Radial Distribution Of Magnetic Field Research Articles

Investigation on the Effect of Debris Position on the Sensitivity of the Inductive Debris Sensor

The uneven radial magnetic field distribution in the planar coil will lead to debris detection errors, especially for inductive debris sensors with high throughput and sensitivity, so the effect of debris position on the detection sensitivity should be addressed. In this study, based on spatial magnetic field analysis of planar coil, the characteristics of impedance signals induced by debris at different positions in planar coil were investigated under different frequencies, debris sizes and velocities. The experimental results demonstrated that the double peaks generated in the induced signals can be eliminated without sacrificing the sensitivity by placing the sensor channel at the coil inner wall, and the sensitivity can be improved by observing resistance signals, increasing the frequencies and reducing debris velocities.

Numerical study of the effect of radial magnetic field on performance of Hall thruster

The Hall-effect thruster has wide applications for commercial aerospace because of the high thrust density and simple structure. In order to further improve the performance of low-power Hall thruster and to solve the problem that the performance of low-power Hall thruster for low-orbit satellites is limited by the input power and maximum magnetic field intensity, the influence of radial magnetic field distribution in the discharge channel on the performance of the thruster is studied by numerical simulation and theoretical analysis in this work through changing the radial magnetic gradient on condition that the axial magnetic profile and the magnetic strength remain unchanged. The results show that the potential of the acceleration zone decreases with the increase of radial distance when the discharge parameters, propellant flow rate and axial magnetic field are unchanged. Therefore, the greater the radial magnetic field gradient near the inner wall of the thruster discharge channel, the greater the kinetic energy of the ions drifting along the axial direction to the thruster outlet, , and the greater the thrust of thruster. The research results of this work provide theoretical support for the magnetic field design and performance optimization of hall thrusters.

Global Coronal Equilibria with Solar Wind Outflow

Abstract Given a known radial magnetic field distribution on the Sun’s photospheric surface, there exist well-established methods for computing a potential magnetic field in the corona above. Such potential fields are routinely used as input to solar wind models, and to initialize magneto-frictional or full magnetohydrodynamic simulations of the coronal and heliospheric magnetic fields. We describe an improved magnetic field model that calculates a magneto-frictional equilibrium with an imposed solar wind profile (which can be Parker’s solar wind solution, or any reasonable equivalent). These “outflow fields” appear to approximate the real coronal magnetic field more closely than a potential field, take a similar time to compute, and avoid the need to impose an artificial source surface. Thus they provide a practical alternative to the potential field model for initializing time-evolving simulations or modeling the heliospheric magnetic field. We give an open-source Python implementation in spherical coordinates and apply the model to data from solar cycle 24. The outflow tends to increase the open magnetic flux compared to the potential field model, reducing the well-known discrepancy with in situ observations.

Numerical Investigations on Magnetohydrodynamic Pump Based Microchannel Cooling System for Heat Dissipating Element

Numerical investigations are performed on the magnetohydrodynamic (MHD) pump-based microchannel cooling system for heat dissipating element. In the present study, the MHD pump performance is evaluated considering normal current density, magnetic flux density, volumetric Lorentz force, shear stress and pump flow velocity by varying applied voltage and Hartmann number. It is found that for a low Hartmann number, the Lorentz force increases with an increase in applied voltage and Hartmann number. The velocity distribution along dimensionless width, the shear stress distribution along dimensionless width, the magnetic flux density along the dimensionless width and radial magnetic field distribution showed symmetrical behavior. The MHD pump-based microchannel cooling system performance is evaluated by considering the maximum temperature of the heat dissipating element, heat removal rate, efficiency, thermal field, flow field and Nusselt number. In addition, the influence of various nanofluids including Cu-water, TiO2-water and Al2O3-water nanofluids on heat transfer performance of MHD pump-based microchannel is evaluated. As the applied voltage increased from 0.05 V to 0.35 V at Hartmann number 1.41, the heat removal rate increased by 39.5%. The results reveal that for low Hartmann number, average Nusselt number is increasing function of applied voltage and Hartmann number. At the Hartmann number value of 3.74 and applied voltage value of 0.35 V, average Nusselt numbers were 12.3% and 15.1% higher for Cu-water nanofluid compared to TiO2-water and Al2O3-water nanofluids, respectively. The proposed magnetohydrodynamic microcooling system is effective without any moving part.

