Page 246 - Fundamentals of Magnetic Thermonuclear Reactor Design

First Wall Components Chapter | 7 227

FIGURE 7.4 Parts of the ITER divertor (EDA phase, 2001).

The vertical targets are in contact with the plasma throughout the discharge
stationary phase absorbing up to 80% of the α-particle flux. The dome and the
baffle are directly exposed to plasma for only 10 s, while the divertor configura-
tion is shaped up. At this stage, the separatrix keeps sliding on their surfaces. Only
the plasma’s electromagnetic radiation and the re-ionisation neutrals hit the dome
and the baffle during the stationary phase. The liner is not exposed to the diver-
tor plasma at all, and the intensity of radiant energy and particle fluxes hitting it
is several times lower compared to what the dome and the baffle are exposed to.
With the divertor operating effectively throughout the stationary phase of
the operation cycle, the only function left for the ITER limiters is to protect the
discharge chamber’s first wall during the discharge start-up and shutdown. For
this reason, they are often referred to as start-up limiters (Fig. 7.5).
The start-up phase begins from a gas breakdown. After that, a toroidal cold
plasma column develops around the outer circumference of the discharge cham-
ber. As the longitudinal plasma current increases under the combined action of the
plasma poloidal magnetic field and the field due to the poloidal coils, the divertor