Photon Rush: A Decade of China's Tech Crusade to Forge a 'Super Eye' for the Micro World

Deep beneath Beijing's Huairou Science City, a massive scientific instrument shaped like a magnifying glass is quietly taking shape. This national flagship project, known as the High Energy Photon Source (HEPS), aims to generate the world's brightest X-rays, striving to tear open a new fissure of understanding in the exploration of the micro world.

Not far away, in a laboratory, another silent battle is underway. The team led by Wei Wei from the Institute of High Energy Physics of the Chinese Academy of Sciences is racing against time to build a super camera for this "giant X-ray machine" – a detector capable of capturing light one trillion times brighter than the sun. As electrons whirl at near-light speeds within the accelerator and pixel units on the detector chip collaborate with microscopic precision, a scientific revolution concerning light and matter is unfolding.

01. Photon Rush: How HEPS Weaves a 'Monster-Revealing Mirror' for the Micro World

The core of HEPS is a feat of energy and light manipulation. Electrons are born in the electron gun, gain initial kinetic energy in the linear accelerator, and then, like sprinters, dash into the booster ring. After nearly ten thousand acceleration cycles, they are injected into the 1.3-kilometer circumference storage ring at 99.999997% the speed of light. On this circular "track," electrons complete 4.5 million laps per second. Each time their path is bent by magnets, they release synchrotron radiation tangentially – a process akin to water droplets flying off a rapidly spinning umbrella, but here, what's shed are extremely high-energy X-rays.

These X-rays are like unpolished jade, requiring meticulous processing within the beamline stations. The Hard X-ray Imaging (HXI) beamline acts as a master craftsman, using multilayer mirrors and zone plates to focus the raw beam into a spot merely a few micrometers in diameter – a precision equivalent to concentrating a flashlight beam to a pinpoint size from a kilometer away. As of January 2025, HEPS's storage ring achieved a beam current exceeding 40 milliamperes and reduced the electron beam emittance to 93 picometer-radians. This means the lateral spread of the electron beam is on the order of one-millionth of an atomic scale, producing X-rays tens of millions of times brighter than conventional sources. This brightness is sufficient to penetrate aircraft engine blades or resolve the atomic structure of viral proteins.

02. Pixel Maze: The 'China Chip' Breakthrough in X-ray Detectors

When HEPS's X-rays illuminate the material world, the ability to capture the trajectories of these photons becomes key to deciphering scientific secrets. Traditional indirect detection technology is like putting "second-hand clothes" on X-rays – converting them to visible light via a scintillator before imaging, which can cause over 30% loss in spatial resolution. Wei Wei's team aimed to create a "photoelectron catcher" that directly converts X-ray photons into electrical signals, a task involving overcoming three major chasms:

• The First Chasm: Making X-rays No Longer 'Transparent'. High-energy X-rays easily penetrate common materials. The team selected high-purity silicon semiconductor as the "light-trapping wall," applying an electric field to create "electron traps." When an X-ray photon strikes a silicon atom, the resulting electron-hole pairs are separated by the field, generating a measurable electrical signal – a breakthrough in "seeing the invisible."

• The Second Chasm: Creating a Miniature Universe within a Pixel Unit. Each pixel unit on the detector chip is a mere 50 micrometers square, yet must integrate complex circuits for charge amplification, threshold discrimination, and data buffering. This is like building tens of thousands of miniature labs on a chip the size of a fingernail, each needing to process signals precisely and transmit data within nanoseconds. Using 130nm CMOS technology and after 12 design iterations, the team finally achieved precise single-photon counting per pixel.

• The Third Chasm: 'Nano-scale Suturing' of Neural Endpoints. The sensor and readout chip are connected via flip-chip bonding, using tiny metal bumps just 50 micrometers in diameter, resembling neural synapses, with a density reaching 250,000 per square centimeter. Initial processes caused many bumps to fail, creating "dead zones" in the images. After 37 process adjustments with the manufacturer, the team achieved a bump reliability exceeding 99.99%, enabling 6 million pixels to work in concert with the precision of a fine timepiece.