Design and Magnetic Field Simulation of Giant Magnetostrictive Bone Conduction Pronunciation Vibrator

Giant magnetostrictive material (GMM) has the characteristics of big magneto-mechanical coupling coefficient, enormous strain and broad frequency response, which is widely used in audio and ultrasonic technology, ultra precision machining, testing technology, fluid control, vibration control and all kinds of sensors in recent years. This paper introduces some of the good qualities of GMM, compared with electromagnetic and piezoelectric materials, which are used extensively for bone conduction hearing device at present; a bow type giant magnetostrictive bone conduction pronunciation vibrator with simple structure and reliable performance is designed; the paper focuses on establishing the vibrator model and the simulation of ANSYS electromagnetics model; the radial magnetic field distribution is also analyzed. All the work provides reference for structure optimization and the selection of coupling materials for the vibrator.

Study on Anomalous Electron Diffusion in the Hall Effect Thruster

Over the last two decades, numerous experimental and numerical efforts have examined physical phenomena in plasma discharge devices. The physical mechanisms that govern the anomalous electron diffusion from the cathode to the anode in the Hall Effect Thruster (HET) are not fully understood. This work used 1-D numerical method to improve our understanding and gain insight into the effect of the anomalous electron diffusion in the HET. To this end, numerical solutions are compared with various experimental HET performance measurements and the effects of anomalous electron diffusion are analyzed. The relationships between the anomalous electron diffusion and important parameters of the HET are also studied quantitatively. The work identifies the cathode mass flow rate fraction, radial magnetic field distribution, and discharge voltage as significant factors that affect anomalous electron diffusion. Additionally, the study demonstrates a computational process to determine the radial magnetic field distribution required to achieve specific thruster performance goals.

Radial distribution of magnetic field in earth magnetotail current sheet

Knowing the magnetic field distribution in the magnetotail current sheet (CS) is essential for exploring magnetotail dynamics. In this study, using a joint dataset of Cluster/TC-1, the radial profile of the magnetic field in the magnetotail CS with radial distances covering 8<r<20RE under different geomagnetic activity states (i.e., AE≤100nT for quiet intervals while AE>100nT for active times) and solar wind parameters are statistically surveyed. Our new findings demonstrate that, independent of the activity state, the field strength and Bz component (GSM coordinates) start the monotonic increase prominently as r decreases down to ~11.5RE, which means the dipole field starts to make a significant contribution from there. At least in the surveyed radial range, the Bz component is found to be weaker in the midnight and dusk sectors than that in the dawn sector, displaying a dawn–dusk asymmetry. The occurrence rate of negative Bz in active times also exhibits a similar asymmetric distribution, which implies active dynamics may occur more frequently at midnight and dusk flank. In comparison with that in quiet intervals, several features can be seen in active times: (1) a local Bz minimum between 10.5<r<12.5RE is found in the dusk region, (2) the Bz component around the midnight region is generally stronger and experiences larger fluctuations, and (3) a sharp positive/negative-excursion of the By component occurs at the dawn/dusk flank regions inside r<10RE. The response to solar wind parameters revealed that the Bz component is generally stronger under higher dynamic pressure (Pdy>5nPa), which may support the dawn–dusk squeezing effect as presented by Miyashita et al. (2010). The CS By is generally correlated with the interplanetary magnetic field (IMF) By component, and the correlation quality is found to be better with higher penetration coefficient (the ratio of CS By to IMF By) when IMF Bz is positive. The implications of the present results are discussed.

Model of Quench Development Inside HTS Coils Including Quench-to-Critical Current Ratio Evaluation

It is well known that the thermal quench current densities jq in high-temperature superconducting (HTS) coils can considerably differ from the “critical” short sample current densities jc(T, B) based on a definite voltage level, for instance 1 μV/cm. The ratio jq/jc (lift-factor) can be higher or lower than one depending on coil parameters. The reasons are smooth voltage-current curves and large temperature margins compared to low-temperature superconducting devices. Several approaches for the description of the quench development in HTS devices are known. However, they are either not suitable for windings with nonuniform magnetic field distribution or were developed for a particular HTS magnet in the limited range of its working parameters. In this paper, we analyzed the simple steady state model of an infinitely long solenoid with nonuniform radial distribution of magnetic field and temperature. It allows to evaluate the main thermal and electrical parameters of HTS coils in j <; jq region as a function of the tape critical properties, n-value of the j - E curve, cooling conditions, and radial thermal conductivity in a broad range of their values.

