Instrument Overview
  ===================
    (excerpted from [KEPPLERETAL1992A])
 
    The EPAC sensor will measure the fluxes, angular distributions,
    energy spectra, and composition of ions in the energy range
    from 300 keV/nucleon to 25 MeV/nucleon.
 
    The instrument generates 12 different classes of data.  All
    events are categorised by their (dE/dx)-signal into three crude
    classes; their respective numbers are transmitted from three
    event memories.  So besides the 32 event strings we also get
    per EDF the total number of events recorded during that time
    interval.  Less detailed information on energy spectra are
    obtained with higher time resolution from 4 groups of ions.  8
    energy channels are formed for each group.  Bands,
    corresponding to the (dE/dx-E) tracks are stored in a RAM
    look-up table.  All events are sorted accordingly for 4 ion
    groups (He, C-N-O, S-group, F-group).  For telescopes 2 and 3
    these are in addition resolved into 8 spin-sectors.  A full set
    will be transmitted in about 34 min.  If only one species is
    selected, time resolution increases to ~ 8.5 min.
 
    Protons are identified separately in 8 channels (3-bit PHA)
    using the B-detector outputs (500 keV to 1.6 MeV).  All
    channels are resolved into eight sectors.
 
    From the A-detector's output, integral fluxes of ions are
    obtained.  Contributions will come from ions above an energy,
    defined by dead-layer thickness and electronic threshold of
    about 145 keV.  Contribution from electrons scattered through
    large angles may contribute to the lowest channel, but as the
    detector thickness corresponds to the range of ~ 25 keV
    electrons, its electron detection efficiency is certainly << 1.
 
    The 4 A-detector outputs are connected to the PHA through a
    multiplexer (as are the B-detectors).  The thresholds of the
    PHA are adjusted such, that in 'High Gain'-Mode channel 1 to 3
    'protons' (Z >= 1), in channel 4 to 5 '[alpha]-particles' (i.e.
    Z >= 2), in channel 6-8 'oxygen' (i.e.  Z >= 6) is detected.
    In 'Low-Gain', the passbands are shifted one channel up:
    channel 1 and 2 record now Z >= 1, channels 3 to 4 Z >= 2,
    channels 5 to 7 Z >= 6 and channel 8 Z >= 10 particles.  The
    latter corresponds to about 500 keV/nucleon.  This class of
    data is obtained in 16 min.
 
    Much higher time resolution is obtained from rates, which
    correspond to the integral over energy of the proton and the Z
    >= 1 spectra.  Telescopes 2 and 3 are resolved in eight
    sectors.
 
    The solar aspect angle varies in the course of the mission from
    ~ 90 [degrees] after launch to less than 11.5 [degrees] at
    Jupiter.  It will again increase during polar passage.  This
    means, that there will be periods, when telescopes 1 or 2 will
    be fully illuminated by the sun and might affect the Z >= 1
    data, but not coincidence rates.
 
    Two electron channels corresponding to 100 keV <= E <= 0.4 MeV
    and to E >= 0.3 MeV are also formed for each telescope.  These
    channels are defined from proper combination of dicriminator
    thresholds.  Their energy range is, however, not very
    accurately defined (due to electron scattering).  For heavy
    ions there are also 16 rate channels for each of the 4
    telescopes and each of the 4 species.  They are read out once
    every 8 minutes.
 
    For each telescope the background rates of detector B and C are
    transmitted, each accumulated over 4 minutes.  The equivalent
    geometrical factor is F[B] = 1.60 cm^2 and F[C] = 6.02 cm^2.
    For coincidence rates of all 3 detectors the geometrical factor
    G = 0.08 cm^2 ster applies.