Minutes of April 20, 2007 LAL ILC-MDI/BDS/ATF2 group meeting (by Yves Rénier)
Definition of adaptative grid in Guinea-Pig for e+e- and e-e- collisions as function of offsets and beam parameters
Guinea-Pig has been used to simulate beam-beam interaction at the IP of ILC (see previous meeting) but, due to ground motion, beam size and offset are changing over large scale. So meshing and size of the grid has to be adapted, function of nature, size and offset of beams interacting (e+e- or e-e-). The size dependence was already implemented, but now the grid can be adaptated according to offset too, allowing Guinea-pig to compute interaction of beams with offset up to 1 mm, in a smaller time (typically about 1 min for 50 000 macroparticles).
Evolution of ILC parameter optimization with center-of-mass energy (for constant beam intensity)
ILC will have to be efficient from “low” energies (100 GeV for Z studies) to its nominal energy (500 GeV). However, luminosity, beamstrahlung emission and aperture needed in Final Doublet are linked to energy. Slides presents some simple equations to try to understand these relations, and suggest how to scale these parameters to try to keep a good luminosity and realistic aperture in FD. Two example scenarios were shown. With no changes in beam parameters, luminosity and beamstrahlung emission simply scale as energy and energy squared, while the required FD aperture scales as energy**-05. On the contrary, if the beta functions at the IP and bunch length are scaled as the energy, then the luminosity and beamstrahlung emission can be kept constant. However, the required FD aperture then scales as energy**-1. Eventually, this becomes the limiting factor.
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