The diffraction-limited storage ring (DLSR) of the Southern Advanced Photon Source (SAPS) use a large number of ultra-high gradient quadrupoles and sextupoles, which leads to the tight tolerance of beam parameters to magnetic errors. We showed the results of the magnetic error effects in previous published article. On this foundation, the magnetic error corrections are finished, including the closed orbit correction, beam optics correction and vertical dispersion correction.

The Southern Advanced Photon Source (SAPS) is a 3.5 GeV, kilometer-scale, ultra-low emittance storage ring to be built next to the CSNS(China Spallation Neutron Source) in Guangdong Dongguan, China. A preliminary lattice design for SAPS storage ring with an emittance of 32 pm.rad has been proposed before. Now, the SAPS lattice is continuously under extensive design and optimization. In this paper, the latest design of lattice is introduced, and the linear and nonlinear optimization is presented.

In the fourth-generation storage ring light sources, the dynamic acceptance is usually small related to the extremely strong nonlinearity inherent in the multi-bend achromat design, making it difficult to implement traditional off-axis local-bump injection. It was found that a double-frequency rf system can be used for longitudinal injection with the help of rf gymnastics. However, such schemes require tuning the RF parameters during injection, which would challenge the RF hardware system and cause the bunch length shrinking of the circulated bunch. In this paper, we find that with proper parameters optimization, a double-frequency RF system with static parameters can be used for longitudinal injection. A detailed design of this scheme for the application in the Southern Advanced Photon Source (SAPS) is presented.

In order to promote the studies of low emittance RF photo cathode and high gradient accelerating structures, a C-band test platform has been initialized since late 2021. In this paper, an overview of the present status and future plans of this platform is given, including a 3.6-cell C-band RF photo cathode and a C-band RF traveling-wave accelerating structure. In addition, other on-going studies on this platform, such as the test of a cryo-copper accelerating structure and the development of short pulse high gradient parallel-coupled structures, are briefly introduced.

In this report, we present our recent progress in the de-sign and high-power testing of the 2nd harmonic cavity for the China Spallation Neutron Source upgrade project. To achieve optimal performance, high-performance mag-netic alloy (MA) cores with dimensions of Ф850mm × Ф316mm × 25mm were meticulously developed and fabricated to serve as the load material for the radio-frequency (RF) cavity. Through rigorous testing, we were able to achieve a remarkable cavity accelerating gradient of over 40 kV/m under 15% duty cycle. To ensure opti-mal cooling efficiency, we conducted a comprehensive fluid dynamics simulation analysis and verified our re-sults through experiments. Finally, to assess the long-term stability and performance of the cavity, we conduct-ed a series of extended operation tests. These experiments successfully confirmed the high-performance capabilities and exceptional stability of the 2nd harmonic cavity.

In the CSNS RCS RF system, a combination of feed-back control and adaptive feedforward control was proposed in in the Low-Level Radio Frequency (LLRF) system to ensure stable beam acceleration. Although the effectiveness of the feedforward control has been confirmed in operation, a detailed study on it is still necessary. This paper presents a detailed study on the feedforward control based on Simulink simulations and proposes an optimization scheme to further improve its performance. The proposed adaptive feedforward control is reviewed, and the simulation results are presented and summarized.