Digital low level rf control system for the International Linear Collider

The International Linear Collider (ILC) aims to employ field programmable gate array (FPGA)-based digital low level radio frequency (LLRF) control system to achieve its rf stability requirements. In this paper, we present a demonstration and evaluation of the minimal configuration of the digital LLRF control system for the ILC. The achieved stabilities are shown to fulfill the ILC requirements. We also developed signal monitoring capabilities using direct sampling technique and we successfully demonstrate the filling on resonance (FoR) method to reduce the required klystron power. Furthermore, we present the possible configurations of digital LLRF control system for the ILC in this paper. We performed the experiments at Superconducting rf Test Facility (STF) in High Energy Research Organization (KEK), Japan during the cavity conditioning in the autumn of 2016.