SupraThermal Ion Compostion Spectrometer (STICS)

The STICS is designed to measure 3-dimensional distribution functions of major ion species with sufficient time resolution to determine source regions (solar wind vs. ionosphere) and acceleration processes of suprathermal ions in the near and distant geomagnetic tail.

STICS separatgely determines the mass, energy and charge state of low energy chaged particles in the range 30 to 230 keV/charge with mass per charge and veleocity determinations continuing to 10 keV/charge (STICS mass bins) . It comprises a quadrispherical deflection system for the selection of particles of the desired energy per charge followed by a TOF telescope for the measurement of particle velocity and energy. A positon measuring system on the START TOF electrode provides information on the entrance angle of the particle into the telescope.

The sensor (cross section diagram) contains the deflection system TOF telescope, HV power supplies and detector preamplifiers. The remainder of the analog electronics, including shaping amplifiers, discriminators, TOF circuits and analog-to-digital converters (ADCs) are located in the separate Analog Electronics box (block diagram). This is done to free the mechanical design of these circuits from the constraints imposed by the odd shape of the sensor package and to make possible the sharing of common layouts with ICS sensor processing. Outputs from the Analog Electronics box pass into the shared EPIC Data Processing Unit where they are processed for transmission to the spacecraft.

A schematic description of the operation of the deflection system and telescope is as follows:

  1. Particles enter the Entrance Aperature through a simple collimator.
  2. Particles are deflected by the E-field in the deflection system. This field is created by the voltage from a pair of high voltage power supplies (the DPPS) applied to the deflection plates. The DPPS is programmed to step the voltage on the plates once per spin. The steps are logarithmically spaced and a sequence of 32 steps takes the system from near 0 volts deflection to the maximum deflection voltage.
  3. Particles of correct E/Q make it through the deflection system and strike the thin carbon foil at the entrance of the TOF telescope.
  4. Secondary electrons ar knocked off the inner surface of the foil.
  5. The incoming particles pass undisturbed into and through the TOF telescope chamber.
  6. The secondary electrons are deflected by E-fields inside the telescope and strike one of the three START MCPs. The deflection preserves the position of origin of these electrons in the position they strike the MCPs.
  7. Six discrete anodes (two per MCP) lie behind the MCPs, providing position information on the incoming particles.
  8. At the far end of the TOF telescope the incoming particles strike one of the three solid state detectors.
  9. Secondary electrons from the from surfaces of the SSDs are deflected onto three STOP MCPs.
  10. Energy information comes from the SSDs. Energy/charge information comes from knowledge of the voltage on the deflection system, elevation angle of the incoming partile comes from the START MCP anodes, clock angle of the incoming particle comes from the S/C spin/sector clock and TOF information comes from the signals from the START and STOP MCP anodes.
  11. From simultaneous measurements fo the TOF (t), the residual energy (Emeas), and a knowlede of the energy per charge (E/Q) from the deflection system, EPIC determines the mass (M), ionic charge (Q), and teh incident energy (E) of each ion.