Research on Stellarators

This magnetic configuration, produced uniquely by the external coils placed around the outside of the vacuum chamber, is non-axisymmetric (the plasma cross-section changes as one moves around the torus). Research is being carried out on several types of stellarator differing mainly in the periodicity of the toroidal and poloidal components of their magnetic field.

Toroidal windings and cryostat	Plasma and divertor plates
Project W7-X, a Heliac-type stellarator (Euratom-IPP, Garching and Greifswald, Germany)

It is difficult to calculate and engineer the correct shape for these helically twisted rings : only with the advent of powerful computers and sophisticated manufacturing techniques could stellarators with three-dimensional and modular coils be designed and built.

In the W7-AS stellarator (Garching, Germany), plasma is created and is heated by electromagnetic waves at the cyclotronic plasma frequency. The confinement quality is similar to that of a tokamak.

The theoretical studies carried out at IPP (Garching) will be of great value in optimizing the configuration of the W7-X stellerator, currently at the design stage. Construction is planned around the turn of the century, at the new German research centre in Greifswald.

Another stellarator with heliac modular coils, TJ-II, is under construction (Madrid, Spain). The vacuum chamber also has a very complex shape to match that of the plasma and to allow good access both to the structure and for diagnostic purposes.

The stellarator's intrinsic advantage is that it has no toroidal current (no transformer, no disruption) and can thus be operated continuously.

Research is being concentrated essentially the same lines as for tokamaks.

	Diagram of the Heliac-type TJ-II stellarator (Euratom-CIEMAT, Madrid, Spain).

General view of the W-7AS stellarator (Euratom-IPP, Garching, Germany).

	View of the Torsatron-type TJ-IU stellarator (Euratom-CIEMAT, Madrid, Spain).