We are still a ways away from proper, useful fusion, but this seems to be a tantalizing taste.
Merged spheromaks. Image: Princeton University
In an unassuming building in an unassuming industrial park south of Los Angeles, nuclear physicists are smashing together rings of plasma at one million kilometers per hour, producing temperatures on the order of a hundred-million degrees Celsius. The goal is nothing less than practical nuclear fusion, the long-sought energy holy grail: no sketchy nuclear waste and self-limiting meltdown-proof reactions.
The physicists are employed by a company called Tri Alpha, a small outfit established in 1997 by University of California researcher Norman Rostoker, who passed away last December. At a symposium held this week in Rostoker's honor, Tri Alpha CTO Michl Binderbauer announced a major advance in the company's fusion efforts, based on what's known as a field-reversed configuration (FRC): 5 milliseconds of decay-free stability. And within a 100,000,000 °C plasma, 5 milliseconds is an eternity.
Tri Alpha isn't big on announcements or PR, despite the presence of Buzz Aldrin and author Frank Braun within its leadership ranks. It doesn't even have a website. The symposium, held at a hotel in Newport Beach, CA and hosted by the University of California, Irvine's physics department, hasn't been that much less shadowy, with Science mag's news blog grabbing an exclusive on this week's announcement. The firm was at least kind enough to provide a few minutes of video content explaining its work.
A bit of background: Fusion is sort of the opposite nuclear reaction to fission. Rather than harvest energy released as atomic nuclei break apart, fusion depends on, well, fusing atomic nuclei together. In fission, the resulting nuclei fragments wind up with less mass than they had when joined together, with the difference being released as energy. As smaller nuclei fuse together, the new nuclei winds up with less mass than the components had separately and, once again, this mass is released as energy.
The difference is that in fusion there isn't shit flying out all over the place—again, it's a process of joining together. This is appealing for many obvious reasons, not the least of which is its relative lack of waste. It is also quite difficult to accomplish in a way that releases more energy than is used to create the reaction. Fusing stuff together is easy, relatively, but as a viable energy source it's taken us nearly a century just to get to this point of just barely, almost using it to harvest real power.
High temperatures are needed in order to give atomic nuclei enough juice to crash into each other hard enough to fuse. That's the basic idea. This is done using a super-high energy plasma in which atoms have been stripped clean of their electrons and exist as positively charge ions in a hot stew of naked nuclei and confused electrons. Electrons and positively-charged nuclei don't like this state at all and would much prefer being again joined together into neutral atoms, which makes the plasma a very unstable arrangement requiring extreme heat and/or extreme pressures to not collapse. Unfortunately, this heat is so extreme that we can't just stash it in some physical container because it would melt right away.
There are two main ways to get around this, with each one being pursued by one of the two big-name global fusion experiments: the US Department of Energy's $4 billion National Ignition Facility (NIF) and the under-construction $20 billion International Thermonuclear Experimental Reactor (ITER). The NIF setup uses brute force, imploding the plasma to the point that inward pressure becomes the plasma container, maintaining the needed conditions for just a moment. ITER uses what's known as a tokamak configuration, which is a plasma-filled donut that uses powerful magnetic fields as a containment mechanism.
Tri Alpha's project uses sort of a combination of the two. A pair of plasma donuts are separated across a wide 23-meter-long tunnel, with each one containing a rotating stream of particles. This rotation creates a strong magnetic field, which then works to maintain the structure of the donut. This is the FRC.
These two opposing donuts are then blasted at each other at a million kilometers per hour, colliding in the middle and creating one great big FRC. The required heat comes from the kinetic energy of the collision, but that's not quite it. Two problems threaten to destabilize the arrangement.
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.
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."