China’s advanced 'Super Microscope' on mission to unlock microworld secrets

57 experiments on new materials to be conducted in the next four months with the help of Super Microscope

The China Spallation Neutron Source (CSNS), located in Dongguan City, south China's Guangdong Province, began a new round of user operation Thursday, with 57 experiments on new materials to be conducted in the next four months.

These experiment proposals, including one applied by a foreign user and five from Hong Kong and Macao users, mainly involve magnetic materials, quantum materials, lithium battery materials, shale, catalytic materials, high-strength steel and high-performance alloys, said Prof. Zhang Junrong of the Institute of High Energy Physics (IHEP) under the Chinese Academy of Sciences (CAS).

Construction of the CSNS project started in 2011 under the direction of the IHEP, with a total investment of 2.3 billion yuan (323 million U.S. dollars).

It was put into use in August 2018, consisting of a linear accelerator, a rapid cycling synchrotron, a target station, three neutron instruments and other auxiliary facilities.

Probing into the microworld

Dubbed as a "super microscope," a spallation neutron source can produce and accelerate protons before smashing them into the target to produce neutrons, and the neutron beams will be directed to hit material samples. Researchers can thus accurately infer the atomic structure of the materials by measuring the distribution of scattered neutrons and their changes in energy and momentum.

But unlike an X-ray from a synchrotron radiation facility, which is also used to explore the microstructure of materials, neutrons are not sensitive to the number of electrons and are a better "probe" when studying materials containing light elements with fewer electrons, such as carbon, hydrogen and oxygen.

Jin Dapeng, deputy director of the IHEP Dongguan Branch, gave an example in the field of energy materials. Hydrogen-powered vehicles are more energy-efficient and environmentally friendly than gasoline-fueled alternatives. Scientists hope to store hydrogen in a denser solid form, but pressurizing hydrogen can easily trigger explosions. So researchers are trying to develop a metal-organic framework that can intake hydrogen for storage and release it when it is needed. Neutron scattering can help scientists study where and under what conditions hydrogen is better stored and released in this material.

Benefiting from the advantages of neutrons in examining light elements, the CSNS's first batch of three neutron instruments for scientific experiments have achieved fruitful research results during the first two rounds of user operation.

From September 2018 to June 2019, the CSNS completed 101 experiments for domestic and overseas users, according to Zhang.

Huang Mingxin, a material researcher from the University of Hong Kong, conducted detailed experiments on one of the CSNS's neutron instruments to test the high-strength steel developed by his team.

He was satisfied with both the precise results and convenient service. He once applied to use Japan's spallation neutron source (J-PARC), but he had to first design the experiment steps, then send the material samples to Japan, and keep waiting for the data to be sent back.

Now, it takes him only an hour and a half driving from Hong Kong to the CSNS, "just like at my doorstep," said Huang.

Focusing on international sci-tech frontiers and serving the country's major development demands, the CSNS has made progress in many research fields, including new lithium-ion battery material, spin Hall magnetic film, high-strength alloy and neutron-induced single event effect in chip. Twelve articles about these experimental results have been published or accepted by academic journals.

The CSNS can provide neutron beams for more than 20 neutron instruments. "We hope to build five to seven new instruments for various demands in the next three to four years," said Jin Dapeng.

Debugging with incredible efficiency

The CSNS is the fourth pulse spallation neutron source in the world after the UK, the United States and Japan, with the debugging efficiency of its researchers surprising their foreign peers.

Proton beam power is one of the key performance of a spallation neutron source. The higher the power, the more neutrons will be produced, the more signals of scattered neutrons will be detected, and thus the less time an experiment will consume and the better the data an experiment will obtain, Jin explained.

Last September, the CSNS ran with a power of 20 KW. "Its operating power had reached 50 KW at the end of 2018," Jin said. They plan to increase the power to 80 KW by the end of this year, which means the original goal of reaching 100 KW in three years can be achieved ahead of schedule.

While gradually increasing the beam power, the accelerator physics group responsible for the commissioning of the accelerators repeatedly tested and examined the parameters of thousands of devices at each power level to find the optimal combination.

"The time jitter of the timing system for the particle beams must be controlled at the nanosecond level," said Xu Shouyan, the group leader of the accelerator physics.

"We have hundreds of instruments installed on the accelerators to measure the states of the particle beams. But the parameters are combined in such a complicated way that even a small deviation could be the result of a mixture of errors from hundreds or thousands of devices," Xu said.

"The CSNS is expected to reach its design beam power of 100 KW in three years or less after it passed the national acceptance because we have taken fewer detours thanks to the experience of our foreign peers. Moreover, we Chinese always work hard," Xu explained.

To Xu and his colleagues, working overtime is quite normal. Xu once worked for about 37 hours straight without a break. "I didn't feel sleepy at all. I used to work on the computer, but when I saw the devices running as expected step by step, I was really excited and couldn't wait to carry out the next test," Xu said.

Scientists hope to eventually increase the beam power of the CSNS from 100 KW to 500 KW. To meet the goal, they have reserved room for further modifications and upgrading in the initial design. Now the researchers have started to work on the plan to upgrade the accelerators for the CSNS phase II project.

"One of the great joys of studying physics is being able to explore and get closer to the essence of the world, and the spallation neutron source is helping us to realize it," Xu said.