Cassini Plasma Spectrometer (CAPS)

Cassini Plasma Spectrometer (CAPS)

The Cassini Plasma Spectrometer (CAPS) team is led by Principal Investigator Frank Crary at Southwest Research Institute with contributions from an international team of co-investigators. The CAPS instrument consists of three sensors: an ion mass spectrometer provided by the Los Alamos National Laboratory (LANL) and CRPE (France), an ion beam spectrometer produced by LANL and VTT (Finland) and an electron spectrometer (ELS) provided by a European team led by MSSL (lead co-investigator Andrew Coates, project manager Gethyn Lewis). The ELS team includes the Rutherford Appleton Laboratory (RAL) and the Norwegian Defence Research Establishment (NDRE), who fulfill similar roles to those that they have in the Cluster PEACE team. An image of the CAPS instrument is on the right-hand side.

Cassini CAPS/ELS in the calibration chamber at MSSL

ELS is a top-hat electrostatic analyser which can measure electrons with energies between 0.5 eV and 26 keV (419 - 100 000 km/s, or 0.001 - 0.3 times the speed of light). The design is very similar to that used for the PEACE/HEEA instrument flown on the Cluster and Cluster II spacecraft. CAPS/ELS data have been used for scientific studies in the magnetospheres of Earth, Jupiter and Saturn, and the Solar Wind. The sensitivity of ELS is such that it can measure electron densities as small as 100 per m3 (there are about 1026 particles m3 in the air that we breath) with temperatures from several eV up to 10s of keV (~10000 to 100 million degrees C). After it was built ELS was calibrated at MSSL. The picture on the right shows ELS in the calibration chamber at MSSL.

Scientific results from CAPS/ELS include:

  • Discovery of an ionosphere over Saturn's rings.
  • Discovery of large negatively charged molecules in Titan's upper atmosphere.
  • Discovery of charged ice grains in plumes of gas escaping from Enceladus' south pole.

Page last modified on 11 jan 12 09:02