Scientists target Omega on fusion

KABOOM--A millimeter-wide pellet of hydrogen explodes under the multiple-angled fire of the Omega laser during a recent experiment at the Laboratory for Laser Energetics.

n the latest in a series of experiments exploring sustainable fusion as a source of future energy, University researchers have successfully imploded a super-cooled laser target comprised of solid hydrogen.

The experiment--carried out by scientists at the University's Laboratory for Laser Energetics--is part of an ongoing test of technologies to explore fusion at the National Ignition Facility.

Omega, the most powerful ultraviolet laser in the world, is a testing platform for the new facility, currently under construction at Lawrence Livermore National Laboratory in California.

"So far we're just testing the system," says David Harding, senior scientist at LLE, "but we have fired on several frozen targets and the results are looking good."

The ultra-cold approach will be used at the NIF to create a fusion reaction that generates more power than it consumes for the first time on Earth. Occurring when atoms are compressed so hard they fuse together and release incredible amounts of energy, sustainable fusion could generate near-limitless power from water.

One of the key limits to fusion is the amount of material being fused. By chilling material to such low temperatures, more can be squeezed in beneath the laser's crosshairs.

To pack the biggest punch in the smallest space, scientists filled a hollow plastic ball thinner than the lead in a pencil with fusion fuel under immense pressure and chilled it to minus 424 degrees Fahrenheit.

The tiny pellet is then mounted inside the target chamber, and in a split second it is stripped of its protective housing and blasted with more energy than 100 times the peak power of the entire U.S. power grid.

In less than a billionth of a second, the laser sends the temperature in the pellet from just a few degrees above absolute zero to nearly 50 million degrees Fahrenheit--twice as hot as the core of the sun.

In the 1980s, Rochester scientists were the first to design a smoothing method that focuses the laser more uniformly than any high-power laser had ever done before, and they developed a way to shift Omega's laser light into the ultraviolet to make its energy strike the target more efficiently.

The method has since been adopted by all high-power solid-state laser fusion programs in the world as researchers strive to close the gap between fusion theory and reality.

Each pellet must be perfect so that the energy from the laser is most efficiently transferred to the pellet to effect the implosion. To create these millimeter-wide objects, researchers heat a hydrogen and hydrocarbon gas and let it condense on a tiny polymer ball, much like moisture from the air condenses on the sides of a cold soda bottle.

When the condensed gas has cooled and formed a shell around the ball, they are both carefully heated again, forcing the polymer ball to essentially melt inside the shell and permeate out as a gas, leaving just the hollow shell.

The NIF will focus 192 laser beams on a frozen target and heat it to more than 100 million degrees Fahrenheit.

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