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Magnetic field effects on collisionless plasma sheath near planar electrode, solving electric and magnetic potentials nonlinear differential equations by numerical scheme
Further hot-ion plasma experiments were conducted in the SUMMA superconducting magnetic mirror facility. A steady-state plasma with mutually perpendicular magnetic and electric fields was formed by applying a strong radially inward dc electric field between cylindrical anodes and hollow cathodes located near the magnetic mirror maxima. Extending the use of water cooling to the hollow cathodes, in addition to the anodes, resulted in higher maximum power input to the plasma. Steady-state hydrogen plasmas with ion kinetic temperatures as high as 830 eV were produced. Functional relations were obtained empirically among the plasma current, voltage, magnetic flux density, ion temperature, and relative ion density. The functional relations were deduced by use of a multiple correlation analysis. Data were obtained for midplane magnetic fields from 0.5 to 3.37 tesla and input power up to 45 kW. Also, initial absolute electron density measurements are reported from a 90 deg Thomson scattering laser system.
The ISEE 1 and 2 magnetometers are used to examine a current sheet which is moving outward with a velocity of about 17 km/sec, and whose current is flowing into the ionosphere. A wave is traveling along the current sheet, from midnight toward the east, at 400 km/sec. The plasma oscillations normal to the current sheet associated with this wave are sufficient for explaining the amplitude of the electric field oscillations in the plane of the current sheet observed by the University of California's electric field detector. The present oscillating current sheet model explains both magnetic and electric field observations.
The Magnetospheric Multiscale (MMS) mission, launched on March 13, 2015, is the fourth mission of NASA's Solar Terrestrial Probe program. The MMS mission consists of four identically instrumented observatories that function as a constellation to provide the first definitive study of magnetic reconnection in space. Since it is frequently desirable to isolate electric and magnetic field sensors from stray effects caused by the spacecraft's core-body, the suite of instruments on MMS includes six radial and two axial instrument-booms with deployed lengths ranging from 5-60 meters (see Figure 1). The observatory is spin-stabilized about its positive z-axis with a nominal rate slightly above 3 rev/min (RPM). The spin is also used to maintain tension in the four radial wire-booms. Each observatory's Attitude Control System (ACS) consists of digital sun sensors, star cameras, accelerometers, and mono-propellant hydrazine thrusters-responsible for orbital adjustments, attitude control, and spin adjustments. The sections that follow describe performance requirements, the hardware and algorithms used for 6-DOF estimation, and then similarly for 6-DOF control. The paper concludes with maneuver performance based on both simulated and on-orbit telem.
Drift velocities and thermal flux vectors in five component nonequilibrium plasma in presence of electric and magnetic fields, using Grad method
Two different observations of Comet Kohoutek (1973f) seem to suggest the existence of substantial magnetic fields (not less than 100 gammas) in its coma and tail. The effects of the currents and hydromagnetic waves associated with these magnetic fields are considered. It is shown that while the currents closing through the inner coma may represent an important source of ionization in that region, the dissipation of hydromagnetic waves may also be a significant, if not dominant, source of heating there.
A ULF pulsation event is discussed on the basis of experimental observations of electric and magnetic field measurements as well as particle measurements from the DE 1 spacecraft. The observations were made near the magnetic equator in a space covering a large range of L shells and magnetic latitudes, and comparisons are made to ground observations. Azimuthal oscillations are observed following gradually decaying long-period compressional waves. Weak interaction between magnetic shells indicates that the source is probably weak, and ground data on magnetic pulsations showed strong signals that did not necessarily correspond to the quasisinusoidal pulsations observed in space. Azimuthal pulsations observed by the spacecraft indicate that there was a plasma density gradient beyond the plasmapause. The ULF pulsations were probably affected by changes in the magnetic field and solar-wind dynamic pressure, and their periods are found to be linked to geomagnetic latitude.
The 3-D nonequilibrium seeded air flow in the NASA-Ames experimental MHD channel has been numerically simulated. The channel contains a nozzle section, a center section, and an accelerator section where magnetic and electric fields can be imposed on the flow. In recent tests, velocity increases of up to 40% have been achieved in the accelerator section. The flow in the channel is numerically computed us ing a 3-D parabolized Navier-Stokes (PNS) algorithm that has been developed to efficiently compute MHD flows in the low magnetic Reynolds number regime: The MHD effects are modeled by introducing source terms into the PNS equations which can then be solved in a very efficient manner. The algorithm has been extended in the present study to account for nonequilibrium seeded air flows. The electrical conductivity of the flow is determined using the program of Park. The new algorithm has been used to compute two test cases that match the experimental conditions. In both cases, magnetic and electric fields are applied to the seeded flow. The computed results are in good agreement with the experimental data.
A self-consistent, newly developed, nonplanar MHD model is used to investigate the evolution of field and current structures in solar active regions due to photospheric shearing motions. It is demonstrated that this model can predict physical parameters that may help improve understanding of the evolution of those field and current structures. Numerical results on the magnetic energy intensity, electric current intensity, and magnetic field configuration are presented.
There has recently been much effort behind the development of NDE methods applicable to the detection of surface/subsurface flaws in thin metallic structures with a rapid scan capability. One such method, an electromagnetic technique using a current-sheet parallel to the surface of a specimen in order to induce eddy current flow shows a high potential for satisfying the rapid scan requirement stated above. The technique is based on the detection of flaw-induced magnetic field components normal to the specimen surface by an appropriate detection mechanism positioned above the current-sheet as shown schematically in Fig. 1. As indicated in this figure, the current-sheet separates the source of the normal magnetic field components from the detector in such a way that the electric and magnetic properties of the current-sheet can be a major factor affecting the strength of the detected signals. The purpose of the present study is, therefore, to perform a detailed investigation on the effect of the material properties of the current-sheet on the detected signal strength and to establish a simple theoretical model for the detection mechanism.
