SNAP Shield SubGroup Meeting 
                 10:00 AM October 29th, 2003 IB1 2nd floor
    Cease, Diehl, Lamoureux, Lanfranco, Nichol, Olis, Page, Peterson, Rakhno


    Meeting Schedule:
    Next meeting: Would be November 12th, 2003 10:00 AM. IB1 2nd floor. 
    Except that's when we will be flying back from LBL. After that the
    next one is November 26th except that's the day before Thanksgiving.
    This seems to be too long if we are getting into December, so I 
    will try to put one together on an irregular week. 

    Agenda might include:
    Results from LBL Collaboration Meeting (all)
    Update on parameterization of Solidworks Model ()
    Ratio of Shield-On to Shield-Off Cosmic Rays in MARS ()
    AOB

    Agenda (of this meeting):
    Simulating Cosmic Rays in Images (Jodi Lamoureux)
    Progress on SNAP Shield Engineering R&D Plan (Tom Nicol)
    Progress on ANSYS Simulation of the Shield Mount (Giobatta Lanfranco)

    Simulating Cosmic Rays in Images (Jodi Lamoureux)
    -------------------------------------------------
    Jodi's slides are available in this directory as file
    lamoureux_oct-29-2003.ps.  She said the following.

    The purpose of the CR fast MC studies is to simulate an image 
    so they could do image-processing tests with CR removal algorithms,
    find the impact on the science. and optimize SNAP mission parameters. 
      She described th SNAP images. 200 micron thick silicon 10.5 micron
    wide pixels. Diffusion is 3.5 micron for 200 micron drift. Note that
    she warned us the silicon might be going down to 150 microns thick.
    SN exposures were simulated at 300 sec (480 exposures), and 
    weak-lensing exposures at 500 sec (4 exposures). Other noise sources
    included were zodiacal light, dark current, and read noise, but those 
    seem to be at a smaller level than the cosmics, at least in the pixels
    that are actually hit. One gets typically 70 electrons per CR.
    She used a CR flux of 4.5/cm^2/s. This is the flux for the galactic 
    component only.  It doesn't include the trapped radiation. 
      She showed a picture of an image. Lines like cosmic rays going
    through a thin plane are seen.  
      After the images are individually corrected, lined-up, and 
    calibrated, the cosmic rays are removed.  The algorithm is something
    like so. One calculates the average "signal" in the 4 overlaid (drizzled)
    pixels. The remove any which are 2 sigma over average.  That tasks out
    18% of the pixels.  If you go back and remove the neighbors that 
    are over minimum signal that increases to 32%.  The one re-averages 
    the remaining exposures. 
      She showed a picture of the weights in the CR-removed image. For a
    picture made from 4 exposures a weight of 4 is good and a weight of zero 
    means we killed the cell in all 4 exposures. 
      
      She asked us to do some calculations for her. We should but I 
    don't expect we will get them done before the collaboration meeting.
    a) better parameterization of the flux. 
    b) pixel death rate.
    c) other relevant stuff.

      We just (10/31) got the MARS code transferred from Rakhno to Diehl. 
    Maybe we can form the ratio of the shielded to unshielded flux or 
    energy deposition as a function of pisition on the focal plane. 
    This would be particularly interesting for the galactic component - 
    maybe we just multiply 4.5/cm^2/s times that ratio.  


    Progress on SNAP Shield Engineering R&D Plan (Tom Nicol)
    --------------------------------------------------------
    We've got a solid engineering team comprised of Tom Nicol (leader),
    Tom Page, Herman Cease, Dan Olis, & Giobatta Lanfranco.  All are 
    presently working on the SNAP shield engineering at some level and 
    all are also working on other things around Fermilab.
      They have come up with a preliminary task list as follows.
    I wrote it down and approximately who is doing what.  This stuff
    isn't cast in stone and it's a good start.  

    SolidWorks Model - interface to LBL.            (Page)
    Support for Radiation Shield Calculations       (Page)   
    Ray Tracing, Optical Shielding, Optical Coatings - 
      the inside of the shield                      (Cease)
    Structural FEA on the shield and support system (Lanfranco)
    Structral Design Criteria (e.g. launch loads, vibration etc. ...)
                                                    (Lanfranco, Olis)
    Inventory and Characterization of allowable materials for 
      the shield and supports (e.g. unobtainium)    (Lanfranco, Olis)
    Thermal Design Criteria                         (Nicol)
    Thermal Modeling to simulate shield, mounts, radiator, 
      thermal links, shutter, etc ...               (Nicol)
    Design Work as necessary (e.g. light shield labyrinth or bellows ...)
                                                    (As necessary)


    Progress on ANSYS Simulation of the Shield Mount (Giobatta Lanfranco)
    ---------------------------------------------------------------------
    Giobatta showed some setup diagrams for an ANSYS model of the shield
    and its support.


 
                                             Cheers,
                                             Tom Diehl