Research on an active control method of double crystal monochromator with disturbance observer

Abstract

The double crystal monochromator (DCM) is the core equipment of high flux and high monochromatic light on the synchrotron beamline, which directly affects the performance of the synchrotron hard X-ray beamline in terms of stability. To meet the requirements for the stability of the nano-radian magnitude of the DCM for the 4th-generation synchrotron light source, this paper presents a method to suppress the primary resonance of the system using an integral lead compensation notch filter and eliminate the higher-order positive and negative resonance peaks with a dual second-order notch filter. The bandwidth of the DCM system is enhanced to meet the system speed requirements. Meanwhile, the mechanical coupling is considered equivalent to the system's internal disturbance. The disturbance observer is designed to ensure the stability and dynamic performance of the DCM system. The simulation results show that after correction by the integral lead compensation notch filter and the dual second-order notch filter, the system bandwidth can reach 308Hz while maintaining a phase margin of approximately 25°. Furthermore, the stability of DCM can reach an RMS of 0.139 nrad, 16.610 nrad, and 1.431 nm in the Pitch, Roll, and Gap direction, respectively, with the help of a disturbance observer. The paper proposes a method to develop stable DCMs in 4th-generation synchrotron radiation facilities while improving the X-ray beamline performance.