Fundamental Technologies Cassini MIMI Pages

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

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)

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

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