Showing papers on "Magnetic flux published in 1977"

An emerging flux model for the solar flare phenomenon

Abstract: An outline is presented of the physical processes involved in the emerging flux model, which appears to explain naturally many solar flare observations. The separate physical phases of the basic model include a preflare heating phase as the new flux emerges, an impulsive phase as high-energy particles are accelerated, a flash (or explosive) phase when the H-alpha intensity increases, and a main phase while it decreases. The extent and morphology of the main phase emission depend on the structure of the magnetic field region in which the new flux finds itself imbedded. It is suggested that a (small) simple loop flare occurs if the new flux appears in a region where no great amount of magnetic energy in excess of potential is stored. A two-ribbon flare occurs if the flux emerges near the polarity inversion line of an active region that has begun to develop filaments.

Superconducting system with weak coupling to the current in the ground state

Abstract: We consider a superconducting ring with a Josephson junction containing magnetic impurities. It is shown that if the tunneling through the magnetic impurities is large enough, then the ground state of such a system is a state with a current and a magnetic flux.

Magnetic field-line reconnexion by localized enhancement of resistivity: Part 1. Evolution in a compressible MHD fluid

Abstract: The temporal dynamics of field-line reconnexion is studied by numerical experiment in a compressible conducting fluid. It is shown that because of localized enhancement of resistivity the reconnexion takes place in an initially antiparallel magnetic field and that an X-type field configuration develops, occupying an extended region. There is also a remarkable release of magnetic energy into kinetic and thermal energies. The global flow pattern can spontaneously be set up through the field-line reconnexion under no specially imposed boundary conditions.

Magnetic field experiment for Voyagers 1 and 2

Abstract: The magnetic field experiment to be carried on the Voyager 1 and 2 missions consists of dual low field (LFM) and high field magnetometer (HFM) systems. The dual systems provide greater reliability and, in the case of the LFM's, permit the separation of spacecraft magnetic fields from the ambient fields. Additional reliability is achieved through electronics redundancy. The wide dynamic ranges of ± 0.5 G for the LFM's and ± 20 G for the HFM's, low quantization uncertainty of ± 0.002 γ (γ = 10−5 G) in the most sensitive (± 8 γ) LFM range, low sensor RMS noise level of 0.006 γ, and use of data compaction schemes to optimize the experiment information rate all combine to permit the study of a broad spectrum of phenomena during the mission. Objectives include the study of planetary fields at Jupiter, Saturn, and possibly Uranus; satellites of these planets; solar wind and satellite interactions with the planetary fields; and the large-scale structure and microscale characteristics of the interplanetary magnetic, field. The interstellar field may also be measured.

Theory of ballooning modes in tokamaks with finite shear

Abstract: We studied ballooning instabilities in tokamaks of arbitrary cross sections and finite shear. These azimuthally localized, ideal magnetohydrodynamic modes have large toroidal-mode numbers, but finite variation along the field and across the flux surfaces. Stability is determined by solving a second-order ordinary differential equation on each flux surface, subject to the proper boundary conditions. Qualitative agreement is achieved with the Princeton PEST stability code.

