Encouraging Signs on the Path to Fusion

For four years, researchers at the National Ignition Facility (NIF) have worked toward an ambitious goal: using powerful lasers to ignite fusion in a tiny target of nuclear fuel. If the fusion reaction releases more energy than the lasers provide—corresponding to a “gain” of greater than 1—NIF could have the makings of a new energy source. But so far, NIF hasn’t been able to pass this gain threshold. And because experiments haven’t matched up with the predictions of simulations, it has been difficult to figure out what to change. Now, researchers (Park et al.) at the Lawrence Livermore National Laboratory, California, where NIF is located, report in Physical Review Letters the first laser ignition experiment that appears to be behaving according to the predictions of current models [1]. The researchers used a different laser pulse shape to heat the target, producing the highest yield of neutrons—and therefore the largest energy output—seen to date. Their result is a major achievement because it gives hope NIF will ultimately find a path to achieving gain greater than $\mathrm{<em><strong>1</strong></em>}$.