Topology of magnetic field and polarization in accretion discs of AGN

In this paper we demonstrate that the wavelength dependence of polarization degree and position angle allows us to derive the distribution of magnetic field in accretion disc. The polarized radiation arises due to scattering of emission light by electrons in a magnetized optically thick accretion disc. Faraday rotation of polarization plane is taken into consideration. Through wavelength dependence of polarization it is possible to derive the value of the magnetic Prandtl number in the accretion disc plasma. The power law index of the polarization wavelength dependence is related with the radial distribution of magnetic field in an accretion disc. This allows us to test the various models of an accretion disc around the central black hole.

Using Kepler transit observations to measure stellar spot belt migration rates

Planetary transits provide a unique opportunity to investigate the surface distributions of star spots. Our aim is to determine if, with continuous observation (such as the data that will be provided by the Kepler mission), we can in addition measure the rate of drift of the spot belts. We begin by simulating magnetic cycles suitable for the Sun and more active stars, incorporating both flux emergence and surface transport. This provides the radial magnetic field distribution on the stellar surface as a function of time. We then model the transit of a planet whose orbital axis is misaligned with the stellar rotation axis. Such a planet could occult spots at a range of latitudes. This allows us to complete the forward modelling of the shape of the transit lightcurve. We then attempt the inverse problem of recovering spot locations from the transit alone. From this we determine if transit lightcurves can be used to measure spot belt locations as a function of time. We find that for low-activity stars such as the Sun, the 3.5 year Kepler window is insufficient to determine this drift rate. For more active stars, it may be difficult to distinguish subtle differences in the nature of flux emergence, such as the degree of overlap of the "butterfly wings". The rate and direction of drift of the spot belts can however be determined for these stars. This would provide a critical test of dynamo theory.

Magnetohydrodynamic rebound shocks of supernovae

Abstract We construct magnetohydrodynamic (MHD) similarity rebound shocks joining ‘quasi-static’ asymptotic solutions around the central degenerate core to explore an MHD model for the evolution of random magnetic field in supernova explosions. This provides a theoretical basis for further studying synchrotron diagnostics, MHD shock acceleration of cosmic rays, and the nature of intense magnetic field in compact objects. The magnetic field strength in space approaches a limiting ratio, which is comparable to the ratio of the ejecta mass driven out and the progenitor mass, during this self-similar rebound MHD shock evolution. The intense magnetic field of the remnant compact star as compared with that of the progenitor star is mainly attributed to both the gravitational core collapse and the radial distribution of magnetic field.

Effects of channel wall material on thrust performance and plasma characteristics of Hall-effect thrusters

The effects of channel wall material on Hall thruster performance and on plasma characteristics were investigated. A laboratory-model Hall thruster THT-III was operated with three channel wall materials of BN, BNSiN and BNAlN. Both the discharge current and the thrust were affected by the nature of the channel wall materials. The measured axial distributions of wall and plasma potentials, radial and axial electron temperatures, and electron number density near the channel walls showed that the wall material affected ionization region and ion wall loss in the channel, resulting from secondary electron emission, although ion acceleration region was determined by the axial distribution of radial magnetic field. The difference in discharge current between channel wall materials was attributed to the difference in axial current density near the inner channel wall, depending on secondary electron emission.

