NIF REACHES MILESTONE
NS&D Monitor
2/14/2014
Scientists at Lawrence Livermore’s National Ignition Facility have reached a major milestone in the quest for ignition, achieving a fuel gain greater than 1 for the first time. The achievement was detailed in the Feb. 12 issue of the journal Nature, explaining that the yield performance during a recent series of experiments has shown an improvement by an order of magnitude. “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 Livermore scientist Omar Hurricane, the lead author of the Nature paper detailing the achievement.
According to the lab, “boot-strapping” occurs when the deuterium-tritium fuel used in the shot gets a boost from alpha particles (helium nuclei produced in the deuterium-tritium fusion process) rather than leaking out. “The alpha particles further heat the fuel, increasing the rate of fusion reactions, thus producing more alpha particles,” the lab said. “Boot-strapping” is essential to achieving ignition, and lab officials say the fusion yield during the recent set of experiments has been steadily increased by more than a factor of 10 compared to previous approaches. NIF remains a long way from achieving ignition, but lab officials welcomed the important milestone. “There is more work to do and physics problems that need to be addressed before we get to the end,” Hurricane said, “but our team is working to address all the challenges, and that’s what a scientific team thrives on.”
NIF failed to achieve ignition in 2012 as planned, and the NNSA has directed the laboratory to rebalance shots on the massive laser in favor of shots designed to improve knowledge for the Stockpile Stewardship Program while opening up the facility to outside users as well. It also has taken a more measured approach to understanding the physics of ignition, which led to a series of shots, known as “high foot” shots because of the design of the capsule. The lab previously said those shots, designed to test the limitations of the lab’s knowledge about ignition, showed a steady increase in self-heating of the capsule as the energy of the implosion is increased, matching computer simulations and predictions.
