The image shows the hybrid magnet of the steady-state strong magnetic field experimental apparatus. Provided by the High Magnetic Field Science Center of Hefei Institutes of Physical Science, Chinese Academy of Sciences.
In the western outskirts of Hefei, Anhui Province, there lies a small island covering less than 3 square kilometers. Surrounded by water on three sides, the environment is tranquil, bearing the quaint name "Science Island."
In this secluded place, away from the hustle and bustle, stands the High Magnetic Field Science Center of Hefei Institutes of Physical Science, Chinese Academy of Sciences (hereinafter referred to as the "Magnetic Field Center"). In August 2022, the steady-state strong magnetic field experimental apparatus (hereinafter referred to as the "experimental apparatus") of this center achieved a significant breakthrough. Its hybrid magnet generated a steady magnetic field of 452,200 gauss, breaking the world record held for 23 years.
What is the use of strong magnetic fields? What exactly is a steady-state strong magnetic field? What difficulties were overcome in the construction of the experimental apparatus? With these questions in mind, a reporter from Science and Technology Daily recently visited the Magnetic Field Center to explore the answers.
Cutting-edge research platform, a national treasure
Entering the lobby of the Magnetic Field Center, a model of the experimental apparatus catches the eye, accompanied by neatly arranged display boards showcasing various achievements made possible by steady-state strong magnetic fields.
Engineer Wang Wenqiang from the Magnetic Field Center began with a science briefing—
Strong magnetic fields are an indispensable extreme experimental environment for conducting cutting-edge scientific research. In strong magnetic fields, scientists can observe many physical and chemical phenomena that are difficult to discern under normal conditions. Depending on the duration, strong magnetic fields are divided into pulsed and steady-state. Steady-state strong magnetic fields can maintain stability for a certain period and at a certain value according to the needs of scientific experiments. There are three main types of magnets that generate steady-state strong magnetic fields: water-cooled magnets, superconducting magnets, and hybrid magnets...
"When it comes to steady-state strong magnetic fields, many may feel unfamiliar, but in fact, it has long been part of our lives," Wang Wenqiang said, "Magnetic resonance imaging is one of the typical applications of steady-state strong magnetic fields, albeit at lower magnetic field strengths."
As Wang Wenqiang spoke, the reporter followed him to the experimental apparatus.
The experimental apparatus consists of 10 magnets, including 5 water-cooled magnets, 4 superconducting magnets, and 1 hybrid magnet.
In the grand experimental hall, four inclined steel columns with a diameter of about half a meter support a giant cylindrical vessel over 6 meters high, resembling a concrete mixing station.
"This is the record-breaking hybrid magnet. The outside is a superconducting magnet with a room temperature bore diameter of 800 millimeters and a magnetic field strength of 112,000 gauss, while the inside is a water-cooled magnet," Wang Wenqiang introduced. Despite its large size, the internal space for placing experimental samples is very limited, with a bore diameter of only 32 millimeters. The water-cooled magnet bears tremendous electromagnetic stress, equivalent to 7 times the water pressure endured by a submarine at a depth of 10,000 meters.
"Pursuing extremely high magnetic fields is like climbing Mount Everest," said Kuang Guangli, academic director of the Magnetic Field Center and president of Anhui University, "As the fifth in the world and the first in China, this national treasure of a steady-state strong magnetic field experimental apparatus provides researchers with a cutting-edge research platform."
Striving for perfection amidst challenges
Over the past century, more than 10 achievements related to strong magnetic fields have been awarded the Nobel Prize.
Before China, only the United States, France, the Netherlands, and Japan had built steady-state strong magnetic field experimental apparatuses. In 2007, the construction of this major scientific facility was approved by the state. In 2008, the Magnetic Field Center was established on "Science Island." After several years of hard work, the project was completed and accepted in 2017, surpassing many performance indicators.
"The water-cooled magnets in this large apparatus are made of specially designed 'bit pieces.' These bit pieces are tightly interlocked with insulating layers, stacked on top of each other," said Zhang Jun, deputy director of the Magnetic Field Center's Magnet Science and Technology Department, pointing to the hybrid magnet. The bit pieces are densely dotted with tiny holes to allow deionized cooling water to flow through. Therefore, the bit pieces must be accurately positioned, with no room for error; otherwise, clogging of the cooling holes would prevent the water-cooled magnet from dissipating heat in time, potentially leading to the destruction of the entire magnet.
