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EPD Geometry Factors

Source: R. W. McEntire, Galileo EPD Science Team Meeting, March 1998

The effective geometry factors for the LEMMS and CMS heads need to be updated, and consistent values adopted for unified analysis.  Several analyses have called some of the values now being used into question.

LEMMS Electrons (Channels E0 to F4)

Electron spectra from Earth and especially Jupiter show minor but consistent slope discontinuities as a function of energy that are non-physical.  The G-factors for these channels are primarily derived from Monte-Carlo modeling of the electron trajectories in the LEMMS field.  Studies from Wu et al. (Wu, McKee and Armstrong technical report; Wu and Armstrong published paper) and Lagg are available.  Differences for most channels are small. A set of G-factors falling between Wu et al. and Lagg (11/97) seem to fit best, and are suggested for adoption.


Barry Mauk is fitting the A0-8 channel responses to the Jovian mix of H, O, and S.  He will discuss channel passbands for these species.


Fits between LEMMS and CMS by Barry Mauk seem to work very well, but only if CMS fluxes are increased by a factor of two relative to LEMMS.  The LEMMS ion G-factors are fairly well known; we thought the CMS was also, but Barry's work called attention to some puzzling angle scans made at MPAe.  These were repeated and extended in some very thorough work by Hartmut Sommer late last year. The CMS front foil active area (about 0.7 cm across) is not as big as the foil itself (1 cm across). This is probably due to some mix of electron optics and MCP anode size.  The back SSD surface active area seems to be about as expected.  The result is a geometry factor about 0.5  of that expected.  This is independent of Barry's results, and fits them very well.

LEMMS C/D Channels

JPL is very interested in the high-energy electron spectra near the orbit of Europa.  We have told them that we don't trust our effective G-factors for high energy electrons, and will need a good Monte-Carlo study. They are getting going on this--we have provided them with instrument drawings and observed channel rates.

Table 24. EPD LEMMS Electron Geometry Factors

Energy Range Channel

Geometry Factors/(cm**2 sec sr)

   Wu '86 Production Prod. E0-.005 Lagg 8/97 Lagg 11/97 Lagg 3/98
LEMMS (MeV)           
0.015-0.029 E00.01 0.010.005 0.0310.015 0.007
0.029-0.042 E10.02 0.020.02 0.0330.038 0.026
0.042-0.055 E20.03 0.030.03 0.0280.04 0.035
0.055-0.093 E30.034 0.0340.034 0.0170.038 0.034
0.093-0.188 F00.03 0.030.03 0.018 0.025 0.025
0.174-0.304 F10.005 0.017 0.017 0.013 0.012 0.017
0.304-0.527 F20.017 0.017 0.017 0.011 0.016 0.016
0.527-0.884 F30.018 0.018 0.018 0.007 0.012 0.012


Next: Geometric Factor Calculation for the EPD LEMMS Telescope

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Updated 2/28/06, T. Hunt-Ward