The SMART (Small Aspect Ratio Tokamak) reactor – an experimental fusion device designed, built and operated by the Plasma Science & Fusion Technology Laboratory of the University of Seville, Spain – has generated its first plasma. SMART is unique because of its flexibility to generate plasmas with different shapes. It will be the first spherical tokamak to fully explore the potential of negative triangularity.
Triangularity refers to the shape of the plasma relative to the tokamak. The cross section of the plasma in a tokamak is typically shaped like the capital letter D. When the straight part of the D faces the centre of the tokamak, it is said to have positive triangularity. When the curved part of the plasma faces the centre, the plasma has negative triangularity. Negative triangularity is expected to offer enhanced performance because it can suppress instabilities that expel particles and energy from the plasma, preventing damage to the tokamak wall.
“This is an important achievement for the entire team; we are entering the operational phase of SMART,” said Professor Manuel García Muñoz, Principal Investigator of the SMART project.
The goal of SMART is to provide both the scientific and technological basis for the design of the most compact fusion reactor possible by combining three technologies; spherical tokamaks, negative triangularity and high magnetic field. This first solenoid-induced plasma represents a major achievement for the SMART project, as well as for progress towards the most compact fusion device possible.
Professor Eleonora Viezzer, co-Principal Investigator of the project, added: “We were all very excited to see the first magnetically confined plasma and we are looking forward to exploiting the capabilities of the SMART device together with the international scientific community. SMART has sparked great interest all over the world.” The results of its first plasma are described in a paper published in November in the journal Nuclear Fusion, Volume 64, Number 12.
The US Department of Energy’s (DOE’s) Princeton Plasma Physics Laboratory (PPPL) collaborated on the design and development of the new fusion device. SMART benefitted from PPPL computer codes as well as the Lab’s expertise in magnetics and sensor systems.
“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,” said Jack Berkery, PPPL’s Deputy Director of Research for the National Spherical Torus Experiment-Upgrade (NSTX-U) and principal investigator for the PPPL collaboration with SMART. “We have to all do this together or it’s not going to happen.”
Professors Garcia-Munoz and Viezzer, both professors at the Department of Atomic, Molecular and Nuclear Physics of the University of Seville as well as co-leaders of the Plasma Science & Fusion Technology Lab and the SMART tokamak project, said PPPL seemed like the ideal partner for their first tokamak experiment. The next step was deciding what kind of tokamak they should build.
“It needed to be one that a university could afford but also one that could make a unique contribution to the fusion landscape at the university scale,” said Garcia-Munoz. “The idea was to put together technologies that were already established: a spherical tokamak and negative triangularity, making SMART the first of its kind. It turns out it was a fantastic idea.”
Garcia-Munoz said negative triangularity is a potential game changer with attractive fusion performance and power handling for future compact fusion reactors. “Negative triangularity has a lower level of fluctuations inside the plasma, but it also has a larger divertor area to distribute the heat exhaust.”
The spherical shape of SMART should make it better at confining the plasma than it would be if it were doughnut shaped. The shape matters significantly in terms of plasma confinement. That is why NSTX-U, PPPL’s main fusion experiment, isn’t squat like some other tokamaks: the rounder shape makes it easier to confine the plasma. SMART will be the first spherical tokamak to fully explore the potential of a particular plasma shape known as negative triangularity.
