In July, scientists at the National Ignition Facility at Lawrence Livermore National Laboratory in California momentarily duplicated the process of fusion that drives the sun by bombarding a pellet of hydrogen with 192 lasers. It was a repeat of an experiment from last December, but this time the scientists got almost twice as much gain as the incoming lasers could provide.
In an interview, Richard Town, the associate programme director of Livermore’s laser fusion programme, said, “We again repeated ignition.” The Denver conference he attended on Monday was when he discussed the July experiment.
The Livermore results provide hope that fusion may one day be used to create enormous amounts of power, despite the fact that it produces neither carbon dioxide nor long-lived radioactive waste.
The experiment, which began in October, gained widespread recognition in December after it generated energy equal to 1.5 pounds of TNT, or around 1.5 times that of the incoming lasers. This was the first occasion when the energy released from a fusion reaction in a laboratory was more than the energy put into the reaction.
The trial in July was nearly identical to the one in December. Dr. Town claimed a similar crop might be expected. About three megajoules in power.
3.88 MJ were generated in reality.
This unexpectedly positive result raises the possibility that minor tweaks might greatly enhance laser fusion. However, minor changes might also lead to unsuccessful fusion studies.
Dr. Town also mentioned that a fusion experiment done in June, less than a month before, only produced between 1.6 and 1.7 megajoules instead of the targeted 3 megajoules.
This month, another attempt of similar laser intensity was made as part of the effort to maintain nuclear weapons stockpiles without resorting to underground nuclear testing.
Scientists at Livermore have evaluated the data and feel they have a better understanding of the problem as a result.
Problems exist, for example, with the 192 lasers. “Every time you fire the laser, there are a few little changes,” Dr. Town said.
The hydrogen fuel capsule was not uniformly squeezed as intended due to an insufficient amount of laser energy. Since part of the energy is lost during the inward implosion, the hydrogen is not heated to the same extent.
Switching around the fuel capsules might potentially affect the fusion processes in subtle ways. The present state of computational modelling implies some leeway in output power.
Dr Town claims that “it could fall as low as 1.4 megajoules.” And if all the stars align and the machinery is in working order, it may generate as much as seven megajoules of power.
Former Livermore facility director and SLAC National Accelerator Laboratory scientist Siegfried Glenzer praised the July progress, saying, “The fact that the gain has gone up on the last shot is encouraging news and shows that the current implosions are not yet fully optimised.”
The National Ignition Facility is about to begin a new round of studies designed to improve the facility’s fusion yields and make them more consistent. We’re bumping the lasers up from 2.05 to 2.2 megajoules of power. The most recent update, from 1.9 MJ, paved the way for these modifications. It is expected that progress will persist even if additional power is used.