INTERPLAY OF TOUSCHEK SCATTERING, INTRABEAM SCATTERING, AND RF CAVITIES IN ULTRALOW-EMITTANCE STORAGE RINGS

When it goes into operation in 2016, the MAX IV 3GeV storage ring will be the first ultralow-emittance storage ring based on a multibend achromat lattice. These lattices make use of a large number of weak bending magnets which con-siderably reduces the amount of power radiated in the dipoles in comparison to power radiated from insertion devices. Therefore parameters such as emittance, energy spread, and radiated power are—unlike 3rd generation storage rings— no longer constant during a typical user shift. Instead, they depend on several varying parameters such as insertion de-vice gap settings, bunch charge, bunch length, etc. Since the charge per bunch is usually high, intrabeam scattering becomes very strong creating a dependence of emittance on stored current. Furthermore, since the bunch length can vary as insertion device gaps change, the emittance blow-up from intrabeam scattering is not constant either. Therefore, the emittance, bunch length, and hence the resulting Touschek lifetime have to be calculated in a self-consistent fashionwith 6D tracking taking into account not only the bare lattice and RF cavity settings, but also momentary bunch charge and gap settings. This paper demonstrates the intricate interplay between transverse emittance (insertion devices, emittance coupling), longitudinal emittance (tuning of main cavities as well as harmonic Landau cavities), and choice of stored current in an ultralow-emittance storage ring as well as some implications for brightness optimization