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Cassini MIMI LEMMS Detector Logic Design: Further Suggestions on LEMMS Head Design
Memo to S. M. Krimigis, Don Mitchell, Erhard Kirsch, and Berend Wilken from Tom Armstrong, July 13, 1993

In response to the fax memo from Kirsch dated June 22 and the email from Mitchell dated July 2, I have reworked the provisional scheme of my June 16 memo. The full calculation results are attached for your inspection. However, let me list the major changes and highlights (I hope strengths) of this scheme.

  1. The assumed opening angle of the 180 degree end is 15 degrees (conical half angle).
  2. The 0 degree end has been calculated and is included here so that coverage of the proton spectrum up to about 10 MeV can be obtained therefrom and the 180 degree end can have a thicker foil (100 microns aluminum equivalent assumed) and use a 150 micron detector.
  3. In this calculation fewer detectors are used than in the June 22 Kirsch diagram. I believe that we can accomplish our objectives with a stack of D1 (150 microns), D2 (700 microns), D3 (1400 microns), B (700 microns), and A (107 microns--Galileo EPD heritage). Further, no thick, inert absorbers are assumed. The platinum and brass do not appear to be necessary to obtain the passband coverages for the protons, alphas, and oxygen. There are also ample opportunities for constructing electron channels up to a few MeV. As before, I haven't spelled out the details of the electron channels owing to the lack of this capability in PAMELA.
  4. In total there are 31 discrimination levels used. For the ions, most are to be set at comfortably high levels and should not require excessive gain or dynamic ranges in pulse amplitude. Coincidence/anticoincidence logic is generously used and it needs to function robustly for this design to have merit. Further, when the detectors are acquired and characterized, this design must be "tweaked" because the energy losses, thicknesses, and electronic thresholds are all coupled in an intricate way in this design. After this design is "tweaked" for the flight detector parameters, it will be necessary to set each discriminator precisely. It would be desirable to have about 1% or so precision in discriminator settings (5% might also work, but there are some close calls as you may note from the calculated tables).
  5. The definition of x-ray and other channels is not precluded in this design. Additional logic can be included as needed.
  6. Responding to the design information that Nick Paschilides needs on the performance of the electronics, I have the following intuition.  This is only intuition because I haven't done number estimates of counting rates yet. I would suppose that if a pulse width of 0.1 microsecond in the preamps and amplifiers can be obtained and the strobing and logic can be done in no more than 0.2 microseconds, that this system will hold up and function acceptably throughout most of the Saturnian environment.  I would expect the degradation introduced by high count rates to be graceful.
  7. The departures from nominal response of this design arising from omnidirectional or bidirectional effects should be minimal.  It is important to keep the detector stack reasonably compact so that all detectors see the same solid angle. For bidirectionality, PAMELA must be run for the inverted stack.  I haven't done that yet (this all takes a lot of time, sports fans), but I will do so in order to avoid surprises.

Table 1. Summary of passbands in July 13, 1993, provisional design

Channel Name Protons (MeV) Alphas
(MeV/nucleon)
Oxygen
(MeV/nucleon)
Electrons
A0 0.030 to 0.055 to 0.017    
A1 0.055 to 0.079 0.017 to 0.024    
A2 0.079 to 0.133 0.024 to 0.040 to 0.016  
A3 0.133 to 0.283 0.040 to 0.085 0.016 to 0.030  
A4 0.283 to 0.526 0.085 to 0.151 0.030 to 0.050  
A5 0.526 to 0.819 0.151 to 0.227 0.050 to 0.072  
A6 0.819 to 1.630 0.227 to 0.427 0.072 to 0.128  
A7 1.630 to 3.230 0.427 to 0.895 0.128 to 0.259  
A8    0.895 to 3.126 0.259 to 6.584  
B0 3.275 to 4.492      
B1 4.534 to 10.479      
B2   3.125 to 4.978 6.581 to 6.894  
B3   4.979 to 9.949 6.894 to 23.118  
BE        
E1        
E2        
E3        
P3 5.550 to 6.817      
P4 6.817 to 9.015      
P5 9.012 to 11.913      
P6 11.913 to 13.697      
P7 1.3697 to 29.559 44.081 to 146.736    
P8 25.753 to 59.795 145.901 to 496.542    
P9 59.795 to 276.144 496.549 to    
H1   3.638 to 5.530    
H2   5.526 to 14.511 193.463 to  
H3   11.913 to 25.676 193.463 to  
H4   25.676 to 44.081    
H5   57.975 to 114.211    
Z1     7.310 to 11.913  
Z2     11.913 to 25.666  
Z3     25.666 to 193.463  

Notes:

  1. Blanks in proton, alpha, and oxygen columns mean that no response is found in the interval 0.01 to 1000. MeV/nucleon.
  2. A missing high or low passband edge means that the passband extends beyond the range of PAMELA's computation (0.01 to 1000. MeV/nucleon).
  3. The electron passbands remain to be filled in.
  4. The channels A0 through BE are from the 0 degree end and E1 through Z3 the 180 degree end.
  5. Responses of the channels to particles penetrating the stack in inverse direction have not been calculated here.  A separate memo will be issued later.

