RFQ Low Level Algorithm Design And Implementation

The radio frequency quadrupole uses an electric field to simultaneously achieve longitudinal and lateral focusing of charged particles.It can be used for low-energy particles emitted from an ion source and often used as an injector for high-energy accelerators or a pre-accelerator for low-energy high-current accelerators.After the RFQ is loaded with electromagnetic waves,the electromagnetic field will generate current on the surface of the RFQ.The temperature of the cavity wall and the surface of the cavity wing will increase due to the loss of power and heat,which will cause deformation and cause detuning of the cavity,resulting in loss of power feeding efficiency and degradation of beam quality.The dynamic tuning of a RFQ is generally achieved via thermal regulation over the vanes and walls.However it takes tens of minutes to reach nominal power.The low-level control system is an important part of the high-frequency system of the accelerator.It stabilizes the amplitude and phase of the accelerating field in the high-frequency cavity,and controls the tuning of the high-frequency cavity.It plays a very important role in ensuring beam quality and safe and stable operation of the accelerator.In order to power an RFQ quickly,a low-level control system implemented with direct digital synthesis and phase-locked loop technology is designed.This system can simultaneously realize dynamic tracking and amplitude-phase feedback control of RFQ resonant frequency.Even if the cooling water does not reach thermal equilibrium,RFQ can also load power and form an accelerating field.This article will introduce the signal processing board structure and debugging.Signal processing board introduction,including the function of pre-function verification board and low-level digital signal processing board,debugging and overall hardware solutions.Design of resonant boost frequency tracking algorithm section describes the main functional chips: the AD9858 direct digital synthesizer and the AD9520 clock signal generator control algorithm as well as digital signal sampling and processing.The implementation of the resonant boost function needs to be based on closed-loop feedback control.The feedback control loop includes a tone loop and amplitude-phase control loop.In order to perform functional tests based on simulation cavity,FIR filter running on Stratix II DSP development board was designed.The test results show that this scheme can achieve ±0.5% amplitude stability and ±0.5° phase stability while tracking the virtual cavity resonance frequency.