A design study of ILC positron source with Alternate Periodic Structure cavity

The International Linear Collider (ILC), which is planned to be constructed in the Kitakami Mountains of Japan, is an electron-positron collider with 250-1000 GeV center of mass energy. The mass production of Higgs boson and top quark and the discovery of supersymmetric particles are expected. The ILC is studying an e-drive method in which an electron beam of several GeV is incident on a metal target as a positron generation method. Since the beam cannot be reused with the linear collider, it is necessary to generate a large amount of electron/positron beams compared to the conventional ring collider. Especially for positrons, it is necessary to improve the generation efficiency and prevent the damage of the generation target. Therefore as a positron capture accelerator, we adopted a π/2 mode Alternate Periodic Structure cavity (APS cavity) that has a large diameter (2a = 60 mm) and can generate a high and stable acceleration gradient. In addition, a more efficient deceleration capture method with a bunching action is used. In this method, positron are placed in the deceleration phase and captured in the acceleration phase by phase slip. In this study, we report the compensation of beam loading in the positron capture accelerator considering the phase change, the positron capture accelerator, the optimization of positron capture by the parameters of ECS, and the overall design. (author)