Subject: Followup to questions during today's electron cloud meeting talk From: Jim Crittenden Date: 10/08/2014 03:57 PM To: Joe Calvey , "Walter H. Hartung" , John Sikora , David L Rubin CC: David Sagan , Gerry Dugan Hi Joe, Walter, David, John cc: Jerry, David Below is some information relevant to questions asked at my talk today about Synrad3D https://wiki.classe.cornell.edu/ILC/Private/CesrTA/ElectronCloud#October_8_44_2014 I found the tables used to calculate the reflectivity in this file in our code database https://accserv.lepp.cornell.edu/cgi-bin/view.cgi/trunk/src/bmad/photon/photon_reflection_mod.f90?revision=31404&view=markup For photon energies below a few hundred eV the smallest angle in the table is 1 degree. The lowest energy is 30 eV. For the SuperKEKB case I discussed where the angles were about 0.1 degree, and the energies below 400 eV, if I suppose that Synrad3D interpolates linearly between the reflectivity at 0 degrees (1.00) and at 1 degree, the reflection probability at 30 eV is 99.6%, at 100 eV is 99.6%, at 200 eV is 99.6%, at 300 eV is 97.0%, and at 400 eV is 98.1%. Yes, there is a minimum at 300 eV. Remember that the direct photon rate without scattering was 1/20 of the absorbed rate with scattering. So for my simulation of 3600 absorbed photons, there would have been only 180 incident direct photons. It wasn't visible on the plots, but there was actually one case of an absorbed photon with no previous scatters. Its energy was about 100 eV. The energy distribution of the incident unscattered photons was heavily weight toward the lower energies, where the reflection probability is higher. So I think that 1 (+-1!) / 180 = 0.5% may be consistent with the average probability of absorption to be expected from the tables. Jim ============================================================ James Crittenden Tel. (607) 255-9424 Wilson Synchrotron Laboratory Fax (607) 255-8062 Cornell University Ithaca, New York 14853-8001