New materials to make fusion feasible

New technologies also often require new materials to cope with the demands engineers are placing upon them. It’s a bit like the new generations of steels and casting methods that accompanied the invention of the steam engine. And in the case of nuclear fusion, the extreme operating conditions, and the high energy of the plasma at the heart of the process, means our present generation of materials can’t cut it, and we need to discover where they are vulnerable and how to make better ones, as Dr Andy London explains to Evelyna Wang…

Andy - There have been some really interesting results from JET. We're really interested there in the impact of the plasma on the wall, and that causes a number of different processes. It can cause erosion where you are removing the material, but the material which can be removed is also deposited. Sometimes that's in a very similar area; You have this erosion deposition process dynamically happening all the time. In other places there's parts of the reactor where you have lots of erosion and places where you have a lot of deposition. If we take a cross section through the material, you can see different layers and those almost correspond to different experiments in jets. Different pulses and different conditions that were run is almost like sectioning through a tree and looking at tree rings; You can see different levels of deposition that happened with certain run parameters. There we're really trying to understand what's the influence of how we're running the reactor on the materials surface's performance. We're looking there at the chemical structure, we're looking at the mechanical property change, because that tells us about how the components will perform, and ultimately feeding into the design of new materials that will be more resilient and help the reactor to run better and for longer.

Evelyna - What's an example of a new material if I'm allowed to ask?

Andy - Yeah, of course. One of the really interesting areas that we're looking at is materials that can withstand really high heat loads. You don't want your material to melt and you don't want it to sputter away. Tungsten is one of the main materials that we've used, but it has some disadvantages, it's quite a brittle material. We are looking at ways of basically making Tungsten more ductile. Instead of it bending and it cracking, which is bad from an engineering perspective, you don't want a component to bend and crack. Ideally you'd want it to bend and then just change shape, then you know that it's failed. You don't want it to crack open because that would be very bad. We can take basically the same principles of other areas of engineering. In composite materials, you can make fibre composites and when you make materials much smaller, you can make them tougher effectively, making Tungsten fibre composite materials. Even within Tungsten in these little fibres, that makes the whole material structure much stronger and much more ductile. Now we're looking at, when you then irradiate that with neutrons, when it has damage, when it has transmutation and it changes from one material into another, do you still get those same good properties and what happens when you expose that with a plasma. Does having these extra fibres in there mean you don't have a smooth surface. Does that mean you get more interaction with the plasma or less? And those are the kind of things that we're looking at.