When it comes to making energy, nuclear fusion is the ultimate goal. It holds the promise of clean limitless energy that’s available on demand. But of course, it isn’t easy, and despite several different promising methods we still haven’t achieved sustained fusion.
But in April 2020, NASA researchers announced they had come up with a new approach to fusion that has the potential to power missions into deep space, and maybe even future laptops here on Earth.
Unlike nuclear fission, where heavy atoms are split to generate energy, fusion is accomplished by smashing lighter elements together, so they combine. It’s the process that powers our Sun, as hydrogen nuclei in its core crash into each other and eventually, create helium through what’s known as the proton-proton chain. But the only reason our sun and other stars can pull off this trick is because of their massive size. They need to be so huge that gravity creates enough pressure and heat to make those hydrogen nuclei collide.
Remember, a hydrogen nucleus is really just a proton, and protons are positively charged. To make two of them collide, they have to overcome their mutual repulsion for each other, known as the Coulomb barrier. It’s kind of like making the like sides of two magnets touch, except the magnets are the size of a subatomic particle, and they need to touch so hard they bind together. So, how do you do it, without getting enough hydrogen together to form a star, that is?
Well, one approach is suspending fuel in a complex magnetic field and heating it until it’s hotter than in the center of the Sun, stripping electrons from the hydrogen nuclei and creating plasma. This is known as magnetic confinement fusion. Reactors that use this approach, like tokamaks and stellarators, currently have trouble keeping the plasma stable and burning.
Another method is to shoot a powerful laser pulse at a fuel source like deuterium, which is an isotope of hydrogen that has a neutron and a proton in the nucleus. Hurdles like distributing the laser energy and engineering a precise enough fuel target have so far kept us from achieving ignition with this method known as inertial confinement fusion.
So scientists led in part by a team from NASA’s Glenn Research Center explored another path called lattice confinement fusion. They used the atoms of a solid piece of metal like erbium or titanium as a lattice and crammed the spaces in between with deuterium gas until the lattice started to break apart. Eventually, the whole thing was so full of deuterium one researcher described it as more like a powder than a lump of metal. Then it needed a kick to get fusion going. Said kick was provided by a beam of high energy gamma rays, which can split a deuterium nucleus into an energetic proton and neutron on contact. When the neutron smacked into another deuterium atom, it accelerated it fast enough to overcome the electrostatic repulsion and fuse with another deuterium nucleus.
The clever thing about lattice confinement fusion is it reaches the energy needed to overcome the Coulomb barrier more easily. The negatively charged electrons in the erbium or titanium effectively shield the deuterium nuclei from each other until just before the collision, kind of like when you’re driving up to an intersection and don’t see a stop sign hidden behind a tree until the last minute.
When two deuterium nuclei fuse, they can either produce a proton and an isotope of hydrogen with two neutrons called tritium, or helium-3 and another energetic neutron that can continue the reaction. Of course, the fast moving deuterium could also collide with the lattice, but even that could produce usable energy.
NASA is interested in this technology as a possible power source for deep space missions, with researchers imagining fusion powering spacecraft for 10 to 30 years, while saving weight and cost by reducing the need for shielding. Fusion power would also revolutionize energy here on Earth, and one researcher proposed this technology could power individual homes or even laptops if it could be made small enough.
But that is a long, long way off. Researchers have shown that this method can fuse atoms, next they need to see if they can make the process more consistent and efficient. It sounds promising, but until more breakthroughs are made we’ll just have to keep relying on our sun for nuclear fusion.
Before sustainable fusion power becomes a reality on Earth, nuclear fission still has its uses.