MARS Simulation Tweaking the material (Dose vs. Shield Composition) Next steps Tom Diehl 03/10/2004

Tweaking the Material I Change the material that makes up the shield (thickness = 2 cm). Lower Z is a little better than higher Z. More weak evidence for “more shield is more bad”. Carbon fiber mix was a little better than everything else that I tried.

Tweaking the Material II Changed the material but kept the shield mass at 25 kg. Possibly lower Z is a little better.

Summary Shield Composition Studies –At constant thickness, lower Z (lower density) is a little better (less energy in silicon). Weak supporting evidence that “more shield is worse”. –At constant mass, lower Z looks a little better. Next –I need to talk to NVM to understand details of the output. –Study Solar Protons and galactic electrons.

MARS Simulation Progress Tweaking the geometry Dose vs. Shield thickness Dose w/ vs. w/o a satellite Next steps Tom Diehl 01/21/2004

Recent History Igor Rakhno & Co. wrote –Preliminary Results from MARS Calculations: FNAL Technical Memo 2221 Mokhov, Rakhno, Striganov, Peterson “Radiation Load to the SNAP CCD” 09/15/03. Modeling the Cosmic Rays SNAP Satellite Model Preliminary Dose Calculations –We know we have some things to improve. –We know we have some systematic tests to carry out. Igor sent me his code.

Shielding and Detector Model (Rakhno)

The Rakhno Model The total mass included amounts to 276 kg. –Shield is 2 cm thick, 35 to 41 kg aluminum. –Cold Plate is 99 kg moly. –Silicon substrate is 5 kg mixture. –Silicon itself is 200  thick amounting to 107 g. –Radiator is 69 kg aluminum. –The rest is deck, optical bench, supports, etc … amounting to 61 kg. I modified the cold plate to 49 kg, close to the nominal design.I did this by halving the density of the molybdenum.

Progress Dec. 10 th to Dec 31 st. I learned MARS 14 tricks, pictures, plots. Reran Igor’s code –Same Orbit (solar minimum) 10M galactic protons => 6.8 R/y. Igor had 7.9 R/y. –Same orbit (solar minimum) 100M trapped protons => 34 kR/y. Igor had 21 kR/y. The program is functioning properly when I run it. Well … I get approx. the same results as Igor does using that geometry.

Dose vs. Shield Thickness (AL) The shield in the nominal geometry is 2 cm thick aluminum cone. Is there an optimal thickness? Test dose in the silicon as change thickness (AL density) of the shield. A much thicker shield will block these protons effectively. No apparent reason to make the shield 35 kg. 2.7 g/cc

Material vs. No Material Jodi L. has a fast cosmic ray simulation using 4 charged particles/cm^2/s. That’s the textbook “unprotected” rate. I can calculate a scale factor that accounts for the material. I set all the material to vacuum, except the silicon, and reran MARS, 10 M galactic protons & 10M galactic electrons, elliptical orbit. –Dose (silicon) = 4.7 R/y, less than with the material around the detector. –Ratio (satellite vs. no satellite) =  0.1 from galactic protons. –R = 2.0+  0.2 from galactic electrons. But the electrons are ~100 x less than the protons, anyway.

More Progress since Dec. 10th “Nibble File” (Cease, Page, Lanfranco) –Solidworks Model -> IDEAS CAD Program –Step through the satellite volume in small cubes –Report the material in each cube, it’s position, density, name, mass, and volume. I can turn this into a table suitable for MARS. Maybe it will be suitable for GEANT, as well.

Summary & Immediate Plan Change to L2 Orbit. –The galactic spectrum will be similar to the elliptical orbit spectrum. –Trapped radiation goes away Verify the shield thickness calculation Test some different materials –Dose vs. Z at constant mass –Polyethylene & Lithiated polyethylene (may not be wise to use poly, but want to check that anyway) –2 material sandwich Start importing simple “nibbled” Solidworks parts.

Buffer slide Stuff here on isn’t part of this talk.

Shielding and Detector Model (1) The trick with MARS is to select the appropriate level of detail. –Include the most important shielding components. Consideration is given to proximity to detector and components mass. –Put a lot of effort into detailing the detector.

Microsoft Project Stuff I sketched this up ~ Nov. Collaboration Meeting. I only show details for MARS stuff. –I rolled up the rest. –This isn’t up to code –& it could already stand to be updated. x x x Done = x 12/30/2003