Showing papers on "Electric current published in 1973"
TL;DR: In this paper, a semiempirical analytic formula for large-scale electric magnetospheric fields is developed that are valid within the inner magnetosphere as well as within the ionosphere.
Abstract: Semiempirical analytic formulas for large-scale electric magnetospheric fields are developed that are valid within the inner magnetosphere as well as within the ionosphere. These electric fields drive ionospheric electric currents. Moreover, field-aligned electric currents must exist in order to maintain the magnetospheric electric field configuration. The model calculations are compared and are shown to be consistent with the shape of the plasmapause, the equivalent electric current systems of DP 1 and DP 2, the available electric field observations at ionospheric altitudes, and the observations of field-aligned electric currents.
488 citations
TL;DR: In this paper, the linear stability problem of a current flowing perpendicularly to a magnetic field is analyzed and compared with the restriction that the growth rate should be larger than the ion cyclotron frequency, all the fast growing electrostatic modes are computed and compared.
Abstract: The linear stability problem of a current flowing perpendicularly to a magnetic field is analysed. With the restriction that the growth rate should be larger than the ion cyclotron frequency, all the fast growing electrostatic modes are computed and compared. It is argued that the most significant modes of the problem (relevant to perpendicular collisionless shocks, pinches and the plasma focus) can be obtained without inclusion of effects due to gradients of the equilibrium quantities. The computations are divided into three broad categories: Te Ti, Te = Ti and Ti = 10 Te. With the aid of computation and analysis an attempt has been made to cover the whole range of parameter space for this problem.
95 citations
TL;DR: In this article, the authors present the results of experimental studies on a discharge in the Tokamak-6 device with a specific instability whose appearance coincides with a sudden jump in the transverse energy of the plasma.
Abstract: The authors present the results of experimental studies on a discharge in the Tokamak-6 device with a specific instability whose appearance coincides with a sudden jump in the transverse energy of the plasma. It is shown that in these discharge regimes the current is carried by a relatively small group of runaway electrons with energies of 10 - 500 keV, while the main plasma with e 3 × 1012 cm−3 has a low temperature (Te, Ti ~ 10 eV) and carries practically no current. Preionization of the working gas or the introduction of a relatively small (~ 2 – 3%) local inhomogeneity in the longitudinal magnetic field converts these runaway discharges into normal Tokamak discharges.
82 citations
TL;DR: In this article, a model has been developed to predict the lifetime τf of integrated circuit metalizations which operate at high dc densities Je, where grain boundary electromigration, internal heat generation, and current crowding at growing voids dominate the rate processes that lead to failure.
Abstract: A model has been developed to predict the lifetime τf of integrated circuit metalizations which operate at high dc densities Je. Grain‐boundary electromigration, internal heat generation, and current crowding at growing voids dominate the rate processes that lead to failure. Joule heating of the stripe causes an initial temperature rise ΔT0 and heat flow into the substrate. If this rise is appreciable an instability exists in the stripe. When vacancies electromigrate down grain boundaries and precipitate on a suitable boundary, forming an elongated void, the electric current will be diverted. This is serious if the crack has a substantial length component perpendicular to the current flow which increases vacancy currents to the crack tip and the local heating. An analytical model considering these effects and the time for a crack to propagate across the stripe width yields a stripe lifetime integral which fits the form Pn =(1/2)(1+0.265γΔT0). Here γ=ΔH/kT2 is the temperature coefficient of the diffusion c...
72 citations
TL;DR: In this paper, the particle, wave, and field changes measured when Ogo 5 traversed an outer-zone trapping boundary of this type on September 7, 1968 are described.
Abstract: Several spacecraft experimenters have reported on the detection of large temporal variations in trapped electron fluxes near L = 5 to 6 at midlatitudes in the night hemisphere. In this report we describe in detail the particle, wave, and field changes measured when Ogo 5 traversed an outer-zone trapping boundary of this type on September 7, 1968. It is shown that thermal proton concentrations and E greater than 50-keV electron fluxes abruptly decreased when electrons with (1-4) keV mean energy were detected. It is also shown that currents flowed along the average geomagnetic field direction near the plasma boundaries and that these were accompanied by intense VLF electrostatic waves. It is proposed that turbulent resistivity produced by current-driven plasma instabilities allows parallel dc electric fields to develop along this boundary.
