Engineering topics

Davis, T. N.

Publications and source records attributed to Davis, T. N..

At least 19 records

NASA NTRS1980

Artificial aurora conjugate to a rocket-borne electron accelerator

An accelerator intended to send electron beams upward along an L = 1.24 magnetic field line was flown from a rocket launched from Kauai, Hawaii, on October 15, 1972. Though the intent was to produce several hundred observable auroral streaks in the Southern Hemisphere, imaging instruments operated there aboard jet aircraft detected only a single aurora. Produced by a 0.155-A beam of energy 22.8 keV, the aurora was of expected brightness and had a diameter (210 + or - 50 m) somewhat larger than expected and an altitude (top 116 + or - 2 km; bottom 92 + or - 2 km) higher than expected.

Davis, T. N.↗

NASA NTRS1980

Active experiments using rocket-borne shaped charge barium releases

A reliable payload system and scaled down shaped charges were developed for carrying out experiments in solar-terrestrial magnetospheric physics. Four Nike-Tomahawk flights with apogees near 450 km were conducted to investigate magnetospheric electric fields, and two Taurus-Tomahawk rockets were flown in experiments on the auroral acceleration process in discrete auroras. In addition, a radial shaped charge was designed for plasma perturbation experiments.

Wescott, E. M.↗

NASA NTRS1979

Chemical releases in the ionosphere

The study of the interaction between the atmosphere, ionosphere and magnetosphere is identified as a major task worthy of pursuit. The present review demonstrates the major contributions to this complex problem already made by active experiments involving the injection of chemicals and energetic electron beams into the atmosphere, ionosphere and magnetosphere. Through the use of chemical releases, it has been possible to investigate a number of quantities including high-altitude winds and electric fields, the detailed configurations of the geomagnetic field within the ionosphere and the magnetosphere, as well as the propagation of energetic particle beams and their interaction with natural neutral and ionized constituents of the high atmosphere. So far, virtually all of this effort has been accomplished using rockets. In the future, it is obvious that satellite platforms will play a greater role, both in making injections and in observing their effects.

Davis, T. N.↗

NASA NTRS1978

Observed characteristics of auroral forms

Observed characteristics of discrete auroral arcs and pulsating aurora are described, and a mechanism for the discrete auroras is considered. Strong horizontal and vertical electric fields characterize the discrete auroras, since their motions and their distortions indicate the presence of shear processes involving substantial charge excesses and magnetic field-aligned currents. Pulsating auroras do not exhibit shearing behavior and this lack of shearing shows that substantial electric fields are not involved. Transitional types of auroras, including black aurora, are considered.

Davis, T. N.↗

NASA NTRS1978

The Tordo 1 polar cusp barium plasma injection experiment

In January 1975, two barium plasma injection experiments were carried out with rockets launched into the upper atmosphere where field lines from the dayside cusp region intersect the ionosphere. The Tordo 1 experiment took place near the beginning of a worldwide magnetic storm. It became a polar cap experiment almost immediately as convection perpendicular to the magnetic field moved the fluorescent plasma jet away from the cusp across the polar cap in an antisunward direction. Convection across the polar cap with an average velocity of more than 1 km/s was observed for nearly 40 min until the barium flux tubes encountered large electron fields associated with a poleward bulge of the auroral oval near Greenland. Prior to the encounter with the aurora near Greenland there is evidence of upward acceleration of the barium ions while they were in the polar cap. The three-dimensional observations of the plasma orientation and motion give an insight into convection from the cusp region across the polar cap, the orientation of the polar cap magnetic field lines out to several earth radii, the causes of polar cap magnetic perturbations, and parallel acceleration processes.

Wescott, E. M.↗

NASA NTRS1977

Rocket measurements of electrons in a system of multiple auroral arcs

A Nike-Tomahawk rocket was launched into a system of auroral arcs northward of Poker Flat Research Range, Fairbanks, Alaska. The pitch-angle distribution of electrons was measured at 2.5, 5, and 10 keV and also at 10 keV on a separating forward section of the payload. The auroral activity appeared to be the extension of substorm activity centered to the east. The rocket crossed a westward-propagating fold in the brightest band. The electron spectrum was relatively hard through most of the flight, showing a peak in the range from 2.5 to 10 keV in the weaker aurora and below 5 keV in the brightest arc. The detailed structure of the pitch-angle distribution suggested that, at times, a very selective process was accelerating some electrons in the magnetic field direction, so that a narrow field-aligned component appeared superimposed on a more isotropic distribution. It is concluded that this process could not be a near-ionosphere field-aligned potential drop, although the more isotropic component may have been produced by a parallel electric field extending several thousand kilometers along the field line above the ionosphere.

