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

Spanning an area comparable to 90 football fields, HEPS is set to be a fourth-generation synchrotron radiation facility and China's first high-energy light source designed to achieve the highest brightness globally.

The facility is expected to commence operations by the end of this year.

In March 2023, HEPS successfully achieved its first electron beam via the Linac, operating at an energy level of 500 MeV. The facility aims to serve as a vital research platform across several disciplines, including material science, chemical engineering, and biomedicine, according to Professor Pan Weimin, director of the HEPS project at the Institute of High Energy Physics.

Professor Pan highlighted that emittance, a parameter evaluating electron beam quality, is critical for the facility's performance.

In January, HEPS achieved a notable electron beam emittance of 93 pm·rad within its storage ring, complemented by a beam current exceeding 40 mA.

This performance enables HEPS to produce high-quality bright synchrotron radiation, as lower emittance facilitates reduced lateral divergence of the electron beam, thereby increasing brightness.

On November 2023, further advancements were noted when the electron beam achieved more than 5 nC of bunch charge at 6 GeV via the booster.

The facility's design comprises accelerators, beamlines, end stations, and supporting facilities, with construction initiated in Huairou district, Beijing, in 2019.

Built on a foundation of 3 meters of plain concrete and 0.8 meters of reinforced concrete, HEPS integrates its entire structure to achieve micro-vibrations of less than 25 nanometers during operation.

This level of precision is essential, as even minor vibrations can disrupt high-precision equipment in such facilities.

Professor Pan remarked on overcoming numerous technical challenges throughout the construction process.

The storage ring features 1,776 magnets, which are responsible for controlling the stable high-speed operation of the electron beam within a complex vacuum track.

As of July 1, 2024, the installation of the last shielded bellows in the tunnel marked the completion of the HEPS storage ring, connecting all components of the facility.

The narrowest part of the electron track has a diameter of merely two to three millimeters, posing installation challenges for vacuum boxes due to potential deformations.

Professor Pan shared an insight derived from repeated experiments that simplifying the process by allowing the materials to settle for one to two weeks effectively alleviated this issue.

On October 12, 2024, the high-energy synchrotron light generated from the W73 undulator in the HEPS storage ring was successfully transmitted to the HXI High Energy Imaging beamline, located 350 meters away.

The Hard X-ray Imaging (HXI) beamline, among the first constructed, is emphasized as a significant experimental platform for investigating internal microstructures in engineering materials.

Dong Yuhui, executive deputy director of HEPS, described the facility as resembling an oversized X-ray machine, with emitted light capable of reaching energy levels of up to 300 keV—sufficient to penetrate several centimeters of steel.

The brightness of the emitted synchrotron light is reported to be a trillion times greater than conventional X-ray machines, greatly enhancing the visibility of the microscopic world.

HEPS is expected to empower researchers to accomplish previously unattainable objectives across various sectors, including aerospace, nanotechnology, biomedicine, and new materials development.