When a CCFE engineer Tom Barrett and colleagues embarked on a European-wide project to design a key component to protect fusion reactors from thermal damage, they never expected their solution could come in the form of a household object.

The component in question is the exhaust system of the 'DEMO' prototype power plant. Known as the divertor, it is a trench where the hot fusion plasma will be deliberately deposited. Doing so enables heat to be conducted away while controlling impurities, and is a way of managing the ejection of power and helium waste.

Divertor target mock-ups manufactured at CCFE, in collaboration with KIT in Germany. © CCFE

The divertor surface will be dotted with thousands of small tungsten blocks, forming the divertor targets. Millimetres below these targets, a water coolant flow removes the waste heat and regulates the divertor's temperature, and so the structural integrity of these components is critical. Damage to the coolant pipe will mean the coolant leaks out and the whole reactor has to shut down for costly repairs. So Tom and his colleagues' job is to find a way of separating the very hot tungsten (1,500 degrees C) from the not-quite-so-hot cooling water (a mere 200 degrees C). One idea is to focus on the so-called 'interlayer' between the tungsten armour and cooling structure.

The Brillo-pads team. © CCFE

 "We think the layer between the two surfaces has to be spongey, but also act as a thermal barrier as well as survive the high heat flux," Tom explains. "From our analysis it looks like a good material for the job is a kind of felt made from copper — a bit like a Brillo pad you'd use to clean your dishes."

The ‘Brillo pad' is part of a wider programme on DEMO divertor design which is funded through CCFE's Technology Programme. And this year, European fusion research consortium EUROfusion has awarded a team of labs including CCFE a five-year funding grant to work on concepts. CCFE has worked in this area since 2011 and results from computer modelling of the proposed design have been encouraging. The project has been run in close collaboration with KIT in Karlsruhe, Germany, and this partnership has so far culminated in the manufacture of new target ‘mock-ups' in Culham's Special Techniques workshops. The next step is a series of conductance experiments on a rig at CCFE before a full trial of mock-ups using high heat flux test facilities.

“The particle exhaust impacting the divertor is a lot of power to deal with over a relatively small area, and it all has to be removed from the reactor in a safe way,” says Tom. “So the divertor is a vitally important area of the plant's design, and we need a feasible solution. This project shows that even a small component, like the interlayer we're developing, can bring about significant gains in performance and play an integral part in putting fusion power on the grid.”