Fusion in Europe (FiE): How are you able to model something as complex as plasmas?

Marie-Line Mayoral (MLM): It takes very powerful codes which we’ve been developing for years. Codes were initially built to explain what happened during an experiment. With each new experiment we learned something new which we built into the codes. They have evolved to the point where we can now model expected results ahead of an experiment.

FiE: How does this help?

MLM: Modelling helps predict what we will have to deal with. Take runaway electron beams for example. They have a lot of energy and can make holes in the machine’s wall if not properly contained. If the modelling predicts runaway electron beams we can mitigate their effects and even avoid them. This helps us avoid costly repairs and downtime. Modelling will become even more important with ITER as a nuclear facility. Its plasmas will be so powerful that predicting the plasma’s energy, the behaviour of runaway elec­trons and the power load on the wall will be essential.

FiE: Could modelling replace the need to run experiments someday?

MLM: It is not clear yet if it could replace experiments but it can help to optimise experiments. The better a code becomes the more confidently we can predict what will happen to the plasma in different machines under different conditions. We are also extrapolating data from one machine to another and most importantly to ITER.

FiE: Who writes these codes?

MLM: For the most part physicists or engineers are writing codes. My boss, Xavier Litaudon, started a unit of software engineers called the EUROfusion Theory and Advanced Simulation Coordination initiative (ETASC). They write and modify the codes purely to reduce run-time, which saves a lot of money. Before EUROfusion the labs worked independently. By pooling resources, sharing codes and optimizing run-times, member labs can model far more efficiently.

FiE: What progress was made in 2018?

MLM: In 2018 we used modelling to optimise the preparation of the second D-T campaign at JET when factoring in cost, radioactivity and the extra safety required. This was a major decision. A lot has changed since the first D-T campaign back in 1997 (DTE1). JET now has enhanced heating, real-time networks and an ITER ­like wall made of beryllium with a tungsten -clad divertor. Our diagnostics have developed a lot since then, enabling us to capture far more data. And advances made in supercomputing let us do far more with this data than ever before. Based on the model’s predictions, we have simulated the range of fusion powers that could be reached in 2020.

FiE: What did the modelling predict?

MLM: The modelling shows that running a second D-T campaign (DTE2) at the upgraded JET facility is feasible and will help us better understand the neutrons and alpha ­particles produced. These are the key learnings we want to add to our codes and extrapolate to ITER. It also predicts 10 to 17 megawatts of output power that could be sustained for up to 5 seconds producing a record of fusion energy - which is a product of power times duration. In addition to the performance, our aim is to improve our understanding of the burning plasma with a sufficient fraction of alpha­heating. To quote Xavier, “(with DTE2) ...we are aiming for stability rather than peak performance. And we will be operating in ITER-like conditions.”

FiE: How does this support EUROfusion in reaching its goals?