Relocation is not much fun, at least for most of the people involved. But Thomas Morgan can hardly wait for his institute to finish moving from the small town of Nieuwegein to the Science Park of the Eindhoven University of Technology. Moving literally beams up the Dutch Institute for Fundamental Energy Research (DIFFER) thanks to several upgrades on its devices Magnum-PSI and Pilot-PSI.

“The delivery of the ion beam and the new magnet is very exciting for us and will offer many opportunities”, says Thomas Morgan, project leader for Advanced Divertor Concepts at DIFFER. The research of the Dutch institute covers Plasma Surface Interactions (PSI) which are part of the European Fusion Roadmap. Now, these devices set new standards with upgrades to their linear plasma generator, Magnum-PSI, and its older sister experiment, Pilot-PSI.

Thomas Morgan, project leader for Advanced Divertor Concepts at DIFFER. (Image: Bram Lamers/DIFFER)

Thomas Morgan, project leader for Advanced Divertor Concepts at DIFFER.
(Image: Bram Lamers/DIFFER)

Fluxes of ITER

The PSI devices at DIFFER aim to create ITER-like scenarios in order to test materials. In ITER, the constituents of the vessel must withstand extremely harsh conditions. “In existing fusion experiments we are unable to attain the conditions expected in ITER. Usually, we operate tokamaks with heat and particle fluxes which are much lower than that, and for timescales that are much smaller. To know how the plasma will affect the surface, we need a device which is able to replicate those high-flux and extended conditions”, explains Morgan. “Right now at DIFFER we can attain the conditions, but not the times.”

In order to operate under such settings, Magnum-PSI’s old copper magnets will be replaced with a superconducting one. This new system offers a stronger magnetic field and does not pose electrical resistance, meaning it keeps the plasma beam switched on for hours on end. Therefore the superconducting magnet will allow Magnum-PSI to explore long-term plasma effects for the first time. For example, the PSI facilities can operate in a pulsed mode on top of the steady state plasma, so that the experiments can mimic the energy outbursts of Edge Localised Modes (ELMs) that wall materials also face in real tokamaks. “Now we can easily create thousands, even millions of these ELM-like events in a reasonable time.”

Material testing in the vacuum

While many diagnostics monitor the plasma and surface evolution during exposure, identifying what is happening in the near-surface region, down to a few micrometres below the surface, is much more difficult. This is where the Ion Beam Facility comes into play, Morgan’s favourite part of the relocation. The new building offers space for this sort of additional large equipment that can be used with Magnum-PSI. DIFFER now owns a 3.5 MV singletron accelerator which was acquired second hand from the local company Accelerator Technologies BV in 2014. The singletron creates a thin stream of high-energy (MeV) ions which can non-destructively give information about what a material is made of and what elements it contains at different depths. This will be used to make insitu ion-beam analysis (IBA) measurements in Magnum-PSI after plasma exposure.

Stop and measure

Normally, scientists carry out the IBA process at a separate facility after they have completed their experiments. Magnum-PSI will improve on this by allowing measurements to be taken directly afterwards, or enabling the scientists to pause halfway through, measure, and then continue. In Pilot-PSI, it is planned to go one step further and carry out ion beam analysis at the same time as intense plasma exposure. “This novel combination allows us to monitor how the sample is changing as we are exposing it to these high flux plasmas”, describes Morgan. “This should open a lot of exciting new possibilities for experiments.”

EUROfusion experiments next summer

Now, the European research on plasma surface interaction can pick up pace. “In November, the tasks for the EUROfusion experimental campaign will be defined”, Morgan explains the next steps. This coming summer, Magnum-PSI will be restarted. By then the enhancements will have been installed and the experiments will have commenced. Researchers from the EUROfusion programme will be able to begin exploring how tungsten monoblocks behave on the long term.

DIFFER operates devices designed to meet EUROfusion’s requirements with regard to Plasma Surface Interactions (PSI), mentioned in Mission 2 of the European fusion roadmap: “heat-exhaust systems”. A device like this must be able to withstand the large heat and particle fluxes of a fusion power plant for a sufficient lifetime. Magnum-PSI and Pilot-PSI create such an environment and enable to study the interaction between the plasma and the surface of the vessel.