53 citations
TL;DR: In this paper, the axisymmetric MHD-equilibria obtained by superposing the magnetic field of the plasma currents and the field of current-carrying conductors situated outside the plasma were numerically calculated by several different iteration methods for solving the non-linear free boundary problem.
Abstract: Solutions are given for axisymmetric MHD-equilibria obtained by superposing the magnetic field of the plasma currents and the field of current-carrying conductors situated outside the plasma. These equilibria were numerically calculated by several different iteration methods for solving the non-linear free boundary problem. They can describe experiments in which the discharge time is long compared with the diffusion time of the magnetic field through the external conducting walls. Equilibria were obtained both for approximately circular plasma cross-sections and strongly elongated (elliptical) ones. Such calculations are of interest for constructing axisymmetric tokamak divertors, as well as for producing elongated crosssections, which have been postulated to be stable for higher values of plasma pressure. The results presented here are restricted to the case of zero plasma pressure and a particular current distribution in order to reduce the number of free parameters and allow more detailed discussion of the dependence of the equilibrium configurations on the arrangement of the external conductors and the currents.
47 citations
TL;DR: In this paper, heat transfer was investigated in a Mach 4.6 low-density Ar plasma in the absence and presence of magnetic fields up to 0.5 Telsa.
Abstract: Heat transfer was mcasured for conducting (copper) and nonconducting (teflon) models in a Mach 4.6 low-density Ar plasma in the absence and presence of magnetic fields up to 0.5 Telsa. Results show the importance of local wall currents both with and without magnetic field. For the conducting model, an electron flux entering the surface increased the stagnation-region heat flux compared to the nonconducting model. For the nonconducting model, theory predicts well the heat transfer for zero field but fails to predict the slight increase at the stagnation region with high magnetic field. (DLC)
42 citations
TL;DR: The split Langmuir probe as discussed by the authors was developed to make in situ measurements of current density and plasma bulk flow, and it was successfully test flown from Fort Churchill on 2 August 1968, with results in reasonable agreement with those from another experiment on the same rocket.
35 citations
TL;DR: The total longitudinal force which acts on a high-frequency heated plasma column is derived for any arbitrary absorption mechanism as mentioned in this paper, which results in particle drifts and poloidal fields which may be relevant to toroidal plasma confinement.
Abstract: The total longitudinal force which acts on a high-frequency heated plasma column is derived for any arbitrary absorption mechanism. This force arises from any departure from longitudinal symmetry (longitudinal plasma motion, a single travelling wave, etc.). It results in particle drifts and poloidal fields which may be relevant to toroidal plasma confinement. High-frequency power of order 105 W is sufficient to replace the driving electric field in a moderate scale tokamak.
33 citations
TL;DR: In this paper, the electrical conductivity, o-, and the total radiant power per unit volume, PR9 of air are measured for temperatures between 8,000 and 12,500°K at atmospheric pressure.
Abstract: The electrical conductivity, o-, and the total radiant power per unit volume, PR9 of air are measured for temperatures between 8,000 and 12,500°K at atmospheric pressure. The measurements are made in a wallstabilized electric arc discharge which produces a pure, stable plasma. Axial electric field strength, £,, and azimuthal magnetic field intensity, B^ are measured as functions of the discharge radius by using probe techniques. Current density, jz9 is obtained as ~]*= V x£//z0, and electrical conductivity is determined by using Ohm's law, o = jJEz. PR is measured with a total radiation thermopile and also by using an electrical technique. Plasma temperature is determined from the absolute intensities of the 4935 A NI and 4368 A OI lines.
TL;DR: The results of measurements of the electric field near the surface of stainless-steel electrodes in vacuum are described in this paper, where it is found that the field is modified by a solid insulator bridging the interelectrode gap.
