Showing papers on "Magnetic field published in 1971"
TL;DR: In this paper, an electrical current in a semiconductor induces spin orientation in a thin layer near the surface of the sample due to spin-orbit effects in scattering of electrons, and a weak magnetic field parallel to the current destroys this orientation.
1,211 citations
TL;DR: In this paper, the Weizsacker-Williams method is used to calculate the gain due to the induced emission of radiation into a single electromagnetic mode parallel to the motion of a relativistic electron through a periodic transverse dc magnetic field.
Abstract: The Weizsacker‐Williams method is used to calculate the gain due to the induced emission of radiation into a single electromagnetic mode parallel to the motion of a relativistic electron through a periodic transverse dc magnetic field. Finite gain is available from the far‐infrared through the visible region raising the possibility of continuously tunable amplifiers and oscillators at these frequencies with the further possibility of partially coherent radiation sources in the ultraviolet and x‐ray regions to beyond 10 keV. Several numerical examples are considered.
929 citations
TL;DR: In this article, the spin correlation functions of the one-dimensional $XY$ model were studied in the presence of a constant magnetic field and it was shown that the asymptotic behavior of these correlation functions depends strongly on the various parameters of the Hamiltonian.
Abstract: The spin-correlation functions of the one-dimensional $XY$ model are studied in the presence of a constant magnetic field. We find that the asymptotic behavior of these correlation functions depends strongly on the various parameters of the Hamiltonian.
679 citations
TL;DR: Magnetospheric plasma clouds equatorial observation by ATS 5 satellite, revealing plasma injection during substorms and dispersion by earth magnetic and electric fields as mentioned in this paper, revealed plasma injection in the Earth magnetic field.
Abstract: Magnetospheric plasma clouds equatorial observation by ATS 5 satellite, revealing plasma injection during substorms and dispersion by earth magnetic and electric fields
573 citations
TL;DR: In this article, the authors present a coherent exposition of the modern statistical theory of the transport of fast charged particles (cosmic rays) in the solar wind, showing that the dominant effect on the motion of cosmic rays is the interplanetary magnetic field, which is irregular and which is best treated statistically, using random functions.
Abstract: This paper presents a coherent exposition of the modern statistical theory of the transport of fast charged particles (cosmic rays) in the solar wind. Observations are discussed only as they illustrate the phenomena under discussion. A brief introductory section surveys the historical development of the theory. The dominant effect on the motion of cosmic rays in the solar wind is the interplanetary magnetic field, which is irregular and which is therefore best treated statistically, using random functions. The magnetic irregularities scatter the cosmic rays in pitch angle, so that to a good approximation the cosmic rays diffuse through the irregular magnetic field. Using a statistical analysis of the equations of motion, one may relate the diffusion tensor to the power spectrum of the magnetic field, which is in principle measurable. The resulting general transport theory relates the motion of cosmic rays, statistically, to the solar-wind velocity and magnetic field. Application of the theory both to the modulation of galactic cosmic rays by the solar wind and to the propagation of solar cosmic rays is discussed in detail. It is concluded that the present theory explains the principal phenomena quite well. Future theoretical work will probably be devoted to obtaining better solutions of the equations, to obtaining better values of the parameters, and to studying higher-order or more subtle effects.
495 citations
TL;DR: In this article, the authors explain the spontaneous generation of magnetic fields in a laser-produced plasma using thermoelectric currents associated with large temperature gradients near the target, using a variety of targets and background pressures.
Abstract: Spontaneously generated magnetic fields of the order of a kilogauss have been observed in a laser-produced plasma, using a variety of targets and background pressures. The generation of these magnetic fields is explained in terms of thermoelectric currents associated with large temperature gradients near the target.
435 citations
TL;DR: In this article, the E-layer conductivity may be too small to close this circuit, so that polarization fields build up in the F-layer, causing the plasma to drift with the wind.
427 citations
TL;DR: In this paper, the spin-dependent tunneling density of superconducting aluminum and ferromagnetic nickel is determined by a polarization of the magnetic moments of the Ni current carriers parallel to the applied field.
Abstract: Tunneling measurements on junctions between very thin superconducting aluminum films and ferromagnetic nickel films in a high magnetic field show that the tunneling current is spin dependent. The effective tunneling density of states in Ni determined by this means implies a polarization of the magnetic moments of the Ni current carriers parallel to the applied field. The technique offers a new method for investigating spin-dependent states in magnetic materials.
399 citations
TL;DR: In this paper, the role of trapped particles for equilibrium, diffusion and stability of plamas in toroidal magnetic devices is discussed and the correspondence between the neoclassical theory of diffusion, the turbulent transport processes due to the instabilities and the existing experimental Tokamak data is discussed.