The stability of sunspots

Abstract: Context. The stability of sunspots is one of the long-standing unsolved puzzles in the field of solar magnetism and the solar cycle. The thermal and magnetic structure of the sunspot beneath the solar surface is not accessible through observations, thus processes in these regions that contribute to the decay of sunspots can only be studied through theoretical and numerical studies. Aims. We study the effects that destabilise and stabilise the flux tube of a simulated sunspot in the upper convection zone. The depth-varying effects of fluting instability, buoyancy forces, and timescales on the flux tube are analysed. Methods. We analysed a numerical simulation of a sunspot calculated with the MURaM code. The simulation domain has a lateral extension of more than 98 Mm× 98 Mm and extends almost 18 Mm below the solar surface. The analysed data set of 30 hours shows a stable sunspot at the solar surface. We studied the evolution of the flux tube at defined horizontal layers (1) by means of the relative change in perimeter and area, that is, its compactness; and (2) with a linear stability analysis. Results. The simulation shows a corrugation along the perimeter of the flux tube (sunspot) that proceeds fastest at a depth of about 8 Mm below the solar surface. Towards the surface and towards deeper layers, the decrease in compactness is damped. From the stability analysis, we find that above a depth of 2 Mm, the sunspot is stabilised by buoyancy forces. The spot is least stable at a depth of about 3 Mm because of the fluting instability. In deeper layers, the flux tube is marginally unstable. The stability of the sunspot at the surface affects the behaviour of the field lines in deeper layers by magnetic tension. Therefore the fluting instability is damped at depths of about 3 Mm, and the decrease in compactness is strongest at a depth of about 8 Mm. The more vertical orientation of the magnetic field and the longer convective timescale lead to slower evolution of the corrugation process in layers deeper than 10 Mm. Conclusions. The formation of large intrusions of field-free plasma below the surface destabilises the flux tube of the sunspot. This process is not visible at the surface, where the sunspot is stabilised by buoyancy forces. The onset of sunspot decay occurs in deeper layers, while the sunspot still appears stable in the photosphere. The intrusions eventually lead to the disruption and decay of the sunspot.

Spiral-vortex expansion instability in type-II superconductors

Abstract: It is shown that a flux vortex, in the presence of a sufficiently large current density applied parallel to its axis, is unstable against the growth of helical perturbations. This instability, which has an analog in magnetohydrodynamics, may play a critical role in current-carrying type-II superconductors subjected to longitudinal magnetic fields.

Electromechanical force motor

Abstract: An electromechanical force motor including an elongate magnetic casing which coaxially enhouses a magnetic armature. An annular electromagnetic coil surrounds the armature and is axially positioned between a pair of permanent magnets having axially directed poles. A magnetic pole is positioned at each end of the armature in a posture juxtaposed to but spaced from the ends of the armature to provide a magnetic flux gap between the armature and poles. A pushrod is connected to one end of the armature and projects outwardly from the casing to produce work upon excitation of the electromagnetic coil.

Order parameter and magnetic field of the distorted vortex lattice and their application to flux pinning in type II superconductors. I. Parallel flux lines

Abstract: A program for the rigorous calculation of the volume pinning force exerted by-imperfections on the flux line lattice in type II superconductors is outlined. As one step of this program, the order parameter, local magnetic field, supervelocity, and elastic energy of the distorted lattice of still parallel flux lines are calculated from the Ginzburg-Landau theory. These general solutions provide a transformation of the Ginzburg-Landau free energy functional of an imperfect material into a mere function of the flux line positions, and thus allow a definition of elastic and pinning force densities which for the first time apply also to large inductions. First, exact solutions for small strains and for fields close toH c2 are derived. Then, approximate solutions are presented applying to larger strains and to arbitrary inductions. The forces on each flux line exerted by a small needle-shaped inclusion parallel to the flux lines are calculated.

Reverse polarity field‐aligned currents at high latitudes

Abstract: The magnetometer on the Isis 2 satellite is used to study a number of magnetic field perturbations which are interpreted as being due to field-aligned currents whose directions are opposite to the direction usually observed. The perturbations are observed mainly on the dawn side of the earth and can be interpreted as a result of two adjacent and oppositely directed current sheets in which the equatorward current is into the atmosphere and the poleward current out of the atmosphere. These perturbations are observed only at times when the interplanetary magnetic field (IMF) has a strong northerly component, and they are found at latitudes above those usually associated with field-aligned currents. The locations of the magnetic field perturbations are compared with simultaneous particle measurements, and the results are discussed in relation to what might be expected from field line merging models.

Ground fault circuit interrupter

Abstract: A device for sensing current flow in an electric conductor employs a ferromagnetic core coupled to the conductor and a control winding on the core for applying a periodic magnetic flux to a part of the core of a magnitude to vary the core permeability, preferably driving a part of the core in and out of saturation. The periodic flux interrupts any flux circulating in the core due to current flow in the conductor. An output winding on the core has a signal voltage induced therein whose amplitude is determined by the rate of change of the interrupted circulating flux. The device effectively amplifies a small current input signal to a relatively high output level. A bias winding may be wound on the core to compensate for stray magnetic fields in the vicinity of the device.

