Instrument Information |
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IDENTIFIER | urn:nasa:pds:context:instrument:vg2.pls::1.0 |
NAME |
PLASMA SCIENCE EXPERIMENT |
TYPE |
SPECTROMETER |
DESCRIPTION |
INSTRUMENT: PLASMA SCIENCE EXPERIMENT SPACECRAFT: VOYAGER 2 Instrument Information ====================== Instrument Id : PLS Instrument Host Id : VG2 Principal Investigator : JOHN W. BELCHER Pi Pds User Id : JBELCHER Instrument Name : PLASMA SCIENCE EXPERIMENT Instrument Type : PLASMA INSTRUMENT Build Date : 1973-01-01 Instrument Mass : 9.900000 Instrument Length : UNK Instrument Width : UNK Instrument Height : UNK Instrument Serial Number : SN001 Instrument Manufacturer Name : MASSACHUSETTS INSTITUTE OF TECHNOLOGY Instrument Description ====================== The Voyager Plasma Science experiment consists of four modulated grid Faraday Cups, three (A,B,C) of which are positioned about the Telemetry Antenna Axis and generally point toward the Earth with the fourth (D) at a right angle to this direction. Ion currents are sampled simultaneously in all four cups, electrons in the D-cup only. The instrument has an energy/charge range of 10-5950 V. Data is taken in four ways, high and low resolution ion modes and high and low energy electron modes, with energy resolution varying between 3.6 and 29%. The integration time for each energy channel can be varied are used at Jupiter and Saturn and 0.93 and 0.21 second integration times are used at Uranus and Neptune. Supersonic flow can be observed only when one of the detectors points into the flow orientation allows determination of the plasma density, temperature, and velocity. Science Objectives ================== The objective of the Plasma Instrument is to characterize plasma conditions throughout the Voyager trajectory, in the solar wind and during the planetary encounters. Operational Considerations ========================== Each detector has an effective field of view which is a cone of half angle 45 degrees falls off quickly at higher angles. Thus, for the instrument to measure ion parameters in a Supersonic or Transonic plasma some of the detectors must look into the plasma flow. Secondary ions and electrons produced within the detectors can also effect the measurements, especially if large fluxes of hot ions or electrons are present and these effects are not well modeled. The instrument does not measure composition, only energy/charge, so a model of plasma composition must be adopted to fit the ion data choice of models can be unambiguous for large Mach number flow (M>3) but is non-unique for lower Mach numbers. After the Jupiter encounter the highest channels of the A, B, and C detectors often contain spurious signal and currents in the upper half of the energy range should be examined carefully before use. Calibration Description ======================= The instrument was calibrated at MIT using ion and electron beams and compared to output from other Faraday cups in the same beam. Current levels are also calibrated in-flight by injecting known currents into the detectors with the modulators on and off. Much theoretical modeling has been done on the response of the detectors to arbitrary plasma conditions. Contact the PI for more information. PLS Detectors 'A', 'B', 'C', and 'D' ==================================== Detector Type : FARADAY CUP Detector Aspect Ratio : 0.000000 Nominal Operating Temperature : 278.000000 The PLS instrument consists of four Faraday cups. Three of these (A, B, C) are arranged in a cone whose central axis is parallel to the direction of the telemetry antenna. The look direction of each of these cups is offset 20 degrees from the central axis. Detector D has a look direction approximately perpendicular to the direction of the telemetry antenna. Each detector consists of three modulator grids, six shield grids and a suppressor grid in front of the collector. It measures ion currents in the range 10-5950 V. Depending on the integration time the detectors measure current from a minimum of 3.e-14 to 2.e-13 AMPS up to a maximum of 6.e-8 AMPS. Sampling varies from .03 to .93 seconds. 