Laser fusion experiment achieves greater-than-unity energy yield

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.”

Laser bombardment yields energy milestone – CNN.com:

 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.

Inertial Confinement Fusion by Bdesham at Wikimedia Commons

Inertial Confinement Fusion by Bdesham at Wikimedia Commons

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).

See also:

National Ignition Facility's target chamber by Lawrence Livermore National Security at Wikimedia Commons

National Ignition Facility’s target chamber
by Lawrence Livermore National Security
at Wikimedia Commons

 

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  3 comments for “Laser fusion experiment achieves greater-than-unity energy yield

  1. Perry
    February 13, 2014 at 8:06 PM

    The science is beyond my understanding but I’m concerned potential success is still so far away, or did I read that wrong? We really needed this yesterday, tomorrow may be too late. It seems to me that this would radically alter all human affairs, save the species that are disappearing in this sixth mass extinction we are in right now, and protect the thin fragile biosphere life depends on.

  2. February 13, 2014 at 9:04 PM

    Finally! I’ve only heard about controlled fusion energy since the 1960s, when I was a child going through an information trailer (this was a physical trailer, not a movie blurb) telling about the future of power/energy production and how electricity will someday (it’s been “ten years in the future” for the last 50 years!) be “too cheap to meter.” I’m so glad I didn’t hold my breath!

    Just reading through your excerpts brings up lots of questions – how much energy (in kilowatt-hours, so I can compare to our current energy costs) does a single exploding pellet generate, and what’s the weight of that gold cylinder? The price of gold had dropped in the last couple years, and I’m wondering … (not really, I can’t imagine investing in such volatiles). It would be interesting to see gold or other rare metals used in the commercial generation of power.

  3. Nathan Miller
    February 13, 2014 at 10:01 PM

    @Ben Bradley  This probably isn’t going to translate well with scale-up of the fuel/cylinder geometry, but the total fuel energy gain for one of the arrangements (Figure 2 (a), and the top of (c) and (d)) was 1.2-1.4 (http://www.nature.com/nature/journal/vaop/ncurrent/fig_tab/nature13008_F2.html). That said, my understanding is that only ~1% of the energy from the laser was actually imparted on the fuel, so that’s a lot of lost photons.
    Further, if they use an alternate ablator material as suggested in their conclusion, I’m not sure any price point would be applicable to an end product. Sorry if that sounds like a cop-out answer.

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