Thanks to a breakthrough at the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory in California, we are one step closer to “Ignition con Fusion.”
For the first time, scientists at the Lawrence Livermore National Laboratory in California say they produced more energy from a reaction in their fuel source than they put into the fuel, said Omar Hurricane, the physicist who led the experiment.
This is an exciting development from the NIF, where researchers had missed a 2012 deadline for achieving the goal of thermonuclear ignition. But, as CNN reports, “There is a bit of fine print”:
The implosion of a tiny pellet holding two hydrogen isotopes did produce more energy than it took to cause it — about 17,000 joules, which Hurricane [the paper's principal author] compared to the force of a downhill skier doing about 36 mph. However, the pellet received only about 1% of the total energy expended in the experiments, he said.
But the reaction also produced a heating effect that appeared to boost the energy output — a process dubbed “bootstrapping” by Hurricane’s team at Livermore’s laser fusion research center, the National Ignition Facility. And that may point scientists toward their ultimate goal of a controlled, sustainable fusion reaction that would provide abundant, safe power, he said.
The paper published by Hurricane’s research team describes their method as manipulating the laser pulse shape to reduce the instability of the resulting implosion as the X-rays, generated by the vaporization of the gold cylinder containing two isotopes of hydrogen, deuterium (2H) and tritium (3H), exert energetic pressure against the fuel.
From the paper’s abstract in Nature:
These experiments show an order-of-magnitude improvement in yield performance over past deuterium–tritium implosion experiments. We also see a significant contribution to the yield from α-particle self-heating and evidence for the ‘bootstrapping’ required to accelerate the deuterium–tritium fusion burn to eventually ‘run away’ and ignite.
As explained further in Hurricane’s paper, alongside the neutrons produced, α-particles (or He2+ ions… basically a Helium nucleus missing its two electrons) are to be used to “redeposit their energy locally” to maintain hotspot ignition temperature within the fuel for the duration of the reaction.
According to the paper, future work is expected to involve “more elaborate schemes” to maintain control over the instability of the vaporization process (“ablation”) of the containing cylinder, or the use of “an alternate ablator material.” This is hoped to bring the researchers even closer to the goal of sustained thermonuclear ignition.
Note that this method differs from other fusion reactors you may be familiar with, which include tokamak reactors (such as the ITER reactor under construction in France to be completed by 2020), polywell reactors (such as you might see demonstrated at conventions such as DragonCon), or fusors (which some DIY Maker-types construct at home - observing all safety and regulatory precautions, of course).
- Hurricane, O. A. et al. Nature http://dx.doi.org/10.1038/nature13008 (2014).
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