Princeton, N.J.

DEBATE about America’s energy supply is heating up: gas prices are rising, ethanol is under attack and nuclear power continues to struggle in the shadow of the Fukushima disaster in Japan.

But an abundant, safe and clean energy source once thought to be the stuff of science fiction is closer than many realize: nuclear fusion. Making it a reality, however, will take significant investment from the government at a time when spending on scientific research is under threat.

Harnessing nuclear fusion, the energy that powers the sun and the stars, has been a goal of physicists worldwide since the 1950s. It is essentially inexhaustible and it can be created using hydrogen isotopes — chemical cousins of hydrogen, like deuterium — that can readily be extracted from seawater.

Fusion energy is created by fusing two atomic nuclei, in the process converting mass to energy, which appears as heat. The heat, as in conventional nuclear fission reactors, turns water into steam, which drives turbines to generate electricity, or is used to produce fuels for transportation or other uses.