The instrument consists of a 0.1 mm thick gold foil of hemispherical shape with three grids at the entrance (entrance grid, charge grid, and shield), as well as an ion collector and channeltron detector.
The maximum sensitive area (for particles moving parallel to the sensor axis) is 0.1 m**2. Upon impact the particle produces a plasma, whose charge carriers are separated by an electric field between the target and the ion collector. Negative charges (mainly electrons) are collected at the target; the positive charges are collected partly by the ion collector and partly by a channeltron.
The channeltron is used as it is insensitive to electric and vibrational noise. See Gruen et al.(1992a) [GRUENETAL1992A] for more information concerning the instrument.
Science Objectives Summary
The objective of the Galileo dust experiment is to investigate the physical and dynamical properties of small dust particles (10**-16 to 10**-6g) in the Jovian environment. The parameters to be determined include the mass, speed, flight direction and electric charge of individual particles. Specific objectives are: - To investigate the interaction of the Galilean satellites with their dust environment in order to study the relationship between dust influx on satellites and their surface properties, and to perform direct measurements of ejecta particles from the satellites; - To study the interaction between dust particles and magnetospheric plasma, high-energy electrons and protons, and magnetic fields, to determine the relationship between dust concentrations and attenuation of the radiation belts, and to investigate the effects of the Jovian magnetic field on the trajectories of charged dust particles; - To investigate the influence of the Jovian gravitational field on the interplanetary dust population and to search for rings around Jupiter.
Positively or negatively charged particles entering the sensor are first detected via the charge which they induce in the charge grid while flying between the entrance and shield grids. The grids adjacent to the charge pick-up grid are kept at the same potential in order to minimize the susceptibility of the charge measurement