Scientists achieve nuclear fusion milestone

By blasting hydrogen isotopes with powerful laser pulses, researchers at the Lawrence Livermore National Laboratory have vastly increased fuel yield, a new paper reports.

Eduard Dewald/LLNL
A metallic case called a hohlraum holds the fuel capsule for NIF experiments. Target handling systems precisely position the target and freeze it to cryogenic temperatures (18 kelvins, or -427 degrees Fahrenheit) so that a fusion reaction is more easily achieved.

The amount of energy the sun generates in an hour is more than enough to satisfy power needs of the Earth for an entire year. What if we could create this energy on Earth?

So far, scientists have failed to do so, but now there is a glimmer of hope.

In a paper titled "Fuel gain exceeding unity in an inertially confined fusion implosion" published in the Feb. 12 online issue of the science journal Nature, scientists at Lawrence Livermore National Laboratory (LLNL) in Calif. detailed a series of experiments which show an "order of magnitude improvement in yield performance over past experiments," according to a press release from LLNL.

Simply put, this step could help scientists successfully carry out nuclear fusion reactions in the future. This is the same kind of reaction that occurs within the sun (and many other stars) where two hydrogen nuclei combine together to form a helium nucleus.

The scientists at LLNL have now managed to successfully carry out a better "ignition" process, which is the key step to achieving a successful nuclear fusion reaction.

Scientists loaded fuel made from deuterium and tritium – two heavy isotopes of hydrogen – into a plastic shell that surrounds and confines the so-called DT fuel as it is compressed with a laser pulse. The capsule explodes, causing the fuel inside the capsule to implode, Paul Springer, one of the co-authors of the paper says.

Essentially, the material gets so dense that the atoms collide with each other, potentially sparking a high-energy chain reaction that will yield a tremendous amount of energy, he adds.

To further improve the ignition, it is important that the capsule be even more spherical in shape so that material can get denser and hotter, he said.

"What's really exciting is that we are seeing a steadily increasing contribution to the yield coming from the boot-strapping process we call alpha-particle self-heating as we push the implosion a little harder each time," said lead author Omar Hurricane.

Boot-strapping results when alpha particles (helium nuclei produced in the deuterium-tritium fusion process) "deposit their energy in the DT fuel, rather than escaping," stated the press release. "The alpha particles further heat the fuel, increasing the rate of fusion reactions, thus producing more alpha particles. This feedback process is the mechanism that leads to ignition."

If successful, nuclear fusion reactions could be fueled by heavy hydrogen extracted from sources such as seawater, Dr. Springer told the Monitor.

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