'PLS' Section Parameter 'ELECTRON CURRENT' ------------------------------------------ Sampling Parameter Name : TIME Section Id : PLS Instrument Parameter Unit : AMPS Minimum Instrument Parameter : 0.000000 Maximum Instrument Parameter : 0.000000 Minimum Sampling Parameter : 0.030000 Maximum Sampling Parameter : 0.930000 Sampling Parameter Unit : SECOND 'PLS' Section Parameter 'ION CURRENT' ------------------------------------- Sampling Parameter Name : TIME Section Id : PLS Instrument Parameter Unit : AMPS Minimum Instrument Parameter : 0.000000 Maximum Instrument Parameter : 0.000000 Minimum Sampling Parameter : 0.030000 Maximum Sampling Parameter : 0.930000 Sampling Parameter Unit : SECOND Electronics =========== Currents from the four detectors are amplified, filtered, and integrated using four different measurement chains. A single 8-bit logarithmic A-D converter samples the four outputs of the measurement chains and transfers the data to the spacecraft. The high voltage modulator supplies a DC pedestal and a super- imposed 400 HZ square wave modulation voltage. For positive ions the modulator grids of all four detectors are driven in parallel. A more complete description and block diagram of the instrument electronics is available in [BRIDGEETAL1977]. Operating Modes =============== The eight operating modes of Voyager PLS are listed below. Instrument power consumption is 8.100000 for all modes. E1-LONG: Low energy electron mode which measures the range 10-140 V with 16 contiguous channels. The integration time for each channel is 0.93 sec. E1-SHORT: Low energy electron mode which measures the range 10-140 V with 16 contiguous channels. The integration time for each channel is 0.21 sec. E2-LONG: High energy electron mode which measures the range 10-5950 V with 16 contiguous channels. The integration time for each channel is 0.93 sec. E2-SHORT: High energy electron mode which measures the range 10-5950 V with 16 contiguous channels. The integration time for each channel is 0.21 sec. L-LONG: Low resolution ion mode which measures the range 10-5950 V with 16 contiguous channels. The integration time for each channel is 0.93 sec. L-SHORT: Low resolution ion mode which measures the range 10-5950 V with 16 contiguous channels. The integration time for each channel is 0.21 sec. M-LONG: High resolution ion mode which measures the range 10-5950 V with 128 contiguous channels. The integration time for each channel is 0.93 sec. M-SHORT: High resolution ion mode which measures the range 10-5950 V with 128 contiguous channels. The integration time for each channel is 0.21 sec. Instrument Mounting =================== The PLS instrument is located on the Science Boom. The center of the main detector cluster (A, B, C) points parallel to the spacecraft telemetry antenna and detector D is at right angles to this direction. |
MODEL IDENTIFIER | |
NAIF INSTRUMENT IDENTIFIER |
not applicable |
SERIAL NUMBER |
not applicable |
REFERENCES |
Barnett, A., and S. Olbert, Response Function of Modulated Grid Faraday
Cup Plasma Instruments, Rev. Sci. Instr., Vol. 57, p. 2432, 1986. Bridge, H.S., J.W. Belcher, R.J. Butler, A.J. Lazarus, A.M. Mavretic, J.D. Sullivan, G.L. Siscoe, and V.M. Vasyliunas, The Plasma Experiment on the 1977 Voyager Mission, Space Sci. Rev., Vol. 21, p. 259, 1977. Bridge, H.S., J.W. Belcher, A.J. Lazarus, J.D. Sullivan, F. Bagenal, R.L. McNutt, K.W. Ogilvie, J.D. Scudder, E.C. Sittler, V.M. Vasyliunas, and C.K. Goertz, Plasma Observations Near Jupiter: Initial Results from Voyager 2, Science, Vol. 206, p. 972, 1979. Scudder, J.D., E.C. Sittler, and H.S. Bridge, Survey of the Plasma Electron Environment of Jupiter: A View from Voyager, J. Geophys. Res., Vol. 86, p. 8157, 1981. Sittler, E.C., Jr., Plasma Electron Analysis: Voyager Plasma Science Experiment, NASA Tech. Mem. 85037, 1983. |