In Physics in Action we take you to a frontier area of physics every week. After a short introduction to the basic physics involved, we give you a taste of the current reseach in the field. As the energy demands of industrialized societies mount, and the limits and risks of conventional energy sources become clear, fusion power is an increasingly attractive alternative. Yet after four decades of research, a working fusion reactor is still at least decades away.
Fusion is difficult to sustain in the lab.
Since hydrogen nuclei are charged particles, they experience a strong electrostatic repulsion, which increases rapidly as the nuclei approach each other. For fusion to occur, the nuclei must hit each other at high speed, which requires a temperature of 100 million degrees. At this temperature, any contact with the container would vaporize it, so the nuclei, which are part of a plasma, must be somehow confined. One approach is to apply strong magnetic fields to keep the charged particles of the plasma off the container walls. The most common containers are shaped like donuts to provide space for the plasma particles, electrons and hydrogen nuclei, to circulate.