Longitudinal Component Of Magnetic Field Research Articles

Measurement of the longitudinal magnetic-field component for FU Ori

The Main Stellar Spectrograph of the 6-m Special Astrophysical Observatory telescope equipped with a polarimetric analyzer was used to measure the longitudinal magnetic-field component of FU Ori on January 24, 2002. The following (3σ) upper limits were obtained for the magnetic field B ‖: B ‖<350–400 G in the formation region of Fe I, Ni I, and Ca I absorption lines (disk + wind), and B ‖<200 G in the formation region of the absorption component of the Hα line with a P Cyg profile. We conclude that the strength of a large-scale magnetic field capable of collimating the disk wind does not exceed 300 G. For the region where the emission component of the Hα line is formed, we found that B ‖<100 G. Such a low value may have been obtained because the magnetic field lines in this region were almost perpendicular to the line of sight at the time of our observations.

Cyclotron resonance in the InAs/GaSb heterostructure in an inclined magnetic field

The mechanism of cyclotron resonance line splitting in the InAs/GaSb heterostructure in an inclined magnetic field has been studied experimentally and theoretically. It is shown that the admixing of electron and hole states leads to anticrossing of the Landau levels and, hence, to splitting of the cyclotron resonance line. In the case of an inclined magnetic field, the splitting is not observed, which is explained by the suppression of the admixing of electron and hole states due to the occurrence of an additional barrier for electrons and holes given a longitudinal magnetic field component.

Study of Current Sheets in Three-Dimensional Magnetic Fields with an X-Line by Holographic Interferometry

Results are presented from experimental studies of the spatial electron density distribution in current sheets formed in three-dimensional magnetic configurations with X-lines. The electron density is measured by using two-exposure holographic interferometry. It is shown that plasma sheets can form in a magnetic configuration with an X-line in the presence of a sufficiently strong longitudinal magnetic-field component B∥ when the electric current is excited along the X-line. As the longitudinal magnetic-field component increases, the electron density decreases and the plasma sheet thickness increases; i.e., the plasma is compressed into a sheet less efficiently.

Search for the general magnetic fields in late-type giants

Surface-averaged longitudinal magnetic-field components (by analogy with the Sun called the general magnetic field) have been measured for 15 late-type giants with an accuracy of several Gauss. Statistically significant fields were detected for nine of these stars. The magnetic-field values obtained suggest the existence of general magnetic fields in these giants.

Experimental study of current sheet evolution in magnetic configurations with null-points and X-lines

A review is presented on experimental research of current sheet formation in 3D magnetic configurations containing null-points and/or singular lines of the X-type. Formation of current sheets is revealed to occur in various 3D configurations, both with and without isolated magnetic null-points, specifically in configurations with X-lines. Local characteristics of 3D magnetic configuration define the parameters of the current sheet, which forms usually a twisted surface with an angular orientation determined by a local value of the transverse magnetic field gradient. A degree of plasma compression into the sheet decreases with a rise of longitudinal magnetic field component, displaying a transition to a behavior of uncompressible plasma. It is established that current sheet formation and magnetic reconnection processes can take place within a limited range of initial conditions, while a gradient of transverse magnetic field is the most important parameter.

Current sheets in magnetic configurations with singular X-lines

The possibility of the formation of current sheets in 3D magnetic configurations with singular X-lines was studied experimentally. It is shown that a sheet can be formed in the presence of the longitudinal magnetic-field component directed along the X-line, in which case the longitudinal component can exceed the transverse component everywhere inside the plasma. Characteristic of the CS formation in 3D magnetic configurations with X-lines are an increase in the longitudinal magnetic-field component inside the sheet and a decrease in the plasma compression ratio as compared to 2D configurations with null-lines. If the longitudinal component exceeds a certain critical value, a sheet cannot be formed: instead of a sheet, there appear two sheaths separated by a cavity with a local minimum in the electron density.

