Heliosphere Instrument for Spectra, Composition & Anisotropy at Low Energies
HI-SCALE is designed to make measurements of interplanetary ions and electrons throughout the entire Ulysses mission. The ions (Ei ≥ 50 keV) and electrons (Ee ≥ 30 keV) are identified uniquely and detected by five separate solid-state detector telescopes that are oriented to give nearly complete pitch-angle coverage from the spinning spacecraft.
Ion elemental abundances are determined by a ΔE vs E telescope using a thin (5 µm) front solid state detector element in a three-element telescope.
Inflight calibration is provided by radioactive sources mounted on telescope covers which can be closed for calibration purposes and for radiation protection during the course of the mission.
Ion and electron spectral information is determined using both broad-energy-range rate channels and a 32 channel pulse-height analyser (channels spaced logarithmically) for more detailed spectra.
Summary of Objectives
HI-SCALE is designed to make significant advances toward understanding physical processes involved in the solar control of low-energy ions and electrons in the heliosphere. The key scientific objectives include:
- Low energy solar particle fluxes will be used as probes of the morphological changes in coronal and interplanetary magnetic field structures as a function of heliolatitude
- Measurements of both relativistic and nonrelativistic energy electrons and nonrelativistic energy ions are used to model the physical conditions in flares and study solar-flare process
- Measurements of the chemical (atomic) composition of low-energy nuclei emitted from the Sun in the active region band and at high heliolatitudes will provide insight into the solar elemental abundances
- Determining the parameters of low-energy solar particle propagation in interplanetary space using measurements of the particle anisotropy and composition as functions of heliographic latitude. Of particular interest is the study of particle propagation in the vicinity of the neutral sheet in the interplanetary magnetic field
- Correlations of non-relativistic electron events with on-board Ulysses radio measurements provide quantitative physical parameters of outward- propagating wave-particle interactions at different latitudes in the heliolatitude-dependent interplanetary plasma
- Changes in particle energy distributions will be measured and the physical processes in the interplanetary medium that cause them will be identified. Particular emphasis will be placed on modelling the changes produced by shock, stochastic, and other possible mechanisms of particle acceleration as the Ulysses spacecraft moves away from the ecliptic plane
- The 'quiet-time' low-energy particle populations in the interplanetary medium will be measured, and the possible separation of the solar, galactic, and planetary magnetosphere components will be made by their different heliolatitude variations
- Measurements of the temporal and spatial variations in low-energy particle intensities and compositions in the vicinity of the Jovian magnetosphere will be made
- The new knowledge gained from HI-SCALE investigations of the global dynamics and structure of the heliosphere will be used to define in a more quantitative way the influences of solar activity on the terrestrial environment and its technological systems