Cassini MIMI Pages
LEMMS 180º End Design Criteria (as agreed by Engineering Team
(Tom Armstrong, 6/1/93)
- Optimize for clean coverage of proton spectrum from ~1 to >20 MeV.
- Obtain several electron channels, 1 - 10 MeV.
- Assume 100 ns time constants (pulse widths).
- Accept incidental x-ray responses to obtain (at least) upper limit fluxes.
- Specific, refined and optimized design parameters are needed ASAP.
- Weight and power constraints may dictate less complexity.
- Use ion implant detectors of least variety (in areas and thicknesses) possible (700 m).
- Consider reducing D1 from 300 m to 100 m
to reduce sensitivity to electrons.
- Consider reducing foil thickness from 100 m (A1 equivalent)
to lower proton threshold to ~1 MeV.
Radical suggestion: Optimize design of 180º end for 1 --> 30 MeV/nuc.
H, He, O (rate channels).
(High duty cycle but low sampling rate.)
Comments on LEMMS 180º End Design for Cassini MIMI
(Tom Armstrong, 6/1/93)
- Saturn magnetosphere is very intense in electrons at 1 MeV and very weak in
protons--there's a proton minimum 1 - 10 MeV.
- ESA0 (200 keV level in 300 m 20 mm2) singles,
shielded like D1. Was ~=104 c/sec at ~3 RS.
PSB3 ~< 1 c/sec > 16 MeV proton.
The electron background is a problem!
- Observing x-rays R < 10 RS is probably hopeless. Is the x-ray source
sufficiently intense to do it at 20 RS? GCR background is the worry here.
- Major unsettled question: Proton spectrum 1 - 20 MeV in inner magnetosphere; how deep
is the minimum electron spectrum? Do the Van Allen resonance features exist? Can
MIMI 180º end settle these?
*Fast time constants ~< 30 ns?
Anomalous components and H, He, O (1 - 20 MeV/nuc) (solar min. 1995, 2006!) should be
strong and interesting at Saturn.
- Mass and power (purchased 1 kg from S/C).
- LEMMS sensor - high energy end and motor (mass, power, rotational mode)
- Event rates on INCA and CHEMS
- Parts issues
- PIR/GIR preparations
TPA (LEMMS high energy end)
- Size of D1, D2, D3 (area)
- Fill proton 1 - 30 MeV
- 1 - 10 MeV electrons
- Accept x-ray sensitivity
- Assume 100 ns resolving time
600 mm2 = A = pd2
d = (600/p)1/2 = 13.82 mm; r = 6.9 mm
300 mm2 = A = pd2; d = 9.77 mm; r =
Reduce conical angle and move detectors back for better definition.
PIPS - low current, low noise, cleanable, bakeable
Canbera semi-conductor have 700 m, 700 m,
Assume 10 minutes = 600 sec; 10 counts = 10/600 = 1/60 c/sec; ~10-2 c/sec.
1-10 MeV protons, J~10-1 (cm2 sec sr MeV)-1 * 10 MeV,
J~1 (cm2 sec sr)
||dW=dfd (cos f)
W=2p (1 - cos 22.5º) = 0.39 ~0.4
G = AW = 6 · 0.4 = 2.4 cm2 sr (Kirsch, June 93)
Jthresh = 10-2 c/sec / 2.4 cm2 sr = 0.4 x 10-2
This could yield about a factor of 100 increased knowledge of proton flux.
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Updated 6/10/08, T. Hunt-Ward