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Solar Wind Ion Composition Spectrometer

SWICS is designed to determine uniquely the elemental and ionic-charge composition, and the temperatures and mean speeds of all major solar-wind ions, from H through Fe, at solar wind speeds ranging from 175 kms-1 (protons) to 1280 kms-1 (Fe8+).

The SWICS sensor, which covers an energy per charge range from 0.16 to 59.6 keV/q in ~ 13 minutes, is based on the technique of particle identification using a combination of electrostatic deflection, post-acceleration, and a time-of-flight (TOF) and energy measurement. The operating principle of the sensor and the functions of the five basic sensor elements employed are:

  • Ions of kinetic energy E, mass m and charge (ionization state) q enter the sensor through a large area, multi-slit collimator which selects proper entrance trajectories for the particles
  • The electrostatic deflection analyzer serves as an energy- per-charge (E/q) filter, allowing only ions within a given energy-per-charge interval (determined by a stepped deflection voltage) to enter the TOF versus Energy system
  • Ions are post-accelerated by a ~ 30 kV potential drop just before entering the TOF versus Energy system. The energy they gain is sufficient to be measured adequately by the solid-state detectors, which typically have a ~ 30 keV energy threshold. An energy measurement is essential for determining the elemental composition of an ion population and ions with energies below ~ 30 keV must be accelerated if their mass is to be identified
  • In the time-of-flight system the velocity of each ion is determined by measuring the travel time τ of the particle between the start and stop detectors separated by a distance of 10 cm
  • The particle identification is completed by measuring the residual energy of the ions in a conventional low-noise solid-state detector

Summary of Objectives

The measurements made by SWICS will have an impact on many areas of solar and heliospheric physics, in particular providing essential and unique information on:

  • conditions and processes in the region of the corona where the solar wind is accelerated
  • the location of the source regions of the solar wind in the corona
  • coronal heating processes
  • the extent and causes of variations in the composition of the solar atmosphere
  • plasma processes in the solar wind
  • the acceleration of energetic particles in the solar wind
  • the thermalization and acceleration of interstellar ions in the solar wind, and their composition
  • the composition, charge states and behaviour of the plasma in various regions of the Jovian magnetosphere

Last Update: 08 December 2006

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