Steady-state Magnetic Field Research Articles

Effects of Particles Blend Ratio on Surface Quality in Surface Polishing Using Magnetic Polishing Liquid (MPL)

This paper describes an experimental investigation of the effects of the particle blend ratio on surface quality in surface polishing using magnetic polishing liquid (MPL). MPL is produced by mixing sub-micrometer- or micrometer-size abrasive particles into a Magnetic Compound Fluid (MCF), a functional fluid composed of MF(Magnetic Fluid) and MRF (Magneto-rheological Fluid), that reacts with magnetic fields. As a step toward establishing the new surface finishing technology using MPL, it is essential to clarify the effects of the blend ratio of particles to solvent in MPL. For this purpose, first five kinds of kerosene-based MPLs with different blend ratios of particles were prepared, then polishing operations involving stainless steel workpieces were carried out on an experimental rig developed in-house. During the experiments, steady state magnetic fields with different strengths were applied while the contact force between the workpiece and the polishing pad was kept constant. The experimental results showed that the blend ratio of particles affects the work-surface quality significantly. Following SEM and optical microscopy observations of the polished work-surfaces, an appropriate blend ratio, under which the surface roughness improved from the original value of Ra100nm to a final one of Ra24nm after polishing for 30min, was recommended.

Infrared surface temperature measurements for long pulse operation, and real time feedback control in Tore-Supra, an actively cooled Tokamak

Tore-Supra is a Tokamak (Ip=1.5MA, Bt=4T) aiming at doing researches in the field of controlled nuclear fusion. It has been constructed with a steady-state magnetic field using super-conducting magnets and water-cooled plasma facing components for high performances long pulse plasma discharges. When not actively cooled, plasma-facing components can only accumulate a limited amount of energy since the temperature increase continuously (T˜sqrt(time)) during the discharge until radiation cooling is equal to the incoming heat flux (T>1800K). Such an environment is found in the most today Tokamaks. In the present paper we report the recent results of Tore-Supra, especially the design of the new generation of infrared endoscopes to measure the surface temperature of the plasma facing components. The Tore-Supra system is described in details, the new JET infrared thermography system is presented and some insight of the ITER set of visible/infrared endoscope is given.

Particle acceleration at a three-dimensional reconnection site in the solar corona

We study test panicle trajectories in the vicinity of a three-dimensional (3D) magnetic null point during spine reconnection. Particles are injected into the steady-state non-uniform magnetic and electric fields derived by Priest & Titov (1996), and the equations of motion numerically integrated. We use input parameters typical of the solar corona, for which reconnection has been suggested as the fundamental mechanism responsible for particle acceleration in flare events. We show that substantial acceleration is possible in the 3D spine reconnection configuration, in the strong electric field regime. The energy gain is strongly dependent on the location of injection into the simulation box, as was the case in 2D X-point configurations. In our 3D geometry, we first vary the location of injection within a plane through the spine, and derive an analytical value for the injection angle for which maximum energy gain is achieved. Secondly we vary the azimuthal location of particle injection and show that as one moves away from the plane with maximum electric field magnitude, higher final energies can be achieved, though this requires substantially longer times.

Enhanced Concentration of the Magnetic Flux in a Superconducting Cylinder

The performance of a flux concentrator using an YBCO oxide superconductor was tested to raise the steady state magnetic field generated by the existing magnet. This concentrator was composed of an outside hollow cylinder and a pair of half cylinders that goes in and out in the outside cylinder. This flux concentrator generated additional magnetic field more than 1.6 T for an applied magnetic field 28 T.

Wall Conditioning on TEXTOR

Proper wall conditioning has been a major element in the development of fusion energy on the way to achieve high fusion plasma performance. Various of these techniques have been pioneered in the TEXTOR tokamak and later applied successfully in various devices worldwide. The main issues are to clean the surface from surface-bounded impurities, to remove hydrogen, and to coat the entire wall surface with a thin film of a proper first-wall material. The main benefits of wall conditioning are to control the oxygen impurity content of the plasma and to offer a suitable first-wall material. Entire coating of the first wall has allowed one to control to some extent the recycling hydrogenic fluxes but in particular to study the complex coupling between the choice of wall materials and the behavior of the plasma edge. This paper presents a review of the different wall-conditioning methods used in TEXTOR and their effects on the plasma behavior. Also, new wall-conditioning concepts, compatible with steady-state magnetic fields, are outlined briefly.

