Interplay of Touschek Scattering, Intrabeam Scattering, and RF Cavities in Ultralow-emittance Storage Rings

When it goes into operation in 2016, the MAX IV 3 GeV 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 considerably 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 no longer constant during a typical user shift. Since the charge per bunch is usually high, intrabeam scattering (IBS) becomes very strong creating a dependence of emittance on stored current. Since the bunch length can vary as insertion device gaps change, the emittance blow-up from IBS is not constant either. Therefore, the emittance, bunch length, and hence the resulting Touschek lifetime have to be calculated in a self-consistent fashion taking into account the bare lattice, RF cavity settings, 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.