Neutral Beam Injection (NBI)
Neutral beam injection was developed in the late 70ties and is now the main heating method for most of the fusion experiments worldwide.
The method is rather simple: neutral atoms are able to overcome the confining magnetic field of a tokomak or a stellarator and are ionised in the plasma via collisons with ions and electrons. The such generated fast ions are also confined in the magnetic field and are able to exchange their energy to plasma ions and electrons.
Typical injection energies are in the range of 50 keV to 130 keV. For comparison: the central plasma thermal energy is at maximum at 15 keV.
The generation of fast neutral atoms occurs in three steps:
- generation of a powerful ion beam in the range of several MW
- neutralisation in a gas target
- transport of the neutral atoms to the torus, deflection of the non-neutralised ions to a so-called ion dump