Energetic Particle Instrument Research Articles

First Plasma Wave Observations at Uranus

Radio emissions from Uranus were detected by the Voyager 2 plasma wave instrument about 5 days before closest approach at frequencies of 31.1 and 56.2 kilohertz. About 10 hours before closest approach the bow shock was identified by an abrupt broadband burst of electrostatic turbulence at a radial distance of 23.5 Uranus radii. Once Voyager was inside the magnetosphere, strong whistler-mode hiss and chorus emissions were observed at radial distances less than about 8 Uranus radii, in the same region where the energetic particle instruments detected intense fluxes of energetic electrons. Various other plasma waves were also observed in this same region. At the ring plane crossing, the plasma wave instrument detected a large number of impulsive events that are interpreted as impacts of micrometer-sized dust particles on the spacecraft. The maximum impact rate was about 30 to 50 impacts per second, and the north-south thickness of the impact region was about 4000 kilometers.

First observations of energetic particles near comet Halley

The TUNDE-M energetic particle instrument aboard the Vega 1 spacecraft detected intense fluxes of energetic (≥40 keV) ions in the vicinity of comet Halley, starting at a distance of 107 km from closest approach. Three regions of differing ion characteristics have been identified. An outer region, several million kilometers in extent, contains pick-up ions in the solar wind. A second region, inside the bow shock (several hundred thousand kilometres in extent), contains the most intense fluxes, whereas the innermost region (several tens of thousands of kilometres) is characterized by lower intensities and sharp spikes near closest approach (∼8,900 km from the nucleus).

Data comparison of EISCAT and the energetic particle instrument on GEOS 2

Flux variations of high energy ( E > 16 keV) electrons, measured by the energetic particle spectrometer onboard the geosynchronous satellite GEOS 2, have been compared to simultaneously observed electron density structures in the lower ionosphere, measured with the incoherent scatter facility EISCAT. The very localized E-region electron density enhancements caused by the precipitation allow a preliminary estimate of the location of the footpoint of the magnetic field line through GEOS 2. Various other results of the intercomparison are discussed.

Multiple‐spacecraft and correlated riometer study of magnetospheric substorm phenomena

Substantial progress has been made in recent years toward the separation of spatial and temporal effects within the magnetosphere through the use of simultaneous multipoint measurements. From 1977 to the present we have had identical energetic particle instruments in geostationary orbit on the two spacecraft, and during 1977–1978 these satellites were separated by ∼4.5 hours in local time. During this same epoch, 13 variously located riometer stations provided broad latitudinal and longitudinal ground‐based coverage of substorm activity. Throughout this period of coordinated investigation we have found numerous examples of substorm growth phase features at widely separated local times. Simultaneous measurements of the magnetosheath and interplanetary magnetic field (north‐south) orientation during substorm growth phases suggest quite close correlations between energy input to the magnetosphere and the development of growth‐phase‐related stresses near geostationary orbit. Thus the results of this study demonstrate the broad local time region in which growth phase features are observable in spacecraft data, and they also support the concept of storage of energy prior to substorms, with the sudden release of this energy at substorm expansion onset.

New magnetic electron spectrometer with directional sensitivity for a satellite application

Design and test of a new magnetic electron spectrometer with excellent angular and rather small energy resolution is described. The system is specifically designed for a space flight application to analyze the angular distribution of energetic electrons. Incident electrons with energies between 15 and 270 keV are focused with respect to the direction of incidence. Reasonable directional focusing is obtained over an angular range of 60 degrees with a resolution of 5 degrees. This magnetic electron spectrometer is part of the energetic particle instrument (EPI) developed for the European Space Agency (ESA) GEOS program. GEOS-1 was launched on April 20, 1977, and injected into a 12-h orbit. The instrument has worked successfully since the switch-on-phase in the beginning of May 1977.