Low-level radio-frequency system upgrade for the IMP Heavy Ion Reach Facility in Lanzhou (HIRFL)

Abstract

The upgrade of the Heavy Ion Research Facility in Lanzhou (HIRFL) began in 2000 to enhance the performance in nuclear physics, atomic physics, irradiative materials, and biology, cancer therapy using heavy ions and hadron physics. The upgraded program of HIRFL aimed to provide all ions from protons to uranium for higher beam intensity. As one of subprojects upgrade program in HIRFL, the low-level radio frequency (LLRF) system is also completely redesigned to better stabilize the beam acceleration parameters during the machine operation.The purpose of this article is to describe the design and implementation of the new fully digital LLRF system for six sets of radio frequency (RF) systems at the HIRFL. All components, including the quadrature demodulation, phase and amplitude detectors, phase shifter, and proportional integral (PI) loop filter, were designed in detail and realized in field programmable gate array (FPGA). A special synchronous RF source was designed to provide a phase reference for the different RF systems. A new tuning system was designed to ensure that the RF system remains in a good working state. An economical compensation method for the temperature drift in the pick-up cables was designed to improve the control accuracy of the system. The new LLRF systems have passed a 24 h high power test on the HIRFL cavities. The phase stabilization control accuracy was |Δϕ|≤0.2o, and the amplitude fluctuation was |ΔA|≤2∗10−3. Compared with the original analog system, the control precision and stability have been improved by an order of magnitude. The extraction beam energy of SFC was measured, and its stability is better than 4.3∗10−3, after this LLRF system is applied successfully.