Instrument Overview
  ===================
 
  The Cosmic Dust Analyser instrument (CDA) on the Cassini orbiter is
  the successor of the dust detectors flown on the Ulysses and the
  Galileo spacecraft. The instrument accomplishes the detection of
  dust impacts by two different means: (1) a high rate detector (HRD)
  using two separate polyvinylidene fluoride (PVDF) sensors, and
  (2) a Dust Analyser (DA) based upon impact ionization.  The DA
  measures the electric charges carried by the dust particle, the
  impact direction, the impact speed, mass, and the chemical
  composition, whereas the HRD is only capable to determine the mass
  for particles with a known speed.  The DA detector consists of
  three components: the charge detection unit, the impact ionization
  detector itself, and the time-of-flight (TOF) mass spectrometer.
 
  Note that the charge detection unit subsystem generates signals
  (so-called  'QP signals')  with a higher sampling rate than the signals
  generated by the impact ionization detector (QI, QT, QC, MP signals.)
  Furthermore, as the charge detection unit subsystem is sensitive
  to big particles only (> 5 microns), it was triggered only 6 times
  during the cruise phase. Therefore, in order to keep the telemetry data
  volume low, the QP signals were not always transmitted to Earth. This
  explains why the QI, QT, QC and MP signals directories in the
  PDS volumes may contain more signals than the QP directory.
 
  For a detailed description of the instrument, please refer to
  [SRAMAETAL2004B] (see CDAREFS.CAT). A separate instrument.cat file
  will be provided for HRD.
 
 
  The Charge Detection Unit
  =========================
 
  The charge detection unit (CDU) consists of 4 entrance grids
  mounted in front of the ionization detector. The outermost and
  innermost grids are grounded, while the two innermost inclined
  grids are connected with a charge amplifier (QP charge signal).
  A charged particle flying through the entrance grid system induces
  its charge onto the innermost grids. The inclined grid mounting
  leads to asymmetric signal shapes which allows the determination of
  the particle direction as well as the particle speed within a
  plane.
 
  The Impact Ionization Detector
  ==============================
 
  The impact ionization detector consists of a hemispherical impact
  target (small inner target made of Rhodium chemical analyser target
  (CAT), a large outer target made of Gold impact ionization target
  (IID), and the ion collector grid system. The plasma constituents
  generated by the dust impact onto the impact target are separated
  by the electric field between the target and the ion grid. The
  plasma electrons are collected at the CAT (QC charge signal) and
  the IID (QT charge signal), while most of the positive plasma ions
  are collected at the ion collector grid system (QI charge signal).
  Ions escaping the impact ionization detector are inducing their
  charges onto the charge detection grids (QP charge signal).  The
  particle mass and the impact speed is deduced from the evolution of
  the impact plasma:  the charge yield of the impact plasma is a
  function of the impactor's mass and velocity, while the plasma
  charge rise time is dependent on the impact speed only.
 
  The Time-of-flight (TOF) Mass Spectrometer
  ==========================================
 
  The TOF mass spectrometer consists of the chemical analyser target
  (CAT), the chemical analyser grid located 3 mm in front of the CAT,
  and the multiplier dynodes connected with the Dynode Logarithmic
  Amplifier (MP signal). Due to the strong electric field between the
  grid and the CAT, positive plasma ions are separated very quickly
  from the plasma and accelerated toward the multiplier, forming a
  time-of-flight mass spectrum.