Method of keeping a plasma in one place long enough for fusion reactions to take place.

A plasma is made up of ions and electrons. In a magnetic field these charged particles will spiral around that field.

In a tokamak, the plasma is restained inside a toroidal shaped device. TFTR in Princeton, US; JT60 in Japan; JET in Oxford, UK and ASDEX Upgrade, Germany are the biggest tokamak devices in the world.

The hydrogen ions and electrons that scientists hope to fuse spiral around in the doughnut shaped tokamak magnetic field. Plasmas can typically be magnetically confined for about twenty seconds.

In the proposed next stage ITER tokamak magnetic confinement device, it is hoped to confine the plasma for a thousand seconds.