Gated time-of-flight plasma composition analyzer for space physics research

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We have constructed and tested a prototype instrument for space plasma physics research. The instrument is capable of measuring total ion velocity distribution functions as well as velocity distribution functions for individual mass-per-charge (m/q) species. The instrument consists of a deflection system, a toroidal energy-per-charge (E/q) analyzer, and a hemispherical condenser that serves either as the second stage of E/q analysis or as a gated time-of-flight velocity filter. The deflection system subtends a full 360° in azimuth and allows one to select ions for analysis in the toroidal section according to their elevation angle with respect to the axis of the instrument. The hemispherical condenser accepts a fraction of the ions transmitted by the toroidal analyzer through an electronic shutter at its entrance plane. With the shutter open, total ion distribution functions are measured. By appropriately gating the shutter and measuring the time of flight of ions introduced into the hemisphere, ion velocities are measured and m/q determined. The dimensions of the instrument have been chosen for measurements of the interplanetary solar wind at distances of 4–20 solar radii (Rsun) from the surface of the sun, consistent with the requirements of a solar probe mission. It can also be adapted to make measurements at 1 a.u.