Starting Fluid for Laser Fusion
The strategy of inertial confinement fusion (ICF) is to use high-power lasers to rapidly heat and compress a hydrogen fuel capsule. The fuel is typically frozen, but new work suggests that a liquid state could be more successful at reaching fusion conditions. The experiments at the National Ignition Facility (NIF) in California achieve fusion temperatures with a liquid mixture of heavy hydrogen as starting material.
Nuclear fusion—obtained through inertial confinement or other techniques—could provide the world with a clean and abundant energy supply. In the case of ICF, hundreds of high-power lasers produce x rays that strike a hollow fuel capsule from all sides, causing the fuel to implode. If the compression is high enough in the center, the fuel nuclei will fuse together in a self-sustaining reaction.
During its initial campaign between 2009 and 2012, NIF utilized capsules containing an ice layer of heavy hydrogen. These experiments produced fusion but not at a self-sustaining rate, partly because asymmetry in the x-ray illumination prevented the high fuel compression that is needed. Rick Olson from Los Alamos National Laboratory, New Mexico, and his colleagues have opted for a liquid layer because it should require less compression than ice. To test this concept, the team used a special foam that absorbs the liquid fuel into a spherically symmetric layer along the capsule wall. When exposed to NIF’s lasers at reduced power, the imploding capsule reached temperatures sufficient to trigger fusion, as evident from a yield of neutrons comparable to ice-based experiments. Further work will test whether this liquid approach can achieve self-sustaining reactions at higher laser power.
This research is published in Physical Review Letters.
Michael Schirber is a Corresponding Editor for Physics based in Lyon, France.
First Liquid Layer Inertial Confinement Fusion Implosions at the National Ignition Facility
R. E. Olson et al.
Phys. Rev. Lett. 117, 245001 (2016)
Published December 7, 2016