Last week, trade association Composites UK announced that Devon, UK-based manufacturer Rockwood Composites has successfully used composites to assemble the central core for the UK’s newest fusion device, Tokamak Energy’s ST40. This involved the very precise application of a glass-fibre/Kapton®/glass-fibre insulation layer to each of the core elements. The whole assembly was then bonded together with precise control of the bond line thickness.

The central core is made of 24 inner elements of toroidal field coils which each needed to be insulated. This was achieved by applying a glass-fiber prepreg/Kapton® insulating layer to each of the core elements.

Rockwood used a silicon intensifier consolidation system to accurately 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 very uniform and consistent insulation layer.

The next challenge was to bond all the insulated column component together with extreme accuracy. This was achieved by using a dry glass-fibre fabric 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 huge magnetic fields in ST40. Again, glass-fibre 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.

The Newton Abbot based composites specialist developed this project from first principles, as no off-the-shelf solution was available. They also supplied the entire cryogenic suspension system for the ST40 system, comprising 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. Rockwood established this process as a means of bonding large structures together very accurately over large distances. It is now developing processing solutions for high temperature super conductors, which is an important element in the challenging work of small scale tokamaks.

Mark Crouchen, Managing Director of Rockwood Composites, said: “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. “This was a technical challenge that we relished engaging with, we knew we had the knowledge, materials and processing expertise to provide a technical and elegant solution. We’re now working with Tokamak Energy on the next stage of development.”