EPD - Energetic Particles Detector

EPD
Energetic Particles Detector
D. J. Williams, Principal Investigator
The Johns Hopkins University, APL

MISSION OBJECTIVES

Measure the energy and angular distribution, composition, and stability of trapped radiation at Jupiter.
Study the interaction of these energetic particles with the Galilean satellites and the solar wind.
Derive thermal plasma flow velocities and temperatures.
Examine adiabatic and non-thermal processes in the trapped radiation.

SUMMARY

The energetic particles detector (EPD) is designed to measure the numbers and energies of ions and electrons whose energies exceed about 20 keV. (An electron volt, eV, is the unit of energy equal to the energy that an electron acquires in falling through an electrical potential of 1 volt.) The EPD can also measure the direction of travel of such particles and, in the case of ions, can determine their composition (whether the ion is oxygen or sulfur, for example).

The EPD uses silicon solid-state detectors and a time-of-flight detector system to measure changes in the energetic particle population at Jupiter as a function of position and time. These measurements will tell us how the particles get their energy and how they are transported through Jupiter's magnetosphere.

The EPD weighs 10.5 kilograms and uses 10.1 watts of power on average.

EPD DESCRIPTION

39K

Instrument is divided into two systems: The Low-Energy Magnetospheric Measurements System (LEMMS) and the Composition Measurements System (CMS).
Both the LEMMS and CMS are contained in one package.
The LEMMS and CMS are bi-directional, solid-state detector telescopes mounted on a platform that rotates via a stepper motor to eight positions.
The forward (0 degree) ends of the LEMMS and CMS have an unobstructed view over the unit sphere and can be positioned behind a shield that contains calibration sources and prevents the entrance of incoming radiation.

DESIGN DETAILS

The LEMMS is a double-ended telescope containing eight heavily shielded silicon solid-state surface barrier totally-depleted detectors.

The LEMMS measures Electron energies from 15 keV to > 11 MeV, and ions from 22 keV to ~55 MeV.
The CMS has two types of energetic particle telescopes: A time-of-flight (TOF) telescope and a pair of \106ExE solid-state detector telescopes.

The CMS measures ions from energies of > 10 keV to > 10 MeV per nucleon and identifies species from H to Fe.
The EPD is located on the Science Boom.
The EPD has an internal alarm monitor that checks four temperatures, one voltage and one current against defined alarm limits.

INSTRUMENT PARAMETERS

Instrument Mass: 10.5 kg
Power Consumption:
- Instrument - 6.0 W
- Heaters - 4.0 W
Microprocessor: 1802 type
ROM/RAM: 6 Kb/2.25 Kb
Fields of View:
- LEMMS - 15 and 45 Degrees
- CMS - 18, 23 and 54 Degrees
Size: 19.5 x 27 x 36.1 cm
Thermal Range:
- Operating (GLL 3-210)
  - Electronics: -25 to 40 Degrees C
  - Detectors: -25 to 25 Degrees C
  - Log Amp.: 15 to 35 Degrees C
  - Motor: -30 to 60 Degrees C
- Non-operating (GLL 3-210)
  - Electronics: -25 to 40 Degrees C
  - Detectors: -25 to 25 Degrees C
  - Log Amp.: -25 to 40 Degrees C
  - Motor: -30 to 60 Degrees C
Instrument Modes:
- Off
- POR
- On
- Safe

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EPD - Energetic Particles Detector