China's High Energy Photon Source enters final construction phase

China's flagship synchrotron radiation facility, the High Energy Photon Source, has entered its final construction stage as it began the joint-commissioning phase, the Institute of High Energy Physics of the Chinese Academy of Sciences announced Thursday.

As one of China's key scientific facilities, HEPS occupies an area approximately equal to 90 football fields, but its mission is to illuminate the microscopic world at the nanometer scale.

It will be a fourth-generation synchrotron radiation facility and China's first high-energy light source designed to offer the highest brightness in the world, which is expected to start operation by the end of this year.

It will serve as a research platform for material science, chemical engineering, biomedicine and other fields, said professor Pan Weimin from IHEP, director of the HEPS project.

Pan said that emittance is a critical parameter evaluating electron beam quality, while 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. The facility is able to produce the world's top high-quality bright synchrotron radiation.

"Lower emittance reduces lateral divergence of the electron beam, thereby producing brighter synchrotron radiation," he said.

HEPS is designed with accelerators, beamlines, end stations and support facilities. The IHEP started the construction in Huairou district in Beijing in 2019.

"The facility is built on 3 meters of plain concrete and 0.8 meters of reinforced concrete, which integrates the entire structure and achieves the goal of micro-vibrations of less than 25 nanometers during operation. In a regular building, even a simple foot stomp could cause nearby equipment to vibrate at the micron level," Pan said, adding that many technical bottlenecks were overcome during the construction process.

The storage ring of the facility is equipped with 1,776 magnets of various colors, which control the electron beam to stably run at high speeds within a thumb-width vacuum track.

The narrowest part of this electron track has a diameter of only two to three millimeters. During the construction of the facility, the installation of the vacuum boxes was prone to slight deformations.

"After repeated experiments, we found that the solution was surprisingly simple—by letting the products sit for a week or two after receiving them, until the metal stress is released, the problem is effortlessly resolved," Pan said in an interview with Beijing Daily.

The Hard X-ray Imaging (HXI) beamline, among the first set of beamlines constructed, is highlighted as one of the distinctive experimental platforms aimed at studying internal microstructures in engineering materials.

"This large facility is like an oversized X-ray machine, with its emitted light reaching an energy of up to 300 keV, capable of penetrating several centimeters of steel," said Dong Yuhui, HEPS executive deputy director.

Compared to a regular X-ray machine, its brightness is a trillion times greater, enabling us to see the microscopic world much more clearly, he said.

"HEPS can assist researchers in completing previously impossible tasks across fields from aerospace and nanotechnology to biomedicine and new materials development," he said.