Nuclear fusion, the process that powers stars like the Sun, has long been hailed as the 'holy grail' of energy, offering the potential for millions of times more energy than burning fossil fuels. However, practical fusion on Earth has been hindered by sudden collapses of heat and plasma disruptions that can damage reactors. Now, researchers have shed light on the cause of these disruptions, bringing us closer to a viable fusion energy source.
In a study published in the journal Physics of Plasmas, Dr Min-Gu Yoo of the US Department of Energy's Princeton Plasma Physics Laboratory and his colleagues traced the collapse to the three-dimensional disordering of magnetic fields that confine superhot plasma inside a tokamak reactor. The team found that when magnetic fields become disordered by instabilities in the plasma, the plasma can rapidly escape and strike the reactor walls, causing significant damage.
Co-author Weixing Wang explained that in major disruptions, field lines become 'totally disordered, like spaghetti', allowing plasma to connect quickly to the wall and release enormous thermal energy. The researchers discovered that the disordered topology forms 'tiny hills and valleys', with valleys trapping plasma particles and hills allowing them to 'roll down' and impact the reactor walls.
Dr Yoo noted that the existence of these 'magnetic hills' is responsible for the fast temperature collapse, or thermal quench, as they allow more particles to escape. The team's key insight was simulating the thermal quench topology as a complex three-dimensional structure, avoiding the oversimplification of previous one-dimensional models. This new understanding could help find innovative ways to mitigate or avoid plasma disruptions in future fusion reactors.
