The National Ignition Facility's preamplifiers, which the first place laser beams are boosted on route to the target chamber. Image: Damien Jemison/LLNL
The solution is described in the video above. High-energy ions are fired from various points around the tunnel at tangential angles to the FRC, which they begin to tightly orbit. These orbiting ions act as an additional stabilizing protective shell. The results still weren't perfect, however.Last year, an earlier version of this setup, dubbed C-2, accomplished 5 milliseconds as well, but with the very significant catch that the plasma decayed over that time. C-2 was reconstructed last fall with help from Russia's Budker Institute of Nuclear Physics, boosting the energy from 2 megawatts to 10 megawatts readjusting the angle of the beams. The upgrade, now known as C2-U, offers five decay-free milliseconds, but at least a full second is required to make the reaction produce more energy than was put into it—"fusion gain," in other words. C-2U will soon be almost completely rebuilt as C-2W, a version of the experiment offering temperatures 10 times as hot as its predecessor and the hope of sparking conventional fusion reactions, e.g. those involving the hydrogen isotopes known as deuterium and tritium.Tri Alpha's goal is still loftier: fusion with hydrogen-boron. This compound requires much more energy to fuse, but has the advantage of being widely available. And, unlike deuterium and tritium, the hydrogen-boron reaction doesn't release neutrons, which means the reactor doesn't have to be shielded.So, we are still a ways away from proper, useful fusion, but this seems to be a tantalizing taste. An anonymous (of course) investor told Science, "for the first time since we started investing, with this breakthrough it feels like the stone is starting to roll downhill rather than being pushed up it."Previous attempts to create long-lasting FRCs were plagued by the twin demons that torment all fusion reactor designers. The first is turbulence in the plasma that allows hot particles to reach the edge and so lets heat escape. Second is instability: the fact that hot plasma doesn't like being confined and so wriggles and bulges in attempts to get free, eventually breaking up altogether. Rostoker, a theorist who had worked in many branches of physics including particle physics, believed the solution lay in firing high-speed particles tangentially into the edge of the plasma. The fast-moving incomers would follow much wider orbits in the plasma's magnetic field than native particles do; those wide orbits would act as a protective shell, stiffening the plasma against both heat-leaking turbulence and instability.