Boyd, J. S.↗

NASA NTRS1976

The Skylab barium plasma injection experiments. I - Convection observations

Two barium-plasma injection experiments were carried out during magnetically active periods in conjunction with the Skylab 3 mission. The high-explosive shaped charges were launched near dawn on November 27 and December 4, 1973, UT. In both cases, the AE index was near 400 gammas, and extensive pulsating auroras covered the sky. The first experiment, Skylab Alpha, occurred in the waning phase of a 1000-gamma substorm, and the second, Skylab Beta, occurred in the expansive phase of an 800-gamma substorm. In both, the convection was generally magnetically eastward, with 100-km-level electric fields near 40 mV/m. However, in the Alpha experiment the observed orientation of the barium flux tube fit theoretical field lines having no parallel current, but the Beta flux-tube orientation indicated a substantial upward parallel sheet current.

Wescott, E. M.↗

NASA NTRS1976

The Skylab barium plasma injection experiments. II - Evidence for a double layer

Television observations of a barium-plasma flux tube extending from near 4500 km to near 10,000 km during a magnetic substorm and dawn-sector auroral display indicated several interesting anomalous events. Beyond 5500 km, there was a rapid increase in brightness accompanied by flux-tube splitting and diffusion, leaving behind a truncated single flux tube. From the orientation of the flux tube compared with theoretical field models, the presence of a substantial field-aligned current sheet is deduced. A suggested explanation of these phenomena is given in terms of a plasma potential double layer.

Wescott, E. M.↗

NASA NTRS1975

Laboratory observations of RF emission at plasma electron frequency and n + 1/2 times the electron cyclotron frequency in electron beam-plasma and beam-beam interactions

Electric field emissions at frequencies of (n + 1/2) times the electron cyclotron frequency have been generated in a large-scale electron beam experiment in a vacuum facility. These emissions arise when a contrastreaming beam configuration exists, the primary beam consisting of monoenergetic electrons (50 eV to 5 keV) and the other beam of lower-energy backscattered secondary electrons. It is suggested that the same mechanism could also be the source of the observed 3/2 times the electron cyclotron frequency emissions at auroral latitudes. In the absence of the beam-beam instability, weak oscillations were observed at the plasma frequency. In the latter case no significant modifications of the primary beam velocity distribution occurred, and the beam configuration is adequately described by single-particle motion in the ambient magnetic field.

Bernstein, W.↗

NASA NTRS1975

AMPS definition study on Optical Band Imager and Photometer System (OBIPS)

A study was conducted to define the characteristics of a modular optical diagnostic system (OBIPS) for AMPS, to provide input to Phase B studies, and to give information useful for experiment planning and design of other instrumentation. The system described consists of visual and UV-band imagers and visual and UV-band photometers; of these the imagers are most important because of their ability to measure intensity as a function of two spatial dimensions and time with high resolution. The various subsystems of OBIPS are in themselves modular with modules having a high degree of interchangeability for versatility, economy, and redundancy.

Davis, T. N.↗

NASA NTRS1975

The L equals 6.7 quiet time barium shaped charge injection experiment 'Chachalaca'

Near dawn on October 9, 1972, UT, a barium plasma injection experiment was carried out from Poker Flat, Alaska, during quiet magnetic conditions (Kp equals 1+). The visible plasma flux tube produced was more diffuse than the flux tubes in previous experiments, but it could be tracked for 30 min out to an altitude of 2.5 earth radii. The flux tube remained integral for about 20 min, when a single striation separated from the main streak. Comparisons of the observed flux tube orientation with theoretical field models show no significant deviations ascribable to field-aligned currents. Cross-field drift rates of the foot of the flux tube indicate an E field of approximately 7 mV/m at 200-km altitude. Although an attempt was made via a jet aircraft flight, barium ions were not detected in the southern conjugate region. No energetic particle precipitation phenomena were observed which could be ascribed to the barium plasma injection.

Wescott, E. M.↗

NASA NTRS1975

Two barium plasma injections into the northern magnetospheric cleft

Two rocket experiments, performed in January 1975, investigated convection of plasma formed by solar photoionization of barium injected into the northern magnetospheric cleft at 13 km/s upward and parallel to the local geomagnetic field. Plasma convection was demonstrated from the cleft's poleward region, directly into and across the polar cap, and possibly into the convection system of the nightside auroral electrojet; plasma injected centrally within the cleft under quiet magnetic conditions remained in the cleft convection system for at least 22 min and revealed a highly structured E-field over about 600 km of longitudinal extent. Cleft location agreed with that predicted by ionosondes.

