The Digital Low Level Control System

The first generation Low-Level radio frequency(LLRF) control system for China ADS injector Ⅱis developed by IMPCAS. This system consists of superconducting cavity amplitude stability controller, phase stability controller and the cavity resonance frequency controller, and the operating frequency of it is 162.5MHz. The system is an all-digital closed-loop feedback control system and based on the IQ quadrature sampling demodulation technique. The design of the digital low-level RF control system, according to several aspects of it, from the hardware design to software, to debug and test the system, and the last on line running, etc., is described in detail. The hardware includes the radio frequency signal pre-processing and data acquisition, processing and recovery section, including the lower machine software code and PC control interface. The stability and performance of this system have been tested on the superconducting cavity, which is running in the temperature range of liquid helium. When the voltage and the phase of the superconducting cavity is locked by this system, the amplitude stability is less than ± 3.4 ‰ and the phase stability is not more than ± 0.3 ° under the cavity running at the Epk=25.1MV/m(the peak electric on the surface of the superconducting cavity). In the subsequent experiment—Beam loading of Superconducting cavity, the stable operation of digital LLRF control system ensures the normal operation of superconducting cavities. The superconducting cavities 10 mA beam loading task is completed. The performance of LLRF control system is verified by the experimental test, the issues emerged during the testing is analyzed, and the performance of LLRF control system is summarized according to the experimental data, the useful experience is accumulated for the future online running of superconducting cavities. According problems encountered during testing, to improve the digital low-level control system provides a basis and provide experimental data for subsequent upgrade the digital low-level RF control system.