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phys.org wrote: The dream of igniting a self-sustained fusion reaction with high yields of energy, a feat likened to creating a miniature star on Earth, is getting closer to becoming reality, according the authors of a new review article in the journal Physics of Plasmas.

Researchers at the National Ignition Facility (NIF) engaged in a collaborative project led by the Department of Energy's Lawrence Livermore National Laboratory, report that while there is at least one significant obstacle to overcome before achieving the highly stable, precisely directed implosion required for ignition, they have met many of the demanding challenges leading up to that goal since experiments began in 2010.

The project is a multi-institutional effort including partners from the University of Rochester's Laboratory for Laser Energetics, General Atomics, Los Alamos National Laboratory, Sandia National Laboratory, and the Massachusetts Institute of Technology.

To reach ignition (defined as the point at which the fusion reaction produces more energy than is needed to initiate it), the NIF focuses 192 laser beams simultaneously in billionth-of-a-second pulses inside a cryogenically cooled hohlraum (from the German word for "hollow room"), a hollow cylinder the size of a pencil eraser. Within the hohlraum is a ball-bearing-size capsule containing two hydrogen isotopes, deuterium and tritium (D-T). The unified lasers deliver 1.8 megajoules of energy and 500 terawatts of power—1,000 times more than the United States uses at any one moment—to the hohlraum creating an "X-ray oven" which implodes the D-T capsule to temperatures and pressures similar to those found at the center of the sun.

"What we want to do is use the X-rays to blast away the outer layer of the capsule in a very controlled manner, so that the D-T pellet is compressed to just the right conditions to initiate the fusion reaction," explained John Edwards, NIF associate director for inertial confinement fusion and high-energy-density science. "In our new review article, we report that the NIF has met many of the requirements believed necessary to achieve ignition—sufficient X-ray intensity in the hohlraum, accurate energy delivery to the target and desired levels of compression—but that at least one major hurdle remains to be overcome, the premature breaking apart of the capsule."

In the article, Edwards and his colleagues discuss how they are using diagnostic tools developed at NIF to determine likely causes for the problem. "In some ignition tests, we measured the scattering of neutrons released and found different strength signals at different spots around the D-T capsule," Edwards said. "This indicates that the shell's surface is not uniformly smooth and that in some places, it's thinner and weaker than in others. In other tests, the spectrum of X-rays emitted indicated that the D-T fuel and capsule were mixing too much—the results of hydrodynamic instability—and that can quench the ignition process."

Edwards said that the team is concentrating its efforts on NIF to define the exact nature of the instability and use the knowledge gained to design an improved, sturdier capsule. Achieving that milestone, he said, should clear the path for further advances toward laboratory ignition.

popsci.com wrote:Researchers at the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory in California have made a major breakthrough toward achieving self-sustaining nuclear fusion.

The NIF is home to the highest-energy laser in the world—a composite of 192 lasers, all trained on one tiny pellet of the hydrogen isotopes deuterium and tritium. The pressure from the lasers is designed to compress the fuel pellet (inside a dime-sized cylinder called a hohlraum) until the deuterium and the tritium fuse together, releasing a huge burst of energy. The process is designed to replicate the inside of a star, mimicking the Sun's long-lasting, self-sufficient energy creation here on Earth for a vast, cheap supply of power.

Scientists have been working towards creating fusion energy in the lab for decades, but creating a system that puts out more energy than it takes in has so far proved impossible. Now, the NIF has reportedly conducted an experiment in which the amount of energy released by the fusion reaction in the hohlraum was greater than the amount of energy that went into the pellet.

This is still a step away from ignition, the point where the reaction releases as much energy as went into the system as a whole, since the system isn't totally efficient and some of the laser energy that goes in doesn't reach the pellet. But it's a major breakthrough nonetheless, the first time in the world that scientists have been able to achieve this level of (minor) efficiency in a fusion energy reaction in the lab.

When the NIF started operating in 2009, the lab promised it would achieve ignition by September 2012, a deadline it obviously blew past. Since ignition researchers couldn't predict when ignition would be achieved, or even what they were doing wrong, the NIF's government funding has been in jeopordy. Proposed budget cuts for the NIF for fiscal year 2014 would reduce the lab's funding by $60 million. "It is impossible at the moment to predict whether ignition can be achieved," Senator Diane Feinstein, a member of the Senate Appropriations Committee, said in May. "Now is the perfect opportunity to reassess the goals of this program." In other words, the government doesn't want to pour its billions into a high-energy pipe dream.

But it seems the NIF has plugged at least some of the leaks allowing energy out of the system. How exactly they managed to achieve this feat, we don't yet know, although a review in Physics of Plasmas published online this summer detailed some of the potential causes of the NIF's performance issues. John Edwards, the associate program director for inertial confinement fusion and high energy density (HED) science and the study's lead author, explained in a press statement that "the NIF has met many of the requirements believed necessary to achieve ignition—sufficient X-ray intensity in the hohlraum, accurate energy delivery to the target and desired levels of compression—but that at least one major hurdle remains to be overcome, the premature breaking apart of the capsule."

Batman wrote:They've been promising me fusion is 'just around the corner' for longer than I've been alive in the real world. I'll get excited when somebody actually gives us an economically viable fusion reactor. You know, the one that lets us toss out (or at least seriously cut back on) fossil fuels or those atrociously inefficient (and expensive) renewable energies approaches.

Lys wrote:Batman, listen to Michael Kaku, he knows what he's talking about. The short version is that, unlike the past 60 years, have now have actual physical plant that is capable of doing more than leaking plasma all over the place. We're basically right on the edge of the break-even point, which I think is a reason to get excited. Frankly, commercially viable fusion is unlikely to lead to the immediate tossing out of fossil fuel energy sources. There will be considerable costs involved in the development and construction of such a thing that will have to be amortized into the price of the energy it produces, as well as not inconsiderable running costs from requiring high end technical expertise to keep the power plant running. What we are likely going to see is a slow transition away from fossil fuels and toward fusion power, much like we were seeing with nuclear power until a coalition of stupid peaceniks and greenies mixed with crappy public education on the subject caused progress on that area to stall and die. Which is really unfortunate because nuclear power has already saved the lives of nearly 2 million people, and would have saved more had progress continued apace on that front.