Jeffries, R. A.↗

NASA NTRS1975

The L = 6.6 Oosik barium plasma injection experiment and magnetic storm of March 7, 1972

A high-explosive shaped charge vaporizing a hollow conical liner of Ba metal and producing a fast field-aligned jet of plasma was detonated at high altitude, during a quiescent phase of a magnetic storm initiated by an ssc 10 hrs prior to the experiment, in an attempt to trace out and observe the dynamics of an auroral field line in the magnetosphere. Observations offer evidence for an upward Birkeland current sheet at the poleward edge of the auroral spiral of 8 x 10 to the minus second power A/m. Unusual features of the substorm leave open the possibility that the plasma injection may have triggered it.

Wescott, E. M.↗

NASA NTRS1974

Television observations of artificial aurora and analyses of flight data from NASA payload 12.18 NE

An accelerator nominally capable of ejecting pulses of electrons up to 6 sec in length, current to 500 ma and energy to 20 keV was flown on a rocket at 1500 October 15, 1972. The Strypi rocket was launched from the Pacific Missile Range Facility at Kauai, Hawaii. The intent was to eject electron pulses of various characteristics upwards along the magnetic field so as to produce artificial auroras in the conjugate (Southern Hemisphere) atmosphere and possibly to produce weaker auroras in the nearby atmosphere as a consequence of backscattered electrons. The accelerator package included a gas jet actuated attitude control system controlled by gyros. Attitude sensing also was accomplished by a two-axis fluxgate magnetometer, and a large foil was deployed to collect ambient electrons to neutralize the accelerator when it ejected high-energy electrons. Scientific instrumentation contained on the flight package included retarding potential analyzers, energetic electron detectors, and detectors to sense very low frequency radio noise. Image orthicon television systems and other optical sensors were operated in the conjugate region aboard two NC-135 jet aircrafts based in Samoa. Similar devices were operated at Haleakala, Hawaii, to attempt detection of auroras caused by backscattered electrons.

Davis, T. N.↗

NASA NTRS1974

Study of a small magnetospheric substorm

Data from a rocket launched into the expansion phase of an auroral substorm have been compared with data from numerous ground stations and several space vehicles. It is shown that this magnetic and auroral substorm has most of the features of larger substorms; thus it is implied that the same plasma processes are involved in all substorms. Some evidence is presented to link the auroral breakup with the field lines conjugate to the inner edge of the plasma sheet. The implications of these two results for substorm morphology and the triggering mechanism of the substorm instability are discussed. It is concluded that spatial gradients in plasma temperature are a likely cause.

Johnstone, A. D.↗

NASA NTRS1974

Low-altitude acceleration of auroral electrons during breakup observed by a mother-daughter rocket

By the use of a mother-daughter rocket combination and ground-based observations with television, time and space variations are resolved in particle measurements in breakup aurora. The spectral variations measured during a temporal variation in the aurora can be explained by a nearly uniform acceleration of all the electrons such as would be caused by an electric potential drop along the magnetic field lines. Many other explanations can be eliminated.

Johnstone, A. D.↗

NASA NTRS1974

L = 1.24 conjugate magnetic field line tracing experiments with barium shaped charges

Description of three experiments involving the injection of barium ions into magnetic flux tubes with the aid of high-explosive shaped charges with hollow conical liners of barium metal. In these experiments (called Alco, Bubia, and Loro, respectively) the explosive charges were detonated at altitudes above 500 km, producing jets of barium plasma with initial velocities ranging from 8 to 20 km/sec. The most interesting result of the experiments, which were carried out near L = 1.24 and were successful in tracing an entire field line some 7000 km to the conjugate ionosphere, was the observation that for Loro and probably Alco the direction and rate of drift of the two ends of the field line were identical, whereas those for Bubia differed significantly. In the case of the Bubia event significant differences in magnitude and direction at the conjugate points are noted, which lead to the conclusion that the field line could not have been equipotential during the interval of observation.

Wescott, E. M.↗

NASA NTRS1973

The resolution of temporal and spatial variations in auroral particle measurements from sounding rockets

The problems involved in the resolution of the temporal/spatial ambiguity in sounding rocket observations are discussed with reference to an experiment involving a mother-daughter rocket combination, together with a flashing light beacon on the rocket and television cameras on the ground. The ambiguity was successfully removed, enabling a proper interpretation of the observations of precipitating low energy electrons to be made.

Johnstone, A. D.↗