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8 Fundamentals of Magnetic Thermonuclear Reactor Design
realised in magnetic mirrors – the open magnetic plasma traps – and the second
underlies toroidal fusion devices (TFDs). Tokamak, the protagonist of the book,
is a member of the TFD family. We are also going to take a closer look at alter-
native plasma devices.
2.2 OVERVIEW
2.2.1 Tokamaks
A tokamak has the following functional features:
l Presence of the rotational transform, an effect due to helicity of a magnetic
field, which keeps the plasma as a whole confined and prevents its drift
towards the sidewalls. The rotational transform is achieved through a com-
bination of the toroidal magnetic field produced by toroidal field (TF) coils
and the poloidal magnetic field of the plasma current flowing along the mag-
netic TF (see Fig. 2.1 that shows the plasma current direction I , and the di-
p
rections of the toroidal and poloidal magnetic fields (B and B respectively)
p
t
and the resultant helical field). The rotational transform µ is a ratio between
the number of field line rotations made at the minor radius and those made
at the major radius of a device.
FIGURE. 2.1 A tokamak functional assembly.
