SNAP Shield Group Meeting August 6, 2003 Dejongh, Diehl, Kerby, Marriner, Mokhov, Nichol, Page, Peterson, Rakhno Next Meeting ------------ Wednesday August 20, 2003 IB1 2nd floor West 10:00 to 12:00 Noonish. This includes the instrumentation meeting with LBL starting at 11:00. Agenda ------ TM-2221 "Radiation Load to the SNAP CCD" - Igor Rakhno Comparison of CREME96 with AMS Primary Protons - Tom Diehl TM-2221 "Radiation Load to the SNAP CCD" - Igor Rakhno ------------------------------------------------------- Nikolai Mokhov, Tom Peterson, Igor Rakhno, and Sergei Striganov have produced a technical memo with a summary of their results to-date. It is TM-2221 "Radiation Load to the SNAP CCD". They estimate ~20% signal degradation over the mission lifetime. To quote from their note this is: "first estimate of radiation load to the SNAP CCD in a simplified geometry model and for realistic radiation envioronment on the orbit. The following items should be refined in further studies: 1. Allowable limits for the CCD and electronics - radiation dose, total fluxes and background rates - to design shielding appropriately. 2. CCD specific: charge transfer efficiency vs. accumulated dose. 3. Add more realism to the CCD detector model. 4. Add other components of the satellite. 5. Add and analyze on-board electronics that needs protection against radiation. 6. Clarify details of the opening in the optical bench box for incoming optical radiation. 7. Add accurate treatment of transport and interactions of alpha particles and possibly heavier ions. 8. Date of the beginning and duration of the mission; it is required to take into account a model of regular solar flares." Igor Rakhno made a partial presentation in our meeting and a full presentation in the Instrumentation Meeting with LBL. Some questions and comments arose. The SNAP material model described in the TM needs significant improvement. The dose depends heavily on the shutter position in this SNAP simulation. I figure that's primarily because the satellite is described with aluminum rather than carbon fiber structures. The CCD signal degradation is calculated on the basis of a one per mil fraction of the dedx energy deposition. I gather that's because the MARS MC doesn't yet transport and calculate secondaries from heavy ions, but it does do dedx. Note that it's intended to improve MARS to handle that. The non-ionizing dose is primarily due to the trapped radiation (protons creating neutrons, which happens to be at the lowest energies) and is, therefore, calls for optimation of the shield material and thickness. Finally, Chris Bebek noted the past literature on the degradation of CCD's has shown to be ~2x more pessimistic than turned out to be the case. I will include links to newer info once I get the references from Chris. The TM can be found in this directory. It is file tm-2221-08-06-2003.pdf. This is a good start, guys. Comparison of CREME96 with AMS Primary Protons - Tom Diehl ---------------------------------------------------------- Our simulations have depended on CREME96 for the calculation of interplanetary particle fluences, trapped radiation, and solar flare radiation. HTD ran CREME96 and compared the primary proton spectrum from CREME96 with the recent AMS data. The CREME96 spectrum goes to much lower energy than AMS. The low energy protons are important for our simulation, as discussed above and in the TM. In the energy range that AMS data exists, CREME96 and AMS primary proton spectrum are in reasonably close agreement. The trapped radiation proton fluences are much higher, especially in kinetic energy range 1 MeV to 10 MeV, than the interplanetary radiation. See the plot in talk diehl_08_06_2003.ppt, in this directory.