Chinese scientists strike early gold in race to nuclear fusion power

At a Shanghai facility the size of a soccer field, Chinese scientists are firing powerful laser beam pulses at a tiny pair of gold cones in a bid to replicate the nuclear fusion process at the heart of the sun.

The cones, as small as pencil tips, have narrow ends which face each other and emit a plasma of hydrogen. When the two hot gas streams collide at precisely the right time and place, and in the right manner, they trigger a fusion reaction – the process which ultimately could provide a source of endless, sustainable energy.

With government funding of 1 billion yuan (US$156 million) over six years, Zhang Zhe and his colleagues from the Chinese Academy of Sciences’ Institute of Physics in Beijing began their unprecedented experiments at the Shenguang II laser facility in Shanghai last summer.

The research team has conducted three tests so far, with another scheduled for next month, and encountered some unexpected challenges. But initial results suggest the theory works and part of the findings were published last week in domestic peer-reviewed journal Acta Physica Sinica.

“Our goal is to achieve sustainable fusion,” Zhang said in a phone interview on Tuesday. For power generation, “the cones can be mass-produced and loaded as bullets in a machine that will rotate and fire like a Gatling gun”.

Chinese ‘artificial sun’ hits new mark in fusion energy mission

The race to fusion power heated up in August, when researchers with the US National Ignition Facility (NIF) achieved an energy output eight times greater than ever before. While the output was still lower than the energy input, the breakthrough gave hope as well as added pressure to research teams in other countries, including China.

The NIF experiment aimed more than 100 extremely strong laser beams at a single target, using some of the largest laser generators on Earth, producing enough heat to deform mirrors but also reducing accuracy after repeated shots.

In China, researchers were looking for a cheaper, simpler way to achieve fusion with a less powerful laser. One result was the double-cone ignition scheme developed in 1997 by Zhang Jie, a leading Chinese physicist and former president of Shanghai Jiao Tong University.

The plasma generated by relatively weak laser beams on a single target was insufficient to create the right conditions for fusion, but when two plasma streams hit each other, the temperature, density and pressure of the gas would increase significantly to allow two atoms to fuse into one and release energy in the process.

The idea remained on paper for two decades because the required cutting edge laser technology was not available. However, Chinese scientists have recently built some of the world’s most powerful ultra-fast laser sources able to release a considerable amount of energy in a split second. It was these new technologies which paved the way for the government’s greenlight of the experiment in Shanghai last year.

The gold cones vaporise after fusion, but “the cost of gold will be extremely small – if not negligible – in the future operation of a power plant”, Zhang Zhe said. “A small grain of gold can make thousands of cones.”

‘Artificial sun’ tipped to provide electricity in decade if Beijing backs it

The “fuels” for fusion inside the cones – icy balls of deuterium and tritium, two isotopes of hydrogen – are more expensive than the precious metal, used because of gold’s large number of electrons, according to Zhang Zhe. The more electrons, the more heat a material can absorb before changing shape. And the softness of gold makes it relatively easy to process mechanically.

Each golden cone in the Shanghai experiment cost a few hundred dollars, compared to the hundreds of thousands of dollars for a target in the NIF experiment. But, for Zhang Zhe and his colleagues, some issues are more challenging than money.

For instance, during the laser bombardment the hydrogen fuel is supposed to compress inside the cone, implode and shoot out like a rocket flame. For better control of the process, the researchers coated the fuel with a thin layer of heat-absorbing plastic material. But they found there were always holes on the plastic’s surface which would turn into bubbles when hit by the laser.

In their experiments, Zhang Zhe and his team found the bubbles were detrimental to the fusion process because they could burst and take away a lot of energy. To tackle this problem, the researchers came up with a number of solutions, including increasing the thickness of the plastic shell and boosting the stability of the laser beams.

“We are making progress one step at a time. By 2026, a new generation of large-scale laser facilities will be finished or near completion in China. They will lift the game to a whole new level,” Zhang Zhe said.

A Beijing-based nuclear fusion scientist said the budget for the Shanghai research was small compared to the investment in other fusion projects. The world’s largest fusion research project, the International Thermal Experimental Reactor in southern France (ITER), for example, has an estimated budget of US$45 to US$65 billion.

The idea of creating an artificial sun to generate an enormous, endless and clean supply of energy has been around for decades, and scientists have come up with different approaches that sometimes compete for resources and attention.

ITER uses the biggest contender for the laser approach (also known as inertial confinement fusion), the tokamak – a device that can generate and trap hot gas with an extremely powerful magnetic field for fusion to take place inside.

“The double-cone scheme is a brilliant idea. The tokamak is generally believed to be more suitable for large-scale power production, but some recent breakthroughs in the laser-powered experiments suggest this approach can be a strong candidate,” said the researcher, who asked not to be named because of his military work.

“It is difficult to predict which approach or which country will win the race at this stage. There are too many uncertainties ahead,” he said. “But in the end, different technologies, different nations may need to unite as one to bring fusion from dream to life.”