S scientists have achieved net energy gain in a nuclear fusion reaction for the second time since a historic breakthrough in December last year in the quest to find a near-limitless, safe and clean source of energy Scientists at the California-based Lawrence Livermore National Laboratory repeated the breakthrough in an experiment in the National Ignition Facility (NIF) on 30 July that produced a higher energy yield than in December, a Lawrence Livermore spokesperson said.
Nuclear fusion involves smashing together light elements such as hydrogen to form heavier elements, releasing a huge burst of energy in the process. The approach, which gives rise to the heat and light of the sun and other stars, has been hailed as having huge potential as a sustainable, low-carbon energy source.
In December, Lawrence Livermore first achieved a net energy gain in a fusion experiment using lasers. That experiment briefly achieved what’s known as fusion ignition by generating 3.15 megajoules of energy output after the laser delivered 2.05 megajoules to the target, the Energy Department said.
 In other words, it produced more energy from fusion than the laser energy used to drive it, the department said.
The US Department of Energy called it “a major scientific breakthrough decades in the making that will pave the way for advancements in national defence and the future of clean power”.
Fusion energy raises the prospect of plentiful clean power: the reactions release no greenhouse gases or radioactive waste byproducts. A single kilogram of fusion fuel, which is made up of heavy forms of hydrogen called deuterium and tritium, provides as much energy as 10m kilograms of fossil fuel. But it has taken 70 years to reach this point.
While scientists generally believe the idea of a fusion power station is decades away, the technology's potential is massive. This is because fusion reactions produce zero carbon, no radioactive waste, and could power a house for almost a century with a small cup of hydrogen.
 The most widely looked at approach for fusion is known as magnetic confinement. This uses massive magnets to hold the fuel in place while it is heated to temperatures exceeding those found on the sun. The NIF however uses a different process. This is known as inertial confinement and uses the world's largest laser, which is then fired at a tiny capsule to trigger and implosion.
US energy secretary Jennifer Granholm called ignition "one of the most impressive science feats of the 21st century" in December. The experience produced around 3.15 megajoules, which is roughly 150% of the 2.05MJ powering the laser.
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