For the past four years, physicists at the National Ignition Facility, or NIF, in Livermore, California, have been trying to harness nuclear fusion, the same reaction that powers the sun and the stars. Supporters of the $3.5 billion facility believe that a successful outcome to the experiments could help usher in an era of nearly limitless energy. But the ambitious fusion research program at NIF now faces an uncertain future, both politically and scientifically.
On the political side, President Obama’s proposed budget for fiscal year 2014 would reduce funding for fusion experiments at NIF by more than $60 million, putting it nearly 14 percent below the 2013 level. Key committees in both the House and Senate favor restoring part of NIF’s funding, and a compromise will eventually emerge, but budget constraints aren’t the only challenge facing NIF. Physicists working on the project expected to have succeeded in their quest for fusion energy by now. They’re currently struggling to figure out what went wrong.
Tiny Stars, Big Lasers
There’s an old joke about fusion: It’s the energy source of the future, and always will be. Physicists have been pursuing the dream of controlling fusion energy for some 60 years now. Unlike nuclear fission, which releases energy when the nucleus of a heavy atom like uranium splits into two lighter nuclei, fusion generates energy when two separate light nuclei smash together to form a single, heavier nucleus. In fission, the energy comes from breaking the bonds of force that held the original heavy atom together; with fusion, the energy source is more esoteric—some of the mass from each of the two light nuclei is converted directly into energy when they fuse, in accordance with Einstein’s iconic law, E=mc2.
Both fission and fusion release tremendous amounts of energy. One pound of enriched uranium used in a conventional nuclear power plant contains about as much energy as a million gallons of gasoline. Fusion yields even more energy—about three to four times as much as fission reactions. And while fission reactions generate waste that remains radioactive for millennia, fusion’s byproducts become harmless within decades. Moreover, the world possesses a nearly infinite source of fusion fuel—the hydrogen atoms found in water.
Unfortunately for the world’s energy needs, fusion presents far greater technical challenges than fission, which physicists mastered in the 1940s. It takes relatively little energy to split a nucleus—fission can even happen spontaneously. But for fusion to occur—that is, to force two nuclei to join—physicists must replicate the hellish temperatures and pressures found inside stars.
