Fusion

scroll

Formation of a heavy nucleus from lighter nuclei releasing energy - the binding energy. Possible fusion reactions:

D + T -> ⁴He + n + 17.58 MeV,
D + D -> ³He + n + 3.27 MeV,
D + D -> T + p + 4.03 MeV,
D + ³He -> ⁴He + p + 18.35 MeV,
p + ¹¹B -> 3 ⁴He + 8.7 MeV.

The deuterium-tritium reaction is the easiest to realize among all possible fusion reactions. Deuterium is available in sufficient quantity in the oceans of the world; tritium can be "bred" from the lithium element - which is also available in abundance - by means of the neutrons generated during the fusion process.

Breeding reactors for the generation of tritium from lithium:

⁷Li + n -> ⁴He + T + n -2.47 MeV,
⁶Li + n -> ⁴He + T + 4.78 MeV.

Fusion principle

During fusion, two atomic nuclei - e.g. nuclei of the hydrogen isotopes deuterium and tritium - must be brought so close together that they fuse in spite of the repellent electric power of their positive nucleus charges. Two nuclei must fly against each other with high speed to overcome their mutual repulsion. The required speeds of the particles are achieved at high temperatures of about 100 million degrees. The atoms of a gas subsequently disintegrate into electrons and nuclei and the gas is ionized. A completely ionized gas is called plasma. Plasma is electrically conductive and its motion can therefore be influenced by electric and magnetic fields. Advantage is taken of this fact in fusion facilities where the hot plasma is enclosed by a magnetic field cage. In a magnetic field, the Lorentz force acts on the charge carriers. As a result of this force, the charge carriers perform a spiral movement along the magnetic field lines. Ideally, a contact with the container wall and thus heat transport to the wall needs to be prevented. As arrangements to magnetically enclose the plasmas within a ring the systems of the type Tokamak and stellarator (see 'Tokamak' and 'stellarator') are usual. (See also 'JET' and 'ITER'). The main research target in plasma physics is to find a suitable procedure allowing a controlled fusion reaction in the form of a chain reaction that enables use of the released energy. During the fusion of deuterium and tritium to form 1 kg helium, an energy of about 120 million kWh is released corresponding to a gross calorific value of 12 million kilograms of coal.

Fusion experimental facilities and the plasma conditions reached by them

back