Abstract: The results of measurements of the electric field near the surface of stainless-steel electrodes in vacuum are described. It is found that the field is modified by a solid insulator bridging the interelectrode gap. The extrapolated cathode field is enhanced sufficiently to equal the value considered necessary to initiate break-down in a plane vacuum gap. The measured fields are greater than the applied field and consistent with the accumulation of positive surface charge on the solid insulator. Analysis of the data suggests that the surface charge results from bombardment of the surface by electrons emitted at the insulator-cathode junction.
TL;DR: In this article, a detailed analysis of the development of the electrostatic turbulence excited by a cross-field current in a high density (ωp e −≫ Ωe) collisionless plasma, as obtained from one-and two-dimensional computer simulations, is given.
Abstract: A detailed analysis is given of the development of the electrostatic turbulence excited by a cross‐field current in a high density (ωp e ≫ Ωe ) collisionless plasma, as obtained from one‐ and two‐dimensional computer simulations. The drift velocity required for instability is found to be only slightly smaller than the critical drift for the unmagnetic two‐stream instability in contrast to the electron cyclotron drift instability. In one dimension the system remains self‐similar in the turbulent phase, /8πnTe ≃ const, while the electron thermal velocity and the effective collision frequency increase linearly with time, ν* ∝ Ωet, in agreement with the theory of coherent trapped‐electron heating by Forslund, Morse, and Nielson. The switch‐off drift velocity, however, is νd ≈ 2cs, and hence the thickness of a magnetic sheath would be Δ ∼ c/ωpi instead of Δ ∼ c/Ωe. In two dimensions two projections are investigated, the j‐B plane and the plane perpendicular to B, the latter being the more relevant. The ...
TL;DR: In this article, the transition between diffusive (saturated current) and sheath-convection (current?voltage?) behavior of the current to a negative probe in a high-pressure, flowing plasma has been studied theoretically.
Abstract: The transition between diffusive (saturated current) and sheath-convection (current?voltage?) behaviour of the current to a negative probe in a high-pressure, flowing plasma has been studied theoretically. By using two physical models, where both effects are considered to be significant, one effect being dominant in one case and the other being dominant in the other case, an approximate relation is derived for the probe current in the transition between these two r?gimes. This transition is found to cover a variation of two orders of magnitude in ionization density if the required 10% accuracy is to be achieved. It is also found that thermoelectric and nonequilibrium effects due to cooling in the thermal boundary layer do not themselves materially affect the diffusion current.
TL;DR: In this article, the trajectories of plasma-sheet protons are computed numerically in magnetic-field models which simulate the neutral-sheet-type configuration observed in experiments, and it is shown that the neutral sheet itself can be a source of such an anisotropy, due to the nonadiabatic behaviour of protons.
TL;DR: In this paper, the angular variation of the critical current at constant field was examined in detail, and data were given for the temperature dependence of the transverse and longitudinal critical current as well as the effect of neutron damage on homogeneous low-α specimens of Nb3Sn.
Abstract: Measurements are reported for the critical current of chemically transported Nb3Sn as a function of applied field from 0 to 104 kG. The angular variation of the critical current at constant field is examined in detail. Data are given for the temperature dependence of the transverse and longitudinal critical current as well as the effect of neutron damage on homogeneous low‐α specimens of Nb3Sn.
TL;DR: In this article, it has been shown that rod-like molecular clusters and their orientation are brought about by the induced dipole of the polymer and/or the electric current through the liquid crystalline solution unlike that in high dielectric solvents.
Abstract: -Liquid crystalline solutions of poly-γ-benzylglutamates have been measured in static electric fields using light scattering methods. It has been made clear that molecular clusters are present in solution when high dielectric solvents are used. Sufficient conditions, though not the necessary ones, have been obtained to indicate that the molecular clusters are rod-like in a very low electric field supporting an idea previously proposed. From the change of the V h scattering mode, polymer (and molecular cluster) orientation can be determined. Change in the scattering mode when the direction of the external electric field is reversed is drastic, and a tentative explanation for this is given. In dioxane, formation of the rod-like molecular clusters and their orientation are brought about by the induced dipole of the polymer and/or the electric current through the liquid crystalline solution unlike that in the high dielectric solvents.
