China Spallation Neutron Source Completes Important Milestone Equipment Installation Task, Beam Power Exceeds 200 kW

To minimize the impact on user operations, the China Spallation Neutron Source Phase II Project (CSNS-II) utilizes the annual summer shutdown window to carry out Phase II equipment installation. During this year's summer shutdown, the project team completed the installation and commissioning of the front-end equipment of the linear accelerator, all solid-state modulators, and the third magnetic alloy cavity of the rapid cycling synchrotron. At this point, all equipment of the CSNS-II accelerator except the superconducting accelerator has been installed. After nearly a month of beam commissioning, on October 20, 2026, the facility's beam power exceeded 200 kW and officially entered user operation, reaching twice the Phase I design beam power. This is also an important milestone in the CSNS-II construction, providing key verification for achieving the Phase II 500 kW goal.

This round of beam commissioning simultaneously serves the improvement of CSNS operational performance and the verification of the CSNS-II power upgrade roadmap. Changes in equipment parameters superimposed with physical factors such as space charge effects and beam impedance instabilities further increased the difficulty of hardware matching and beam loss control under high-power conditions.

For key sections such as the RFQ and MEBT that were put into beam commissioning for the first time after the linear accelerator upgrade and modification, the accelerator team carried out parameter adjustment and beam matching, gradually improving the beam stability of the linear accelerator and creating conditions for high-power beam commissioning.

On this basis, reducing beam loss and improving beam transmission efficiency remain key to ensuring stable operation of the synchrotron. Focusing on beam loss control under high-power conditions, the accelerator team made major adjustments and optimizations to the operating mode, solved the beam collective instability problem, and achieved a beam density index exceeding the highest level of comparable international accelerators; while increasing power, beam loss was further reduced.

The CSNS neutron target station team completed the installation and commissioning of the No. 8 (T8) target body on September 25. The team designed a new heat dissipation scheme for 200 kW operating conditions, added target plate temperature monitoring and analysis methods, and provided key experimental verification for the CSNS-II high-power target design. Based on refined thermal calculations of the target—moderator—reflector system, the team optimized the beam spot height distribution on the target surface, improved the operating conditions of the target station cryogenic system and water cooling system, and ensured the safe and stable operation of the target system at 200 kW beam power.

The 11 neutron spectrometers officially opened to users at CSNS have completed maintenance of key components such as scattering chambers, choppers, detectors, and sample environments during the summer maintenance period. At 200 kW beam power, the spectrometers will provide users with higher-quality neutron beams, more efficient measurement methods, and richer experimental conditions, supporting the smooth implementation of CSNS key tasks and user projects.

The beam commissioning period coincided with the Mid-Autumn Festival and National Day holidays. Key positions such as the central control room and operational emergency duty posts implemented shift rotations. Researchers and operators stayed at the front line to ensure continuous beam commissioning work, ultimately achieving stable operation of CSNS at 200 kW average power and official beam delivery.

This 200 kW beam commissioning verified the relevant technical schemes, validated the CSNS-II power upgrade technical roadmap, and accumulated valuable experience for the subsequent beam commissioning work of increasing the linear accelerator beam energy to 300 MeV.

At present, the CSNS-II project is nearly halfway through its schedule, and construction is progressing smoothly. The civil construction works were successfully completed at the end of September, with the project team completing expansion construction under the complex conditions of the Phase I operational facility area. On October 15, the core equipment of the accelerator cryogenic system——a 1 kW-class 2K helium refrigerator——was successfully installed. Next, the project team will continue to coordinate and advance equipment installation, commissioning, and other tasks, making every effort to ensure the Phase II project is completed on schedule and with high quality. Once the Phase II project is completed, it will greatly enhance neutron beam performance, expand multidisciplinary frontier research capabilities, and provide a higher-level neutron science platform for basic research and technological breakthroughs in materials science, life sciences, energy, and other fields in China.