PWS - Plasma Wave Subsystem

PWS
Plasma Wave Subsystem
Donald A. Gurnett, Principal Investigator
University of Iowa

MISSION OBJECTIVES

Investigate the role played by plasma waves and radio emissions in controlling the scattering and/or loss of trapped radiation in the Jovian magnetosphere.
Derive fundamental plasma parameters, such as electron density, from observations of plasma wave phenomena.

SUMMARY

Particles of plasma are bound to the magnetic field. Motions within the plasma can perturb the surrounding magnetic and electric fields. Changes with time of the electric and magnetic fields within plasma are called "plasma waves." There are a great many different sorts of waves that affect a plasma or are excited by a plasma. Some of these waves can cause particles to be lost from the magnetosphere. The Plasma Wave Subsystem (PWS) is designed to measure the properties of varying electric fields over the frequency range from 5 hertz to 5.6 megahertz and of varying magnetic fields from 5 hertz to 160 kilohertz - and to identify the plasma waves present.

An electric dipole antenna (a simple antenna of the form that one often sees to improve radio reception on Earth) will study the electric fields of plasmas, while two search coil magnetic antennas will study the magnetic fields. The electric dipole antenna is mounted at the tip of the magnetometer boom. The search coil magnetic antennas are mounted on the high-gain antenna feed. Nearly simultaneous measurements of the electric and magnetic field spectrum will allow electrostatic waves to be distinguished from electromagnetic waves.

The PWS weighs 7.1 kilograms and uses an average of 9.8 watts.

PWS DESCRIPTION

18K

The PWS consists of one 6.6-m tip-to-tip electric dipole antenna (mounted on the end of the 10.6-m magnetometer boom) and two search coil magnetic antennas (mounted on the high-gain antenna feed).
The dipole antenna has two elements, with a preamplifier assembly between them, mounted in opposing directions perpendicular to the magnetometer boom and the spacecraft spin axis. The dipole antenna measures electrostatic waves in the frequency range of 5.62 Hz to 5.6 MHz.
One search coil magnetic antenna is optimized for low frequencies (5 to 3.5 KHz) and is oriented parallel to the electric dipole antenna. The other search coil magnetic antenna is optimized for high frequencies (1 to 50 KHz) and is oriented perpendicular to the electric dipole antenna. Two search coil preamplifiers are mounted on the high gain antenna near the search coils.
The electronics for processing the signals from the antennas preamplifiers is contained in a single package.

DESIGN DETAILS

The main electronics package is mounted in the spacecraft body near the base of the magnetometer boom and contains a low rate system for survey spectra and a high rate system for wideband spectra.
The low rate system contains three spectrum analyzers:
1. A high-frequency analyzer with 42 frequencies between 100.8 KHz and 5.645 MHz with delta-f/f of 10.0%, dynamic range of 100 dB, spectrum sweep time of 18.67 sec, and a bandwidth of 1.34 kHz.
2. A medium-frequency analyzer with 112 frequencies between 40 Hz and 160 KHz with delta-f/f of 8.0%, dynamic range of 100 dB, and spectrum sweep time of 18.67 sec. This frequency range is divided into four bands, of 28 frequencies, with bandwidths of 4.26, 6.67, 120, and 1510 Hz.
3. A low-frequency analyzer with four logarithmically-spaced channels between 5.62 and 31.1 Hz, a delta-f/f of 67%, dynamic range of 110 dB, and bandwidths of 0.83, 1.86, 2.75, and 4.79 Hz. All four channels are sampled in 2.67 sec.
The high rate receiver provides waveform measurements in three frequency bands, 5 Hz to 1 kHz, 50 Hz to 10 kHz, and 50 Hz to 80 kHz.

INSTRUMENT PARAMETERS

Instrument Mass: 7.14 Kg
Power Consumption:
- Instrument - 6.8 W
- Suppl. Heaters - 3.0 W
Microprocessor: 1802 type
ROM/RAM: 0 /512 b
Size: 41.8 x 17.8 x 12.2 cm
Thermal Range:
- Operating (GLL 3-210)
  - Mag. Search Coils: -105 to 80 Deg. C
  - Mag. Field Pre-amp: -20 to 82 Deg. C
  - Elect. Field Pre-amp: -25 to 55 Deg. C
  - Elect. Dipole Ant.: -190 to 151 Deg. C
  - Elect. Dipole Latch: -15 to 40 Deg. C
  - Elect. Dipole Hinge: -171 to 40 Deg. C
- Non-operating (GLL 3-210)
  - Mag. Search Coils: -105 to 80 Deg. C
  - Mag. Field Pre-amp: -20 to 90 Deg. C
  - Elect. Field Pre-amp: -40 to 55 Deg. C
  - Elect. Dipole Ant.: -190 to 151 Deg. C
  - Elect. Dipole Latch: N/A
  - Elect. Dipole Hinge: N/A
Instrument Modes:
- Off
- POR
- On
- Wideband waveform modes:
  - * Mode 1 (50 Hz-10 KHz)
  - * Mode 2 (50 Hz-80 KHz)
  - * Mode 3 (5 Hz-1 KHz)
- Waveform Resolution Modes:
  - * Mode 1 (4-bits, 25200 samples/sec)
  - * Mode 2 (4-bits, 201600 samples/sec
  - * Mode 3 (4-bits, 3150 samples/sec)

Return to Project Galileo Homepage
Return to Galileo's Science Instruments

PWS - Plasma Wave Subsystem