An Introduction to Space Instrumentation,
Edited by K. Oyama and C. Z. Cheng, pp. 203-215.
© TERRAPUB, 2013.

Imaging thermal ion mass and velocity analyzer

Andrew W. Yau, E. Peter King, Peter Amerl, Kaare Berg, Greg Enno, Andrew Howarth, Ivan Wevers, and Andrew White

Department of Physics and Astronomy, University of Calgary, 2500 University Dr NW Calgary, Alberta T2N1N4, Canada

Abstract: The aim of an imaging thermal ion mass and velocity analyzer is to apply imaging techniques to measure in-situ the mass composition and detailed velocity phase space distributions of a thermal plasma population in a planetary ionosphere or magnetosphere and use the measured distributions to derive the bulk plasma parameters and to detect the possible presence of non-thermal distributions. A hemispherical electrostatic analyzer (HEA) with a planar entrance aperture can sample simultaneously incident ions or electrons over an extended energy range and the full 360° range of incident azimuth, and disperse them by their energy-per-charge while retaining their incident azimuth, thus providing a means to image the 2-dimensional (2D) ion or electron energy-per-charge and angular (azimuth) distribution. Therefore an ion mass and velocity analyzer consisting of a HEA embedded with an ion-mass spectrometer is capable of imaging the 2-D detailed ion velocity distribution—and measuring the 3D distribution on a spinning spacecraft if the planar entrance aperture is aligned along the spacecraft spin axis. For 3D velocity distribution measurements on a 3-axis stabilized spacecraft, an analyzer with electrostatic deflection capability will be required to deflect ions at arbitrary incident elevation angles into the planar entrance aperture for sampling. An imaging thermal ion mass and velocity analyzer is presented that combines a HEA, a time-of-flight ion mass spectrometer, and a pair of electrostatic deflectors, and is capable of sampling low-energy ions (∼1 to 100 eV/e) of all mass species (1 to > 40 AMU/e) from all incident directions on a non-spinning platform, at up to (10% energy resolution (ΔE/E) and ∼5° angular resolution. Using the HEA to measure the energy-percharge of each detected ion and the time-of-flight gate to measure the transit time of the ion inside the analyzer, this instrument can resolve all major ion species in the ionosphere including H+, He+ and O+, and adjacent molecular ion species such as N2+, NO+ and O2+ under favorable conditions. In addition, it can image the 2D and measure the 3D velocity phase space distributions of each major ion species.
Key words: Ion mass spectrometer, plasma analyzer, hemispherical analyzer.

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