To investigate the mechanism of flow-induced vibrations in the cooling system of a double crystal monochromator (DCM), this paper utilizes a multi-physics numerical simulation approach, employing ANSYS and FLUENT platforms to simulate the flow state of liquid nitrogen in the cooling system and explore the amplitude response of the DCM. Initially, simulations were conducted to examine the flow state of liquid nitrogen with varying frequency and amplitude pulsations. Subsequently, modal analysis was employed to investigate the amplitude response of the DCM in the pitch direction vibrations under pulsating excitation. Finally, this research investigated the influence of high heat load-induced liquid nitrogen boiling on a DCM. The results indicate that pipe resistance is the fundamental cause of vibration induced by pulsating excitation. Low-frequency excitation enhances the amplification factor of DCM vibration. In contrast, due to the rapid conversion of fluid kinetic energy to pressure potential energy, high-frequency excitation increases the pulsation amplitude in the pipe. Additionally, there is a linear relationship between the amplitude of liquid nitrogen velocity fluctuations and the response amplitude of a DCM. The slug flow formed after liquid nitrogen boiling generates low-frequency pulse signals, and intermittent fluid impacts cause significant vibrations in the DCM. These research findings provide a reference for the analysis and design of ultra-high-stability DCM cooling systems.

With the continuous development of synchrotron radiation light sources, higher requirements have been put forward for the stability of double-crystal monochromators in synchrotron radiation facilities. This paper designs an active adjustment mechanism for a double-crystal monochromator to improve its stability. Firstly, three spatial degrees of freedom are designed based on the active adjustment mechanism of flexible leaf spring parallel coupling, and the prototype of the mechanism is fabricated. Secondly, system identification experiments are carried out and the system transfer function curve is fitted by the nonlinear least squares method. Thirdly, the controller based on non-singular terminal sliding modes and a finite-time disturbance observer was designed for stability control and disturbance compensation. Finally, the effectiveness of the controller is verified by a model-in-the-loop approach based on the performance of the real-time target machine. The results show that the non-singular terminal sliding mode + finite-time disturbance observer control strategy can reduce the RMS value of the vibration displacement of Axis-1/Axis-2/Axis-3 by 81.25%, 78.53%, and 71.82%.

The double crystal monochromator (DCM) is a spectrometer in synchrotron radiation beamlines, and its stability directly impacts the quality of the emitted light. In order to meet the requirements of the fourth generation of synchrotron light sources, researchers have designed a DCM using an active control method to ensure stability by actively compensating for crystal displacement through voice coil motors. The active control method imposes high demands on the vibration isolation performance of the DCM frame. In response to external excitation characteristics, this paper proposes a quasi-zero stiffness (QZS) isolation system based on a compressed buckling beam structure. Random vibration simulations using finite element analysis revealed that, under different operating conditions, the 3σ displacement of the core part of the DCM is maintained at the nanometer level. Moreover, this paper presents a calculation method based on elastic potential energy to establish force equilibrium equations for negative stiffness and analyzes stress distribution in the beam during vibration using the derived deflection curve. Validation through finite element simulations confirms the method’s accuracy in calculating negative stiffness and stress distribution. Because of the structural similarities, some of the results of this paper can be applied to the study of negative stiffness honeycomb materials.