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| Fuel capsule as seen through a cutaway of the hohlraum wall. (Courtesy: Eddie Dewald, LLNL) |
Scientists at the Lawrence Livermore National Laboratory (LLNL) in California have achieved a "fuel gain" of greater than one at the National Ignition Facility (NIF). Using NIF's ultra-powerful laser to crush tiny pellets of deuterium–tritium fuel, they have produced more energy from fusion reactions than was deposited in the fuel. Although still far from the long-sought-after goal of "ignition", the latest results are nevertheless an important step on the road to realizing fusion energy, say researchers.
NIF was completed in 2009 at a cost of $3.5bn and uses 192 laser beams to deliver 1.8 MJ of energy to a tiny target over a period of just a few billionths of a second. The target consists of a hollow gold cylinder a few centimetres long, known as a hohlraum. At its centre sits a peppercorn-sized sphere of frozen deuterium and tritium encased inside a plastic shell. Laser pulses heat the inside of the hohlraum thereby generating X-rays that rapidly remove or "ablate" material from the outside of the shell, so causing the fuel to implode. This implosion creates a shock wave that heats up the fuel to temperatures of about 50 million degrees Celsius, causing the nuclei to overcome their mutual repulsion and fuse, producing alpha particles (helium nuclei) and neutrons.
Between 2009 and 2012, researchers at NIF worked on a project designed explicitly to achieve ignition, the point at which heat provided by alpha particles increases the rate of fusion reactions such that they release more energy than is supplied by the laser. However, that work proved to be disappointing, leading to energy outputs about 1000 times smaller than the input. After scrutiny by Congress, the National Nuclear Security Administration, which oversees NIF, announced a new, more deliberative strategy designed to work out what went wrong. The strategy also emphasized the importance of alternative approaches to "inertial-confinement fusion", such as "fast ignition" and "Z-pinch".
A fuel gain means nuclear power utilized safely in the United States without the nasty byproduct of waste with half-lives of tens of thousands of years, and the subsequent facilities to store it: they wouldn't be needed. A fuel gain means one step closer to getting off fossil fuels, which would mean less wars in the Near East and jobs here. It would positively stress education again to prepare operators, technicians, engineers and scientists for the plants that could only exist here in the US to power the grid (that is sorely in need of update - more jobs). Food prices would no longer be as tied to fuel costs paid by grocers to shipment companies. Our lives could change drastically, and for the better when this becomes reality. We are inching ever closer to energy independence and geopolitical freedom.
Physics World: Laser fusion passes milestone
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