Wind SMS Suite SupraThermal Ion Composition Spectrometer (SMS/STICS) Energy-Resolved Pitch-Angle Distributions (ERPAs), Level 2 (L2), 30-minute Data in Magnetosphere

The E/Q voltage is stepped through 32 values, sitting at each value for approximately 24 sec., to measure ions over the full E/Q range of 6 - 200 keV/e. Ions then pass through a carbon foil and TOF chamber, before finally impacting on a solid-state detector (SSD) for energy measurement. STICS combines these three measurements of E/Q, TOF and residual energy, producing PHA words.

This triple-coincidence technique greatly improves the signal to noise ratio in the data. Measurements of E/Q and TOF without residual energy also produce PHA words. These double-coincidence measurements are characterized by better statistics since ions whose energy does not allow them to be registered by the SSD can still be counted in double-coincidence measurements.

However, ion identification in double-coincidence measurements are limited to a select number of ions that are well separated in E/Q - TOF space. The STICS instrument provides full 3D velocity distribution functions, through a combination of multiple telescopes and spacecraft spin. The instrument includes 3 separate TOF telescopes that view 3 separate latitude sectors, as shown in Figure 1 (spdf.gsfc.nasa.gov/pub/data/wind/documents/wind_stics_lv2_release_notes_revD.pdf).

In addition, the WIND spacecraft spins, allowing the 3 telescopes to trace out a nearly 4π steradian viewing area. The longitudinal sectors are shown in Figure 2. The solar direction is in sectors 8-10 while the earthward direction is in sectors 0-2.