HEPS: Super Microscope for Micro World

From above, it looks like a giant magnifying glass. The High Energy Photon Source (HEPS), located in Huairou district, Beijing, is China's first high-energy synchrotron light source and Asia's first fourth-generation synchrotron light source, according to Pan Weimin, director of the HEPS project and researcher at the Institute of High Energy Physics (IHEP), Chinese Academy of Sciences (CAS).

Since December 2025, HEPS has been under trial operation and by mid-February, it had supported 222 project experiments from 91 institutions, providing nearly 5,000 hours of user computing time. On the back of this, HEPS recently launched its first official call for proposals.

How HEPS works

"Like a large microscope in the hands of scientists, HEPS can help us to see the experiment samples clearly and analyze the microstructure and evolving process of materials," Pan said.

For example, HEPS can observe the changes of atomic structure of metal materials under extreme conditions, helping scientists design stronger alloys. It can also inspect chip circuits — which are a thousand times thinner than a human hair — for defects, making sure that smartphones and computers operate more efficiently.

In the HEPS storage ring, electrons travel at close to the speed of light. As they pass through bending magnets, they emit extremely bright synchrotron radiation along the tangent of their orbit. This radiation is directed to beamline stations, where it "illuminates" experimental samples like a spotlight, allowing researchers to uncover the secrets of the microscopic world.

"This process is similar to when we spin an umbrella quickly on a rainy day: droplets of water fly off along the tangent to the edge of the umbrella," Pan said. The accelerator for the light source acts like this umbrella, and the flying droplets are the X-rays, called synchrotron light.

Compared with the third-generation synchrotron light source, HEPS can "see" samples more clearly and faster, according to Pan. The electron beam has an energy of six billion electron volts, enabling it to emit X-rays of 300 kilovolt-electron volts or higher, allowing for the clear visualization of thicker samples.

Meanwhile, its brightness is one trillion times that of sunlight, making it capable of capturing molecular motion at the scale of one-ten-billionth of a second.

Tackling key tech bottlenecks

The overall performance of HEPS has reached a "leading level" among similar international facilities, with a source brightness nearly 100 times higher than that of third-generation facilities, enabling a continuous supply of high-quality X-rays, according to Dong Yuhui, deputy director of the HEPS project and researcher at IHEP.

The perimeter of HEPS's accelerator is 1.36 kilometers, and the area within the circle is as large as 20 football fields, Dong said. The high energy electron beam, which can accelerate to six billion electron volts and travel at a speed close to that of light, radiates a synchrotron light source.

To help the electron beams travel more steadily and generate brighter light, the research team tackled a series of world-class technological challenges.

They implemented a world-first recirculating in-axis replacement injection scheme, enabling stable operation of a single-beam group with high charge density. They also innovatively adopted a 48-cell hybrid seven-bend achromat magnetic focusing structure.

"By increasing the number of bending magnets and optimizing their layout, we have reduced the natural emittance of the electron beam to below 60 pm·rad," said Dong.

"A picometer describes the transverse size of the electron beam, while a radian refers to its divergence angle during motion. The smaller the product of the two, the more tightly the beam remains focused at high speed, with less spread," Dong explained. "This value means that the electrons maintain a compact 'formation' as they travel, with a divergence of only a few micrometers."

The R&D team has overcome several other key core technological challenges. For example, small-aperture magnet technology has reduced the magnet aperture to approximately 25 millimeters, resulting in a magnetic field gradient four times that of third-generation light sources, thereby enabling more precise control of the electron beam.

Trial operation beyond expectation

On October 29, 2025, HEPS passed the technical acceptance inspection organized by CAS, and began trial operation in December. Now, the facility operates in an alternating cycle of "user trials + performance optimization."

The research covers cutting-edge fields such as defect and fatigue assessment of aerospace components, in-situ studies of power battery charging and discharging, ultrafast 3D printing processes, brain and organ imaging and semiconductor testing.

In the aerospace sector, HEPS utilizes its high penetration capability to detect defects in aerospace components at deeper levels, thereby contributing to aerospace safety; in life sciences, it advances brain research by characterizing neuronal networks in primate brains.

"User feedback indicates that the trial results have far exceeded expectations. Some samples that cannot be observed clearly by other light sources can be distinguished by HEPS," Li Gang, researcher at IHEP, said. While advancing the facility towards acceptance after meeting performance targets, the research team is also actively communicating with research institutes and leading enterprises to address their critical needs, Li said.

"We plan to add several new beamlines and supporting accelerator equipment to further enhance our user service capabilities," Pan said, adding that the next-generation light source is expected to reduce the beam divergence to the diffraction limit, truly enabling scientists to "see every atom."

Source: Science and Technology Daily