This Tuesday (Dec. 13th), the US Department of Energy and its National Nuclear Security Administration announced the first-ever achievement of fusion ignition. The breakthrough should reportedly "pave the way for advancements in national defense and the future of clean power."

In the fusion process, two light nuclei combine to form a single heavier nucleus, releasing a large amount of energy. This is what was achieved – for the first time in a laboratory setting – on Dec. 5th at the US Department of Energy's Lawrence Livermore National Laboratory (LLNL).

On that day, scientists used 192 laser beams to deliver a total of 2.05 megajoules (MJ) of ultraviolet energy to a tiny cryogenic fuel pellet, which in turn produced 3.15 MJ of fusion energy output. In other words, the fusion reaction produced more energy than the amount of laser energy that was used to trigger it.

As far back as the 1960s, LLNL scientists hypothesized that lasers could be used to induce fusion in a laboratory setting. They proceeded to build a series of increasingly powerful laser systems, culminating in what is known as the National Ignition Facility (NIF), which was used for this month's fusion experiment.

Located in Livermore, California, the stadium-sized NIF is the world’s largest and most energetic laser system. It utilizes powerful laser beams to create temperatures and pressures replicating those in the cores of stars and giant planets, and inside exploding nuclear weapons.