TL;DR: In this article, small coaxial cables smaller than RG-58 were exposed to intense pulsed irradiation from a plasma focus device, and the currents induced on the center conductors were measured in a vacuum environment.
Abstract: Subminiature coaxial cables smaller than RG-58 were exposed to intense pulsed irradiation from a plasma focus device, and the currents induced on the center conductors were measured in a vacuum environment. The incident photons had energies mostly below 70 keV, and filters were used to vary the average hardness of the irradiation. The measured cable responses in units of Coulomb/rad(Si)-cm were compared to values calculated on the basis of photoemission from metal surfaces and electron ranges in insulators. It was found that the currents induced on the center conductors were several times larger than predicted for an ideal coaxial geometry because of small gaps between the dielectric surface and overlapping braid wires. For a given cable type, such as RG-174/U, large variations in cable responses were found according to each manufacturer's construction techniques.
TL;DR: In this article, a review of the basic properties of force-free fields under circumstances when the conductivity of the medium is finite is given, where the electric current density is related not only to the magnetic field, but also by Ohm's law to the electric field and plasma velocity.
Abstract: A review is given of some of the basic properties of force-free fields under circumstances when the conductivity of the medium is finite. Then the electric current density is related not only to the magnetic field, but also by Ohm's law to the electric field and plasma velocity, which must be considered in the solutions. It is pointed out that the natural constraint that the electric field and plasma velocity should be finite everywhere is not fulfilled in some previously used models. Models with a constant ratio α of the electric current density and magnetic field intensity have been used extensively in the past. They are of some importance since solutions with the plasma at rest are possible only if α is constant. However, it is shown that solutions of constant α cannot be matched to an external current-free region of finite conductivity since α can have no discontinuity in a medium where the conductivity varies continuously. Hence, for most applications models with a varying α and a moving plasma must be used. Some new, simple and consistent models, especially of cylindrical symmetry, are derived by prescribing the form of the magnetic field lines, or one electic field component, or one time-dependent electric current component.
TL;DR: In this paper, an electric current exerts a dragging force on ferromagnetic domain walls, and when the current density exceeds a certain "coercive" value j c, the domains are set into motion in the same direction as the charge carriers.
TL;DR: In this paper, the application of probe theories to flame plasmas is examined and the effects of this upon measured values of ion concentration and electron temperature are discussed and a correction procedure proposed.
Abstract: The application of probe theories to flame plasmas is examined. For low-pressure laminar flames with small double spherical probes, the electric Reynolds number is less than unity and the theory of Su and Lam is often applicable. The effect upon plasma potential of drawing current to the probes is examined experimentally and it is shown that under certain conditions there is a significant shift of plasma potential. The effects of this upon measured values of ion concentration and electron temperature are discussed and a correction procedure proposed. The effects upon the measured value of electron temperature of the probe being cooled below the gas temperature are examined theoretically.
TL;DR: In this article, the ion cyclotron turbulent ring current precipitation model of magnetic storms is reexamined in light of recent experimental and theoretical developments, and it is shown that the dominant ring currents occur outside the plasmasphere in agreement with recent theories of the high beta, large anisotropy ioncyclotron and electrostatic ion loss cone waves.
Abstract: The ion-cyclotron turbulent ring current precipitation model of magnetic storms is reexamined in light of recent experimental and theoretical developments. The ring current-plasmapause spatial coincidence results from the proton Alfven layer shielding of the convection electric field. Observations indicate that the dominant ring current precipitation occurs outside the plasmasphere in agreement with recent theories of the high beta, large anisotropy ion cyclotron and electrostatic ion loss cone waves. Hydrogen arc proton precipitation may be caused by parallel electric fields at the equatorward edge of the auroral oval. During the main phase, convection may be both the source and major sink of the asymmetric ring current. During the rapid recovery phase, neutral-wind-induced convection may be the dominant ring current loss process. At this time there is no definitive evidence that ion cyclotron turbulence inside the plasmapause constitutes a major sink for the ring current or generates a SAR arc by electron Landau damping.
