PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT PUBLICATION_DATE = 1998-05-01 NOTE = "INST.TXT contains the instrument description." END_OBJECT = TEXT END Principal Investigator: R.E. Vogt The following section on instrumentation has been extracted from the NSSDC documentation for the Voyager Cosmic Ray Subsystem (Reference_ID = NSSDCCRS1979). Instrument Overview =================== As its name implies, the Cosmic Ray Subsystem (CRS) was designed for cosmic ray studies [STONEETAL1977B]. It consists of two high Energy Telescopes (HET), four Low Energy Telescopes (LET) and The Electron Telescope (TET). The detectors have large geometric factors (~ 0.48 to 8 cm^2 ster) and long electronic time constants (~ 24 [micro]sec) for low power consumption and good stability. Normally, the data are primarily derived from comprehensive ([Delta]E[1], [Delta]E[2] and E) pulse- height information about individual events. Because of the high particle fluxes encountered at Jupiter and Saturn, greater reliance had to be placed on counting rates in single detectors and various coincidence rates. In interplanetary space, guard counters are placed in anticoincidence with the primary detectors to reduce the background from high-energy particles penetrating through the sides of the telescopes. These guard counters were turned off in the Jovian magnetosphere when the accidental anticoincidence rate became high enough to block a substantial fraction of the desired counts. Fortunately, under these conditions the spectra were sufficiently soft that the background, due to penetrating particles, was small. The data on proton and ion fluxes at Jupiter were obtained with the LET. The thicknesses of individual solid-state detectors in the LET and their trigger thresholds were chosen such that, even in the Jovian magnetosphere, electrons made, at most, a very minor contribution to the proton counting rates [LUPTON&STONE1972]. Dead time corrections and accidental coincidences were small (< 20%) throughout most of the magnetotail, but were substantial (> 50%) at flux maxima within 40 R[J] Of Jupiter. Data have been included in this package for those periods when the corrections are less than ~ 50% and can be corrected by the user with the dead time appropriate to the detector (2 to 25 [micro]sec). The high counting rates, however, caused some baseline shift which may have raised proton thresholds significantly. In the inner magnetosphere, the L[2] counting rate was still useful because it never rolled over. This rate is due to 1.8- to 13-MeV protons penetrating L[1] (0.43 cm^2 ster) and > 9-MeV protons penetrating the shield (8.4 cm^2 ster). For an E^-2 spectrum, the two groups would make comparable contributions; but in the magnetosphere, for the E^-3 to E^-4 spectrum above 2.5 MeV [MCDONALDETAL1979], the contribution from protons penetrating the shield would be only 3 to 14%. The LET L[1]L[2]L[4] and L[1]L[2]L[3] coincidence- anticoincidence rates give the proton flux between 1.8 and 8 MeV and 3 to 8 MeV with a small alpha particle contribution (~ 10^-3). Corrections are required for dead time losses in L[1], accidental L[1]L[2] coincidences and anticoincidence losses from L[4]. Data are given only for periods when these corrections are relatively small. The energy lost in detectors L[1], L[2] and L[3] was measured for individual particles. For protons, this covered the energy range from 0.42 to 8.3 MeV. Protons can be identified positively by the [Delta]E vs. E technique, their spectra obtained and accidental coincidences greatly reduced. Because of telemetry limitations, however, only a small fraction of the events could be transmitted, and statistics become poor unless pulse-height data are averaged over a period of one hour. HET and LET detectors share the same data lines and pulse- height analyzers; thus, the telescopes can interfere with one another during periods of high counting rates. To prevent such an interference and explore different coincidence conditions, the experiment was cycled through four operating modes, each 192 seconds long. Either the HETs or the LETs were turned on at a time. LET-D was cycled through L[1] only and L[1]L[2] coincidence requirements. The TET was cycled through various coincidence conditions, including singles from the front detectors. At the expense of some time resolution, this procedure permitted us to obtain significant data in the outer magnetosphere and excellent data during the long passage through the magnetotail region. Some of the published results from this experiment required extensive corrections for dead time, accidental coincidences and anticoincidences ([VOGTETAL1979A], [VOGTETAL1979B]; [SCHARDTETAL1981]; [GEHRELSETAL1981]). These corrections can be applied only on a case-by-case basis after a careful study of the environment and many self-consistency checks. They cannot be applied on a systematic basis and we have no computer programs to do so; therefore, data from such periods are not included in the Data Center submission. The scientists on the CRS team will, however, be glad to consider special requests if the desired information can be extracted from the data.