AC loss of multifilamentary superconducting AC wire caused by longitudinal and azimuthal AC magnetic field components

AC loss characteristics of multifilamentary NbTi AC wires under AC external magnetic field were experimentally and theoretically investigated. The authors measured AC transport current losses of AC wires with various twist pitches under the AC external magnetic field which included longitudinal and transverse components. It was shown by the measurement that the AC transport current losses decreased with decreasing the twist pitches when the external and self longitudinal fields were in the same direction. The measured dependence of the AC losses on the twist pitches and the applied longitudinal field component were well explained by their previously derived model. They also theoretically estimated the AC losses caused by the longitudinal and azimuthal field components. It was found that the AC losses can be substantially reduced by properly selecting the twist pitch and the external longitudinal field component.

The nature of the B(3) field

The nature of the B (3) field is determined through deductions from its mathematical definition; B (3) is a vector function of the magnetic field of electromagnetic radiation. The sign and magnitude of B (3) measure the polarization of the radiation, and it is re-normalized to define the Polarization Index (a dimensionless number of magnitude unity), which proves to be identical with one of Stokes's parameters. This is revealed to be the essential nature of the B (3) field. The definition of B (3) (and of the Polarization Index) is generalized in terms of all components of the electromagnetic field rather than only the transverse magnetic components. The analysis leads to internal inconsistencies if the B (3) field is presumed to be the longitudinal component of the physical magnetic field of electromagnetic radiation as asserted by M.W. Evans (the originator of the theory of the B (3) field). This inference explains the failure of experimental investigations to detect the hypothetical longitudinal magnetic field of radiation. It also corroborates a disproof by counter-example by E. Comay.

AC loss of low temperature superconducting AC wire caused by longitudinal and azimuthal AC magnetic field components

We investigated the AC loss characteristics of a low temperature NbTi AC wire by measuring the AC transport current losses in the external AC magnetic field whose components are the longitudinal and transverse ones. The measurement results showed that the AC losses were significantly dependent on the directions and magnitudes of the external longitudinal field component. The AC losses caused by the longitudinal and azimuthal field components were estimated by our previously derived model. The theoretical results well explained the dependence of the AC losses on the longitudinal field components. It was also shown that the AC losses can be substantially reduced by the proper choice of the twisting way.

AC losses characteristics of AC superconducting wire in combined action of AC magnetic field and AC transport current

External magnetic field is usually applied to the superconducting wire which is used for superconducting machines. Phases of the external field and self field are generally not the same. This difference of the phases is known to have an important role in the generation of the AC loss. The AC loss is influenced mainly by longitudinal magnetic field component which is generated by the twisted-structure of the filament and strand. This paper describes the AC loss of an AC superconducting wire under the combined action of an AC transport current and AC magnetic field for various phase differences. Experimental results are compared with calculated results.

交流用超電導極細多芯線の縦磁界成分及び周方向磁界成分による交流損失

交流用超電導極細多芯線の縦磁界成分及び周方向磁界成分による交流損失

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Magnetohydrodynamic Waves in Solar Coronal Arcades

