Technological planning

Development of the theoretical concept allowed the technological planning of the device.


The core piece of the device is a wreath of 50 superconducting niobium-titanium magnet coils about 3.5 metres high. Cooled with liquid helium to superconduction temperature close to absolute zero, they need hardly any energy after being switched on. Their bizarre shapes are the result of the optimisation calculations: They are to produce a particularly stable, thermally insulating magnetic cage for the plasma.

The magnetic field they generate has a five-fold symmetry. Seen from above, the plasma is therefore not exactly circular, but resembles a pentagon. This is because the magnetic system is made up of five identical modules. Each module contains ten coils, with two of each coil having the same shape but arranged upside down. In total, the coil wreath is made up of only five different types of coils.

To allow the magnetic field to be varied a second set of 20 planar, likewise superconducting coils is superposed on the stellarator coils. A massive ring-shaped support structure keeps the coils in the exact position despite the high magnetic forces.

The entire coil wreath is surrounded by a thermally insulating outer shell 16 metres in diameter, viz. the cryostat. A refrigeration plant provides 7000 watts of liquid helium to cool the magnets and their support structure, i.e. a total of 425 tons of material, to superconduction temperature.

Inside the coil wreath is the steel plasma vessel composed of 20 sections, whose peculiar shape is matched to the twisted plasma ring. Through over 250 apertures the plasma is observed and heated. An equal number of ports with good thermal insulation are passed through between the cold coils, connecting these apertures with the outer wall of the cryostat.

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