Probe eyes interactions in nuclear fusion reactors

A new probe tool could help in understanding the interactions between plasma and vessel walls in nuclear fusion reactors as they happen in real time.

It is hoped the probe could help inform the design of new materials for reactor vessels — one of the major stumbling blocks for producing viable fusion energy.

‘Currently we don’t have the materials needed to sustain these large plasma and thermal fluxes,’ said Jean Paul Allain, a nuclear engineer at Purdue University who supervised the design of the probe. ‘Some completely break down and melt. We need to understand how to operate and control the wall itself and the plasma together as they interact.’

In a tokamak nuclear fusion reactor, a doughnut-shaped ring of plasma is held in place by powerful magnets within a reactor vessel.

Scientists have historically used ‘wall conditioning’, on the inside of the vessel by applying thin films of materials to induce changes to plasma behaviour.

The effects of plasma on surface materials are then investigated by removing test specimens from the lining after a year of running the reactor. This approach shows only the cumulative results of hundreds of experiments, whereas scientists would prefer seeing the fine details associated with individual experiments.

‘It’s been primarily an Edisonian approach,’ Allain said. ‘We don’t know what mechanisms are primarily at work and we need to if we are going to perfect fusion as an energy technology.’

The materials analysis particle probe, or MAPP, that Allain’s team has designed will be connected to the underside of the tokamak.

It will allow scientists to study how specific materials interact with the plasma and yield data within minutes after completing an experiment. Data from the analyses would be used to validate computational models and guide design of new materials.

’It’s a new type of surface-analysis diagnostic system designed to be integrated in a tokamak.The device is completely remote controlled, in principle from anywhere in the world,’ Allain said.