Fusion Research Milestone Reached

Scientists at the  U.S. Department of Energy’s Lawrence Livermore National Laboratory (LLNL) have achieved a significant milestone in the development of fusion energy: achieving fuel gains greater than 1 for the first time ever at any facility.

Ignition—when the energy released is equal to or greater than the energy required to confine the fuel—remains the “holy grail,” but in a paper published in the Feb. 12 online issue of the journal Nature, scientists at LLNL’s National Ignition Facility (NIF) detail experiments showing an order of magnitude improvement in yield performance from alpha-particle self-heating over past experiments. As the researchers explain, “A key step on the way to ignition is to have the energy generated through fusion reactions in an inertially confined fusion plasma exceed the amount of energy deposited into the deuterium–tritium fusion fuel and hotspot during the implosion process, resulting in a fuel gain greater than unity.”

In the NIF inertial confinement fusion experiments, the energy of 192 powerful laser beams is fired into a pencil eraser–sized cylinder called a hohlraum (photo), which contains a tiny spherical target filled with deuterium and tritium, two isotopes of hydrogen.

LLNL fusion research
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. Photo by Eduard Dewald/LLNL

“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,” lead author Omar Hurricane is quoted as saying in the Feb. 12 LLNL story.

As the lab explains, “Boot-strapping results when alpha particles, helium nuclei produced in the deuterium-tritium (DT) fusion process, deposit their energy in the DT fuel, rather than escaping. 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. As reported in Nature, the boot-strapping process has been demonstrated in a series of experiments in which the fusion yield has been systematically increased by more than a factor of 10 over previous approaches.”

LLNL notes that the chief mission of the NIF is “to provide experimental insight and data for the National Nuclear Security Administration’s science-based Stockpile Stewardship Program” and that this experiment “represents an important milestone in the continuing demonstration that the stockpile can be kept safe, secure and reliable without a return to nuclear testing.” However, arguably more scientists and energy industry watchers are interested in the work on ignition physics for its potential application to the development of fusion energy for electricity production.

Fusion energy, industry watchers have been saying for 50 years, is 50 years in the future and always will be. Despite the challenges, several countries have been working on fusion research, and a consortium of countries have been working on the massive International Thermonuclear Experimental Reactor (ITER) project in France. NFI scientists speculated in 2010 that a prototype nuclear fusion power plant could be operational within a decade.

Gail Reitenbach, PhD, Editor (@GailReit, @POWERmagazine)

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