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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Interaction of Inner Heliosheath Ions with Electromagnetic Ion Cyclotron Waves

Abstract Inner heliosheath (IHS) ions are expected to be exposed to various waves, shocks, and turbulence, which can affect ion distributions and thus their charge-exchange rates with interstellar neutral atoms. This work addresses the potential significance of electromagnetic ion cyclotron (EMIC) waves under expected IHS conditions. From a kinetic dispersion relation, we find the possibility of frequent triggering of EMIC instability in the IHS. The threshold anisotropy of proton temperatures required for the instability is small, ( T ⊥ – T ∣∣ )/ T ∣∣ ≈ 0.1 or less, mainly due to high plasma β (ratio of the plasma to magnetic pressures). Numerical calculations on the scattering of ions (protons, He + , and He 2+ with energy of 0.01–50 keV) based on two models for EMIC waves with a moderate intensity indicate significant scattering in the pitch angle (mostly a few tens of degrees) and energy (mostly a few tens of percent) although details depend on the energy and pitch angle of each species and adopted EMIC wave models. This occurs on a short timescale (<100 times the gyro-period of each ion species). Resonant scattering in a few to a few tens of keV (corresponding to the expected pickup ion energy in the IHS) is easily expected unless the wavenumber is too large. The scattering effect is distinguished among different species such that for lower gyrofrequency ions (He + versus He 2+ and He 2+ versus protons), the main scattering effect moves toward a lower energy domain. All these results imply continuous disturbance of ion distributions by possibly prevailing EMIC waves in the IHS.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1971

The equilibrium and stability of the gaseous component of the galaxy, 3

The stability of a self-gravitating, nonrotating, isothermal gas layer threaded by a one-dimensional equipartition magnetic field, immersed in a rigid isothermal layer of stars, is considered with respect to waves with motions in and perpendicular to the X plane, where X is the equilibrium magnetic and gravitational field vectors. When motions are perpendicular to the X plane, the magnetic field hinders gravitational instability, increasing the minimum length necessary to produce instability by the factor (1 + alpha) to the 1/2 power, where alpha is the ratio of magnetic pressure to gas pressure. When motions are in the plane, no such simple analytical solution is found. However, the resulting system of equations reduces to a single fourth order differential equation in the perturbed gas potential that defines an eigenvalue problem for the marginally unstable state when the four appropriate boundary conditions are considered.

Kellman, S. A.↗
NASA NTRS1971

Hollow cathode, quasi-steady MPD arc

A quasi-steady MPD accelerator has been operated with four different hollow cathodes over a power range from 5 kilowatts to 5 megawatts. The absolute level of the argon mass flow, as well as the fractional division of the flow between the cathode and the six standard chamber injectors, is varied over a range of 1 to 12 grams per second. For a fixed total current, it is observed that the voltage increases monotonically with mass flow rate, compared to the usual experience with solid cathodes where the voltage decreases with mass flow rate. For a fixed percentage of flow through the cathode, each hollow cathode configuration displays a minimum impedance at a particular value of the total mass flow. It is asserted that in order to keep the discharge inside the hollow cathode the magnetic pressure and gasdynamic pressure have to match inside the cavity.

Parmentier, N.↗
NASA NTRS1971

Rocket propulsion by thermonuclear micro-bombs ignited with intense relativistic electron beams.

Discussion of a method for the ignition of a thermonuclear microbomb by means of an intense relativistic electron beam with regard to its potential application to rocket propulsion. With such a system, exhaust velocities up to 1000 km/sec, corresponding to a specific impulse of 100,000 sec, seem to be within the realm of possibility. The rocket is propelled by a chain of thermonuclear microbombs exploded in a concave magnetic mirror produced by superconducting field coils. The magnetic pressure of the field reflects the fireball generated by the explosion. For the large capacitor bank required to generate the intense relativistic electron beam, a desirable lightweight design may be possible through use of ferroelectric materials. Because of the high cost of the T-D and He 3-D thermonuclear material, the system has to be optimized by minimizing the T-D and He 3-D consumption by a proper TD and He 3-D fuel to hydrogen propellant mass ratio, leading to a larger total system mass than would be absolutely necessary.

Winterberg, F.↗
NASA NTRS1972

Magnetospheric plasma.

