Fusion Research - how the sun and stars produce energy
Fusion, that is, the merging of atomic cores, is the process by which the sun and the stars produce their energy. It is an ancient dream of mankind to "bring the sun down on earth" and to make use of this energy. Fusion research work in Germany is an integral part of the European fusion research programme and ranges from very basic studies of plasma physics to the realization of technologically demanding components for fusion plants and the construction of the large-scale project "Wendelstein 7-X" in Greifswald.
The sun radiates light because its hydrogen cores are constantly melting in a phased process to become helium cores and thereby release energy. However, the probability of this process is very low despite the considerably high temperature and density inside the sun. On the one hand, this means that fortunately the sun will continue to exist for a very long time. On the other hand, the existing "fuel" quantity in the form of hydrogen is so large that a sufficient amount of energy is continuously released to enable life on earth in spite of the low reaction probability.
The sun's fusion reactions are too slow under the conditions that can be achieved on earth. Therefore, the fusion of two different kinds of hydrogen cores is to be used here: deuterium and tritium. They are quasi interim steps on the way from hydrogen to helium. Tritium can be derived from lithium under fusion reaction conditions. Deuterium as well as lithium exist in large quantities which means that there will not be a bottleneck for energy production in the case of successful fusion research. The decisive advantage over the present main method of energy production of burning fossil fuels is therefore the avoidance of carbon dioxide emissions on the one hand and the sustained availability of resources on the other. Fusion would therefore complement the increased use of renewable energies, particularly in view of worldwide energy consumption, which will rise significantly over the coming years and decades.
A fusion reaction only occurs if it is possible to overcome the electrical repulsion between the atomic cores involved. In the sun, gravity confines particles with the necessary energy - fast, charged particles, or "ions", which together with free electrons form a plasma. On earth, such a plasma can only be confined by strong magnetic fields or inertia. Fusion research in Europe focuses on magnetic confinement, while researchers in the US are also studying inertial confinement fusion.
The complexity of the very demanding technologies which are necessary for the realization of the fusion process was underestimated in the early years of fusion research. However, an awareness has developed and efforts are being made to pool the necessary knowledge by means of international cooperation. Thus, fusion research has become a model for international cooperation, which has brought about substantial progress and success in the last decade in particular. An important interim goal was reached: fusion performance of several megawatts, thereby coming very close to the so-called break-even point at which the fusion performance generated in the plasma is equal to the energy needed to start the reaction. These results were achieved primarily at the European JET
facility. They are the basis for starting construction of the ITER ("The Way") international large-scale experiment to study a plasma which generates energy under power plant-like conditions.
In Germany, the Max Planck Institute for Plasma Research (IPP)
, Garching and Greifswald, as well as the Karlsruhe Institute of Technology
and the Research Centre Jülich
are working in the field of fusion research. Their work is integrated in the European Fusion Research Programme
under Euratom and is coordinated at international level by the International Energy Agency (IEA)
. The fields of work of the German fusion centres cover everything from demanding basic research in the area of plasma physics to the solution of complex technological issues, and are organized in the Fusion Programme of the Helmholtz Association (HGF)
with the following programme topics:
- ITER - the next step
Includes all fundamental preliminary physical and technological work for the construction of the next large fusion experiment ITER in international cooperation.
- Fusion technology
Includes the development of materials and components which are required for a future power plant (vis-à-vis an experimental reactor).
- Tokamak physics
"Tokamak" is a form of magnetic confinement of plasmas which has been researched most extensively worldwide and which is therefore used as a basis for ITER applications. Current Tokamak research tries to record, shape, describe in theoretical terms and directly influence the different conditions a plasma can adopt in this confinement.
- Stellarator research
In addition to the Tokamak line, the Stellarator line has been established as a promising confinement concept which allows for continuous operation, in contrast to Tokamak. With "Wendelstein 7-X", Greifswald is conducting the most advanced experiment of this type worldwide.
The following large-scale facilities and national research institutions are being used for this work, among others:
- ASDEX Upgrade, a Tokamak experiment at the IPP which is also being intensively used by other European fusion laboratories.
- TEXTOR, a Tokamak experiment at the Research Centre Jülich involving the participation of Belgian and Dutch partners.
- TOSKA, a low-temperature test facility for superconducting magnet coils at Karlsruhe Research Center.
- Karlsruhe Tritium Laboratory (TLK), a unique institution in Europe for handling tritium for procedure development.
- Wendelstein 7-X, the most significant Stellarator experiment worldwide (under construction).
International fusion experiment ITER (lat.: the way) is the culmination of decades of fusion research. In June 20015, the international partners - European Union, China, Russia, Japan, USA, India (since December 2005) and South Korea - agreed on plans to build the facility in Cadarache, France. ITER will be the first fusion facility to generate net energy. As such, it represents a crucial step on the path towards producing commercial energy from fusion.
In contrast to the worldwide most studied "Tokamak principle" for inclusion of the fusion plasma, the Stellarator principle allows continuous operation. The largest and most advanced experiment of this principle so far is currently being constructed at the Max Planck Institute for Plasma Physics in Greifswald. Operation of Wendelstein 7-X is planned to start step by step in 2014, and the first plasma is expected in 2015.