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Galileo Energetic Particles Detector

Space Science Reviews Article: LEMMS

The Low Energy Magnetospheric Measurements System

The LEMMS telescopes are designed to measure low to medium energy ion and electron fluxes with wide dynamic range and high angular (<20 deg) and temporal (1/3 to 4/3 s) resolution. As stated previously, a full 4pi coverage of the unit sphere is obtained by the use of a stepping platform in conjunction with satellite spin.

The LEMMS detector head is a double-ended telescope containing eight heavily shielded silicon solid state surface barrier totally depleted detectors providing measurements of electrons from 15 keV to > 11 MeV, and ios from 22 keV to eV to ~55 MeV, in 32 rate channels.

Detail of the EPD LEMMS detector head.
Graphical summary of EPD energy and species rate channel coverage. Additional high energy resolution and detailed species identification are obtained from pulse height analysis data gathered simultaneously with the rate channel data show.

LEMMS Channel Descriptions

Channel         Species         Energy Range    Geometric Factor
Name                            (MeV)           (cm**2 sr)
--------------------------------------------------------------------------------
A0              Z >= 1          0.022-  0.042   0.006
A1              Z >= 1          0.042-  0.065   0.006
A2              Z >= 1          0.065-  0.120   0.006
A3              Z >= 1          0.120-  0.280   0.006
A4              Z >= 1          0.280-  0.515   0.006
A5              Z >= 1          0.515-  0.825   0.006
A6              Z >= 1          0.825-  1.68    0.006
A7              Z >= 1          1.68 -  3.20    0.006
A8              Z >= 2          3.50 - 12.4     0.006
B0		Z  = 1		3.20 - 10.1     0.006
B1		electrons      ~1.5  - 10.5	0.006
B2		Z  = 2	       16.0  -100.	0.006
DC0		Z >= 1	       14.5  - 33.5     0.5
DC1		Z >= 1	       51.   - 59. 	0.5
DC2		electrons	     >~ 2.	0.5
DC3		electrons	     >~11.	0.5
E0              electrons       0.015-  0.029   0.006*
E1              electrons       0.029-  0.042   0.020*
E2              electrons       0.042-  0.055   0.030*
E3              electrons       0.055-  0.093   0.033*
F0              electrons       0.093-  0.188   0.028*
F1              electrons       0.174-  0.304   0.007*
F2              electrons       0.304-  0.527   0.016*
F3              electrons       0.527-  0.884   0.018*
AS		singles		all counts	0.006
				in detector
BS		singles		all counts	0.006
				in detector
CS		singles		all counts	0.5
				in detector
DS		singles		all counts	0.5
				in detector
EB1		background	sidewise penetrators
EB2		background	E1E2 coincidences
FB1		background	Sidewise penetrators
FB2		background	F1F2 coincidences

*  Geometric factor determined from table in paper by Y. Wu, T.P.
   Armstrong.

The geometric factor of the collimator and magnetic optics system has been analyzed by extensive computer modeling (Wu and Armstrong, 1988). The energy dependent aperature-integrated geometry factors for detectors E1 and F1 are shown here.

Response of the EPD LEMMS low energy electron detectors. The geometric factor, as calculated from a detailed simulation shown as a function of energy.

A diagram of the LEMMS analog electronics is included next. The unbuffered preamp tail-pulse output signals are sent down the polytwist wiring harness to three LEMMS analog boards, where the signals are amplified and shaped. All signal processing in the LEMMS channels is done in the linear domain. Comparator-like discriminator circuits assigned to each of the eight channels fire whe pre-defined threshold levels are exceeded.

The resulting discriminator outputs are sent to the rate logic electronics, where combinatorial logic is used to define 32 rate channels (event bins).

LEMMS data also are processed through a pulse height analyzer (PHA) that produces 13 46-channel energy spectra per major frame.

Block diagram of LEMMS analog electronics.

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Updated 10/18/02, T. Hunt-Ward
tizby@ftecs.com