‘There is no doubt in my mind’

The promise of fusion energy seems fantastic and unapproachable: It is the power behind the sun and the stars. The spark comes when hydrogen nuclei fuse to become heavier atoms. The tremendous burst of energy released in the resulting transformation creates sunlight, and the conditions that enabled our creation. Without it, the universe would be cold, dark and lifeless.

Since the 1930s, scientists have been trying to harness fusion, thinking that it could run the electric power plants of the future and even send people to other planets.

The fusing of hydrogen atoms requires incredible heat and pressure, and for decades fusion research has been the exclusive province of big science, like ITER , a 35-nation thermonuclear project in the south of France that covers 100 acres and is expected to ultimately cost more than $20 billion.

Such initiatives, though, have made slow progress toward the ultimate goal of building a machine that generates more power than it takes in.