A major milestone was marked in the construction of High Energy Photon Source (HEPS) when electron beams with currents higher than 10mA were successfully stored in the HEPS storage ring on August 18, 2024. This achievement signifies the completion of the accelerator complex and the start of beam commissioning.

The HEPS accelerator complex consists of an injector and a diffraction-limited storage ring. The injector includes a 500 MeV Linac and a 6 GeV booster. The commissioning of the injector was completed in 2023, meeting the performance objectives and marking the start of routine operation.

The electron storage ring, with a circumference of 1360.4 meters, is the main component of the HEPS accelerator complex. It stores ultra-low emittance electron beams. The storage ring is composed of 48 seven-bend achromats, meticulously designed to achieve a horizontal natural emittance of less than 60 pm·rad at a beam energy of 6 GeV.

The HEPS storage ring is one of the largest synchrotron light source accelerators in the world and the largest in China. Its primary function is to store high-energy, high-quality electron beams and generate high-performance synchrotron radiation.

HEPS commenced the HEPS storage ring commissioning on July 23 this year, after the completion of fabrication, installation, and joint conditioning of all equipment in the storage ring. 

Electron beams were transmitted through the entire high-energy transport line connecting the booster and the storage ring on the same day, and then injected into the storage ring. The whole procedure was completed within two hours. About four hours later, electron beams successfully traveled more than one circle in the storage ring, facilitated by tuning a few correctors near the injection point.

This quick achievement indicated that the joint conditioning was effectively completed, and all equipment was aligned and powered with high precision as expected, according to PAN Weimin, project director of HEPS.

By July 29, 2024, electrons could circulate in the ring more than a dozen times. Subsequently, the RF cavities started operation, coupled with further optimization of the injected beam parameters and storage ring settings, and resulted in the beam circulating more than one hundred times. The sextupoles were then turned on and gradually ramped to their design gradients, leading to the first stored beam with a current of approximately 50 μA and a lifetime of over 10 seconds on August 6, 2024.

Multi-bunch injection was later realized with the stored beam parameters and those of injected bunches continuously optimized. On August 18, 2024, HEPS successfully achieved beam with current of well above 10 mA, one hundred times than that achieved about one week ago. 

“Commissioning of the HEPS storage ring will continue in the next few months, with the aim to achieve higher beam currents with sufficiently long beam lifetime for vacuum conditioning and beamline commissioning,” said JIAO Yi, deputy director of the HEPS accelerator division.

As one of China’s key scientific and technological infrastructure projects during the 13th Five-Year Plan, construction of HEPS began in Huairou Science City on June 29, 2019.

The project is expected to be ready for operation by the end of 2025. Once completed, HEPS will be the first high-energy light source in China, and one of the brightest fourth-generation synchrotron radiation facilities in the world.

Fig.1. Screenshot of the HEPS accelerator status displays on Aug, 18 showing a beam current of about 12 mA. (Credit: IHEP)