LLNL NIF: There was Probably Break Even Fusion, but...

One unintended effect of the U.S. federal shutdown is that helpful press officers at government labs are not available to provide a reality check to some of the wilder stories that can catch fire on the Internet. They would have come in handy this week, when a number of outlets jumped on a report on the BBC News website. The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in California, it reported, had passed a "nuclear fusion milestone." NIF uses the world's highest energy laser system to crush tiny pellets containing a form of hydrogen fuel to enormous temperature and pressure. The aim is to get the hydrogen nuclei to fuse together into helium atoms, releasing energy.

The BBC story reported that during one experiment last month, "the amount of energy released through the fusion reaction exceeded the amount of energy being absorbed by the fuel - the first time this had been achieved at any fusion facility in the world." This prompted a rush of even more effusive headlines proclaiming the "fusion breakthrough." As no doubt NIF's press officers would have told reporters, the experiment in question certainly shows important progress, but it is not the breakthrough everyone is hoping for.

A memo sent out on 29 September to collaborating labs from NIF Director Ed Moses—which has been seen by Science—describes a fusion shot that took place at 5:15 a.m. on 28 September. It produced 5x1015 neutrons, 75% more than any previous shot. Neutrons are a product of fusion reactions, so they are used as a measure of success.

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One requirement for ignition is that energy output should exceed the energy input from the laser, i.e., that gain (output divided by input) should be greater than 1. NIF's laser input of 1.8 MJ is roughly the same as the kinetic energy of a 2-tonne truck traveling at 160 km/h (100 miles/h). The output of the reaction—14 kJ—is equivalent to the kinetic energy of a baseball traveling at half that speed. Numerically speaking, the gain is 0.0077. The experiment “is a good and necessary step, but there is a long way to go before you have energy for mankind,” Campbell says.

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