Task Force Leaders Piero Martin, Marc Beurskens and Hendrik Meyer plus ASDEX Upgrade’s technical project leader Arne Kallenbach review this first MST1 campaign. (Ed. note: The other two MST1 Task Force Leaders Stefano Coda (CRPP) and Thomas Eich (IPP) were not present.) We were just talking about the fact that EUROfusion’s scientific interests sometimes took the machine to the limit, thus leading to quite powerful disruptions. (Ed. note: During a disruption the plasma thrusts all its energy rapidly onto the vessel wall.) The Task Force Leaders were just appreciating Arne’s and IPP’s openness for these challenging experiments when the news comes in that a tile appears to have fallen off the wall during last Friday’s disruption, thus putting an end to this day’s experiments at least. But despite the damage to the machine and that fact that the Task Force Leaders need to strike today’s experiments off their list, the atmosphere is filled with comradeship. They all think that taking risks in today’s experiments is a necessity to ensure a safe operation of ITER. It is this productive atmosphere within the MST1 team and between it and its host, the ASDEX Upgrade team that has been a key element of the conversation. (Ed. note: The tile has since been replaced and the machine inspection has shown that the vessel was otherwise in good shape.) We are looking back at 40 experimental days, during which about 300 scientists from all over Europe were working on ASDEX Upgrade.

What is your verdict after this very first MST1 campaign?

From left: Mike Dunne, Thomas Pütterich, Eleonora Viezzer, Hans-Werner Müller and Hendrik Meyer

From left: Mike Dunne, Thomas Pütterich, Eleonora Viezzer,
Hans-Werner Müller and Hendrik Meyer

MARC: “Considering that this is a totally new organisation, things have gone rather well. We have dealt with a large group of new scientists, which none of us had really expected. And we had very clear ideas of what we wanted to achieve, although we only had a few weeks to design the scientific programme, and this really contributed to the good progress we made.”
ARNE: “Especially at the beginning, training these new people was quite a burden on all of us. But next year, we will be able to benefit. We also need to design the experimental programme to permit more contingency time.”
PIERO: “I think that this large number is a success. It not only reflects the way Europe now organises and funds fusion research, it also tells us that we designed an attractive science project. We hope that colleagues from all the labs will feel more and more at home in the MST experiments.”

Are you happy with the scientific work that was done?

From left: Hendrik Meyer, Marc Beurskens, Arne Kallenbach, Piero Martin

From left: Hendrik Meyer, Marc Beurskens, Arne Kallenbach, Piero Martin

MARC: “In my area, which is the investigation of confinement in metal wall fusion devices, we made good progress. Experiments with the JET ITER-Like Wall showed that plasma confinement was, in some cases, up to 40 percent lower than with the same plasma and a carbon wall. Similar but not so extreme findings had been made at ASDEX Upgrade. We knew it was possible to recover the confinement by seeding impurities into the plasma, but we did not quite understand why. In MST1, using experiments comparing deuterium-methane and nitrogen seeding, we have confirmed that the absence of carbon in a metal wall device may lead to a confinement reduction. We also took a detailed look into the role of other impurities, such as helium and krypton, on the confinement. These are key experiments for future fusion reactors.”
HENDRIK: “Investigating ELM mitigation via magnetic perturbation fields made good progress, too. We benefitted from the fact that people from various machines in which such experiments had been conducted came together at ASDEX Upgrade. Everyone involved said that they really benefitted from this part of the programme.” (Ed. note: Edge Localised Modes (ELMs) are potentially harmful plasma edge instabilities.)
ARNE: “Each machine had different explanations for ELM mitigation, but these did not always match. This very complicated situation is starting to become clearer because people from different machines have worked together and exchanged their views. We now know what measurements to do and, at some point, we will hopefully be able to better predict how such perturbation coils will work for ITER.”
PIERO: “Runaway electrons are another topic. They develop during a disruption, it is difficult to slow them down and when they hit the wall in a strong, collimated beam they may cause considerable damage. Disruptions and runaways are a big concern for ITER and their study is a high priority for us.”
ARNE: “… which is challenging for the machine operator, because these electrons are really quite dangerous. We were not particularly keen on doing this experiment (everyone laughs) but the pressure from ITER really convinced us to try it. I am quite happy that we found a scenario which is manageable, reproducible and not so harmful for ASDEX Upgrade.”
MARC: “We’ve also done some smaller experiments, such as helium transport. Those are important for deuterium and tritium plasmas, which ITER will use in its activated phase. D-T fusion produces helium and the problem is how to remove it, because it may not be allowed to dilute the plasma. We’ve done some nice transport experiments to study the profile of helium and how quickly it dissipates. Surprisingly, we found that the helium profile shape followed the electron profile shape. That’s not explained by the theories and now we have a lot of questions to answer. This experiment only obtained a couple of shots but has already produced some nice results.”

WITHIN THE MEDIUM SIZE TOKAMAK PROJECT, three national fusion devices — ASDEX Upgrade (IPP), MAST (CCFE) and TCV (CRPP) — make experimental time directly available to the EUROfusion consortium. In a way, these laboratories hand over their machine to a group of European scientists who conduct experiments necessary to pursue the Fusion Roadmap. All this is done under the management and guidance of the Project Task Force Leaders and the host machine’s team.