Control of closed orbit deviation due to synchrotron radiation

The energy loss by synchrotron radiation in electron-positron storage rings occurs in every bending magnet and is thus distributed around the ring, while the energy gain occurs at the rf cavities, which are usually lumped in only a few locations. This type of orbit distortion is usually negligibly small compared to the design allowance in existing synchrotrons and storage rings; however, in the case of the larger storage rings now being contemplated, the distortion can be substantial in comparison to beam size and is different for electrons and positrons. This difference between the two closed orbits can produce horizontal separations and crossing angles between the two beams at the interaction regions. There are at least three possible solutions to this problem. The first is to use a lattice in which the dispersion and its derivtive are zero at the interaction regions and at the locations of the rf system. The second is to use transverse electric fields to produce the necessary corrections in the orbits of the two beams. The last is to distribute the rf accelerating system around the ring in such a way that the closed orbit deviations are within acceptable limits. For studying this problem, the thin-lens lattice design program MAGIC has been modified to compute the closed orbit distortion for any distribution of the rf system operating at any configuration. We discuss the computation of the closed orbit the different options and give the reasoning that we have used to decide on the solution of distributing the rf system for PEP. 2 refs., 2 figs