From February to July 2026, I had the opportunity to carry out my Master’s thesis at the Princeton Plasma Physics Laboratory (PPPL) in New Jersey, USA. This six-month internship marked the end of my Master’s degree in Nuclear Engineering, jointly organized by EPFL and ETH Zurich, and was partly made possible by the financial support of FuseNet.
My research focused on the transport of tungsten impurities in fusion plasmas. Tungsten has been selected for plasma-facing components in several magnetic-confinement fusion devices because of its favorable mechanical and thermal properties. However, if even a small quantity of tungsten reaches the plasma core, it can radiate a large amount of energy and reduce plasma performance. Understanding how tungsten moves through a turbulent plasma is therefore important for the operation of present and future fusion devices.
During my thesis, I studied how collisions between tungsten ions and the main plasma ions, deuterium, can affect this transport. These interactions had not previously been included in the gyrokinetic simulation code GX and had received relatively little attention. I first derived a new collision model from the Fokker–Planck equation and adapted it to the mathematical representation used by GX. I then implemented the model in the code and carried out several numerical tests to assess its convergence and consistency.
The new model was applied to plasma conditions based on the WEST tokamak in France. The simulations showed that collisions with deuterium can strongly modify the response of heavy impurities to plasma turbulence. In particular, the turbulent motion of deuterium ions exerts a frictional force on tungsten ions. Under the conditions investigated, this mechanism generated an inward tungsten particle flow. Such a flow may contribute to the accumulation of tungsten in the plasma core and should therefore be investigated in other plasma regimes.
Beyond the scientific results, my stay at PPPL was an extremely enriching experience. Working in an international research laboratory allowed me to meet scientists working on many different aspects of fusion and plasma physics. Seminars, group discussions and daily exchanges with researchers helped me gain a much broader understanding of the field. This project also taught me what life as a researcher can involve, from theoretical derivations and code implementation to the analysis of results and the writing of scientific documents. I could not have hoped for an experience that matched my expectations more closely.
Living in Princeton and meeting people from different countries made these six months equally valuable on a personal level. I am very grateful to my PPPL supervisor, Dr. Julien Dominski, to everyone at PPPL who contributed to this experience, and to all the friends I made outside work who made daily life so much more enjoyable.
