INSTRUMENT : PLASMA SCIENCE EXPERIMENT
  SPACECRAFT : VOYAGER 1
 
  Instrument Information
  ======================
    Instrument Id                  : PLS
    Instrument Host Id             : VG1
    Principal Investigator         : JOHN D. RICHARDSON
    Pi Pds User Id                 : JRICHARDSON
    Instrument Name                : PLASMA SCIENCE EXPERIMENT
    Instrument Type                : PLASMA INSTRUMENT
    Build Date                     : 1973
    Instrument Mass                : 9.900000
    Instrument Length              : UNK
    Instrument Width               : UNK
    Instrument Height              : UNK
    Instrument Serial Number       : SN002
    Instrument Manufacturer Name   : MASSACHUSETTS INSTITUTE OF
                                     TECHNOLOGY
 
 
  Instrument Description
  ======================
    The Voyager Plasma Science experiment consists of four
    modulated Grid Faraday Cups, three (A, B, C) of which are
    positioned about the Telemetry Antenna Axis and generally point
    toward the Earth with the fourth (D) at a right angle to this
    direction.  Ion currents are sampled simultaneously in all four
    cups, electrons in the D-cup only.  The instrument has an
    energy/charge range of 10-5950 V.  Data is taken in four ways,
    high and low resolution ion modes and high and low energy
    electron modes with energy resolution varying between 3.6 and
    29%.  The integration time for each energy channel can be
    varied; 0.21 s/channel is used at Jupiter and Saturn.
    Supersonic flow can be observed only when one of the detectors
    points within 45 degrees of the plasma velocity, subsonic flow
    is observed at all orientations.  The current observations as a
    function of energy/charge allows determination of the plasma
    density, temperature, and velocity.
 
 
  Science Objectives
  ==================
    The objective of the Plasma Instrument is to characterize
    plasma conditions throughout the Voyager trajectory, in the
    solar wind, during the planetary encounters, and in the
    interstellar medium.
 
 
  Operational Considerations
  ==========================
    Each detector has an effective field of view which is a cone of
    half angle 45 degrees; the detector response falls off quickly
    at higher angles.  Thus, for the instrument to measure ion
    parameters in a supersonic or transonic plasma some of the
    detectors must look into the plasma flow.  Secondary ions and
    electrons produced within the detectors can also effect the
    measurements, especially if large fluxes of hot ions or
    electrons are present.  These effects are not well modeled are
    rarely significant.  The instrument does not measure
    composition, only energy/charge, so a model of plasma
    composition must be adopted to fit the ion data.  The choice of
    models can be unambiguous for large Mach number flow (M>3) but
    is non-unique for lower Mach numbers.  After the Jupiter
    encounter the highest energy/charge channels of the A, B, and C
    detectors often contain spurious signal and currents in the
    upper half of the energy range should be examined carefully
    before use.
 
 
  Calibration Description
  =======================
    The instrument was calibrated at MIT using ion and electron
    beams and compared to output from other Faraday cups in the
    same beam.  Current levels are also calibrated in-flight by
    injecting known currents into the detectors with the modulators
    on and off.  Much theoretical modeling has been done on the
    response of the detectors to arbitrary plasma conditions.
    Contact the PI for more information.
 
 
  Detectors 'A', 'B', 'C', and 'D'
  ================================
    Detector Type                  : FARADAY CUP
    Detector Aspect Ratio          : 0.000000
    Nominal Operating Temperature  : 278.000000
 
    The PLS instrument consists of four Faraday cups.  Three of
    these (A, B, C) are arranged in a cone whose central axis is
    parallel to the direction of the telemetry antenna.  The look
    direction of each of these cups is offset 20 degrees from the
    central axis.  Detector D has a look direction approximately
    perpendicular to the direction of the telemetry antenna.  Each
    detector consists of three modulator grids, six shield grids
    and a suppressor grid in front of the collector.  It measures
    ion currents in the range 10-5950 V.
 
    Depending on the integration time, the detectors measure
    current from a minimum of 3.e-14 to 2.e-13 AMPS up to a maximum
    of 6.e-8 AMPS.  The integration time for each energy channel
    can be varied from .03 to .93 seconds.  The time between
    successive spectra varies from 12 to 192 s.
 
 
    'PLS' Section Parameter 'ELECTRON CURRENT'
    ------------------------------------------
      Sampling Parameter Name        : TIME
      Section Id                     : PLS
      Instrument Parameter Unit      : AMPS
      Minimum Instrument Parameter   : 0.000000
      Maximum Instrument Parameter   : 0.000000
      Minimum Sampling Parameter     : 0.030000
      Maximum Sampling Parameter     : 0.930000
      Sampling Parameter Unit        : SECOND
 
 
    'PLS' Section Parameter 'ION CURRENT'
    -------------------------------------
      Sampling Parameter Name        : TIME
      Section Id                     : PLS
      Instrument Parameter Unit      : AMPS
      Minimum Instrument Parameter   : 0.000000
      Maximum Instrument Parameter   : 0.000000
      Minimum Sampling Parameter     : 0.030000
      Maximum Sampling Parameter     : 0.930000
      Sampling Parameter Unit        : SECOND
 
 
  Electronics
  ===========
    Currents from the four detectors are amplified, filtered, and
    integrated using four different measurement chains.  A single
    8-bit logarithmic A-D converter samples the four outputs of the
    measurement chains and transfers the data to the spacecraft.
    The high voltage modulator supplies a DC pedestal and a super-
    imposed 400 HZ square wave modulation voltage.  For positive
    ions the modulator grids of all four detectors are driven in
    parallel.  A more complete description and block diagram of the
    instrument electronics is available in [BRIDGEETAL1977].
 
 
  Operating Modes
  ===============
    The four operating modes of Voyager PLS are listed below.
    Instrument power consumption is 8.1 W for all modes.
 
    E1: Low energy electron mode which measures the range 10-140 V
        with 16 contiguous channels.
 
    E2: High energy electron mode which measures the range 10-5950
        V with 16 contiguous channels.
 
    L:  Low-resolution ion mode which measures the range 10-5950 V
        with 16 contiguous channels.
 
    M:  High resolution ion mode which measures the range 10-5950
        V with 128 contiguous channels.
 
 
  Instrument Mounting
  ===================
    The PLS instrument is located on the Science Boom.  The center
    of the main detector cluster (A, B, C) points parallel to the
    spacecraft telemetry antenna and detector D is at right angles
    to this direction.