"It was like feeling our way across the river by touching stones!" recalling the construction process, Fang Zhen, leader of the water-cooled magnet group at the Magnetic Field Center, said, "We first conducted theoretical analysis and simulation to determine the materials and the size of the boreholes before proceeding with construction."
The research team encountered a series of thorny problems. For example, the required "copper-silver alloy" material was extremely scarce at the time, and they spent a lot of effort to obtain it. Additionally, there were no ready-made high-power rectifiers domestically. Researchers had to negotiate with manufacturers, paying upfront costs and clearly stipulating that development costs would not be refunded in case of failure, before the manufacturers agreed to develop and produce them.
"Every step was extremely difficult, and the development of the measurement system was even more challenging," Kuang Guangli likened it to searching for a needle in a haystack, "Extracting useful information from the complex electromagnetic environment of the magnet operation is like searching for a needle in a haystack."
The spirit of relentless pursuit of perfection can be seen in a set of data: Take the low-temperature valve box as an example, its design took 5 years, and the team drew about 1200 drawings for it. In the narrow space of about 1.5 cubic meters, the total length of various pipes used by the team amounted to 2,460 meters, and the total number of welds on the valve box reached 5,811.
On the second day of the Lunar New Year in 2017, the hybrid magnet was successfully debugged.
Recalling that moment, Kuang Guangli exclaimed excitedly, "Completing the task assigned by the country is even more exhilarating than winning a big prize!"
The completion of the project acceptance is not the end; researchers take it as a starting point and continue to move forward.
Supporting multiple experiments, yielding numerous achievements
Recently, Professor Wang Lei's team from the School of Physics at Nanjing University has been conducting testing experiments on two-dimensional materials using the hybrid magnet of the steady-state strong magnetic field experimental apparatus.
As early as the end of last year, the team submitted an experiment application. After strict evaluation by the expert committee of the Magnetic Field Center, the experiment was finally able to proceed smoothly in mid-March of this year. "Every year, experiments are conducted here by over 70 units and hundreds of projects, running from 8 a.m. to midnight," introduced Xi Chuanying, Deputy Director of the Operational and Experimental Measurement Department at the High Magnetic Field Center.
"It's very popular! Scientists are enthusiastic about conducting experiments on this device," said Kuang Guangli.
In December 2018, the research group led by Professor Xiu Faxian from Fudan University, relying on the experimental device, discovered direct evidence of a novel three-dimensional quantum Hall effect, marking a crucial step in quantum Hall effect research from two-dimensional to three-dimensional systems. Additionally, a collaboration between Zhejiang University's team led by Xu Zhu'an and Zheng Yi, and Xialinqin from Central South University, relying on the experimental setup, first discovered the strong spin-orbit coupling effect controllable by an external electric field in thin layers of black arsenic. Meanwhile, the Magnetic Resonance Life Science Department at the High Magnetic Field Center discovered, in experiments conducted in a 270,000 gauss strong magnetic field, that strong magnetic fields can interfere with the spindle within cancer cells, inhibiting their division, which is of great significance for developing new methods for cancer treatment in the future.
"There have been thousands of such achievements, each one remarkable," said Kuang Guangli.
By the end of 2023, the experimental facility had provided experimental conditions for over 3,000 projects from nearly 200 domestic and foreign units, contributing to the production of nearly 2,500 papers. Meanwhile, several achievements resulting from research relying on the experimental setup, such as combined scanning probe microscopy techniques and Class I anti-cancer innovative targeted drugs, have been successfully transformed into practical productivity.
General Secretary Xi Jinping emphasized that true national heavyweights must be in our own hands.
"We are leading the construction of the 'Strong Light and Magnetic Integration Experimental Facility,' which, once completed, will be another major national asset!" Kuang Guangli expressed full confidence, stating that he and his team will spare no effort to build and utilize the large scientific apparatus, contributing actively with a pioneering spirit to accelerate the realization of high-level technological self-reliance.
