Study Of Transient Beam Loading And Feedforward Compensation Of CiADS

As one of the cores of the China initiative Accelerator Driven System(CiADS),the function of the superconducting proton linear accelerator is to provide a high-power proton beam with an energy of 500 MeV and a current of 5 mA.During the beam power loading process,the beam mode gradually transitions from pulse to approximately con-tinuous wave.The transient beam loading effect caused by the pulsed beam passing through the superconducting cavity will seriously affect the stability of the electric field amplitude and phase in the superconducting cavity,so that the subsequent beam can-not be effectively accelerated,which affects the quality of the beam.It may even cause beam loss.First,this thesis briefly introduces the basic theory of beam load effect and the ba-sic model of low-level control loop.In order to facilitate the analysis of the changes in the amplitude and phase of the superconducting cavity in a single pulse,according to the principle of equivalent circuit,the time-domain field-building formula of the super-conducting cavity is derived,and the simulation model of the superconducting cavity high-frequency system is established.Using this model,simulation analysis of the in-fluence of different beam current strength,pulse width and feedforward timing jitter on the cavity pressure amplitude and phase stability,and on the ADS prototype,using the same beam parameters to carry out the simulation results verification.The results show that the agreement between the theoretical and experimental values of the amplitude and phase offset in the superconducting cavity under beam loading is less than 0.2%and 0.02~°.Based on this model,this paper further systematically analyzes the influence of the beam loading effect,feedforward error and other factors on the intracavity electric field amplitude and phase stability in the CiADS superconducting proton linear accel-erator,and gives the beam pulse widths with different current intensities,Feedforward timing jitter,tolerable threshold of ripple amplitude and ripple frequency.The research results provide theoretical guidance and data support for the beam stability and debug-ging mode of CiADS.At the same time,the cavity pressure in the acceleration section of Ellip062 changes greatly,and the beam loading effect of some superconducting cav-ities is more serious.The simulation results show that increasing the bandwidth of the superconducting cavity can effectively reduce the influence of beam load and further improve the tolerance of the acceleration section.In order to solve the problems of low efficiency and low accuracy of fixed-quantity feedforward compensation debugging currently adopted by ADS,this paper adds a P-type ILC adaptive feedforward simulation model to the original feedback loop model.Through this model,the learning gain and convergence speed of beam loading effect compensation for different types of superconducting cavities are simulated and ana-lyzed.The results show that under the control of the P-type ILC loop,compared with the negative feedback loop,the amplitude and phase shift caused by the beam loading effect can be greatly reduced.