Showing papers by "Peter M. Banks published in 1988"

An analysis of whistler mode radiation from the Spacelab 2 electron beam

Abstract: During the Spacelab 2 mission the plasma diagnostics package (PDP) was released from the Shuttle to free fly. At times during this free flight, when the PDP was magnetically connected to the Shuttle, Stanford's fast-pulsed electron generator, located in the Shuttle cargo bay, ejected a 1-keV 50-mA electron beam. The PDP plasma-wave instrument detected intense whistler-mode radiation during these beam ejections. This paper presents a study of a whistler mode emission detected during one particular continuous electron beam firing. Calculations indicate that the beam radiated approximately 1.6 mW in the whistler mode as the beam traversed the 200 m from the Shuttle to the PDP. The emissivity also decreased by about a factor of 10 over this same distance. The measured wave powers are 10 to the 7th greater than wave powers expected from incoherent Cerenkov radiation, verifying that the radiation is generated by a coherent process. Estimates of the emissivity based on measured electric field intensities in the beam indicate that the whistler-mode noise is produced by radiation from electron bunches created by an electrostatic beam-plasma instability.

Observations of electron beam structure in space experiments

Abstract: Observations of a 100-mA, 1-keV electron beam were made with a low light level TV system and other instruments aboard the space shuttle STS 3 in March 1982. When fired at a moderate pitch angle with respect to the magnetic field, the beam electrons initially moved outward along a classical helical trajectory. Within a short distance, however, the beam electrons were deflected away from the helical trajectory into paths parallel to magnetic field lines threading the primary helix. This resulted in the formation of a thin-walled, cylindrical electron beam structure having a radius equal to the primary beam gyroradius. This structure, which is consistent with earlier laboratory vacuum chamber observations and recent two-dimensional computer electrostatic plasma simulations, has important implications for determining the extent to which pulsed electron beams can radiate electromagnetic energy in the ionosphere.

Tethered rocket experiment (Charge 2): Initial results on electrodynamics

Abstract: The tethered mother-daughter rocket experiment (Charge 2) was carried out by a NASA sounding rocket, Black Brant 9, at White Sands Missile Range in New Mexico in December 1985. It was intended to perform a new type of active experiment in space by applying a high voltage between the two payloads, as well as by injecting an electron beam from the tethered rocket system. An insulated conductive wire connecting the two payloads was deployed up to its maximum length of 426 m during the flight. An electron beam from 0.5 to 48 mA at 1 keV was injected from the mother payload. A voltage up to 500 V was applied between the two payloads with and without the beam injection. This paper describes the initial results on the electrodynamic effects induced by the potential difference between the two payloads. Measurements of the v×B electromotive force and the voltage/current characteristics up to 500 V have been explained by a model in which the ion current to the negatively biased payload effectively limited the tether current. Two kinds of VLF waves were observed when the bias voltage was applied between the two payloads; narrow-band emission at 2–4 kHz and broadband emission up to 15 kHz, depending on the applied voltage. The characteristic features of these emissions suggest that the lower hybrid instability (modified two-stream instability) driven by the potential difference between the rocket and the ambient plasma was responsible for the wave generation.

VLF wave emissions by pulsed and DC electron beams in space, 1, Spacelab 2 observations

Abstract: The properties of radio waves generated by electron beams in space were investigated using data from the wideband wave receiver on the Spacelab 2. The VLF observations were found to confirm the results of the STS 3/OSS-1 mission. It was found that a 1-keV electron beam injected from the orbiter produced copious broadband electromagnetic emissions. When the electron beam was square-wave modulated, narrow-band emissions at the pulsing frequency and harmonics of that frequency were produced along with the broadband emissions. The observations indicated that dc 50-mA electron beams and pulsed 50-percent duty-cycle 100-mA beams produce broadband radiation which is comparable in intensity and spectral shape at all points for which the wave field was sampled.

VLF wave stimulation by pulsed electron beams injected from the space shuttle

Abstract: Among the investigations conducted on the Space Shuttle flight STS-3 of March 1982 was an experiment in which a 1-keV, 100-mA electron gun was pulsed at 3.25 and 4.87 kHz. The resultant waves were measured with a broadband plasma wave receiver. At the time of flight the experimental setup was unique in that the electron beam was square wave modulated and that the Shuttle offered relatively long times for in situ measurements of the ionospheric plasma response to the VLF pulsing sequences. In addition to electromagnetic response at the pulsing frequencies the wave exhibited various spectral harmonics as well as the unexpected occurrence of 'satellite lines' around those harmonics. Both phenomena occurred with a variety of different characteristics for different pulsing sequences.