The "Sky Catcher" Builders on the 4,400-meter Plateau

How long does it take to walk 1.3 square kilometers? A normal adult needs about 10 to 20 minutes. In the early spring of 2017, Hu Bin, the design project manager of the Daocheng High Altitude Cosmic Ray Observatory of the China Power Construction Chengdu Institute, took 4 hours to walk 1.3 square kilometers at an altitude of 4,410 meters, carrying an oxygen tank and breathing heavily.

This 1.3 square kilometer plateau is located on Haizi Mountain in Daocheng, Sichuan Province. Three arrays are arranged here to form a "big network", forming the world's highest altitude, largest scale, and most sensitive gamma-ray detection device - the High Altitude Cosmic Ray Observatory (LHAASO), built to "catch the sky". Now the observatory has successfully passed the national acceptance and will become an international cosmic ray research center with China as the main body and the participation of many countries.

For the first time, the Chengdu Institute project team followed experts from the Chinese Academy of Sciences to the uninhabited area hidden in the sea of ​​clouds on the top of the mountain. They measured the land where the design work was about to begin inch by inch with their footsteps, and felt more deeply the harsh natural environment and weak ecological environment here.

"The mountain has a long snow and ice period, and is cold and oxygen-deficient. It is very difficult to ensure normal construction from a design perspective," Hu Bin said. "In addition, there are many lakes on the mountain, which is a nature reserve, and high standards of environmental protection must be met."

Under the constraints of the natural environment, the project proposed the engineering standards of "one avoidance and five preventions" of light avoidance, seepage prevention, dust prevention, pollution prevention, rust prevention and frost prevention. "The Water Cherenkov Detector Array (WCDA) we designed consists of three large pools, which need to store water all year round. On a mountain with an altitude of more than 4,000 meters, such engineering standards have never been done before, and there is no precedent for reference at home and abroad." said Chen Xugang, deputy chief designer of the project.

From March to July 2017, the four months were both short and long for everyone in the project department. The project milestones were pressed step by step, and the technical problems were difficult to overcome. Therefore, everyone hoped that time would go slower and slower. However, to overcome the unprecedented engineering difficulties, it was necessary to read a lot of information, refer to a lot of data, repeatedly calculate, analyze many times, and continuously optimize. This "mental torture" made everyone pray that such days would end soon.

In May of that year, the preliminary design plan for the project feasibility study was completed; in July, the construction design drawings passed the review; on July 14, all members of the project department rushed to the site for technical briefing, using "speed" and "quality" to ensure that this major scientific and technological infrastructure construction project started on schedule. In April 2019, the 1/4 scale water Cherenkov detector device was put into trial operation, and in July 2021, the full scale water Cherenkov detector device was put into trial operation with good results.

During the engineering design process, in order to ensure that the project meets scientific research needs, the design team innovatively proposed site stream diversion and control, reinforced concrete cantilever thin-wall retaining wall combined with a light steel structure roof hybrid structure system, HDPE flexible anti-seepage and detector suspension system, and a thermal environment control system without active heating pool under high cold conditions. These solutions solved problems such as groundwater freezing damage, flood control standards, anti-seepage and anti-corrosion, moisture absorption and insulation, met the requirements for the placement of optical detectors, and ensured the realization of major national scientific research goals.

In 2021, the High Altitude Cosmic Ray Observatory (LHAASO) observed and recorded a large number of ultra-high energy cosmic accelerators, gamma photons with an energy of 1.4 peta-electron volts, and the brightness of high-energy astronomical standard candles, ushering in the era of "ultra-high energy gamma astronomy". Among them, the water Cherenkov detector array pool is known as the "world's most sensitive very high energy gamma-ray source survey observation device".

"During the construction process, the design team often had to go to the site to solve problems encountered during the construction. Construction was carried out in winter, which was really a double whammy for the already harsh climate in the high-altitude areas. We often rushed to the site from the airport without time to adapt to the plateau environment. During the day, our eyes were swollen and our heads hurt, sometimes accompanied by frequent vomiting. At night, we had difficulty sleeping due to altitude sickness." Hu Bin recalled, "The project was completed under such circumstances."

Time will not change because of human will, but time will give the best answer to all efforts. A new research field has been opened up because of the High Altitude Cosmic Ray Observatory (LHAASO), and the design team of the Chengdu Institute has also won many awards for the Water Cherenkov Detector Array (WCDA). Behind the glory is the mentality of lack of oxygen and uncertainty, the courage to move forward the more difficult it is, and the spirit of not fearing challenges and daring to innovate.