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- 24 April 2014 11:45 am , Vol. 344 , #6182
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Q&A: What Would You Do With the World's Most Powerful Laser?
15 February 2014 6:30 pm
CHICAGO, ILLINOIS—This week, the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in California announced an important milestone on the road to achieving ignition, which could lead to producing controlled fusion reactions here on Earth. But NIF isn’t just about harnessing the energy of the stars—it’s also about learning how stars produce their energy in the first place. In fact, pushing matter to extreme pressures and temperatures lets scientists explore all sorts of unanswered questions. Here, at the annual meeting of AAAS, which publishes Science, four physicists sat down with us to discuss NIF’s basic science potential and what experiments they would do if they had the laser all to themselves.
Q: What was NIF designed to do?
Johan Frenje (Massachusetts Institute of Technology in Cambridge): NIF is a laser that’s the size of three football stadiums, with 192 beams. We use those lasers to implode capsules to very, very high densities and, hopefully, high temperatures during what we call “shots.” When we reach those conditions, we may be able to ignite, where you produce more energy than you put in. We’ve made a significant amount of progress, but we have a long way to go before we achieve ignition.
Ani Aprahamian (University of Notre Dame in Indiana): With ignition, we would have a power source like the sun, producing endless energy. But there have been some technical difficulties on the way to get there.
Q: In addition to fusion research, what other kids of science can you do at NIF?
A.A.: The work at NIF is really is at the gut of understanding matter. We think we understand a lot about plasmas and nuclear matter, but in reality, we don’t. What you can do with NIF is at the frontiers of knowledge.
J.F.: To me, the biggest issue is understanding plasma at very high temperatures and pressures. Some of that physics is not understood yet, so we have quite a bit of work to do.
Narek Gharibyan (Lawrence Livermore National Laboratory in California): NIF is a wonderful source of neutrons that we can use to do basic science measurements. In particular, we’re trying to look at isomeric states, which is when an atomic nucleus gains energy and jumps from its ground state to an excited state. Those states aren’t stable, so it’s very difficult to do any measurements on an excited nucleus. But because NIF produces so many neutrons, you can actually create that state and measure it during the same shot. There are models that predict what these measurements would be, but experimental results are always needed to prove that what we think we know is actually right.
René Reifarth (Goethe University in Frankfurt, Germany): When you look at normal temperatures on Earth, we get up to around 300 kelvin, or 30°C. Inside a NIF shot, we reach temperatures of 150 million kelvin, which is more like the inside of a star. You cannot do that anywhere else, and even at NIF, you can only do it for very, very short times. This is the only chance we have to touch something that hot. There are more questions that can be addressed if you put matter under very extreme conditions.
Q: How similar is a NIF shot to the inside of a star?
R.R.: It depends on the star, and it depends on the shot. But in NIF, you can reach temperatures that are quite similar to typical stellar temperatures. Of course, the cores in the stars are much bigger and also stay at those extreme temperatures and pressures for much longer. NIF can only create those conditions during an implosion. Still, if we can explain what happens inside a NIF capsule, we hope that we can explain what happens inside a star. NIF tests our basic understanding of fusion, of explosions, all kinds of things.
Q: If you had NIF all to yourself for a week, what kind of experiment would you do?
R.R.: I would dope the capsules with heavy elements and see what happens.
N.G.: We always talk about collecting literally everything that comes out of the capsule as it implodes to be able to study what happens when the plasma forms and well as how it cools For example, we don't know if the debris is atomized or in chunks. There’s a lot of interesting things we could do with our own time at NIF.
J.F.: I would look at charged particle transport, or how energy and particles are transported in plasmas. It’s a big problem, and we don’t understand it very well. There are lots of theories out there but there’s no experimental data on how the process works. People have been trying to do this for 30 years but it’s extraordinarily hard. I think there’s a lot of potential to do very high quality measurements with NIF.
A.A.: I don't think we'd be running short of ideas.
See more of our coverage from AAAS 2014.