Control of a Nuclear Fusion Plasma

At the Eindhoven University of Technology (the Netherlands) we are working on controlling instabilities in fusion plasmas. Nuclear fusion is possibly a clean alternative for ordinary energy plants (using coal or nuclear fission). Essentially, if one can create a little sun on earth, one could use it to extract energy. The sun is a very hot (millions of degrees Kelvin) plasma (i.e. an ionized gas, electrons and ions are devided, so a plasma can conduct electrical current).

In the 1950s a method to confine a small but very hot plasma (up to hunderd million degrees Kelvin) was found in the, then, Soviet Union. The toroidal device was called a Tokamak (a Russian acronym for toroidal chamber). However, there were (and are) big problems in making this device work as a reliable energy plant. One of the big problems originates in the fact that the hot plasma is confined within a very strong magnetic field, with a strength of several Tesla's. Because of the interplay between the magnetic field and the plasma a large zoo of instabilities can arise. Some of these instabilities can be bad for the isolation of the plasma, and thus part of the huge amounts of heat created in the plasma can escape and cause damage.

Too influence the plasma there are several devices that can locally heat the plasma or drive a local current somewhere in the plasma. We are trying to understand how to use these devices to make the plasma more stable.

JET in the UK is currently the biggest Tokamak in the world. At the right a hot plasma can be seen.

For an accessible explanation about controlling a certain periodic instability (the sawtooth instability), read this blog post:
http://activescience.wordpress.com/2012/06/22/a-pacemaker-for-nuclear-fusion-plasmas/
http://steinbuch.wordpress.com/2012/06/23/672/#respond

Essentially, this periodic instability causes the central temperature of the plasma to oscillate. In nonlinear dynamics and biology it is pretty well known that nonlinear oscillations often react in a very peculiar way if the system can be influenced with a periodic signal with a certain period that is close to natural period of the oscillation. Under certain conditions the period of the system will change towards the period of the signal. This phenomenon is pretty universal and is called locking or entrainment. In following blog posts I will explain what is behind this phenomenon and how it can be used to control periods in a plasma.