Drive laser system for the DC-SRF photoinjector at Peking University

Photoinjectors are widely used for linear accelerators as electron sources to generate high-brightness electron beam. Drive laser, which determines the timing structure and quality of the electron beam, is a crucial device of photoinjector. A new drive laser system has been designed and constructed for the upgraded 3.5-cell DC-SRF photoinjector at Peking University. The drive laser system consists of a 1064 nm laser oscillator, a four- stage amplifier, the second and fourth harmonic generators, the optical system to transfer the UV pulses to the photocathode, and the synchronization system. The drive laser system has been successfully applied in the stable operation of DC-SRF photoinjector and its performance meets the requirements. 266 nm laser with an average power close to 1W can be delivered to illuminate the Cs2Te photocathode and the instability is less than 5% for long time operation. The design consideration for improving the UV laser quality, a detailed description of laser system, and its performance are presented in this paper.Comment: 6 pages, 8 figures, submit to CP

Modeling and Dynamic Characteristic Analysis of a Ball Screw Feed Drive System Based on Receptance Coupling

Modeling and modal analysis method based on receptance coupling are proposed for a vibration mode of a ball screw feed drive system, which cannot be determined by axial and torsional modal shape curves through a traditional method. In this study, the mathematical model for ball screw feed drive system is obtained by improved receptance coupling. The natural frequencies of different assembly states are calculated in the modeling process. The vibration modes of the feed drive system are determined by comparing the natural frequency distributions of different assembly states for a detailed analysis of the dynamic characteristics of the feed drive system. In the proposed method, a self-developed ball screw feed drive system is selected to study the influence of worktable position, worktable mass, and screw lead on the dynamic characteristics of the ball screw feed drive system. A change in the worktable position mainly affects the vibration of the ball screw itself. A change in the worktable mass mainly affects the coupling vibration between the ball screw and the rotor or bearing. The screw lead has an opposite influence on axial and torsional vibrations of the feed drive system, and the stability of the feed drive system improves with the screw lead. The validity of the proposed method is verified by the case study

Multi-Position Identification of Joint Parameters in Ball Screw Feed System Based on Response Coupling

Existing methods of parameters identification do not consider the torsion characteristics of a ball screw and the worktable position simultaneously. Therefore, this paper proposes a multi-position identification method based on receptance coupling. Firstly, the mathematical model of the feed drive system is established by the improved receptance coupling, and this model considers both axial and torsional vibration of the ball screw. Secondly, the identification equation is established by minimum error of the modal parameters of multiple worktable position, and differential evolution algorithm is used to calculate the stiffness and damping of the joint. Finally, the self-developed ball screw feed drive system is used for experimental study. The maximum error of the first four orders of natural frequencies predicted through multi-position identification results is 2.95%, and the multi-position method is more robust than the common method identification at one position. The experiment study showed that the proposed method is accuracy and necessity

Grid scale measurement of carbon compensation in Chongqing City: Based on the perspective of land use

[Objective] Improving the carbon compensation mechanism is an important action to cope with climate change and realize the goal of carbon neutrality. At the grid scale, the establishment of carbon compensation between administrative units can provide a reference for regional low-carbon coordinated development based on land use change. [Methods] Using land cover and socioeconomic data at a grid scale of 5 km×5 km, this study calculated the carbon source/sink of land use in Chongqing from 2000 to 2020, and then explored the spatiotemporal evolution characteristics of the carbon source/sink. Further more, the carbon compensation value with the revised net carbon emissions was estimated. Finally, the path for Chongqing to achieve carbon compensation was discussed. [Results] During the research period, carbon emissions in Chongqing showed a continuous increase, with a total increase of 37.29 million tons. The carbon absorption was slowly increasing, with a total increase of 0.059 million tons. The carbon emissions showed a “core-periphery” spatial structure with the central urban area as the high-value center and gradually decreasing towards the two wings. The areas with reduced carbon emissions were mainly in Changshou, while the areas with increased emissions mainly occurred in Yubei, Jiulongpo, Shapingba, and the northwest of Ba’nan. The carbon absorption showed a distribution pattern of “high in two wings and low in the middle” in general. Fengjie, Yunyang, and Wanzhou were areas of carbon sink growth, while the northeast of Chongqing and some areas in the central urban area showed the reduction of carbon sink. The carbon compensation paying areas were concentrated in the central urban area, central Liangping, southeastern Kaizhou, and southwestern Fengdu, with a total payment amount of 2.337 billion yuan. The regions that can receive carbon compensation were mainly distributed in the two wings and a small number within the main urban area, with a total amount of 1.406 billion yuan. [Conclusion] Carbon emissions in Chongqing far exceed carbon absorption, and there exists spatial heterogeneity in the carbon compensation value at the grid scale. It is recommended to formulate differentiated compensation funding policies according to the actual situation, so as to ensure the economic interests of carbon compensation receiving areas and emphasize the ecological protection responsibility of carbon compensation paying areas. It is also necessary to promote cross-regional and county-level horizontal ecological compensation through multiple channels, and create a win-win situation between ecological protection and economic development

Screw lifetime prediction based on wavelet neural network and empirical mode decomposition

To predict residual lifetime of ball screw, screw lifetime prediction technology based on wavelet neural network (WNN) and empirical mode decomposition (EMD) is proposed. Screw accelerated lifetime test platform is introduced. Accelerometers are installed to monitor ball screw lifetime. With the method of principal component analysis (PCA), high dimension features are mapped to low dimensional space and stored into sample library together with screw expected remaining lifetime. Training samples and testing samples are randomly selected from the sample library to train and test the WNN. Then EMD is used to extract output tendency of WNN. Finally, screw lifetime prediction model can be obtained. The experimental results show that the maximum error of the training samples is 602 hours while the maximum error of the testing samples is 652 hours, which meet the need of screw lifetime prediction