- Overview
The Charged Particle Measurement
Experiment (CPME) was designed and built at JHU/APL.
The original Principal Investigator was S. M. Krimigis. The
current Principal Investigator is R. B. Decker
( robert.decker@jhuapl.edu).
The
CPME (photo)
consists of a number of detector assemblies whose fields
of view and orientation relative to the ecliptic plane are shown in
CPME schematic.
A description of the CPME can be found in the published paper by Sarris
et al. [J. Geophys. Res., 81, 2341, 1976]. A detailed account
of various instrumental characteristics (energy passbands, flux conversion
factors, data formats, etc.) can be found in the unpublished CPME
handbook by Armstrong [1976].
Most of the detectors have their fields of view centered in the ecliptic plane,
so that fairly comprehensive angular distributions in this plane can be obtained
for several species, as indicated in column seven of the
CMPE PET Table,
by using the spin of the spacecraft. Orientations of the 8, 45-degree
(full-angle) sectors of the CPME on IMP-8 are illustrated in
CPME sector look directions.
Relevant information for each detector element of the
CPME is given in Armstrong's comprehensive handbook [1976].
- PET Assembly
The detector element designated as PET (proton-electron
telescope) in the
CPME schematic
is shown in the
PET schematic.
The PET is of particular interest because it provides measurements of proton,
alpha particle, Z>=3, Z>=6, and Z>=20 ion fluxes and of high energy electron fluxes
in several differential energy ranges, with relatively high time resolution.
Note also from the
CMPE PET Table
that angular information is available in 8, 45 deg sectors for six PET channels.
As illustrated in the
PET schematic,
a 45 deg wide acceptance cone leads to a four-
element detector stack, faced on the front with a 0.3 mg/cm^2 nickel foil to
reject light contamination. D1 and D2 are silicon surface barrier, totally
depleted detectors placed close together near the front of the telescope to
take advantage of the entire forward field of view; the geometrical factor for
the D1D2 combination is 1.5 cm^2-sr. D3 is a thick lithium-drifted detector
placed farther back along the telescope axis; the geometrical factor is thus
reduced to 0.32 cm^2 sr for D2D3 coincidence.
The final detector is a plastic scintillator cup configured as an
anticoincidence counter surrounding the D1-D2-D3 stack.
The anticoincidence cup eliminates most signals from off-axis
penetrating particles. The tungsten absorber was included to extend the
proton energy range using multiple dE/dx measurements to 145 MeV.
Ten differential proton channels, operated in anticoincidence with the
scintillator, are defined by on-board logic over the energy range 0.29-145
MeV. An additional proton channel defined by logic D2D3 is sensitive to
protons in the energy range 190-440 MeV, but is not operated in
anticoincidence with the scintillator; therefore, it accepts particles
entering from both the forward and backward directions.
Additional on-board logic defines six differential alpha particle
channels in the energy range 0.59-52 MeV/nucleon, two channels
that respond to Z>=3 nuclei in the ranges 0.70-3.3 and 6.0-105 MeV/nucleon,
and two channels that respond to Z>=6 and Z>=20 nuclei in the ranges
1.45-3.30 and 3.3-8.8 MeV/nucleon, respectively. There are three
electron channels that respond over the energy range 0.22-2.5 MeV.
The PET assembly was extensively calibrated over the energy range 0.20-
576 MeV at the Goddard Space Flight Center Van de Graff, at the Naval
Research Laboratory cyclotron, and at the Space Radiation Effects
Laboratory synchrocyclotron. Details of calibration and channel logic
definitions are described by Cashion et al. [Rep. CP-025,
JHU/APL, 1973].