TL;DR: In this article, a model of a neutralized electron beam in which the electrons make helical orbits about the axis is described, and three particular cases corresponding to (1) uniform charge density in a solid beam, (2) uniform current density, and (3) uniform charges in a hollow beam are analyzed.
Abstract: A model of a neutralized electron beam in which the electrons make helical orbits about the axis is described. This differs from previous models in that there is no longitudinal field or azimuthal current. Three particular cases, corresponding to (1) uniform charge density in a solid beam, (2) uniform current density in a solid beam, and (3) uniform charge density in a hollow beam are analyzed. In none of these configurations is there a current limit, and all the electrons move in the forward direction.
TL;DR: In this article, a couple of parallel-plate electrodes have been made of Nesa glass, and the NMR spectra of liquid-crystalline solutions of poly-γ-benzyl-L-glutamate in static electric fields obtained using these electrodes are reliable.
Abstract: A couple of parallel-plate electrodes have been made of Nesa glass. NMR spectra of liquid-crystalline solutions of poly-γ-benzyl-L-glutamate in static electric fields obtained using these electrodes are reliable. The signal of a solvent molecule such as dichloromethane or dibromomethane splits into a doublet owing to magnetic dipole-dipole interactions as in the case of the magnetic orientation of these solutions, indicating that the solvent molecules orient in the direction of the electric field. Dilute liquid-crystalline solutions which still do not contain isotropic portions evidently have a strong center signal showing presence of free solvent molecules. Orientation of the solvent molecules is apt to be disturbed by a weak electric current through the solution and magnitude of the steady-state separation of the doublet can not be used as a measure for the polymer (and molecular cluster) orientation.
Patent•
04 Sep 1973TL;DR: In this paper, the first and second derivatives of a magnetic field are measured by two pairs of spaced superconducting sensing coils which are aligned along a common axis with the individual coils of each pair connected in electrical opposition so that the net current flowing therethrough is proportional to the gradient of the magnetic field in which these pairs are disposed.
Abstract: The first and second derivatives of a magnetic field are measured by two pairs of spaced superconducting sensing coils which are aligned along a common axis with the individual coils of each pair connected in electrical opposition so that the net current flowing therethrough is proportional to the gradient of the magnetic field in which these pairs are disposed. Superconducting switches associated with these coils are selectively operated to direct these net currents through a superconducting field coil during mutually exclusive time intervals. The resultant magnetic field is measured by a magnetometer which provides an indication of the average value of the magnetic field gradient and the second derivative thereof.
TL;DR: In this article, the main characteristics of current mechanisms are examined, giving attention to photoemission from the cathode, thermionic emission, minority-carrier extraction, and the tunneling of electrons.
Abstract: An investigation is conducted concerning the mechanisms by which a steady flow of current proceeds through the contact when an external voltage is applied. The main characteristics of current mechanisms are examined, giving attention to photoemission from the cathode, thermionic emission, minority-carrier extraction, and the tunneling of electrons. A high-field domain analysis is conducted together with experimental studies. Particular attention is given to the range in which tunneling predominates.
TL;DR: In this article, the numerical solution to the potential gradient problem is discussed and conditions for convergence of the iterative program for Eχ are derived and tested for two values of displacement velocity, using a 37 × 37 node mesh.
Patent•
09 Jan 1973
TL;DR: In this article, a probe comprises a metallic wire formed into a core on itself or on an insulating coil and arranged so as to form a plurality of turns of the same cross section and distributed regularly along an axis.
Abstract: The probe comprises a metallic wire formed into a core on itself or on an insulating coil and arranged so as to form a plurality of turns of the same cross section and distributed regularly along an axis. The coil is adapted to surround the conductor traversed by the variable current to be measured so that this current induces a measuring signal in said turns. The metallic wire is resistant to electric current being made, e.g., of at least 10% Ni and at least 30% Cr. The circuit of the metallic wire is closed by a resistance and capacitor in series, these components having low value relative to that of the metallic wire. First and second voltmeter means are provided at the terminals of the resistance and the capacitor respectively.