BBA and Coupling Correction at CLIC RTML

The CLIC Ring To Main Linac (RTML) must transport the electron and the positron bunches through more than 20 km of beamlines with minimal emittance growth. The turnaround loops (TAL) are one of the most critical sections, featuring a lattice designed to minimize emittance growth due to synchrotron radiation emission and chromaticity, while being isochronous to avoid bunch lengthening. With such a design, the impact of static imperfections like element misalignment is particularly critical. In this paper a study of the Beam-Based Alignment (BBA) techniques in the TAL of the CLIC RTML is presented. In order to reduce the emittance growth, the one-to-one and dispersion-free corrections have been tested. The results showed that the emittance growth budgets can be met both in the horizontal and vertical planes. The impact of coupling errors due to magnets rolls on the emittance has also been studied and a coupling correction section has been designed and inserted in the lattice.