Study of the extracted beam and the radial magnetic field of electron cyclotron resonance ion source at HIMAC

Experimental results on an 18 GHz electron cyclotron resonance (ECR) ion source (NIRS-HEC) and a 10 GHz ECR ion source (NIRS-ECR) at National Institute of Radiological Sciences (NIRS) show that an extracted beam intensity strongly depends on the radial magnetic field distribution generated by a permanent sextupole magnet. In order to understand these results, we simulated beam extraction under strong influences of space charge. In the simulation, a current intensity at a different position of an extraction slit is assumed to be roughly proportional to a corresponding transverse area of the ECR zone under the assumption that ions are extracted along a longitudinal magnetic flux line. The calculations show that an optimum value of the sextupole magnetic field strength may exist for a given extraction configuration and beam intensity. Based on the simulation, beam intensity measurements have been performed with six sextupole magnets having different magnetic field strengths for two ion sources, and the experimental results are consistent with the calculations.

Simulation of a coronal streamer: Alfvén wave acceleration

A self-consistent simulation of the plasma flow in a dipole-like magnetic field configuration is performed. The features of the present formulation are: incorporation of the heat and momentum addition due to WKB Alfvén waves propagating outward from the Sun and providing additional acceleration to the coronal plasma flow; extension of the computational domain out to 1 AU. The governing dissipationless single-fluid MHD equations are solved in the equatorial plane of the spherical coordinate system. In agreement with Ulysses observations, the results of simulation demonstrate (i) absence of a marked gradient in the radial magnetic field distribution across the polar high-velocity stream, (ii) the velocity does not change considerably in this stream, but slightly increases toward its center, (iii) the momentum flux density is higher over the pole than near the equator, while the mass flux density shows a slight increase toward the equator.

Control of Spontaneous Processes in High Beta Plasma with Antiparallel Magnetic Structure

By programming formation of compact toroidal configuration, it was possible to control the losses and spontaneous plasma dynamics during transitional processes. Previously formation modes were studied mainly by the macroscopic parameters. Here trapped flux, magnetic and thermal energy, radial distribution of magnetic field and the other internal parameters have been measured by the combination of internal and external diagnostics. 8 refs., 3 figs.

Magnetic circuit analysis of magnetizing fixture for a ring magnet in two-axis optical gyroscope

A method is investigated to design the magnetizing fixture of a ring magnet used in a two-axis optical gyroscope by using magnetic analysis. The magnetic field distribution of the ring magnet can be controlled by the magnetic circuit of the magnetizing fixture. The radial magnetic field distribution of the ring magnet with smooth sine wave is suitable for the application of a two-axis optical gyroscope. The peak value of magnetic field strength for an Alnico six ring magnet is in the range of 1200 to 1300 G.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Microwave emission from a sunspot

From the gyroresonance brightness temperature spectrum of a sunspot, one can determine the magnetic field strength by using the property that microwave brightness is limited above a frequency given by an integer-multiple of the gyrofrequency. In this paper, we use this idea to find the radial distribution of magnetic field at the coronal base of a sunspot in the active region, NOAA 4741. The gyroresonance brightness temperature spectra of this sunspot are obtained from multi-frequency interferometric observations made at the Owens Valley Radio Observatory at 24 frequencies in the range of 4.0–12.4 GHz with spatial resolution 2.2″–6.8″. The main results of present study are summarized as follows: first, by comparison of the coronal magnetic flux deduced from our microwave observation with the photospheric magnetic flux measured by KPNO magnetograms, we show that theo-mode emission must arise predominantly from the second harmonic of the gyrofrequency, while thex-mode arises from the third harmonic. Second, the radial distribution of magnetic fieldsB(r) at the coronal base of this spot (say, 2000–4000 km above the photosphere) can be adequately fitted by $$B(r) = 1420(1 \pm 0.080)\exp \left[ { - \left( {\frac{r}{{11.05''(1 \pm 0.014)}}} \right)^2 } \right]G,$$ wherer is the radial distance from the spot center at coronal base. Third, it is found that coronal magnetic fields originate mostly from the photospheric umbral region. Fourth, although the derived vertical variation of magnetic fields can be approximated roughly by a dipole model with dipole moment 1.6 × 1030 erg G−1 buried at 11000 km below the photosphere, the radial field distribution at coronal heights is found to be more confined than predicted by the dipole model.

Experimental investigation of a toroidal diffuse pinch

In a toroidal screw-pinch device a radial magnetic field distribution was established which theoretically should be MHD-stable. The experiment showed however after 3 μsec a very fast growing instability which might be of the resistive type.