Page 53 - Fundamentals of Magnetic Thermonuclear Reactor Design

Facilities With Magnetic Plasma Confinement Chapter | 2 35

FIGURE 2.17 Sketch of the HELIAS-5B modular stellarator reactor [25].

components, blanket and radiation shielding call for considerable engineering
efforts.
That is why the development of a ‘major’ stellarator design in parallel with
ITER should be high on the agenda. It should fill in the gap of engineering and
physical uncertainties between the existing machines and DEMO, the future
demonstration stellarator reactor. The ‘major’ stellarator design, now in prog-
ress, looks like a 3× W7-X machine. The previous (W7-AS → W7-X) design
was 2× scaling.
The HELIAS-5B modular stellarator (Fig. 2.17) exemplifies the evolution of
design solutions [25]. The project started with a three-period stellarator configu-
ration, which appeared to be too large. A four-period design promised a much
more compact device. After a comprehensive comparison of several optimised
versions, a five-period, W7-X-like configuration with a minimum necessary
scaling coefficient of around four won out.
Its magnetic coils are close in size to ITER TF coils. Hence, many ITER
technologies are applicable for stellarators that gives clear advantage to reactors
of stellarator type [28]. It is impossible to conclude now, which branch of the
MFR will be chosen for a commercial reactor finally, although the agreement
for the DEMO reactor has been made in favour of the tokamak.
In conclusion, it is useful to highlight again the main advantages of the stel-
larator reactor with respect to the tokamak one:

1. No net plasma toroidal currents and therefore no plasma instabilities linked
with such a current.
2. No plasma disruptions and intrinsic steady-state operating conditions.