Abstract: The review is devoted to the discussion of the role of trapped particles for equilibrium, diffusion and stability of plamas in toroidal magnetic devices. The motion of single particles in a toroidal magnetic field, the neoclassical transport processes due to the trapping of particles and trapped-particle instabilities in toroidal geometry are discussed. The correspondence between the neoclassical theory of diffusion, the turbulent transport processes due to the instabilities and the existing experimental Tokamak data is discussed.
380 citations
TL;DR: In this article, the adiabatic theory for charged particles moving in a region where the main component of the magnetic field reverses its direction is presented for charge-reconnection geometry.
Abstract: The adiabatic theory is presented for charged particles moving in a region where the main component of the magnetic field reverses its direction. The unperturbed field configuration is one-dimensional and involves two regions of uniform and opposite magnetic fields separated by a reversal region of small but finite extent. The adiabatic theory is capable of describing particle orbits when gradual spatial and/or temporal field variations are added to this configuration. Several applications are given. These include orbits during a null-sheet compression, orbits in the sheets studied by Alfven and Speiser, and orbits in the vicinity of the magnetic null line of the so-called field-reconnection geometry.
TL;DR: Galactic magnetic field generation by dynamo process with nonuniform rotation and turbulence in gaseous disk was described in this article, where the authors proposed a dynamo-based approach to generate magnetic field.
Abstract: Galactic magnetic field generation by dynamo process with nonuniform rotation and turbulence in gaseous disk
TL;DR: In this article, it was shown that the variable *, the conductivity-weighted, vertically averaged velocity is important in the generation of both local and large-scale electric currents.
Abstract: Motionally induced electric and magnetic fields are investigated in the sea, crust, and mantle for large-scale low-frequency oceanic flows. It is shown that three-dimensional flows generate large-scale horizontal electric currents not present in two-dimensional motions. The resulting induced magnetic fields penetrate into the mantle inducing there electric currents. The degree of mutual induction between the ocean and the mantle depends on the parameter δmL, the ratio of the electromagnetic skin depth of the mantle to the horizontal scale of the flow. For δmL≫1 there is little mutual induction whereas for δmL≪1 there is strong coupling between the ocean and the mantle. It is shown that the variable *, the conductivity-weighted, vertically averaged velocity is important in the generation of both local and large-scale electric currents. Expressions are derived showing that , the vertically averaged velocity, can be determined from measurements of the induced electric and magnetic fields at the sea floor. Several special cases are calculated illustrating the influences of the mantle, the conducting sediments, and the horizontal scales of the motion.
TL;DR: In this paper, an experimental and theoretical investigation of the angular distribution of the electric field of a short radio frequency probe in a plasma in a magnetic field is described, where the field becomes very large along a resonance cone whose axis is parallel to the static magnetic field and whose opening angle is observed to vary with incident probe frequency, cyclotron frequency, and plasma frequency in agreement with cold plasma dielectric theory.
Abstract: An experimental and theoretical investigation of the angular distribution of the electric field of a short radio frequency probe in a plasma in a magnetic field is described. The field is observed to become very large along a resonance cone whose axis is parallel to the static magnetic field and whose opening angle is observed to vary with incident probe frequency, cyclotron frequency, and plasma frequency in agreement with simple cold plasma dielectric theory. The relationship of these cones to the limiting phase‐ and group‐velocity cones which appear in the theory of plane wave propagation is discussed. The addition of electron thermal velocities (warm plasma effects) is examined in the limit of a large static magnetic field. A fine structure appears inside the cones and is shown to result from an interference between a fast electromagnetic wave and a slow plasma wave. This interference structure is observed experimentally and measurements of the angular interference spacing are shown to agree with the warm plasma theory. The use of measurements of the resonance cones and structure as a diagnostic tool to determine the plasma density and electron temperature in a plasma in a magnetic field is discussed.
TL;DR: In this article, the critical currents of unbounded relativistic electron beams with a plasma were studied and compared with experiment results. But the authors did not consider the effect of finite longitudinal dimensions of the system on critical currents in electron beams.
Abstract: CONTENTS 1. Introduction 163 2. Formulation of problem and initial equations 164 3. Limiting currents in uncompensated electron beams 165 4. Critical currents in compensated unbounded electron beams 168 5. Influence of finite longitudinal dimensions of the system on the critical currents in electron beams 170 6. Interaction of unbounded relativistic electron beams with a plasma 172 7. Stability of bounded electron beams in a plasma 174 8. Critical currents of relativistic electron beams in a plasma 175 9. Comparison of theory with experiment 176 Cited literature 178
TL;DR: In this article, the authors show that the mid-latitude ionosphere may be in a continual dynamic state if the storms occur sufficiently often and that the density and flux profiles expected during the subsonic phase of the recovery are still not reached after an elapsed time of 10 days and correspondingly there is still a net loss of plasma from the ionosphere to the magnetosphere.