Table 2. Cassini MIMI LEMMS 0 Degree End, July 13, 1993;
provisional design (enhanced Galileo EPD)

ABSORBER NAME Contact A B D3
ABSORBER THICKNESSES, MICRONS 0.1 107.0 700.0 1400.0
ABSORBER MATERIAL ALUM. SILICON SILICON SILICON
THICKNESS VARIATION, MICRONS 0.0 50.0 10.0 10.0
CONICAL HALF ANGLE, DEGREES 7.5 7.5 7.5 15.0
DETECTOR NOISE, MEV 0.0 0.0 0.0  0.010
ELECTRONIC NOISE, MEV 0.0 0.006 0.010 0.0
NUMBER OF THRESHOLDS SET 0.0 9.0 4.0 5.0
THRESHOLD LEVEL NO. MEV    1 0.0 0.012 0.100 0.050
THRESHOLD LEVEL NO. MEV    2 0.0 0.030 1.000 0.400
THRESHOLD LEVEL NO. MEV    3 0.0 0.050 2.800 3.000
THRESHOLD LEVEL NO. MEV    4 0.0 0.100 13.000 6.000
THRESHOLD LEVEL NO. MEV    5 0.0 0.250 0.0 16.000
THRESHOLD LEVEL NO. MEV    6 0.0 0.500 0.0 0.0
THRESHOLD LEVEL NO. MEV    7 0.0 0.800 0.0  0.0
THRESHOLD LEVEL NO. MEV    8 0.0 1.600 0.0 0.0
THRESHOLD LEVEL NO. MEV    9 0.0 3.500 0.0 0.0 
AVERAGE PROJECTED DEPTH, MIC 0.2 107.5 703.0 1424.3
EST.RMS VARN.PROJ.DEPTH, MIC 0.0 0.65 3.0 24.7
NET RMS THICKNESS VARN. (MIC) 0.0 50.0 10.4 26.6
LOWER LIMIT THICKNESS (MIC) 0.1 57.5 692.6 1397.6
UPPER LIMIT THICKNESS (MIC) 0.2 157.5 713.5 1450.9

 

Logic Table for Electron and
Proton Channels
Logic Table for Helium and Medium Channels

Table 3. Cassini MIMI LEMMS Detector Logic Design,
LEMMS_J, July 12, 1993 version, 180 degree end

ABSORBER NAME Foil D1 D2 D3 B
ABSORBER THICKNESSES, MICRONS 100.0 150.0 700.0 1400.0 700.0
ABSORBER MATERIAL ALUM. SILICON SILICON SILICON SILICON
THICKNESS VARIATION, MICRONS 0.0 10.0 10.0 10.0 10.000
CONICAL HALF ANGLE, DEGREES 15.0 15.0 15.0 15.0 15.000
DETECTOR NOISE, MEV 0.0 0.012 0.007  0.010 0.010
ELECTRONIC NOISE, MEV 0.0 0.0 0.0 0.0 0.0
NUMBER OF THRESHOLDS SET 0.0 7.0 6.0 5.0 4.000
THRESHOLD LEVEL NO. MEV    1 0.0 0.050 0.050 0.050 0.100
THRESHOLD LEVEL NO. MEV    2 0.0 0.100 1.500 0.400 1.000
THRESHOLD LEVEL NO. MEV    3 0.0 0.300 3.000 3.000 2.800
THRESHOLD LEVEL NO. MEV    4 0.0 0.760 6.000 6.000 13.000
THRESHOLD LEVEL NO. MEV    5 0.0 1.600 12.000 16.000 0.0
THRESHOLD LEVEL NO. MEV    6 0.0 4.000 40.000 0.0 0.0
THRESHOLD LEVEL NO. MEV    7 0.0 16.000 0.0  0.0 0.0
AVERAGE PROJECTED DEPTH, MIC 101.7 152.6 712.1 1424.3 712.1
EST.RMS VARN.PROJ.DEPTH, MIC 1.8 2.6 12.3 24.7 12.3
NET RMS THICKNESS VARN. (MIC) 1.8 10.3 15.9 26.6 15.9
LOWER LIMIT THICKNESS (MIC) 100.0 142.3 696.2 1397.6 696.2
UPPER LIMIT THICKNESS (MIC) 103.5 162.9 728.0 1450.9 728.0

 

Logic Table for Electron
and Proton Channels
Logic Table for Helium and Medium Channels

For brevity, the figures are not included here. Please refer to the final figures.

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Updated 6/10/08, T. Hunt-Ward
tizby@ftecs.com