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

We have constructed and tested a prototype instrument for space plasma phys ics research. The instrument is capable of measuring total ion velocity dis tribution functions as well as velocity distribution functions for individu al mass-per-charge (m/q) species. The instrument consists of a deflection s ystem, a toroidal energy-per-charge (E/q) analyzer, and a hemispherical con denser 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 degrees in azimuth and allows one to select ions for analysis in the toroid al section according to their elevation angle with respect to the axis of t he instrument. The hemispherical condenser accepts a fraction of the ions t ransmitted by the toroidal analyzer through an electronic shutter at its en trance plane. With the shutter open, total ion distribution functions are m easured. By appropriately gating the shutter and measuring the time of flig ht of ions introduced into the hemisphere, ion velocities are measured and m/q determined. The dimensions of the instrument have been chosen for measu rements of the interplanetary solar wind at distances of 4-20 solar radii ( R-sun) from the surface of the sun, consistent with the requirements of a s olar probe mission. It can also be adapted to make measurements at 1 a.u. ( C) 1999 American Institute of Physics. [S0034-6748(99)04907-2].