A modulated-grid, split-collector-plate Faraday cup, is used to
study the positive ions and electrons in the solar wind,
transition region, and magnetotail. Parameters derived on a
routine basis are proton velocity, number density, and temperature
(most probable thermal speed).
The collector plate split is perpendicular to the spacecraft spin
axis in order to measure the flow angle of the ions in a
meridional plane; the flow angle in the spacecraft equatorial
plane is determined from the fluxes measured as the spacecraft
Electrons are measured using 21 logarithmically-spaced energy
windows covering the energy/charge range between 23 and 1935
volts. Positive ions are studied using 24 energy windows covering
the range between 50 and 7000 volts.
The instrument has three operating modes. The tracking mode
yields the best time resolution which is about 1 minute. A single
energy window is used during a spacecraft rotation. The ion
spectrum is obtained in eight spacecraft revolutions using a
subset of the energy windows that track the peak of the solar
wind. In this mode, fluxes are measured during 11.25-degree
sectors of the spacecraft spin while the instrument is looking
within the 90 degree sector centered on the sun direction and
during 45 degree sectors for the remainder of the rotation. The
other modes yield a spectrum using all 24 windows (with the same
angular sectors described above) or a spectrum that results from
integrating the observed fluxes over 45 degree sectors for the
entire spacecraft rotation.
Electron data are obtained in all modes, but are not usually
Parameters derived on a routine basis are proton velocity, number
density, and temperature (most probable thermal speed). Those
parameters are obtained from a non-linear, least-squares fit to
the observed fluxes using a convected, isotropic Maxwellian model.
Key Parameters for the Plasma instrument are computed at MIT using
Level Zero data that are staged to the ISTP/CDHF approximately two
weeks after being received on Earth. Thus the plasma instrument's
Key Parameters lag real time by something greater than 2 weeks,
but less than four.
The PI is Dr. Alan Lazarus, Room 37-687, MIT, Cambridge, MA, 02139; email: firstname.lastname@example.org and he should be contacted early in the process before use of these data for publication or at a conference.
See also the Plasma Instrument Homepage.