First Light fires first shots from gun built for pulsed fusion

First Light Fusion, based in Oxford, U.K., announced on May 13 that it has completed construction of the gun as part of its experimental efforts to use inertial confinement fusion to create the extreme temperatures and pressures required for fusion—work the company hopes will lead to commercial fusion energy. First Light has successfully fired the first test shots from the gun; fusion experimental shots are planned for June.

How does it work? First Light’s 38-mm gun, which weighs 25,000 kg and uses up to 3 kg of gunpowder, compresses hydrogen to about 10,000 times atmospheric pressure and fires a 100-gram projectile that can reach a maximum velocity of 6.5 km/s (14,500 mph)—about 20 times the speed of sound—before it hits the fusion target.

According to Hugo Doyle, head of experimental physics at First Light, the first stage of the two-stage light gas gun uses gunpowder to push a piston to speeds just under 1 km/s. Doyle explained the concept in a video released on Twitter.

“As [the piston] accelerates down this tube, which we call the pump tube, it compresses the hydrogen gas ahead of it,” Doyle said. A conical central section steps the diameter down to the second stage. “As the piston compresses the hydrogen gas into that cone,” he said, “the hydrogen gas gets pressures around 10,000 bar. That 10,000 bars of hydrogen then accelerates this projectile, which is sitting just at the beginning of the launch tube . . . and it accelerates that projectile, which weighs up to 100 grams, from 0 km/s into the end, where it comes out looking exactly the same as it went in.” There is one big difference, however: The solid projectile is now traveling at about 6.5 km/s.

“Hyper velocity” gas guns are used by astrophysicists to simulate meteorite impacts, and a similar gun was used to test the panels on the International Space Station to ensure that it could withstand impact from small objects traveling at massive speed, according to First Light.

Plan of use: The gun will be used in parallel with First Light’s Machine 3—an electromagnetic launch pulsed power machine—and will allow engineers to explore a different parameter space by launching larger but slower projectiles.

“Our fusion technology is driven by the impact of a projectile traveling at significant speed into a fusion target,” said Nick Hawker, chief executive officer of First Light Fusion. “These targets trade pressure and size, amplifying the pressure from initial impact to final collapse of the fuel capsule, which is a small part of the whole target. This new gun will deliver lower pressure than Machine 3, so we will have to rely on designs that amplify more. The larger size means we can do this and still get good performance. With both facilities together we can make more than twice as much progress on the most important aspect of our technology, which is the target.”

First Light Fusion was founded at the University of Oxford by Yiannis Ventikos, head of the Mechanical Engineering Department at University College, London, and by Hawker, who was formerly an engineering lecturer at Oxford. The company was spun out from the university in July 2011.