Heating of dense interstellar clouds by magnetic ion slip: a constraint on cloud field strengths.

Abstract: Observations suggest that fragmentation into stars occurs at densities comparable to those of massive interstellar clouds. However, fragmentation cannot occur if the magnetic field strength and density are related by B=B/sub 0/n/sup y/ with y=2/3, as for isotropic contraction with a frozen-in field. A semiempirical upper limit to the parameter y is derived by considering the thermal equilibrium of a cloud heated by magnetic ion slip (ambipolar diffusion) and requiring that the theoretical temperatures do not greatly exceed observed temperatures. Cooling by rotational transitions of CO, H/sub 2/, and HD and by inelastic gas-grain collisions is included in the equilibrium calculations. It is found that a value of y as large as 2/3 would result in gas temperatures in excess of 100 K at densities greater than 10/sup 4/ cm/sup -3/ and can therefore be excluded by the observations. A value of yapproximately-less-than0.55 is required if the scale of the magnetic field gradient is of the same order as the cloud radius. The calculated value of this upper limit is sensitive to the choice of B/sub 0/. The value of y can be decreased by preferential flow of gas along field lines or by magnetic ion slip. The time scalemore » for magnetic ion slip is reexamined.« less

Vehicular magnetic coded signalling apparatus

Abstract: Coded binary signals are coupled to an automotive vehicle by a magnetic signpost embedded in a traversed roadway lane. The signpost includes polarity coded magnetic pole faces having vertically directed flux lines at differing spaced longitudinal regions along the lane. Pole faces are arranged so a flux null is between adjacent longitudinal regions. Differing signals are coupled to vehicles going in opposite directions in adjacent lanes by unambiguously coding the signpost in opposite directions and arranging the pole faces so that magnetic flux continuously extends across a majority of both lanes. A detector on a vehicle includes a magnetic field concentrator including a pair of vertically extending and aligned low reluctance magnetic pole pieces having an air gap between them, in which a Hall plate is positioned. The pole piece closest to the road has shorter length than the pole piece remote from the roadway. A waveform derived by the detector includes a base line subject to drift due to ambient conditions and a pulse as the transducer crosses each region. To eliminate base line drift, a circuit with a negative feedback loop derives an analog offset signal indicative of base line drift. Fail safe circuitry prevents spurious magnetic flux variations from being recognized as a signpost by assuring that a predetermined number of bits occurs in each signpost, and that the distance between the leading and trailing edges of the same pulse and the distance between adjacent pulses are in accordance with certain distances. Valid signals are derived if a vehicle stops or backs up while over a signpost.

Evolution of open magnetic structures on the sun - The Skylab period

Abstract: High-resolution harmonic analysis of the measured photospheric magnetic field of the sun is used to construct models of open magnetic structures over a period of 11 solar rotations. The models successfully reproduce the surface location and topology of all coronal holes during the Skylab period. In addition, there is persistent evidence in the models that open field lines are associated with active regions in a systematic way. These associations are listed for the period studied; they suggest that open field lines are a basic feature of solar magnetism. Specific examples of the evolution of coronal holes and of calculated open structures are presented. Quantitative study of the measured field strength within and neighboring a hole confirms the fact that coronal hole regions are indistinguishable by local magnetic properties. However, the calculated field strengths at the footpoints of open field lines within coronal holes show distinct evolutionary patterns and may indicate that, at least in young coronal holes, a significant amount of magnetic flux is closed. Problems of studying magnetic field divergence by using these models are discussed.

Measurements of magnetic fluxes and field strengths in the photospheric network

Abstract: We present digital pictures of an active region network cell in five quantities, measured simultaneously: continuum intensity, line-center intensity, equivalent width, magnetogram signal, and magnetic field strength. These maps are derived from computer analysis of circularly polarized line profiles of FeI λ 5250.2; spectral and spatial resolution are 1/40 A and 1.5″, respectively. Measured Zeeman splittings show the existence of strong magnetic fields (1000–1800 G) at nearly all points with a magnetogram signal exceeding 125 G. The mean and rms deviation of the field strengths change by less than 20% over a factor-of-four range of fluxes. From the significant disparity between measured fluxes and field strengths, we conclude that large flux patches (up to 4″ across) consist of closely-packed unresolved filaments. The smallest filaments must be less than 0.7″ in diameter. We also observe the dark component of the photospheric network, which appears to contain sizable transverse fields.

