Composites featured in UK's newest fusion device

Rockwood Composites has used composites to successfully assemble the central core for the UK’s newest fusion device, Tokamak Energy’s ST40.


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Rockwood Composites (Devon, UK) announced June 8, that it has used composites to successfully assemble the central core for the UK’s newest fusion device, the ST40 from Tokamak Energy (Oxfordhire, UK).

The central core of the device is made of 24 inner elements of toroidal field coils, each of which was insulated with a glass-fiber pre-preg/Kapton/glass-fiber pre-preg layer. A silicon intensifier consolidation system was used to control the position and pressure during the cure. This enabled air and resin to be progressively squeezed out from under the Kapton film and ensure that the Kapton tightly bonded to the toroidal field coil to give a uniform and consistent insulation layer.

The assembly was then bonded together with precise control of the bond line thickness. A  dry glass-fiber fabric was used to control the bond line thickness and a dispersed adhesive system, which provided a consistent 0.1mm bonded joint.

Rockwood applied the same insulation approach to the solenoid winding, which creates one of the many magnetic fields in ST40. Again, glass-fiber pre-preg and Kapton was applied this time in a helical overlapping manner during the winding process and applied between each of the coils. Finally, the whole solenoid was overwrapped with glass pre-preg.

Rockwood also supplied the cryogenic suspension system for the ST40 system, comprised of a large number of bespoke carbon fibre bands. The technology is also being used in ITER, the world’s largest fusion experiment in France involving engineers and scientists from 35 countries.

Mark Crouchen, managing director of Rockwood Composites, says, “Fusion devices are built to create one of the most extreme environments you can get – more extreme temperatures than anywhere in the solar system! The properties of composites are instrumental in enabling the ST40 to achieve these extremely high temperatures – hotter than the center of the Sun.”

Graham Dunbar, ST40 project manager, adds, “We were faced with a real problem in the manufacture of the central core of our high magnetic field tokamak. We approached Rockwood Composites and their fantastic team of engineers were able to find the best solution through an innovative use of composites.”

The ST40 is designed to show that fusion temperatures – 100M°C – are possible in compact, cost-effective devices.