World-leading Achievements in High-Quality Factor 1.3 GHz Superconducting Acceleration Module (2023-06-06)

After nearly three years of relentless innovation, the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences (CAS) has completed the R&D, assembly and overall commissioning of China's first high-quality factor 1.3 GHz superconducting acceleration module. We have conquered the core key technologies urgently needed for national major science and engineering projects, and achieved world-leading results.

On June 5th, IHEP organized and held the achievement appraisal meeting for the "High-Quality Factor 1.3 GHz Superconducting Acceleration Module". The appraisal expert group consists of 14 experts including Academician Zhan Wenlong and Academician Deng Jianjun, who are from the Institute of Modern Physics of CAS, Shanghai Advanced Research Institute, Dalian Institute of Chemical Physics of CAS, Peking University, Tsinghua University, Huazhong University of Science and Technology, China Academy of Engineering Physics, China Institute of Atomic Energy, etc. Professor Liu Kexin from Peking University served as the leader of the appraisal expert group. The expert group listened to the R&D report by the project team and the test report by the test expert group, and inspected the 1.3 GHz superconducting acceleration module on site.

The expert group pointed out that IHEP has successfully developed the 1.3 GHz superconducting acceleration module with medium-temperature annealing technology for the first time in the world. The total cavity voltage, total heat load of the module, as well as the average accelerating gradient and quality factor performance of 8 1.3 GHz 9-cell superconducting cavities meet the design requirements of the superconducting acceleration module for the Dalian Advanced Light Source (DALS), and also exceed the design indicators of the superconducting acceleration module for the US Linac Coherent Light Source-II (LCLS-II) and its energy upgrade project (LCLS-II-HE), which represent the current highest international design indicators. The average quality factor of the superconducting cavities is better than that of the batch superconducting acceleration modules with nitrogen doping technology for LCLS-II-HE.

The expert group held that through technological research, the project team has made major breakthroughs and innovative achievements in the R&D of high-quality factor 1.3 GHz superconducting acceleration modules, taking the lead in realizing the technical route of medium-temperature annealing high-quality factor superconducting cavity modules in the world with completely independent intellectual property rights. The performance of the module is at the international leading level, making China's high-quality factor superconducting accelerator technology stand at the international forefront. The successful development of the module marks that the medium-temperature annealing process is stable, reliable and easy to implement, which can be used as the main technical route for future high-quality factor superconducting accelerators. This achievement has completed the verification of key technologies and prototypes of high-quality factor superconducting cavities and modules for China to build an internationally leading continuous wave electron accelerator, with great practical significance and broad application prospects. The expert group agreed that the "High-Quality Factor 1.3 GHz Superconducting Acceleration Module" passed the achievement appraisal.

The high-quality factor 1.3 GHz superconducting acceleration module is the commanding height of the current international competition in advanced accelerator technology, and a key core device for many major science and engineering projects in China and the world. With extremely complex technology and high cost, it is a core technology that "cannot be asked for, bought or begged for", and a national heavy weapon in the accelerator field.

Many major scientific and technological infrastructure projects under construction and planning in China, such as the Shanghai High Repetition Rate XFEL and Extreme Light Facility (SHINE), the Shenzhen Medium-Energy High Repetition Rate X-ray Free Electron Laser (S3FEL), and the future Circular Electron-Positron Collider (CEPC), all require a large number of high-quality factor 1.3 GHz superconducting acceleration modules. It is urgent to conquer this key core technology and realize its localization to achieve a new era of high-level scientific and technological self-reliance in key fields. Otherwise, it will lead to a substantial increase in the cost of accelerator construction and operation, or we have to spend a lot of money to buy foreign products and components.

Led by Researcher Pan Weimin, the IHEP project team, after first improving the medium-temperature annealing process and successfully realizing the medium-temperature annealing process for 1.3 GHz 9-cell superconducting cavities in the world in 2020, adheres to independent innovation to meet national strategic needs and strives to tackle key problems at the highest international level. We have realized a more advanced technical route of medium-temperature annealing high-quality factor superconducting cavity modules than nitrogen doping technology, set a world record for the quality factor of superconducting accelerators, and met the urgent needs of China's relevant major science and engineering projects. The high-power level test of the module shows that when the total cavity voltage of the module is 133 MV, the total heat load at 2 K is 80 W, and the average accelerating gradient of 8 1.3 GHz 9-cell superconducting cavities is 16.1 MV/m with an average quality factor of 3.8×10¹⁰. When the total cavity voltage of the module is 174 MV, the total heat load at 2 K is 122 W, the average accelerating gradient is 21 MV/m with an average quality factor of 3.75×10¹⁰. The stable operating total cavity voltage of the module is more than 191 MV, and the average accelerating gradient reaches more than 23 MV/m.

During the development of the module, the project team carried out two module assemblies and several cooling tests, repeatedly explored and conquered many technical problems encountered in the clean assembly of cavity strings, module integration, cooling and conditioning tests, and carried out a number of structural optimization improvements and process innovations of the module. IHEP Ruixin Co., Ltd. has closely cooperated with the Accelerator Center to form a complete set of assembly specifications and processes, and cultivate a high-level technical team, laying an important foundation for the mass production of modules in the future.

This project has been supported by the pre-research of Dalian Advanced Light Source, the pre-research of CEPC, the Beijing Advanced Light Source Technology R&D and Test Platform, and the High-performance Continuous Wave 1.3 GHz Superconducting Cavity Research and Test Platform.

Assembly of 8×9-cell superconducting cavity string in Class 10 clean room

Assembly of 9-cell superconducting cavity string with cold mass

Overall assembly of 1.3 GHz 9-cell superconducting acceleration module

Module installed in the horizontal test station

Horizontal test of the 1.3 GHz superconducting acceleration module