Optimisation of the CLIC positron source at the 1.5 TeV and 3 TeV stages

Positron source is very important for many accelerator experiments. The optimisation of positron source is therefore a crucial problem to be solved. In this report, a new simple, general and effective optimisation strategy is proposed, based on iterations of scan of free parameters, which has the advantage of easily handling realistic parametric problems. The new strategy in principle can be 25 times faster than the old optimisation method. The optimisation of the CLIC positron source at the 3 TeV and 1.5 TeV stages with the new strategy is presented. Positron yield is improved by 43% compared with previous studies, mainly due to the removal of the distance between the targets. The validation of the simulation code is carried out with a cross-check with the ILC positron source results. In addition, studies on mesh grid size for PEDD estimation and matching of positron beam to the latest design of the injector linac are also presented. Positrons can be transported in the matched injector linac almost without losses, with a final accepted yield of 2.14 e+/e-.