An international agreement was reached in June 2005 on the construction of ITER (International Thermonuclear Experimental Reactor). The ITER project combines research efforts of Europe, Japan, China, South Korea, Russia and the United States and is the next important step in fusion research. Currently the largest tokamak in the world is JET (Joint European Torus), located in Culham, close to Oxford in the United Kingdom. The talk will introduce the ITER project and summarize recent results obtained on JET, in preparation of ITER.
JET and other tokamaks in the world have led to solutions for basic problems of controlled thermonuclear fusion (heating and confinement of the plasma, minute long pulses, etc.). The next step is to provide a sufficient number of fusion reactions in order to be able to study the impact of the 'ash' of the fusion reaction (helium nuclei or alpha particles) on a 'burning' plasma. This is hardly possible with the current generation of tokamaks, including JET, because the amount of alpha particles produced, even in the most performant D-T plasmas in JET, is too low. Producing more alpha particles is equivalent to producing more fusion reactions per unit of time, and this in turn, implies a larger energy confinement time than can be achieved with tokamaks operating today.
Essentially all existing tokamaks are too small to fulfill this goal. Scaling laws derived from fusion experiments on many tokamaks in the world show that in order to do that we have to build a tokamak that is between 2 and 3 times larger (in linear dimensions) than JET. ITER is designed to realize a Q value (ratio of power produced from fusion reactions to the power needed for heating of the plasma) of at least 10, equivalent to about 500MW of fusion power. In such plasmas the contribution of the alpha particles to the total heating power will be about 70%, compared with maximum ~10% on JET. This will allow to study for the first time the influence of alpha particles on the stability of the plasma, the removal of fusion alpha particles from the plasma, the plasma heating by the alfas, etc. Other major questions that will be addressed at ITER are the interaction of the plasma with the first wall (sputtering, erosion), breeding tritium from lithium, fuelling the plasma with 50%-50% D-T etc.
ITER is not the end of the fusion quest. It is the bridge between the tokamaks of the 1980s and a demonstration fusion power plant. ITERs role is essential to validate the tokamak concept. ITER is a great technological challenge, but in light of the urgent need to develop new energy sources - inexhaustible and compatible with the environment - an absolute necessity.
