Fusion experiment exceeds unity fuel gain

Scientists at Lawrence Livermore National Laboratory (LLNL) last week provided details on a series of fusion experiments at the National Ignition Facility (NIF). They achieved fuel gains greater than unity, which means that the fusion reaction generated more energy than the amount of energy deposited via laser into the deuterium-tritium (DT) fusion fuel.

The results were presented in a paper published in the February 12 online issue of the journal Nature.

“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, as reported by Breanna Bishop at LLNL.

The experiments represent a milestone on the path to ignition—in which the released fusion energy equals or exceeds the total amount of energy used to confine the fuel. Joel Achenbach in the Washington Post cautions, “There’s still a long way to go before anyone has a functioning fusion reactor, something physicists have dreamed of since Albert Einstein was alive.”

Writes Achenbach, “Only about 1% of the energy from the laser actually winds up in the fuel, according to Debra Callahan, a co-author of the Nature paper. Most of the laser energy gets absorbed by surrounding material—a gold cylinder called a hohlraum, and a plastic capsule within that—before it reached the fuel, which coats the inside of the capsule….”

Achenbach quotes Mark Herrmann, director of the Pulse Power Sciences Center at the Sandia National Laboratories, as saying of the LLNL researchers, “They’ve got a factor of about 100 to go. We want a lot of fusions. They made 5 million billion fusions, but we want more than that. We want 100 times than what they made.”

Nevertheless, Bishop at LLNL reports that the experiments achieved an order of magnitude improvement over previous results and offer batter matches to computer simulations. Achenbach at the Post quotes Jeff Wisoff, the principal associate director of NIF and photon science at the lab, as saying, “The real significance of this is, we’re now matching our models, we have our feet back on the ground where we know where to go forward. We have a number of knobs we can turn.”

See related post “PPPL drives fusion progress, gains pundit's support.”