There's just one big problem.
"The only working fusion power plants right now in the universe are stars," said Dennis Whyte, professor of nuclear science and engineering at Massachusetts Institute of Technology.
The U.S. was first to large-scale use of fusion with a hydrogen bomb test in 1952. In the seven decades since, scientists around the world have been struggling to harness fusion reactions for power generation.
Fusion reactions occur when hydrogen atoms reach extreme enough temperatures that they fuse together, forming a super-heated gas called plasma. The mass shed during the process can, in theory, be turned into huge amounts of energy, but the plasma is hard to control. One popular method uses powerful magnets to suspend and control the plasma inside a tokamak, which is a metal donut-shaped device. Another uses high-energy lasers, pointed at a peppercorn-sized pellet of fuel, rapidly compressing and imploding it.