The Giotto implanted ion spectrometer (IIS): physics and techniques of detection

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Abstract
The implanted ion spectrometer (IIS) is a dedicated instrument for the analysis of ionised cometary particles and their interaction with the solar wind. The particle identification principle used in IIS is based on ion deflection in an electrostatic analyser in combination with time-of-flight techniques. The constructed particle identifier function considers the ionic charge as a known quantity, since ionisation by solar UV radiation is the dominant process. The instrument uses novel principles to accommodate a low-power/low-weight state-of-the-art spectrometer. A multisensor system with miniature time-of-flight detectors together with the spacecraft spin motion provide a uniform, though not contiguous, angular coverage of the unit sphere. New detector multiplexing techniques permit the operation of IIS with maximum sensitivity without sacrificing time or angular resolution because of duty cycle effects. IIS is an integral but physically separate part of the solar wind ion analyser JPA in the Giotto payload. The sensor system and the operation of IIS are described. The flight performance is illustrated by observations in the undisturbed solar wind and near the comet.

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