Shorting rings in dual-coil dual-gap loudspeaker drivers

Loudspeakers and other transducers of the dual-voice-coil/dual-magnetic-gap type can be improved by the addition of one or more annular shorting rings (16A-16S) strategically located in the vicinity of the two magnetic gaps. The shorting rings have no effect on a steady state magnetic field but act in opposition to any change in flux density or any displacement of the flux lines such as those that occur under the loading imposed when the voice coils (10A, 10B) are driven hard with audio frequency current. Thus a plurality of rings can be strategically deployed at different locations so as to optimally suppress both even and odd order harmonic distortion and to reduce the voice coil inductance.

定常変動磁界中におけるYBCO超電導バルク溶融体の2次元表面磁束密度分布の測定

定常変動磁界中におけるYBCO超電導バルク溶融体の2次元表面磁束密度分布の測定

Steady-State Approach to Low-Aspect-Ratio Reversed-Field Pinch Nuclear Fusion Reactor

According to a simplified costing algorithm for a steady-state fusion reactor power plant, the relative attractiveness of advanced physics modes mainly depends on the stability and noninductive current drive of the equilibrium. The high-stability beta and the good alignment of the equilibrium current profile with a self-induced plasma current profile are compatible with the low-aspect-ratio neoclassical Reversed-Field-Pinch equilibrium solved self-consistently considering the self-induced plasma current. The high-stability beta is due to the hollow current profile making the magnetic shear increase and the force-free field dominant. The good alignment of the current profile significantly reduces the power required for noninductive current drive to generate the steady-state magnetic field configuration. As a result, the fusion power plant based on the neoclassical RFP equilibrium with low aspect ratio enables electricity to be generated at relatively low cost.

On the role of magnetic field spin effect in photoconductivity of composite films of MEH-PPV and nanosized particles of PbS

The photoconductivity of thin films consisting of a conjugated polymer poly[2-methoxy, 5-(2′-ethyl-hexyloxy)-p-phenylene-vinylene] (MEH-PPV) and dispersed nanosized particles of an inorganic semiconductor lead sulphide (PbS) was investigated using steady-state photoconductivity and magnetic field spin effect (MFSE) techniques. It was shown that the addition of small amount of PbS nanoparticles leads to the reduction of the photocurrent while higher concentration of PbS increases the photocurrent.

Magnetic and Electric Fields of Direct Currents in a Layered Earth (Short Note)

We derive a numerical solution of the steady-state magnetic field due to a DC current source in a layered earth model. Such a solution is critical for interpretation of magnetometric resistivity (MMR) data. Our solution is achieved by solving a boundary value problem in the spatial wavenumber domain and then transforming back to the polar spatial domain. The propagator matrix technique is used to interrelate solutions between layers. Two simplified cases are examined to promote understanding of the magnetic fields. In particular, the derived formula illustrates why surface MMR data are insensitive to ID conductivity variations and why borehole measurements are effective in finding conductivity contrasts.

Three‐dimensional finite element eddy current analysis by using high‐order vector elements

AbstractSets of high‐order basis functions of a tetrahedral element are systematically constructed and applied to finite element analysis of eddy current problems. A polynomial space is divided into a lot of subspaces assigned on the edges, faces, and a volume of the tetrahedral element. Lagrange‐type vector basis functions of the subspaces are presented. The effect of the high‐order vector elements is investigated by a cubic conductor model located in AC steady‐state magnetic fields. In the calculations using the fundamental and second‐order elements, no convergent value of the eddy current power loss can be obtained in spite of fine meshes because the eddy current shifts to the surface of the conductor. The higher‐order vector elements give the convergent solutions in the coarse meshes. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(4): 60–67, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10306

On the magnetic ordering of the iron storage proteins in tissues

Abstract Small angle neutron scattering data are indicative of ferritin aggregation in tissues (Rg of ca. 21–25 nm) in contrast to the isolated purified ferritin protein (Rg of ca. 5 nm). Dependence of the shape and position of the ferritin electron spin resonance spectra in tissues upon sample orientation relative steady state magnetic field points to the magnetic susceptibility anisotropy of ferritin aggregates. The magnetic ordering of ferritin results in dramatic increase in magnetic susceptibility of the ferritin iron in tissues compared to the crude and purified ferritin extracts.

