The three-dimensional velocity distribution of positive ions in the neighbourhood of Comet Halley was measured by an instrument which included two complementary sensors. The fast ion sensor measured the energy/charge distribution from 10 eV/q to 20 keV/q once per revolution of the spacecraft. It obtained the characteristics of the solar wind flow near the comet. The implanted ion sensor measured the energy/charge distribution from 90 eV/q to 90 keV/q with discrimination into five mass groups in a period of 32 spacecraft revolutions. These observations provided the angular distribution of the cometary ions formed by the ionisation of gas molecules sublimed from the cometary nucleus. The relation between the raw count rates and the plasma parameters for the fast ion sensor is derived on the basis of a complete energy angle scan of the sensor in a calibration source. The accuracy of the analysis was tested by two techniques using data collected during the mission.

This instrument measures the three-dimensional (3-D) distribution function of positive ions at the UKS. Novel electrostatic analyzers using 2600 turning angle cover all viewing angles as the spacecraft rotates. The instrument has sufficient resolution to measure the solar wind as well as giving full 3-D coverage within a spin period. The operation of the experiment and organization of the data are synchronized to the spacecraft spin. A sample of the real-time data showing magnetospheric boundary crossings is presented.

A new type of plasma analyser, capable of covering the three-dimensional energy distribution of charged particles from a spinning spacecraft, has been built for the AMPTE and GIOTTO spacecraft. The novel features are the use of 260° of deflection in a spherical plate electrostatic analyser to obtain energy discrimination simultaneously with dispersion in angle and the use of a microchannel plate with position-sensitive readout to obtain the angular distribution. The sensor achieves a field of view greater than 140°; a well-defined and nearly-ideal shape for the acceptance volume in velocity space and a relatively large geometric factor.

An imaging photon detector has been developed for a number of research applications in geophysics and astrophysics. S20/S25 photocathodes provide sensitivity extending to the near-infrared, and a pair of microchannel plates (MCP), mounted in a chevron arrangement provide an electron gain of about 4*106. At a voltage difference of about 2.0 kV across the two MCPs, this gain is adequate to drive a proportional amplitude-sensing system based on a linear resistive anode, and a resolution of about 200 mu m can be obtained over an effective diameter of 20 mm. Over a limited range the resolution is inversely proportional to the gain, with a value of approximately 100 mu m for a gain of 2*107.