view Abstract Citations (26) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Magnetohydrodynamic Waves in Solar Coronal Arcades Oliver, R. ; Hood, A. W. ; Priest, E. R. Abstract The propagation of magnetohydrodynamic (MRD) disturbances in a solar coronal arcade is investigated. The equations of magnetoacoustic fast and slow waves are presented in a very general form: a pair of second-order, two-dimensional partial differential equations in which the two dependent variables are the components of the velocity perturbation parallel and normal to the magnetic field. In deriving these equations, a general two-dimensional equilibrium structure with no longitudinal magnetic field component has been assumed. Thus, the equations are valid for rather general configurations. Alfvén waves are decoupled from the magnetoacoustic modes and give rise to an Alfvén continuous spectrum. The solutions to the wave equations have been obtained numerically, and the perturbed restoring forces (plasma pressure gradient, magnetic pressure gradient, and magnetic tension), responsible for the oscillatory modes, have also been computed. These forces give rise to the propagation of MRD waves, and their interaction determines the physical properties of the various modes. Therefore, the spatial structure of the forces and their interplay are basic in characterizing fast and slow modes. Pure fast and pure slow waves do not exist in the present configuration, although for the considered parameter values, all modes possess either fast-mode or slow-mode properties. "Slow" modes in these two-dimensional equilibria can propagate across the magnetic field only with difficulty and so display a structure of bands, centred about certain field lines, of alternate positive and negative parallel velocity component. On the other hand, "fast" modes are isotropic in nature, and their spatial structure is not so intimately linked to the shape of field lines. In addition, as a consequence of the distinct characteristic propagation speeds of fast and slow modes, their frequencies typically differ by an order of magnitude. Publication: The Astrophysical Journal Pub Date: April 1996 DOI: 10.1086/177071 Bibcode: 1996ApJ...461..424O Keywords: MAGNETOHYDRODYNAMICS: MHD; SUN: CORONA; WAVES full text sources ADS |

AC losses in multifilamentary superconductors carrying transport current and exposed to external magnetic field-analysis of temporal evolution of current distribution

The temporal evolutions of current in multifilamentary superconductors were calculated numerically, while they were carrying the transport current and exposed to the spatially-distributed external magnetic field. Multifilamentary superconductors were represented with an electrical circuit model assuming the axisymmetric current distribution. The current distribution is substantially influenced by the axial distribution of the longitudinal magnetic field. AC losses were calculated from the temporal evolutions of the current distribution. Influence of the transport current and the longitudinal component of the external magnetic field distributed spatially on the losses was studied. The additional losses due to the transport current and the longitudinal magnetic field are not negligible as compared to the losses due to the transverse magnetic field.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

RoAp stars

Among the A stars there is a subclass of peculiar stars, the Ap stars, which show strongly enhanced spectral lines of the Fe peak, rare earth and lanthanide elements. These stars have global surface magnetic fields several orders of magnitude larger than that of the Sun, 0.3 to 30 kGauss is the measured range. For stars with the strongest magnetic fields, the spectral lines are split by the Zeeman Effect and the surface magnetic field strength can be measured. Generally, though, the magnetic fields are not strong enough for the magnetic splitting to exceed other sources of line broadening. In these cases residual polarization differences between the red and blue wings of the spectral lines give a measure of the effective magnetic field strength - the integral of the longitudinal component of the global magnetic field over the visible hemisphere, weighted by limb-darkening. In the Ap stars the effective magnetic field strengths vary with rotation. This is well understood in terms of the oblique rotator model in which the magnetic axis is oblique to the rotation axis, so that the magnetic field is seen from varying aspect with rotation.

THE EXPERIMENTALLY OBSERVED OPTICAL COTTON–MOUTON EFFECT: EVIDENCE FOR THE PHOTON'S LONGITUDINAL MAGNETIC FIELD, B(3)

The recent experimental observation of the optical Cotton–Mouton effect is consistent with the induction of magnetization by the longitudinal component of the photon's magnetic field, whose classical counterpart is the equivalent flux density B(3). In the optical Cotton–Mouton effect observed by Zon et al.,16 the field B(3) acts at second order and is independent of the polarization of the inducing laser beam propagating parallel to a permanent magnetic field. The optical Cotton–Mouton effect is therefore proportional to the laser intensity as observed.16