Magnetic field effect on indole exciplexes: an anomalous dielectric dependence

Individual exciplex formation between various aromatic hydrocarbons, anthracene, pyrene, all- s-trans-1,4-diphenylbuta-1,3-diene and a heteroaromatic amine, 1,2-dimethylindole, was investigated by steady-state fluorescence and magnetic field effect (MFE). A comparative study was carried out with two other exciplex systems 9-cyanophenanthrene-1,2-dimethylindole and 9-cyanophenanthrene- N-methylindole. The extent of charge transfer and dielectric dependence of MFE reveals the potential role of specific interactions related to exciplex geometry.

Electrolyte vortex flows induced by a steady-state magnetic field in the vicinity of a steel wire used as an accelerator of the chemical reaction rate

Electrolyte vortex flows induced by a steady-state magnetic field in the vicinity of a steel wire used as an accelerator of the chemical reaction rate

The time-averaged magnetic field in numerical dynamos with non-uniform boundary heat flow

SUMMARY The time-averaged geomagnetic field on the core‐mantle boundary is interpreted using numerical models of fluid dynamos driven by non-uniform heat flow. Dynamo calculations are made at Prandtl number Pr = 1, magnetic Prandtl numbers Pm= 1‐2, Ekman numbers E = 3×10 −4 ‐ 3 × 10 −5 and Rayleigh numbers 10‐30 times the critical value for different patterns of heat flow on the outer boundary of a rotating, electrically conducting spherical shell. The results are averaged over several magnetic diffusion times to delineate the steady-state magnetic field and fluid motion. When the boundary heat flow is uniform the time-averaged flow approaches axisymmetry and the magnetic field is mostly a geocentric axial dipole (GAD). The largest departure from GAD in this case is the octupole field component. When the amplitude of the boundary heat flow heterogeneity exceeds the average heat flow, the dynamos usually fail. Lesser amounts of boundary heterogeneity produce stable dynamos with time-averaged magnetic fields that depend on the form of the boundary heterogeneity. Elevated heat flow in the northern hemisphere produces a time-averaged axial quadrupole magnetic field comparable to the inferred paleomagnetic quadrupole. Azimuthally periodic boundary heat flow produces a time-averaged magnetic field component with the same azimuthal wavenumber, shifted in longitude relative to the heat flow pattern. Anomalously high and anomalously low magnetic flux density correlate with downwellings and upwellings, respectively, in the time-averaged fluid motion. A dynamo with boundary heat flow derived from lower-mantle seismic tomography produces anomalous magnetic flux patches at high latitudes and westward fluid velocity in one hemisphere, generally consistent with the present-day structure of the geodynamo.

The role of magnetic helicity transport in nonlinear galactic dynamos

We consider the magnetic helicity balance for the galactic dynamo in the framework of the local dynamo problem, as well as in the no-z model (which includes explicitly the radial distribution of the magnetic fields). When calculating the magnetic helicity balance we take into account the redistribution of the small-scale and large-scale magnetic fields between the magnetic helicities, as well as magnetic helicity transport and diffusion due to small-scale turbulence. We demonstrate that the magnetic helicity flux through the galactic disc boundaries leads to a steady-state magnetic field with magnetic energy comparable to the equipartition energy of the turbulent motions of the interstellar medium. If such flux is ignored, the steady-state magnetic field is found to be much smaller than the equipartition field. The total magnetic helicity flux through the boundaries consists of both an advective flux and a diffusive flux. The exact ratio of these contributions seems not to be crucial for determining the strength of the steady-state magnetic field and its structure. However at least some diffusive contribution is needed to smooth the magnetic helicity profile near to the disc boundaries. The roles of various transport coefficients for magnetic helicity are investigated, and the values which lead to magnetic field configurations comparable with those observed are determined.

