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February 24, 2013

Search for Modifications and Alternatives after the NIF fusion laser missed key milestone

The world's biggest laser missed a key target date on the road to producing clean energy via nuclear fusion, an independent review panel says the technology holds enough promise to continue the quest – with a few modifications.

NIF's approach was to fire a 192-beam laser at a metal shell the size of a pencil eraser, holding a ball of frozen hydrogen. This produces a burst of X-rays that heats and compresses the hydrogen, fusing the nuclei in a brief implosion.

When NIF was being built in the 1990s, computer models predicted that short laser pulses delivering 1.8 megajoules of energy would create the pressures needed for ignition. The giant laser surpassed this energy level last year but still wasn't achieving enough pressure.

Until we know why NIF fell short, the panel recommends trying out other options, such as shifting to a different type of laser. For instance, firing an electron beam through a mixture of krypton and fluorine produces bright laser pulses at a shorter wavelength. This technology is less mature, but if it works it could implode the targets more uniformly than NIF's lasers.

Developers might also try changing the target. NIF was designed to fire its lasers at a metal cylinder because this was thought to be the best way to spread compression energy evenly over the hydrogen ball. But new optical techniques have fired laser pulses directly at the hydrogen and still seen uniform compression. The panel wants to test this technique at NIF's energy levels. Another suggestion is to get rid of the lasers entirely and fire heavy ions from a particle accelerator, akin to the ones used to recreate the conditions of the big bang at facilities like the Large Hadron Collider near Geneva, Switzerland. Ion beams can transfer energy to targets just as efficiently as lasers, although for now the beam energies we can achieve are far short of what's needed for fusion. If you liked this article, please give it a quick review on ycombinator or StumbleUpon. Thanks
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