THE congenial Professor Duan Xuru doesn't look like a stereotypical mad scientist as he shows guests into a cluttered laboratory filled with canisters, vacuum pumps and patched-up pipes tied together with spirals of blue wire and rubber tubing.

But Duan, based in Chengdu, capital of Sichuan Province, is working on an audacious project described as a "man-made sun." He hopes it will eventually create almost unlimited supplies of cheap and clean energy.

Duan is no maverick either, but a pioneer in one of the many expeditions that China has launched to map out its nuclear energy options in the future.

Old-fashioned atom splitting has been in the spotlight after Japan's biggest earthquake and tsunami left an aging nuclear reactor complex on the northeast coast on the verge of catastrophic meltdown. While Germany and Italy have turned their backs on nuclear power, China is pressing ahead with an ambitious plan to raise capacity from 10.8 gigawatts at the end of 2010 to as much as 70 or 80 GW in 2020.

Many of the nuclear research institutes across the country are working on advanced solutions to some of the problems facing traditional reactors, from the recycling and storage of spent fuel to terrorist attacks.

Holy Grail

But Duan and his state-funded team of scientists are on a quest for the Holy Grail of nuclear physics: a fusion reactor that can generate power by forcing nuclei together instead of smashing them - mimicking the stellar activity that brought heavy elements into existence and made the universe fit for life.

Duan said fusion could be the ultimate way forward: it is far safer than traditional fission, requires barely 600 grams of hydrogen fuel a year for each 10-gigawatt plant, and creates virtually no radioactive waste.

"Due to the problems in Japan, the government hopes nuclear fusion can be realized in the near future," said Duan, the director of fusion science at the Southwestern Institute of Physics, founded in 1965 and funded by the state-owned China National Nuclear Corporation (CNNC).

While fusion has moved some way beyond the purely hypothetical after more than half a century of painstaking research, it still remains some distance away from being feasible. Critically, the energy required to induce a fusion reaction far exceeds the amount of energy produced.

Fusion might be the ultimate goal, but in the near future, all China's practical efforts will continue to focus on a new model of conventional fission reactors. While China's nuclear industry awaits the results of a government review in the wake of the Fukushima crisis, all signs point to China pushing ahead with its long-term strategy.

The National Development and Reform Commission said China would continue to support the construction and development of advanced nuclear reactors and related nuclear technologies.

"Suddenly, China has become even more important to the world - as other people ask whether they still want to go ahead, China still seems intent on going ahead at full speed," said Steve Kidd, deputy secretary general with the London-based World Nuclear Association.

If traditional nuclear power represents the civil application of the atomic weapons dropped on Hiroshima and Nagasaki in 1945, fusion is an extension of the hydrogen bomb, first tested by the United States in 1952.

Slow progress

Showing Reuters around a sweltering, hermetically-sealed lab designed to bring hydrogen isotopes to an unthinkable 55-million degree boil in a 1.65-meter vacuum chamber, Duan said progress had been slower than first expected at the dawn of the nuclear age.

"It took about nine years to go from the atomic bomb to nuclear power, and we hoped it would take a maximum of 20 years to get from the first H-bomb to a fusion reactor," he said. "But in reality it was very difficult because there were so many technical and scientific challenges."

Described by one observer as an attempt to put the sun in a box, nuclear fusion has been derided as the province of cranks and charlatans - the modern equivalent of the perpetual motion machines that plagued US patent offices in the 19th century. Sceptics scoff the world is now 50 years away from fusion power - and always will be.

Duan shrugged off the criticism. He has spent over 20 years in the field, including eight years in Germany, and found reasons to be optimistic.

"Actually, the concept of nuclear fusion is very simple," he said with a wry smile. "The first thing is to generate the plasma. The second thing is to heat the plasma to a few hundred million degrees. And then you need to confine it."

As Japan's stricken Fukushima plant lurched from crisis to crisis in March and April, the safety of nuclear power was called into question - including in China. Five days after the quake and tsunami knocked out the 40-year-old Fukushima Daiichi complex, China said it was suspending approvals for nuclear power plants pending safety checks of plants in operation or under construction.

China by most calculations is already the world's biggest energy consumer, and demand for power is set to soar in the next decade. But its dependence on fossil fuels have also turned it into the world's biggest source of greenhouse gas.

Duan's fusion reactor could be the answer to China's energy conundrum. It does not require acres of space or tonnes of scarce fuel or water resources. It produces no CO2 emissions or waste, and is completely safe, even if struck by an earthquake.

Tokamak focus

A large part of China's fusion research is now focused on the tokamak, a Russian acronym meaning "toroidal magnetic chamber." It is a doughnut-shaped vacuum vessel wrapped in superconducting magnetic coils that confine and control the ultra-high temperature soup of ions and electrons known as plasma.

But tokamaks can only run a few seconds in experiments conducted every five months or so, creating a brief 500-megawatt burst of energy before fizzling out.

Unlike the tokamak, new conventional technologies are on the cusp of being commercialized, including "third-generation" designs imported from US-based Westinghouse, owned by Toshiba, and France's Areva.

Also on the horizon are fourth- and fifth-generation technologies that go by names like fast-breeder, travelling wave, or high-temperature gas-cooled, as well as small and versatile "modular" reactors with shorter construction times.

"(China) has investments in the more exotic reactor designs and they also have got cooperation on fast reactors with the Russians," said Kidd. "They are keeping their options open, and Fukushima will encourage that tendency towards next-generation reactors."