Theories which describe currents collected by conducting and non-conducting bodies immersed in plasmas have many of their concepts based upon the fundamentals of sheath-potential distributions and charged-particle behavior in superimposed electric and magnetic fields. Those current-collecting bodies (or electrodes) may be Langmuir probes, electric field detectors, aperture plates on ion mass spectrometers and retarding potential analyzers, or spacecraft and their rigid and tethered appendages. Often the models are incomplete in representing the conditions under which the current-voltage characteristics of the electrode and its system are to be measured. In such cases, the experimenter must carefully take into account magnetic field effects and particle anisotropies, perturbations caused by the current collection process itself and contamination on electrode surfaces, the complexities of non-Maxwellian plasma distributions, and the temporal variability of the local plasma density, temperature, composition and fields. This set of variables is by no means all-inclusive, but it represents a collection of circumstances guaranteed to accompany experiments involving energetic particle beams, plasma discharges, chemical releases, wave injection and various events of controlled and uncontrolled spacecraft charging. Here, an attempt is made to synopsize these diagnostic challenges and frame them within a perspective that focuses on the physics under investigation and the requirements on the parameters to be measured. Examples include laboratory and spaceborne applications, with specific interest in dynamic and unstable plasma environments.
Measurements by the magnetometer on the Pioneer Venus orbiter have established that during conditions of low solar wind dynamic pressure, large-scale magnetic fields are not present in the ionosphere of Venus but that during conditions of high solar wind dynamic pressure the ionosphere of Venus is magnetized. The source of the magnetic field is thought to be currents induced in the ionosphere by the solar wind. We will show that ionospheric polarization electric field can act as a source, or 'battery', producing a small magnetic field, even without any initial magnetic field. We have calculated this polarization source as a function of altitude and solar zenith angle. The magnetic field was then determined using a 2D kinematic dynamo model of the ionosphere of Venus. The magnetic field attains a maximum strength of about 5 nT at a solar zenith angle of about 120 deg. This magnetic field might act as a 'seed' field for magnetic flux ropes and terminator waves.
Magnetic and electric field aligned plasma diffusion in the ionosphere to examine conditions for ambipolar diffusion
The work is presented in four parts. First, main differences between the plasma environments in geostationary orbit and low polar orbit with regard to high-voltage charging situations are reviewed. Next, results are presented from a calculation of secondary-electron escape currents from negatively-charged spacecraft surfaces having various orientations relative to the local magnetic-field direction. It is shown that for finite ranges of combinations of electric and magnetic field directions, secondary-electron escape is completely suppressed and therefore cannot help to discharge the spacecraft. In such circumstances, secondary electrons may travel distances many times their gyroradii before reimpacting, and this may produce greatly increased secondary-electron surface currents. Thirdly, a simple rough estimate of the required conditions for high-voltage auroral-zone charging is developed. The results suggest that for any given spacecraft, surface potentials are likely to depend more strongly on the ratio of ambient flux of high-energy electrons to that of all ions, than on any other environmental parameter. Finally, preliminary results are presented of numerical simulation work directed toward testing this hypothesis. Numerical instabilities encountered in doing this simulation work probably are closely related to physical sensitivities inherent in the physics of the ion wake behind the spacecraft, and especially to beam-like constituents of the ion population in the wake.
We have developed a new canonical separator line type magnetospheric magnetic field and electric field model for use in magnetospheric calculations, we determine the magnetic and electric field by controlling the reconnection rate at the subsolar magnetopause. The model is applicable only for purely southward interplanetary magnetic field (IMF). We have obtained a more realistic magnetotail configuration by applying a stretch transformation to an axially symmetric field solution. We also discuss the Stern singularity in which there is an electric field singlarity in the canonical separate line models for B(sub y) not = to 0 by using a new technique that solves for the electric field along a field line directly instead of determining it by a potential mapping. The singularity not only causes an infinite electric field on the polar cap, but also causes the boundary conditions at plus infinity and minus infinity in the solar wind to contradict each other. This means that the canonical separator line models do not represent the open magnetosphere well, except for the case of purely southward IMF.
Simultaneous measurements were made of the electric and magnetic field spectral densities in the earth's bow shock by a plasma wave experiment on the Imp 6 spacecraft. The frequency range of the plasma wave detector was 20 Hz to 200 kHz. Electric fields were measured with high-sensitivity 100-m long dipole antennas and magnetic fields were measured with single-turn loop antennas. Two components are distinguished in the electric field spectrum in the bow shock: one component has a broad peak centered in the region 200-800 Hz, while the other component increases monotonically with decreasing frequency. The magnetic field spectrum has only one component that increases monotonically with decreasing frequency and has an upper cutoff frequency near the local electron gyrofrequency. This magnetic field turbulence is judged to be caused by whistler mode waves. The monotonic component of the electric field spectrum is thought to be the electric field spectrum of these whistler mode waves.
Electron beam experiments using rocket-borne instrumentation will be discussed. The observations indicate that reflections of energetic electrons may occur at possible electric field configurations parallel to the direction of the magnetic lines of force in an altitude range of several thousand kilometers above the ionosphere.
Electric field measurements for turbulence in collision-free shocks, noting power spectra of magnetic and electric fluctuations and electron density