaxation processes that are characterized by large relaxation lengths and pronouncedly nonlocal properties. Currently, the superposition of magnetic fields gets increasing interest [S. Nakamura, P. L. G. Ventzek, and K. Kitamori, J. Appl. Phys. 85, 2534 (1999)] to additionally control or tune those plasmas that are especially used in plasma processing and laser applications by the imposed magnetic force. This evolution has motivated to extend the spatial relaxation studies to plasmas acted upon by crossed electric and magnetic fields. Thus, based on a consequent kinetic treatment, the present article reports on the considerable modifications of the relaxation behavior of the electrons enforced by the additional electron cyclotron motion in the magnetic field.

交流磁界重畳による脈動を有する直流電流の光学計測

交流磁界重畳による脈動を有する直流電流の光学計測

Hysteretic time dependence of the critical intergrain transport current in sintered YBa 2Cu 3O 7

In our experiments we have found that the intergrain critical transport current I c in sintered, non-oriented high- T c superconductors shows a hysteretic time relaxation behavior. As a function of prior magnetic field cycling the I c-relaxation rate ∂ c/∂ t be positive or negative with different magnitudes and can also be made to vanish. Not only I c but the whole E-I-characteristics is shifting with time. We explain these results qualitatively in the frame of a magnetic field superposition model at the grain boundaries, with our earlier measurements on the relaxation of the intragrain magnetization. This could also be of importance for superconducting electronic applications.

The effect of magnetic fields on natural convective mass transport at inclined circular disk electrodes

The effect of magnetic field superposition on electrolysis at inclined, parallel circular-disk electrodes has been studied in an experimental cell. The variation of mass transport rates with magnetic flux density and inclination angle is interpreted by an approximate analysis based on the theory of magnetohydrodynamics and convective diffusion.