PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT PUBLICATION_DATE = 1977-12-01 NOTE = "INST.TXT contains the instrument description." END_OBJECT = TEXT END INSTRUMENT: PLASMA SCIENCE EXPERIMENT SPACECRAFT: VOYAGER 1 Instrument Information ====================== Instrument Id : PLS Instrument Host Id : VG1 Principal Investigator : JOHN D. RICHARDSON Pi Pds User Id : JRICHARDSON Instrument Name : PLASMA SCIENCE EXPERIMENT Instrument Type : PLASMA INSTRUMENT Build Date : 1973 Instrument Mass : 9.900000 Instrument Length : UNK Instrument Width : UNK Instrument Height : UNK Instrument Serial Number : SN002 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; 0.21 s/channel is used at Jupiter and Saturn. Supersonic flow can be observed only when one of the detectors points within 45 degreesof the plasma velocity, subsonic flow is observed at all orientations. The current observations as a function of energy/charge 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, during the planetary encounters, and in the interstellar medium. Operational Considerations ========================== Each detector has an effective field of view which is a cone of half angle 45 degrees; the detector response 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. These effects are not well modeled are rarely significant. The instrument does not measure composition, only energy/charge, so a model of plasma composition must be adopted to fit the ion data. The 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 energy/charge 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. 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. The integration time for each energy channel can be varied from .03 to .93 seconds. The time between successive spectra varies from 12 to 192 s. '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 four operating modes of Voyager PLS are listed below. Instrument power consumption is 8.1 W for all modes. E1: Low energy electron mode which measures the range 10-140 V with 16 contiguous channels. E2: High energy electron mode which measures the range 10-5950 V with 16 contiguous channels. L: Low-resolution ion mode which measures the range 10-5950 V with 16 contiguous channels. M: High resolution ion mode which measures the range 10-5950 V with 128 contiguous channels. 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.