Of the different fusion approaches magnetic fusion is by far the most developed. It relies on the idea that the motion of charged particles is restricted across regions of high magnetic field (due to the Lorentz force). A “magnetic bottle” can therefore be used to suspended a soup of positive and negative charges (plasma) away from cold material surfaces – allowing extremely high temperatures to be sustained (roughly 150,000,000 C). Under such conditions, charged ions can overcome their mutual repulsion allowing nuclear fusion to occur – releasing energy in the process. Various bottles have been proposed over the years but the torus (doughnut) is the shape currently favoured by the international fusion community and specifically the Tokamak is the device currently receiving most attention (see ITER project).
To reach the extreme fusion temperatures energetic beams of particles are injected. Once the plasma “ignites”, energetic fusion products should in principle heat the plasma in a self sustained way. Unfortunately all these energetic particles also have a tendency to destabilise the plasma, reducing overall performance and potentially damaging material components.
The overall aim of this research is to gain an understanding of these instabilities and develop ways to mitigate any undesirable consequences.
More technical details
A magnetically confined neutral plasma cannot be in thermodynamic equilibrium . As such the plasma has a tendency to ripple and churn – using the naturally occurring electromagnetic oscillations to achieve some form of lower energy state. Energetic particles drive the plasma further away from thermodynamic equilibrium, creating more potential for instability [2,3]. What we are now understanding is that the instabilities can be relatively benign, or more dramatic in character – it depends on the amount and type of collisions between the energetic particles and the plasma. Furthermore, the dissipative processes that one might initially expect to suppress instabilities are now understood to actually be enhancing them.