Nuclear fusion. For many of us the words call to mind a dream of cheap, clean, virtually unlimited power.

It’s a dream many scientists have been pursuing for decades, but for some of them, President Obama’s proposal for next year’s pared-down budget marks a step backward. The Washington Post reports that the president’s budget request cuts domestic fusion research by 16 percent, or $48 million. That would mean the closure of a Department of Energy-backed fusion lab at MIT, and a staff reduction at another lab at Princeton University.

Obama isn’t proposing cutting funding for fusion overall. The $48 million would go to the International Thermonuclear Experimental Reactor (ITER). ITER is based in the south of France and backed by the European Union, Russian, China, India, South Korea and Japan, as well as the U.S. The project’s estimated costs total $23 billion, a figure that has risen over the years as its start date has been pushed back.

The European Union, facing more severe budget constraints than the U.S., has also proposed cutting other programs to keep funding ITER.

Nuclear fusion — the process that powers the stars — is exactly the reverse of the nuclear fission that runs today’s nuclear power plants. Instead of splitting atoms, it fuses them together. The energy results from the conversion of some of the mass of the original atoms into energy.

Scientists developing the technology say that, used as an energy source, fusion would be safer and more powerful than fission and would create far less nuclear waste.

Yet the technology is still far from commercialization. Some estimate ITER could produce energy for the grid in 2040, and other say it will take much longer than that. Another project working toward fusion technology, the National Ignition Facility at Lawrence Livermore National Laboratory in California, claims it may be able to run the first fusion-based electrical plant in the country — but not until at least the 2020s.

Photo of National Ignition Facility at Lawrence Livermore National Laboratory in California. Credit: Flickr/jurvetson