Upgrade Of HLS? LINAC Low Level RF System Based On MTCA

The performance of Hefei Light Source(HLS-?)has improved a lot after major maintenance and reconstruction.In order to further providing continuous and stable light,providing better experimental conditions for long time and high precision experiments,HLS-? is needed to be upgraded to top-off mode,making the light source always working under one certain beam current,no need to clean the field when beam injecting,ensuring the consistency of the experimental environment.Because the latest chassis frame,Micro Telecom Computing Architecture(MTCA)has the characteristics such as high reliability,high integration,and its chassis mechanical structure is strong,and heat dissipation and power supply system are reliable,has advantages of modular,redundancy design,so in this paper a digital low level RF control system based on MTCA is designed and implemented to control the amplitude and phase of RF field which used to accelerate electrons.This system is composed of digital board cards based on FPGA,RF board cards,MTCA chassis and frequency synthesis system.Rf board cards is used for up and down conversion of analog signals.It can down-convert high-frequency signals to intermediate frequency signals and up-convert baseband signals to high-frequency signals.ADC and DAC are provided on the digital board.The intermediate frequency analog signal is converted into digital signal and then start digital signal processing.The baseband IQ signal is demodulated.After feedback control and other algorithms,the baseband signal is output by DAC digital-analog conversion.The frequency synthesis system provides necessary signals such as clock and local oscillator signals.The MTCA Carrier Hub(MCH)of MTCA chassis is not only responsible for the management of PCIe,fan or power supply,but also runs EPICS system in the embedded Linux system,docking with Hefei light source software control system to realize remote control of low level RF system.This low level RF control system works on the 2856MHz of S band,with phase and amplitude stability up to 0.2 degrees and 0.4 per thousand respectively,which meets the requirements of top-off mode for the 0.25 degree RMS phase value of the digital low-level RF system in LINAC.