Results of magnetographic line‐ratio measurements

AbstractWe adapt the line‐ratio method to magnetographic measurements. The method yields information on inhomogeneous magneitc fields without resolving their fine structure. Supplementing the magnetic field measurements, each day several polarization calibrations were made to eliminate the influence of the instrument. Modified theoretical calibration curves served for the transformation into inclination angles and magnetic field strength. The circular polarization along some scans across two sunspots practically shows the same distributions in both wings. The linear polarization in these selected scans attained only about half as large values as the circular polarization. The maxima were found in the steep parts of the V distributions. Comparing the two lines a similar behaviour was found, but also differences of about 0.5 percent, which may be significant.The inclination angles determined by means of calibration curves also seem to be more accurate than those calculated from transverse and longitudinal magnetic field components. As an evidence the results in sunspots and faculae are quoted. The values separately determined for the lines scattered only by 3 respectively 7 degrees from the mean values. In the darkest points of an umbra practically accordance of inclination and heliocentric angle was obtained, i.e., the magnetic vector was directed perpendicular to the surface. From the amount of the circular polarization in faculae comparing it with results of model calculations the filling factors were determined. Our results arranged between 3 and 11 percent nearly agree with the values by SOLANKI and STENFLO (1984).The line‐ratio method in the version adapted to our magnetograph yielded from the V ratios in sunspots an average of 1880 G, but from the Q0 ratios an average of 2240 G. In faculae both values are practically identical and run to 1980 G. These results show that the line‐ratio method is superior to the old reduction procedure of magnetographic measurements.

Solar coronal and magnetic field observations near the time of the 1988 March 18 solar eclipse

Observations made during the interval March 1-31, 1988, are presented which were designed to provide a synoptic context in which data from the March 18, 1988, total solar eclipse can be interpreted. Daily observations made with the Mark III K-coronameter and the H-alpha prominence monitor at the Mauna Loa Solar Observatory, along with photographic records of the Sun in H-alpha from the flare patrol at Mees Solar Observatory on Haleakala, Maui, are included. Observations of the longitudinal component of the photospheric magnetic field made at Mees Solar Observatory were also gathered around the period of the eclipse. Together with the white-light image of the corona at the eclipse, these coronal and magnetic field observations assembled into synoptic maps for this epoch, are presented. On the basis of these observations, an interpretation of the global density distribution of the corona at the time of the eclipse is constructed.

Delta-configurations: Flare activity and magnetic-field structure

Complex sunspots in four active regions of April and May 1980, all exhibiting regions of magnetic classification delta, were studied using data from the NASA Marshall Space Flight Center vector magnetograph. The vector magnetic field structure in the vicinity of each delta was determined, and the location of the deltas in each active region was correlated with the locations and types of flare activity for the regions. Two types of delta-configuration were found to exist, active and inactive, as defined by the relationships between magnetic field structure and activity. The active delta exhibited high flare activity, strong horizontal gradients of the longitudinal (line-of-sight) magnetic field component, a strong transverse (perpendicular to line-of-sight) component, and a highly non-potential orientation of the photospheric magnetic field, all indications of a highly sheared magnetic field. The inactive delta, on the other hand, exhibited little or no flare production, weaker horizontal gradients of the longitudinal component, weaker transverse components, and a nearly potential, non-sheared orientation of the magnetic field. We conclude that the presence of such sheared fields is the primary signature by which the active delta may be distinguished, and that it is this shear which produces the flare activity of the active delta.

Magnetic reconnection in a high-temperature plasma of solar flares

Simple self-consistent models for ‘non-neutral’ current sheets are considered. Characteristics of high-temperature turbulent current sheets (HTCS) with a small transverse component of magnetic field are determined for conditions in the solar corona. The energy output of such an HTCS is much larger than that of a neutral sheet. This makes it possible to consider the HTCS as an energy source not only in long-lived X-ray loops but also in flaring loops during the ‘not’ or ‘main’ phase of a flare. In this case, the magnetic reconnection velocity agrees with the observed velocity of the loop rise. Thus, these phenomena can be interpreted as a result of magnetic reconnection, for example, between new flux emerging from under the photosphere and an ‘old’ magnetic field. The role of a longitudinal magnetic field in a current sheet is less important for HTCS. As a result of the compression of a longitudinal field, there appears an electric current circulating around the sheet. This current may induce strong Joule heating, if the compression is large. This ‘additional’ heating is realized because of the annihilation of the main component, not the longitudinal component of magnetic field. The effect is small for HTCS, but may be significant for preflare current sheets.