Researchers at a US government nuclear fusion laboratory say they have found a way to downsize the huge magnets that are necessary for controlling fusion plasma in what they think is another step toward creating a viable fusion reactor.
Nuclear fusion refers to the process of joining two atomic nuclei together to form one, heavier atom. However, the mass of the new heavier atom is slightly less than that of the two individual atoms, and this leftover mass is released as energy that can be harnessed to produce electricity.
Nuclear fusion happens naturally all the time in the cores of stars, such as our sun, where hydrogen atoms are fused together to form helium under enormous heat and pressure. While scientists have managed to recreate nuclear fusion artificially, the problem is sustaining a reaction for long enough to viably power an electric grid.
The other problem is that scientists have so far been unable to get a nuclear fusion reactor to produce more energy than it consumes, since recreating the intense heat needed for fusion to take place requires a lot of power.
Still, scientists and governments are chasing a working nuclear fusion reactor since it promises a clean, powerful, and virtually limitless source of energy. Small breakthroughs are bringing humanity incrementally closer to such a reactor, but one that breaks even with energy out versus energy in and can be used on a national grid is thought to be at least a decade away.
One of the leading approaches to fusion involves a machine called a tokamak, in which hydrogen is heated to such high temperatures that it becomes a plasma—a soup of protons and electrons—in which fusion can occur. The plasma is contained within the tokamak using powerful magnets that direct it in a circle.
However, progress with regular tokamaks has generally been slow and now scientists are eyeing up a new version called a spherical tokamak, which is like the usual ring-shaped tokamaks, but with less of a gap in the middle.
According to scientists at the US Department of Energy-owned Princeton Plasma Physics Laboratory (PPPL), which is managed by Princeton University, smaller magnets could make it much easier to work on spherical tokamaks since they could be positioned apart from other machinery in the central cavity. In other words, the magnets could be repaired without having to take anything else apart.
Creating such small magnets is exactly what scientists at PPPL say they have done, thanks to superconducting wires that can transmit the same amount of current as a much wider copper wire and also produce much stronger magnetic fields.
“A lot depends on the [tokamak’s] center,” said Jon Menard, PPPL’s deputy director for research in a press release. “So if you can shrink things in the middle, you can shrink the whole machine and reduce cost while, in theory, improving performance.”
Another benefit is that smaller magnets mean more space for support structure that will help future spherical tokamaks withstand their own huge magnetic fields.
“Also, the smaller, more powerful magnets give the machine designer more options to design a spherical tokamak with geometry that could enhance overall tokamak performance,” said Thomas Brown, a PPPL engineer who contributed to the research. “We’re not quite there yet but we’re closer, and maybe close enough.”
The use of the new wires for the magnets is enabled by a technique refined by researchers at the University of Colorado, Boulder, and the National High Magnetic Field Laboratory in Florida.
A study outlining the development was published in the journal IEEE Transactions on Applied Superconductivity in April this year.