The High Energy Photon Source (HEPS), China’s flagship synchrotron radiation facility, has officially begun its joint-commissioning phase after successfully completing photon beam commissioning, the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences, which developed the facility, announced on March 27 in Beijing.

HEPS achieved a world-class electron beam emittance of 93 pm·rad in its storage ring this January, following a beam current exceeding 40 mA. Emittance is a critical parameter evaluating electron beam quality, according to Prof. PAN Weimin from IHEP, director of the HEPS project. Lower emittance reduces lateral divergence of the electron beam, thereby producing brighter synchrotron radiation.

Additionally, HEPS announced the successful demonstration of swap-out injection based on high-energy accumulation in the booster. Instead of building a separate high-energy accumulator ring, HEPS repurposed its booster to function both as an accelerator and an accumulator. This innovation significantly reduces infrastructure costs.

Extracted bunches from the storage ring are reinjected into the booster rather than being dumped. These bunches merge with low-charge bunches, are accelerated in the booster, and then injected back into the storage ring. This approach effectively addresses the challenge of generating high-charge bunches while maintaining injection efficiency and beam stability.

“This injection scheme allows for electron beam recycling, enhancing the environmental sustainability of the process,” said Prof. JIAO Yi from IHEP, deputy head of the accelerator division.

The advantages of the storage ring directly enhance the sensitivity and precision of experiments conducted on the beamlines. On October 12, 2024, high-energy synchrotron light from the W73 undulator was accurately delivered to the endstation of the HXI High Energy Imaging beamline, located 350 meters away. Following intensive photon beam commissioning, imaging experiments focusing on internal micro-defect structures in engineering materials were initiated.

The HXI beamline incorporates both a set of insertion devices and a long sample-source distance to achieve higher coherence, deeper penetration, a wider field of view, and higher resolution—surpassing conventional X-ray sources.

“Coupled with in-house-developed detectors featuring ultra-high pixels and modulation transfer function, the HXI beamline will revolutionize studies in aerospace materials and whole-brain neural networks, offering greater efficiency and precision,” said Prof. DONG Yuhui, HEPS executive deputy director.

Meanwhile, several other beamlines have also completed photon beam commissioning, marking HEPS' official transition to the joint-commissioning phase.

HEPS is a key scientific and technological infrastructure project included in China’s 13th Five-Year Plan and approved by the country’s National Development and Reform Commission. Once completed, the fourth-generation synchrotron radiation facility will be China’s first high-energy light source and is designed to offer the highest brightness in the world.

Phase I of the project includes construction of 14 user beamlines and one test beamline. Construction of HEPS began in June 2019 and is scheduled for completion in late 2025. Over the past five years, the accelerator complex and first set of beamline installations have been completed.

The civil construction of the HEPS was completed (photo in August 2024). (Image by IHEP)

In March 2023, the first electron beam of HEPS achieved via the Linac with an energy of 500 MeV. (Image by IHEP)

In November 2023, the electron beam of HEPS achieved a bunch charge of more than 5 nC at 6 GeV via the booster. (Image by IHEP)

On July 1, 2024, the last shielded bellows was installed in the tunnel, completing the installation of the HEPS storage ring and signifying that all components of the storage ring have been linked up. (Image by IHEP)

In August 2024, electron beams with currents higher than 10mA were successfully stored in the storage ring. (Image by IHEP)

Phase I of the project includes the construction of 14 user beamlines and a test beamline. (Image by IHEP)

On October 12, 2024, the high-energy synchrotron light from the W73 undulator in the HEPS storage ring was accurately delivered to the endstation of HXI High Energy Imaging beamline, located 350 meters away.(Image by IHEP)

In January 2025, HEPS achieved a world-class electron beam emittance of 93 pm·rad in the storage ring, meeting the national acceptance criteria. (Image by IHEP)

The swap-out injection with high energy accumulation in the booster was successfully demonstrated on January 2, 2025. (Image by IHEP)