Optics Design of a novel Beam Delivery System for CLIC: the case of two Interaction Regions. First experiments for the validation of the ultra-low βy∗ nanometer beam size at ATF2

The Compact Linear Collider (CLIC) could provide e+e− collisions in two detectors simultaneously at a bunch train frequency in the linac twice the baseline design value. In this thesis, a novel dual Beam Delivery System (BDS) design is presented in order to serve two Interaction Regions (IR1 and IR2) including optics designs and the evaluation of luminosity performance with synchrotron radiation (SR) and solenoid effects for both energy stages of CLIC, 380 GeV and 3 TeV. IR2 features a larger crossing angle than the current baseline. The luminosity performance of the novel CLIC scheme was evaluated by comparing the different BDS designs with and without the detector solenoid field effects. It has to be highlighted that the impact of the detector solenoid on luminosity had not been evaluated for the current CLIC baseline, which amounts to a loss of about 4% that corresponds to the same value of the old baseline design. At 380 GeV the 2 IRs of the novel dual BDS design feature same luminosities than the current baseline. However at 3 TeV the luminosity performance is reduced by 2% from the baseline design for the IR1 and by 33% for the IR2. The dual CLIC BDS design provides adequate luminosities to two detectors and proves to be a viable candidate for future linear collider projects. One of the main requests for future linear colliders is to achieve a nanometer vertical beam size at the Interaction Point (IP). Accelerator Test Facility 2 (ATF2) represents a scale down implementation of the Final Focus System (FFS) to test the novel local chromaticity correction scheme that is implemented in the International Linear Collider (ILC) and the Compact Linear Collider (CLIC) designs. After several years of operations and commissioning, σy∗ of 41± 3 nm was measured at ATF2 with the nominal βy∗ opticsin2016. This thesis reports the experimental tuning study done with the ultra-low βy∗ during March 2019 beam operation. This optics has a level of chromaticity comparable with CLIC one and it is expected to reduce σy∗ below 40 nm.