Why is fusion for deriving energy not yet feasible?
Reproducing the energy source of the sun and stars here on earth is a great challenge. This requires that sustainable fusion reactions be produced in a plasma – an ionised, ultra low density gas – with a temperature of 100 million degrees. Fusion research is now on the threshold of demonstrating an energy-yielding plasma with the international ITER experimental reactor, now being built at Cadarache in France.
It has been a long way this far: Right after the start of research in the 1950s it became evident that in order to develop fusion intense fundamental research was needed to comprehend the highly complex, multiply interconnected processes in a plasma. Since then the goal has been approached step by step. The first devices were a factor of 50,000,000 short of the plasma values needed for ignition. At present the shortfall is just an order of magnitude. The record holder is the JET device, the Joint European Torus, at Culham, England, which has already achieved a fusion power of 16 megawatts. The JET plasma is, however, too small to attain a net gain of energy.
This is the objective of ITER, which is being worked on by fusion scientists from all over the world. It is to yield a fusion power of 500 megawatts, this being ten times as much as is needed for heating the plasma. ITER will then be succeeded by a demonstration device providing all functions of a power plant. In view of the planning, building and operation times needed for ITER and its successor a fusion power plant could thus be capable of yielding economically useful energy towards mid-century.
The reason for this persistence: The fuel for fusion, viz. deuterium and lithium, from which tritium is produced in the power plant, is available in unlimited quantity throughout the world. One gramme of it could release as much energy as eleven tons of coal.