Thin film microcalorimeter for heat capacity measurements in high magnetic fields

Si–N based membrane calorimeters are a promising technology for the study of thermal properties of small quantities of materials in both pulsed and steady-state magnetic fields to 60 T and beyond. We present results that demonstrate our ability to measure the heat capacity of thin film samples from 2–300 K in steady-state fields up to 8 T. These measurements include the magnetoresistance of the Pt and Nb–Si thermometers and focus on confirming that the thermal conductance of the Si–N membrane does not change significantly in magnetic fields. This means the thermal conductance needs to be measured only in zero field, reducing the measurement time in high field. This is particularly important for future measurements in fields up to 60 T.

New iterative method for three-dimensional eddy-current problems

A new iterative method for computing three-dimensional steady-state magnetic fields with eddy currents is presented. By using the proposed method, the numerical computation of eddy current fields can be divided into two successive stages on flux density and eddy current calculations. The convergent field solution is then obtained iteratively. The coefficient matrices arising from the proposed method contain relatively few variables and are real. As these matrices need to be eliminated only once in the iteration procedure, the requirement upon the computer resource can be reduced substantially. The convergence of the presented iterative method is also discussed in detail. The instructions for choosing the penalty factor and relaxation factor in order to obtain the globally convergent potentials with sufficiently accurate field solutions are also given. Some sample calculations show that the new iterative method is highly computationally efficient for studying large-scale unbounded eddy-current problems in engineering.

Temporal integration in the human auditory cortex as represented by the development of the steady-state magnetic field

The threshold for detecting amplitude modulation (AM) decreases with increasing duration of the AM sound up to several hundred milliseconds. If the auditory evoked steady-state response (SSR) to AM sound is an electrophysiological correlate of AM processing in the human brain, the development of the SSR should follow this course of temporal integration. Magnetoencephalographic recordings of SSR to 40 Hz AM tone-bursts were compared with responses to non-modulated tone-bursts at inter-stimulus intervals (ISIs) of 3, 1, and 0.5 s. Both types of stimuli elicited a transient gamma-band response (GBR), an N1 wave, and a sustained field (SF) during stimulus presentation. The AM stimulus evoked an additional 40 Hz SSR. The N1 amplitude was strongly reduced with shortened ISI, whereas the amplitudes of SSR, GBR, and SF were little affected by the ISI. Magnetic source-localization procedures estimated the generators of the early GBR, the SSR, and the SF to be anterior and medial to the sources of the N1. The sources of the SSR were in primary auditory cortex and separate from GBR sources. The SSR amplitude increased monotonically over a 200 ms period beginning about 40 ms after stimulus onset. The time course of the SSR phase reliably measured the duration of this transition to the steady state. At stimulus offset the SSR ceased within 50 ms. These results indicate that the primary auditory cortex responds immediately to stimulus changes and integrates stimulus features over a period of about 200 ms.

Dynamo and Electrical Jet in Hall Plasmas, Application to Astrophysics

The magnetic field in Hall plasmas is frozen in the electron component and is advected not only with the plasma motion but also with the electrical current flow. Its coupling with the plasma may be not as strong as characteristic of the MHD approximation. The rotation and slipping of the magnetic field result in a very different and less efficient magnetic field generation by dynamo-rotating plasma disk in magnetic field. We found some exact analytical solutions of nonlinear equations describing the dynamo. In particular, the dynamo may not dissipate the energy in the steady state limit. The 3-component magnetic field and magnetic energy are generated and accumulated during the transition time only. An electrical jet is another unusual phenomenon for MHD. It was investigated theoretically and experimentally for laboratory plasmas during the last 15 years and now is used for fast current switching. We found periodical or shock-like nonlinear wave traveling along a Hall plasma column and not associated with plasma motion. A nonlinear equation describing a possible steady state magnetic field distribution and current flow in a Hall plasma conductor is derived, which differs from the Grad-Shafranov equation. In conclusion we discuss how transfer our results onto astrophysical plasmas. This physics could be important for understanding the evolution of dusty plasma disks and jets around new stars.