\def\descr{Tokamak (GOLEM) basic concept}


\def\default{
Tokamaks are machines with a strong magnetic field whose mission is to, one day, become fusion reactors fueling clean and safe power plants. The basic task of a tokamak reactor is to heat and confine its fuel, a 50:50 mixture of deuterium and tritium, allowing thermonuclear fusion reactions to take place. These reactions generate heat (14.1 MeV per reaction) which is subsequently converted into electricity via the standard steam-turbine cycle.
\par
One of the main challenges in current tokamak research is to confine the burning fuel. Although the fuel is very thin (its density is 5-8 orders of magnitude lower than the density of air), its temperature is extremely high, up to $\sim$100 million K. This is to ensure that when deuterium and tritium nuclei collide, they have sufficient energy to overcome the repulsive electrostatic barrier and fuse, hence \textit{thermonuclear} fusion. Such high temperatures mean that the fuel is in the state of plasma, a collection of ionized nuclei and free electrons, and also that it must never directly touch the reactor walls. (For one, the plasma would cool down and cease to exist; for two, the reactor walls might melt.) Tokamaks confine the fuel using the Lorentz force $q \textbf{v} \times \textbf{B}$, which forces charged particles to rotate around magnetic field lines rather than travel across them freely. Thus the strong magnetic field confines the plasma in the center of the tokamak chamber.
}



\def\GWfigure#1{
\GWifigure{#1}{Theory/Tokamaks/BasicConcept/Sketch.golem/fig/drawing.pdf}{\descr}{fig:Theory/Tokamaks/BasicConcept/Sketch.golem}
}

\def\GWpar{
\GWfigure{width=0.8\tw}
The basic mission of the tokamak technology is to  \emph{heat} and
\emph{confine} for a sufficiently long time the fusion fuel (deuterium-tritium
mixture) up to $\approx$ 100 milions degrees Celsius - a sufficient temperature
to fuse these light nuclei into a heavier Helium nucleus and a neutron. At these
high temperatures the fuel is in a state of matter called plasma: a collection
of ionized nuclei and free electrons. These charged particles are confined by a
strong magnetic field.
The
fusion reaction products have a significantly higher kinetic energy and heat the
surrounding plasma. This fusion-generated heating power can then be used for
electricity production.
\par
The basic structure of a tokamak (see e.g. \cite{wesson99science}) can be seen
in Figure \ref{fig:Theory/Tokamaks/BasicConcept/Sketch.golem}. The confining magnetic field structure is the result of the superposition of the toroidal magnetic field $B_t$ generated by external coils and the poloidal magnetic field $B_p$ generated by a strong toroidal plasma current $I_{p}$ induced by the transformer. 
}


\def\GWparzmb{The tokamak (see Fig. \ref{fig:Theory/Tokamaks/BasicConcept/Sketch.golem}) is a device where in its simplest possible description it is necessary to heat the fuel /deuterium-tritium mixture/ to the plasma state up to 100 milions centigrades while securing the insulation of such a hot media from the reactor vessel. Both requirements are reached providing a very  special configuration of electric and magnetic fields applied on the toroidal geometry of the reactor.}