03. A Decade of Refinement: The 'Pixel Long March' from Lab to Beamline

This technological crusade began in 2012 from a state of near scarcity. When Wei Wei's team started the chip design, there were no domestic precedents for such detectors, and foreign companies guarded key technologies closely. The first tape-out cost 1.3 million RMB, exhausting half the project's initial funding. Working under immense pressure, the team entered a "chip prenatal care" mode – core members worked overtime verifying circuits even while their wives were on bed rest during risky pregnancies, fusing the challenges of research and personal life into the chip design.

In 2015, the first detector module was born, but faced a "mechanical tolerance crisis" during assembly. Insufficient machining precision caused modules to press against each other, forcing the team to hand-polish the mechanical frames, akin to adjusting gear clearances in a精密钟表. This detail exposed shortcomings in domestic precision machining but also pushed the collaborating manufacturer to upgrade equipment, ultimately achieving mechanical part tolerances within 5 micrometers – one-tenth the width of a human hair.

By 2023, the third-generation prototype passed tests, its performance surpassing mainstream international products: a dynamic range over 1 million:1, capable of distinguishing the faintest and brightest photon signals; a high-speed imaging rate of 1,500 frames per second, able to capture the rotation of a fan blade. When the team installed their self-developed detector at a HEPS test beamline and obtained clear X-ray diffraction images for the first time, the voices that once doubted "China can't make this" were silenced by the stable waveforms in the experimental data.

04. Light-Chain Revolution: The Butterfly Effect from Scientific Facility to Industrial Blue Ocean

The synergistic innovation between HEPS and domestic detectors is reshaping research paradigms across multiple fields. In aerospace, the HXI beamline can perform 3D tomography on turbine blades, detecting internal micron-level cracks with 50 times the efficiency of traditional non-destructive testing. In life sciences, highly coherent X-rays enable mesoscopic imaging of entire brains, offering new tools for early diagnosis of Alzheimer's. In medicine, the team's photon-counting CT technology can reduce radiation dose by 70% while improving the detection rate of tiny tumor lesions.

A more profound impact lies in breaking technological monopolies. A single imported high-end X-ray detector can cost over 8 million RMB, while domestic versions reduce costs by more than 60%. The detectors required for HEPS's 90 beamlines are projected to save over 500 million RMB in research funds, money that can be reinvested in frontier exploration. Furthermore, the precision machining and integrated circuit technologies matured during detector development are now feeding back into international high-energy physics projects, upgrading segments of the domestic semiconductor industry chain.

05. Light of the Future: When Pixel Arrays Meet Cosmic Rays

At the critical juncture of HEPS's beam commissioning, Wei Wei's team is already looking further ahead. The next generation of detectors will incorporate 3D integration technology, embedding memory within stacked chips for real-time data processing. New sensors based on Cadmium Zinc Telluride (CZT) semiconductor will extend the detectable energy range to hundreds of keV, meeting nuclear physics experiment needs. Concurrently, plans are afoot to further enhance HEPS's brightness, aiming to reduce electron beam emittance below 50 picometer-radians – equivalent to controlling the distance error between Beijing and Shanghai within a hair's breadth.

This decade-long technological crusade is, in essence, a response to the challenge of overcoming critical technological dependencies. As the High Energy Photon Source illuminates the fundamental structure of matter, and as domestic detectors capture the slightest flicker of each photon, Chinese scientists are demonstrating that on the racetrack of advanced scientific instrumentation, breakthroughs are never miracles of sudden inspiration. They are the result of countless late nights spent refining chip layouts, the persistence in conquering micron-level processes alongside manufacturers, and the systematic engineering of decomposing "impossible" into "I'm possible."

Just like the relentless electron beam within the storage ring, the journey of scientific exploration has no finish line. When HEPS officially opens for users in 2025, and when domestic detectors capture the first experimental light at the beamlines, those once "overambitious" technological concepts will finally become new torches illuminating the boundaries of human understanding. And the first-generation chip sample resting on Wei Wei's desk, quietly reflecting the laboratory light, is not merely an integrated circuit. It is a microscopic footnote to China's technological journey from "catching up" to "running stride for stride."