This paper reviews the principal features of the distribution of plasma in the magnetosphere as inferred from observations of particles with energies in the keV range and below. Low energy electrons are found within the equatorial region of the magnetotail, where they form the plasma sheet, and throughout the outer magnetosphere, where they envelop the earth with a complicated and as yet only partly explored structure. The sum of particle and magnetic pressures is roughly constant across the plasma sheet. The intense electron fluxes of the plasma sheet terminate at the so-called inner boundary of the plasma sheet, which is located at about 11 earth radii in the evening side of the magnetosphere and approaches the plasmapause near the midnight meridian. During substorms, the inner boundary moves closer to the earth, while deep in the magnetotail the plasma sheet first becomes thinner and then expands. Comparison between magnetotail electron densities and whistler measurements suggests that the observed plasma sheet particles may constitute the thermal particle population of the magnetotail.

Vasyliunas, V. M.↗
NASA NTRS1972

The earth's bow shock in an oblique interplanetary field.

The pressure, magnetic field, temperature, particle density, and stream velocity throughout the magnetosheath have been calculated in the plane containing the interplanetary field and solar wind velocity vector for various orientations of the interplanetary magnetic field and various assumed ratios of specific heats of the compressed solar wind. Jump conditions at the bow shock gave initial conditions in the shocked plasma from which the appropriate hydromagnetic equations (for blunt bodies in the subsonic region near the subsolar point and for the method of characteristics in the supersonic region back in the tail) were integrated numerically back to the surface of the magnetosphere. Explicit consideration of the magnetic field shows that a net asymmetrical force on the magnetopause produces a side force, or 'lift' in addition to the well-known drag on the magnetosphere.

Shen, W.-W.↗
NASA NTRS1972

Measurements of lunar magnetic field interaction with the solar wind.

Study of the compression of the remanent lunar magnetic field by the solar wind, based on measurements of remanent magnetic fields at four Apollo landing sites and of the solar wind at two of these sites. Available data show that the remanent magnetic field at the lunar surface is compressed as much as 40% above its initial value by the solar wind, but the total remanent magnetic pressure is less than the stagnation pressure by a factor of six, implying that a local shock is not formed.

Dyal, P.↗
NASA NTRS1972

Performance of the new Efratom optically pumped rubidium frequency standards and their possible application in space relativity experiments

The characteristics of Efratom optically pumped rubidium frequency standards are discussed. The Efratom units were compared with cesium beam and hydrogen maser standards and showed a stability of approximately 5 times 10 to the minus 12th power over two one-week periods. Dependency of frequency upon the environmental parameters of pressure, magnetic field, temperature, supply voltage, and acceleration was measured. A package of three units with automatic phase comparison and recording was designed and constructed to allow a measurement of relativistic effects on time with high accuracy during space missions.

Alley, C. O.↗
NASA NTRS1975

The nature of the sunspot phenomenon. III - Energy consumption and energy transport. IV - The intrinsic instability of the magnetic configuration

The basic relation is described between conversion of thermal energy into convective fluid motion and convective transport of thermal energy, and the equilibrium configuration of a sunspot's magnetic field is shown to be unstable to the hydromagnetic exchange instability. It is determined that heat transport necessarily accompanies convective driving of fluid motion and that the formation of cool sunspots requires convection extending coherently over several scale heights, a distance of at least 500 km. Several theoretical possibilities for sunspot stabilization are reviewed, and it is suggested that a suitable redistribution of cooling in the umbra may be the stabilization mechanism. It is believed that if cooling extends to a great depth in an elongated portion of a sunspot, the magnetic pressure on the boundary will be reduced, tending to reduce the elongation.

Parker, E. N.↗
NASA NTRS1977

Ionization fronts as phase transitions

Model weak D-type ionization fronts have been constructed which include the effects of magnetic pressure and H I coolants. Ly-alpha cooling is found to suppress the high-temperature peak of 15,000 to 20,000 K found in earlier models. Ionization fronts are found to be closely related to phase transitions.

