Evrim Yazgin
Cosmos science journalist
An international collaboration is trying to solve the world’s energy crisis by building a unique kind of fusion reactor.
SMART (SMall Aspect Ratio Tokamak) is a fusion device being put together at the University of Seville in Spain. Over the past month, the team behind its construction has published several papers outlining the fusion technology behind SMART.
“The SMART project is a great example of us all working together to solve the challenges presented by fusion and teaching the next generation what we have already learned,” says Jack Berkery, principal investigator for the US-based Princeton Plasma Physics Laboratory’s (PPPL) team in the project. “We have to all do this together or it’s not going to happen.”
A fusion future?
Fusion reactors operate on the basic principle which drives the production of energy in stars – the fusion of hydrogen atoms to make heavier elements like helium.
This process, the opposite of fission which drives current nuclear energy technology, promises to provide huge amounts of energy. But at the moment it requires huge amounts of energy to drive the reaction, more than the reaction produces, so it’s unfeasible.
However in 2022 when a US team announced the first nuclear fusion reaction which created more energy output than the energy input. The net output was 0.7 megajoules (MJ) – roughly equivalent to running an average toaster for 10 minutes.
Scientists agree that nuclear fusion is decades away from being a viable alternative energy.
But the SMART project aims to take us a step forward in the quest for fusion reactors that could power the future.
Turning a negative into a positive
Most fusion reactors are based on a doughnut-shaped “tokamak” machine which confines plasma using magnetic fields.
The cross-section of the plasma in a typical tokamak is shaped like a capital letter D. The straight edge of the D faces the centre of the doughnut. This is called “positive triangularity”. If the curved part faces inward, then it has “negative triangularity”.
SMART is unique because it is the only tokamak with negative triangularity.
“The idea was to put together technologies that were already established: a spherical tokamak and negative triangularity, making SMART the first of its kind,” says Manuel Garcia-Muñoz from the University of Seville. “It turns out it was a fantastic idea.”
Negative triangularity may offer enhanced performance because it can suppress instabilities in the device which leads to particles escaping the plasma, damaging the tokamak wall.
“It’s a potential game changer with attractive fusion performance and power handling for future compact fusion reactors,” Garcia-Muñoz says.
Decoding and diagnosing fusion
A paper by the SMART collaboration, published in Nuclear Fusion, explores computer codes developed at PPPL to assess the stability of plasmas inside SMART.
Two papers published in the Review of Scientific Instruments discuss the design of diagnostic tools to provide information about impurities in the plasma such as oxygen, carbon and nitrogen.
“The diagnostic itself is pretty simple,” says co-author on one of the papers Stefano Munaretto from PPPL. “It’s just a wire wound around something. Most of the work involves optimizing the sensor’s geometry by getting its size, shape and length correct and selecting where it should be located .”
Munaretto says many involved in SMART’s diagnostics are young students. “They are eager to learn, and they work a lot. I definitely see a bright future for them.”
Hopefully that means a bright future for nuclear fusion as well.
