Nuclear Fusion Achieves Energy Gain

Popular Science

Popular Science

For the first time, scientists at the National Ignition Facility (NIF) in Livermore, California have successfully produced more energy with a fusion reaction than was used to start it.

Fusion is the process that hydrogen nuclei undergo inside of stars due to the intense heat and pressure found there; if fusion reactions could be mastered for commercial use, the technique would be incredibly efficient and entirely renewable, providing us with enough energy to sustain our current usage for billions of years. Scientists have been trying for decades to create a self-sustaining fusion reaction with an overall gain in energy, a process called ignition.

NIF is funded by the U.S. Department of Energy’s National Nuclear Security Administration and has been in operation since 2009. The facility describes how its laser-driven approach begins on its website:

A weak laser pulse—about 1 billionth of a joule—is created, split, and carried on optical fibers to 48 preamplifiers that increase the pulse’s energy by a factor of 10 billion, to a few joules. The 48 beams are then split into four beams each for injection into the 192 main laser amplifier beamlines.

From there, the 192 laser beams are split into quads of 2×2 arrays and pass through a final optics assembly, where they are converted from infrared to ultraviolet light and aimed at a gold chamber, which converts the lasers’ energy into X-rays. Four of these pulses squeeze a small fuel pellet containing deuterium and tritium (isotopes of hydrogen), causing the pellet to implode and undergo fusion. By the time the process has completed, the original lasers have traveled 1500 meters over the course of 1.5 microseconds.

Though NIF researchers have successfully achieved an energy gain by adjusting the laser setup to hit the gold chamber in three pulses, heating it faster, there are still a few roadblocks ahead. While their experiment, which produced 15 kJ of energy, used 10kJ of fuel, the laser setup itself, the total energy input was around 2 MJ (yes, megajoules). Much of the energy is lost along the way in the conversion of light, so the team still has a long way to go, but this is an important milestone on the road toward ignition.

Even if the team does reach its goal of ignition, there are still engineering issues that need to be resolved to make it a practical energy source: creating the fuel and setting up the lasers is a burdensome process and the intense laser blasts degrade the machine too quickly for long-term commercial use.

If all of the above issues can be solved, the world certainly has a brighter energy future ahead than would otherwise be the case.