Abstract:
Fusion energy – ready for use by 2050?
Friedrich Wagner, Professor, Max-Planck-Institut für Plasmaphysik, Greifswald
Fusion – the energy source of the sun and the stars – is one non-fossil option for future electricity supply, which offers the prospects of meeting the requirements of operational safety, environmental compatibility and sustainability. Deuterons and tritons fuse to Helium, releasing a neutron and energy. The energy within one gram of fusion fuel corresponds to that of 12 tons of coal. Deuterium can be gained from sea-water; Tritium is bred from Lithium which is contained in the earth crust. The conditions for the release of fusion energy are difficult to meet. As repelling Coulomb forces have to be overcome, a temperature of about 150 Mill degrees is necessary for fusion. Under these circumstances, the fuel is in the plasma state which allows the use of strong magnetic fields to confine all charged particles involved. Toroidal systems with the plasma in the shape of a donut are the most advanced systems whereat the tokamak – a Russian invention – is closest to the ignition conditions of a reactor. In nowadays experimental devices like JET, the largest fusion device, operated in Europe, temperatures in the range of 400 Mill degrees can be produced by pressing a knob. Techniques to heat the plasma, to exhaust He, the ash of the fusion process, and processes to control the global plasma instabilities and to tame plasma turbulence have been successfully developed. Also alternatives to the tokamak, as the stellarator, have been developed with promising characteristics.
16 MW of fusion energy have been produced by JET in a short pulse. This was the signal to realise the first fusion reactor. ITER, the International Thermonuclear Experimental Reactor, will be built in Cadarache, France, by seven partner countries. The goal of ITER, a tokamak, is the operation of deuterium-tritium plasmas under conditions, which allow the production of fusion energy at the level of 500 MW and with a power amplification factor of 10. Following ITER in about 2030, DEMO will demonstrate all the technology of a fusion reactor – the proper materials to withstand the high neutron fluxes giving rise to several tens of dpa’s per year, the in-situ breeding of tritium, the safety issues in connection with tritium and activated structural materials and finally the economy of the concept. Fusion energy should be available from middle of the century.