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Description
Low-level radio frequency (LLRF) systems play an essential role in cyclotron control, and the beam quality is closely tied to the overall performance of the RF system. Efforts have been carried out by the individuals of the China Institute of Atomic Energy (CIAE), focusing on the design of a self-excited digital LLRF system for ultra-lightweight high-temperature superconducting cyclotrons in special environment applications. In CIAE, a self-excited digital LLRF controller has recently been developed and tested for the cyclotron RF control. In practice, for this special cyclotron, however, it is uneconomical to construct a dedicated vacuum tank just for the hot test of the RF system. Since the Q value and thermal drift of the cavity can be made identical under atmospheric or vacuum conditions, an alternative testing method has been developed to evaluate the performance of the LLRF control system, along with the cavity and the high-power RF amplifier. The cavity is excited by a 20kW solid-state power amplifier using a directional coupler, with a Q value of 2500, at a frequency of 77 MHz. Two dedicated digital signal processors, together with the ADCs, are included in the reported LLRF to achieve amplitude-phase control. Communication between DSPs is achieved through dual-port SRAM. A fast PID algorithm for IQ modulation was designed, achieving a group delay of less than 800 ns. This paper reviews the design of the self-excited digital LLRF, along with preliminary test results.
Footnotes
*: Corresponding Author, Dr. Zhiguo Yin, Email: yinzhiguo@cnncmail.cn