TL;DR: In this paper, the authors measured the variation in direction of the horizontal component of remanent magnetisation with depth in the sediments of the South basin of Windermere, England, and concluded that the sediment of freshwater lakes contain an accurate record of the directional variations of the magnetic field during the period of sedimentation and that these variations can provide a time scale in such materials.
TL;DR: In this article, the effects of a nonlinear interaction between a whistler wave and the particles resonating with it are considered in some detail, and the possibility of having a self-sustained process of phase-bunching and emission is investigated.
Abstract: In this paper, the so-called triggered emissions of whistlers are considered. The effects of a nonlinear interaction between a whistler wave and the particles resonating with it are considered in some detail. The interaction gives rise to two closely related effects, namely a change in the amplification or absorption by the plasma, and a phase-bunching of the resonant and near-resonant particles, thus giving rise to a current. The current due to the phase-bunched particles has roughly the same structure (frequency and wave number) as the wave causing it, and will therefore give rise to emission of a new whistler wave, acting like an antenna. The possibility of having a self-sustained process of phase-bunching and emission is investigated. The structure of a region where this process can take place is proposed, and the corresponding conditions that must be met are stated.
TL;DR: In this article, the threshold ac electric field required for the excitation of the purely growing "oscillating two-stream" and decay instabilities is found to increase when the density gradient scale length H becomes less than the mean free path.
Abstract: The threshold ac electric field required for the excitation of the purely growing “oscillating two‐stream” and decay instabilities is found to increase when the density‐gradient scale length H becomes less than the mean free path. For a plasma with no magnetic field, the threshold field is given by E2/4πnTe≈2(k‖H)−1, where k‖≲(1/4)D−1 is the wavenumber of the instability in the direction orthogonal to the density gradient. (D is the electron Debye length.) Qualitative arguments suggest that this result should hold in the presence of a magnetic field. Recent experimental measurements of the threshold field agree well with these theoretical calculations. The reason for the threshold field increasing is that, in an inhomogeneous plasma, the unstable region has a finite extent spatially and energy (in the form of electron plasma waves) can propagate out of this region, thus creating an energy loss not found in uniform plasmas.
TL;DR: Magnetospheric substorms relationship to interplanetary magnetic field and solar wind plasma parameters was examined in this article, with the dominant effect of inter-planetary southward component.
Abstract: Magnetospheric substorms relationship to interplanetary magnetic field and solar wind plasma parameters, noting dominant effect of interplanetary southward component
TL;DR: In this paper, the authors developed a theoretical solution for the electromagnetic response of a two-dimensional inhomogeneity in a conductive half-space, in the field of a line source of current.
Abstract: A theoretical solution is developed for the electromagnetic response of a two‐dimensional inhomogeneity in a conductive half‐space, in the field of a line source of current. The solution is in the form of an integral equation, which is reduced to a matrix equation, and solved numerically for the electric field in the body. The electric and magnetic fields at the surface of the half‐space are found by integrating the half‐space Green’s functions over the scattering currents. One advantage of this particular numerical technique is that it is necessary to solve for scattering currents only in the conductor and not throughout the half‐space. The response of a thin, vertical conductor is studied in some detail. Because the only interpretational aids available previously were scale model results for conductors in free space, the results presented here should be useful in interpreting data and in designing new EM systems. As expected, anomalies decay rapidly as depth of burial is increased, due to attenuation in...
TL;DR: In this paper, the static electrical conductivity tensor of an electron gas in the presence of a magnetic field has been derived in the case of scattering by spinless (point) impurities, using a Green's function method.
TL;DR: In this paper, the effect of strong magnetic fields on neutron stars or white dwarfs is calculated for Thomson scattering in a fully ionized collisionless plasma, and the photon mean free path can be greatly extended for propagation nearly parallel or, for the extraordinary mode, nearly perpendicular to the field.
Abstract: The effect of a strong magnetic field on neutron stars or white dwarfs is calculated for Thomson scattering in a fully ionized collisionless plasma. The photon mean free path can be greatly extended for propagation nearly parallel or, for the extraordinary mode, nearly perpendicular to the field.
TL;DR: In this paper, the structure of turbulent electric and magnetic field fluctuations is described, and the internal dynamics of the associated velocity fluctuations are compared with those of fluid turbulence, and it is suggested that the plasma turbulence is qualitatively similar to fluid turbulence but with the turbulent elements elongated along the mean magnetic field to form rolls.
