United States fusion research may be hitting serious funding problems just as scientists' hopes are rising of producing commercially viable energy within 30 years, the American Association for the Advancement of Science heard when it met in Atlanta last week.

Marshall Rosenbluth, of the University of California in San Diego, told the conference that there had been dramatic improvements over the past year in producing power from fusion. "There are no obvious (scientific) problems that look insoluble," he said.

"The past few years have been really extremely successful and exciting from a scientific point of view in fusion research. But in spite of the fact that technically we are all quite proud of the accomplishments I have to paint a dim picture for the future of fusion.

"In the 1970s we were told that funding was going to double," he said. "In fact it has about halved. To really do the things we need to do in fusion we require a doubling or even a tripling in the budget over the next ten years."

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Fusion energy is released when two atoms of heavy hydrogen are forced to overcome their huge repulsion towards each other and join together, releasing energy from the nucleii. So far, scientists have produced ten megawatts of power from one reactor.

The three major fusion projects in which the US is involved include the International Thermonuclear Experimental Reactor, a joint venture between Europe, Japan, the US and Russia. The plan is that after ITER, there should be sufficient know-how to build a demonstration reactor, which would be "almost a real commercial power plant," said Dr Rosenbluth.

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He said that the international nature of the project, although welcome, had increased its cost to the US by half, because of the difficulties of getting consensus.

The two all-American experiments are the Tokamak Fusion Test Reactor, which is now producing 10 megawatts, and the National Ignition Facility.