Solar cycle variation of magnetic flux emergence.

Abstract: The number of X-ray bright points (XBP) has been measured from solar X-ray images obtained during two rocket flights in 1976. When compared with the data obtained during the Skylab mission (1973), the number is found to be higher by a factor of 2. As the probability of obtaining the result by chance is less than 1 in 5 million, it is concluded that the number of XBP has increased in the three year interval. As all other indicators of activity have decreased between 1973 and 1976, the cyclical variation of the short-lifetime end of the magnetic-flux-emergence spectrum is out of phase with the solar cycle as defined by active regions or sunspots. Since XBP in 1973 contributed more to the emerging magnetic flux than did active regions, the possibility exists that the total amount of emerging magnetic flux may be maximized at a sunspot minimum.

Pipe current detector with plural magnetic flux detectors

Abstract: Apparatus for measurement, above the surface of the ground, of an electrical current flowing in a buried pipeline, comprises a pair of magnetic flux detectors oriented with their axes vertical, and spaced apart, in a frame, which is moved along the earth at a substantially constant elevation above the surface, with the plane through the two vertical detectors substantially perpendicular to the direction of the pipe. Means are provided, including a vertical core and coil centered on the frame, for indicating the position of the frame laterally with respect to the buried pipe. There is also a second core and coil displaced laterally from the first core and coil, for determining the depth of the pipe below the frame. When the frame is centered over the pipe and there is current in the pipe, flux will pass upwardly through a first flux detector core and downwardly through the second flux detector core. One or a plurality of coils and suitable measuring instruments can determine the magnitude of the flux through the core and therefore, the magnitude and direction of the current flowing in the pipe.

Large-Scale Solar Magnetic Fields

Abstract: Measurement of solar magnetic fields is reviewed. Topics covered include: large-scale magnetic surface features; the solar activity cycle and the large-scale patterns; and magnetic fields in the corona. (GHT)

Method and apparatus for detection of magnetization

Abstract: A method of, and apparatus for, the detection of magnetization of a magnetic circuit, especially for the detection of a current flow interlinked with the magnetic circuit, wherein a timed or temporal cyclic magnetic flux change is generated by means of a detection-current flow used for detection purposes and interlinked with the magnetic circuit and a detection signal is formed as a function of time intervals dependent upon the magnetization.

Apparatus for damping rotation of turntable

Abstract: A disc record player in which a turntable is driven by a motor comprising a rotor magnet having plural magnetic poles arranged separately along the periphery of the turntable, stator coils disposed in the magnetic field of the rotor magnet and Hall-effect elements sequentially coupled magnetically to the poles of the rotor magnet for generating output signals having polarities corresponding to the polarities of the poles of the rotor magnet, and causing the rotor magnet to rotate by supplying the output signals of the Hall-effect elements to the stator coils, wherein a first and a second speed detecting coils for generating signals having phases different from each other are disposed in the magnetic field of the rotor magnet, wherein the output signals of the first and second speed detecting coils respectively turn the gate circuit off and on and when the turntable is to be stopped, the gate circuit is turned on by the output signal of the second speed detecting coil, and wherein the rotation of the turntable is damped by controlling the polarities of the output signals of the Hall-effect elements with the output signal of the gate circuit and thereby causing the stator coils to generate the magnetic flux to rotate the rotor magnet in the reverse direction.

The quenching of NO2 fluorescence by a magnetic field

Abstract: It has been observed that the fluorescence from NO2 excited in the visible region is partially quenched by an applied magnetic field. The pressure dependence of the fluorescence intensity versus magnetic field strength curve indicates that the magnetic quenching is due to an increase in the collisional quenching cross section caused by the magnetic field. The magnetic quenching is observed to be a strong and erratic function of the exciting wavelength and this is shown to be consistent with the admixture of a nonradiating state where the amount of admixture is everywhere dominated by local perturbations. Magnetically induced changes in the absorption coefficient are also observed, and these are attributed to the tuning of energy level differences into and out of resonance with the exciting light by the magnetic field.