Hill, J. K.↗
NASA NTRS1978

Magnetic fields, plasmas, and coronal holes: The inner solar system

In situ magnetic field and plasma observations within 1 AU which describe MDH stream flows and Alfvenic fluctuations, the latest theories of those phenomena are discussed. Understanding of streams and fluctuations was enhanced by the acquisition of nearly complete sets of high resolution plasma and magnetic data simultaneously at two or more points by IMPs 6, 7, and 8, Mariner-Venus-Mercury, HELIOS 1, and HELIOS 2. Observations demonstrate that streams can have very thin boundaries in latitude and longitude near the sun. This has necessitated a revision of earlier views of stream dynamics, for it is now clear that magnetic pressure is a major factor in the dynamics of stream in the inner solar system and that nonlinear phenomena are significant much closer to the sun than previously believed. Simultaneous IMP 6, 7, and 8 observations of Alfvenic fluctuations indicate that they are probably not simply transverse Alfven waves and suggest that Alfvenic fluctuations are better described as nonplanar, large-amplitude, general Alfven waves moving through an inhomogeneous and discontinuous medium, and coupled to a compressive mode.

Burlaga, L. F.↗
NASA NTRS1978

Plasma fluctuations in the solar wind

Using Ogo 5 plasma and magnetic field data, the power spectra of solar wind fluctuations are calculated over the 10 to the -3 to 10 to the -1 Hz range. It is found that the spectra calculated from flux measurements equal the density power spectra times the square of the average solar wind speed. The power spectrum relative density is of the same order of magnitude as the power spectrum of speed fluctuations relative to the Alfven speed. In cases where density and field fluctuations are inconsistent with magnetosonic waves, static inhomogeneities with a balance between electron thermal and magnetic pressures is assumed. It is also felt that a resonant proton cyclotron instability driven by the solar wind's proton thermal anisotropy may cause the observed power enhancements near 1 Hz.

Neugebauer, M.↗
NASA NTRS1977

Analysis of the passive stabilization of the long duration exposure facility

The nominal Long Duration Exposure Facility (LDEF) configurations and the anticipated orbit parameters are presented. A linear steady state analysis was performed using these parameters. The effects of orbit eccentricity, solar pressure, aerodynamic pressure, magnetic dipole, and the magnetically anchored rate damper were evaluated to determine the configuration sensitivity to variations in these parameters. The worst case conditions for steady state errors were identified, and the performance capability calculated. Garber instability bounds were evaluated for the range of configuration and damping coefficients under consideration. The transient damping capabilities of the damper were examined, and the time constant as a function of damping coefficient and spacecraft moment of inertia determined. The capture capabilities of the damper were calculated, and the results combined with steady state, transient, and Garber instability analyses to select damper design parameters.

Siegel, S. H.↗
NASA NTRS1979

Sunspots and the physics of magnetic flux tubes. IX - Umbral dots and longitudinal overstability

The dynamical properties of the sunspot field and of a column of hot gas confined by such a vertical magnetic field are examined in order to understand the umbral dot within the context of the magnetic sunspot structure. Attention is given to the conditions necessary for gas intrusion, longitudinal as well as convective overstability, the growing modes, and the even mode. With the hypothesis that the subsurface magnetic field of a sunspot splits into many separate flux tubes with field-free gas between, it is suggested that the field-free columns occasionally punch their way up through the overlying magnetic field to the surface, appearing there as the bright, field-free umbral dots. Effects fostering the phenomenon are also discussed, that is, the enhanced temperature of a column of rising gas, the strongly reduced overhead magnetic pressure, and the initiated upward intrusion; these effects are illustrated with examples.

Parker, E. N.↗
NASA NTRS1981

Interplanetary magnetic clouds at 1 AU

Magnetic clouds are defined as regions with a radial dimension approximately 0.25 AU (at 1 AU) in which the magnetic field strength is high and the magnetic field direction changes appreciably by means of rotation of one component of B nearly parallel to a plane. The magnetic field geometry in such a magnetic cloud is consistent with that of a magnetic loop, but it cannot be determined uniquely. Forty-five clouds were identified in interplanetary data obtained near Earth between 1967 and 1978; at least one cloud passed the Earth every three months. Three classes of clouds were identified, corresponding to the association of a cloud with a shock, a stream interface, or a CME. There are approximately equal numbers of clouds in each class, and the three types of clouds might be different manifestations of a coronal transient. The magnetic pressure inside the clouds is higher than the ion pressure and the sum is higher than the pressure of the material outside of the cloud.

Klein, L. W.↗