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Report on LEMMS Passband Design from T. P. Armstrong to Cassini MIMI Team, October 20, 1994

This memo covers the distribution to you of the results of calculations that I have recently made on the subject design. Highlights of the changes from the October 1993 version (and substantially recapitulated in March 1994) are the following:

  1. Detectors D1 and A have been changed in thickness from 100 microns to 150 microns so that standard Canberra detectors can be used. This also reduces the capacitances and makes the attainment of lower noise more secure. In several instances the passbands begin at slightly higher energy, but this disadvantage is offset by the technical simplification of using more trusted, standard detectors and having less capacitance-generated noise.   Detector D1 will be the most susceptible to electron pile-up and its shaping time constants should be as short as reasonably attainable.  The channel logic design takes account of the possibility of pile-up and uses the highest feasible thresholds to define the proton passbands.
  2. The electron range-energy table that PAMY uses has been revised to include only collisional energy loss and to exclude radiative energy loss. This should much more accurately estimate the energy deposition from high energy electrons in the LEMMS assembly. Before this change was made, the apparent energy losses of electrons were unrealistically high and electron responses were appearing in lower energy proton channels where they shouldn't be.  As a consequence of this change in the range table for electrons, the logic for E5, E6, E7 has been revised. The new E5 is not as "nice" a channel as I would prefer.  In fact, it is integral and duplicative and I would suggest dropping it.  I suggest replacing it with different logic, called E0 in the tables here, that is a D1 singles-based channel for 100 to 180 keV electrons.  Looking at the Voyager Saturn data, that is a very important and interesting part of the spectrum that is also covered by the deflected electron system.   This will make a good cross-calibration for flight data.
  3. I have done a calculation of the expected response of the LEMMS 180 degree assembly to particles penetrating the stack from the 0 degree end (OBVERSE) to verify that we don't have trouble with bidirectionality.
  4. I have approximated the spectra of protons, electrons, helium, and oxygen for several positions in the Saturnian radiation zones and show estimated count rates.

I will fax an early and partial version of this memo to Livi and Kirsch at Lindau and Mitchell and Jaskulek at APL for their use in preparation for the Lindau team meeting. I will distribute it in full and comment on it at the team meeting.

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