Flux flow noise power spectra in the presence of local pinning interactions

Abstract: We derive expressions for the dc flux flow voltage and for the flux flow noise power spectrum in type II superconductors using a model in which flux bundles travel a distance1 less than the sample widthL before being stopped for finite times by local pinning interactions. The frequency dependence of the power spectrum is shown to be identical to our earlier derivation, where we assumed that pinning and release of flux bundles occurred in zero times, an assumption we now show to be incorrect. This frequency dependence has been shown to lead to good agreement for experimentally measured transit times, which have repeatedly been shown to be too short when obtained from models of uninter-rupted flux transit across the sample width. The concept of a pinned fraction arises naturally in our model, and occurs because of two factors; first, in certain regions the Lorentz force is not sufficient to overcome pinning, and second, in regions where flux flow occurs, fluxoids will be held up for brief periods because of interaction with local pinning centers. The expressions for the noise power at zero frequency and the dc voltage are modified by factors that depend on averages of1.

Magnetic thermal vibrational device for the treatment of arthritis and the like

Abstract: A device for simultaneously applying electromagnetic alternating directional energy, thermal, and vibrational energy to various areas of the body which has been found to reduce or even eliminate the pains and symptoms caused from arthritis, bursitis and other bone joint maladies. The device includes a housing, an electromagnet disposed in said housing, an elastic band having a pair of permanent magnets coupled magnetically on each side of the band to each other with the elastic band being suspended at each end to the housing and positioned within the alternating magnetic field of the electromagnet. The electromagnet has a shaped steel core which acts to concentrate the magnetic flux lines through the suspended permanent magnets and is driven by low frequency alternating current causing the suspended magnets to vibrate. The electromagnet core is contructed in such a way to contribute heat for thermal application to the body simultaneously in conjunction with the concentrated magnetic field and vibration. The resulting simultaneous effects of the low frequency alternating (in direction) magnetic field, the vibrating elastic band and thermal concentration of energy is found to be extremely effective for the reduction or elimination of pain and other body disorders caused by arthritis, bursitis and other related bone joint diseases.

Multi-phase motor

Abstract: A polyphase motor is disclosed in which each coil of the stator winding of, for example, a squirrel cage induction motor is connected in series with a capacitor so that the capacitor, together with the input voltage, causes the stator core to periodically switch from a nonsaturated to a saturated condition and vice-versa so that the flux density is maintained at a uniformly high level. A control winding is provided to generate magnetic flux in the stator to vary the volt-second capacity of the magnetic material of the stator in accordance with varying line, load or other selected conditions. The current in the control winding can be externally controlled or may be provided by a feedback winding wound on the stator.

Radio and soft X-ray evidence for dense non-potential magnetic flux tubes in the solar corona

Abstract: The source positions of solar radio bursts of spectral types I, III(U) and III(J) and V observed by the Culgoora radioheliograph are found to lie almost radially above soft X-ray loops on pictures taken by the S-056 telescope aboard Skylab. The radio source positions and the X-ray loops occur near magnetic loops on computed potential field maps. However, the magnetic induction required to explain the radio observations is much greater than the computed potential field value at that height. Dense current-carrying magnetic flux tubes emanating from active regions on the Sun and extending to ≲ 1.5R⊙ above the photosphere provide a satisfactory model for the radio bursts.

Probability distribution functions of microscale magnetic fluctuations during quiet conditions

Abstract: A statistical study of microscale magnetic fluctuations in the interplanetary and magnetosheath region during quiet conditions is approached from the concept of probability distribution function. Magnetic field data from Explorer 34 were used to reconstruct the distribution functions and to calculate some of their moments. The distribution functions are found to be nearly tri-Maxwellian as the background field is relatively quiet. The direction of maximum fluctuations is found to be nearly perpendicular to that of the background magnetic field, but the fluctuations are rarely circularly polarized. Across the Earth's bow shock, the degree of fluctuation anisotropy increases, but no noticeable change in relative fluctuation intensity has been observed.