Abstract: The structure of turbulent electric and magnetic field fluctuations is described, and the internal dynamics of the associated velocity fluctuations are compared with those of fluid turbulence. It is suggested that the plasma turbulence is qualitatively similar to fluid turbulence but with the turbulent elements elongated along the mean magnetic field to form rolls. This suggests that an appropriate comparison might be with the hypothetical two‐dimensional limit of fluid turbulence, in which energy is expected to be transferred toward long wavelengths rather than to short wavelengths as for isotropic turbulence. In the plasma case, the direction of energy flow is inferred to be toward short wavelengths but the measured form of the triple correlation is close to that expected for two‐dimensional turbulence; we cannot, therefore, make a clear choice between the two alternatives. Effects arising from the particle structure of the plasma do not appear to be important, except that at low pressures an increased damping occurs which may be ion Landau damping. The source of the turbulent energy is not primarily convection due to the pressure gradient but involves some mechanism of direct coupling with the plasma current associated with the “excess resistance” of the discharge.
TL;DR: Polar cap electric field measurements and model for Hall current auroral electrojet continuity and polar cap magnetic disturbances are presented in this article, where the model is extended to include magnetic disturbances.
Abstract: Polar cap electric field measurements, and model for Hall current auroral electrojet continuity and polar cap magnetic disturbances
TL;DR: The VLF-E.M. (Very Low Frequency-Electro Magnetics) method was first used for geophysical surveying in 1964 as mentioned in this paper, and many hundreds of surveys have been carried out; several variations on the original design have been introduced; and the method has become airborne.
TL;DR: In this paper, a theory is presented to explain the origin of triggered discrete VLF emissions that is more complete than earlier theories, in that it is not restricted to the discussion of kinematical relations but evaluates the dynamics of the problem.
Abstract: A theory is presented to explain the origin of triggered discrete VLF emissions that is more complete than earlier theories, in that it is not restricted to the discussion of kinematical relations but evaluates the dynamics of the problem. Resonant electrons are phase correlated with the wave magnetic field by a finite length whistler train moving in the opposite direction. The time for phase correlation is of the order of the period of oscillation of a particle in the effective ‘potential well’ of the wave. It is recognized that the wave acceleration due to the inhomogeneous magnetic field of the earth must be small enough for the particle to stay trapped in the potential well. The phase-correlated electrons are subject to an instability in the form of an emitted whistler with a growth rate γ/ω ∼ (n/no)2/5(υ⊥/c)2/5 (ωp/Ω)2/5, where (n/no) is the fractional density of the resonant particles, υ⊥ is their mean transverse velocity, and ωp and Ω are local cold plasma and gyrofrequencies. The emitted frequency varies according to ω = k(ω)υ∥ − Ω, where υ∥ is the zero order longitudinal velocity of the resonant electron, and the wave vector k is a function of frequency ω through the whistler dispersion relation. The theory is in good agreement with observation.
TL;DR: Simultaneous two magnetometer measurements of weak magnetic fields in interplanetary space, near moon and planets by satellites in presence of spacecraft field were performed in this article, where two magnetometers were used to measure the magnetic field of the Earth.
Abstract: Simultaneous two magnetometer measurements of weak magnetic fields in interplanetary space, near moon and planets by satellites in presence of spacecraft field
TL;DR: A Nike-Tomahawk rocket equipped to measure electric and magnetic fields and charged particles from a few eV to several hundred keV energy was flown into an auroral band on April 11, 1970 as discussed by the authors.
Abstract: A Nike-Tomahawk rocket equipped to measure electric and magnetic fields and charged particles from a few eV to several hundred keV energy was flown into an auroral band on April 11, 1970 The purpose of this flight was to obtain evidence of the low-energy electrons and protons that constitute a field-aligned sheet current, and also to obtain the magnetic signature of such a current and the electric field in and near the auroral-arc electric current system Particular attention was given to a sudden increase in the field-aligned current associated with a prior sudden increase in the electric field and a sudden change in the magnetic field, all occurring near the edge of a visual auroral arc Data obtained are discussed and analyzed; they present an important contribution to the problem of mapping of atmospheric auroral phenomena to the magnetospheric equatorial plane
TL;DR: Galaxy gaseous disk as low mode dynamo, calculating turbulent diffusion coefficient for passive magnetic fields, calculated by as discussed by the authors, is a low-mode dynamo for the Galaxy Gaseous Disk.
Abstract: Galaxy gaseous disk as low mode dynamo, calculating turbulent diffusion coefficient for passive magnetic fields