Stellarators are advanced magnetic confinement devices designed for plasma fusion research. Understanding and controlling impurity transport within the stellarator environment is crucial for optimizing plasma performance and maintaining the stability of the fusion process. This research project aims to make important steps towards a comprehensive simulation model to study the transport of impurities in a stellarator, with the ultimate goal of enhancing the efficiency and reliability of future fusion reactors. The primary objectives are to develop a numerical model for simulating collision-driven impurity transport in a geometry close to the complex magnetic geometry of a stellarator, to investigate the impact of various plasma parameters, magnetic configurations, and to identify and analyze potential mechanisms influencing impurity confinement in a stellarator plasma.

To this end, the Gysela is a gyrokinetic code developed at CEA-IRFM, parallelized and exploited on supercomputers. It is able to describe both kinetic ions and kinetic trapped electrons. It was initially developed to describe the plasma behavior in the core of a tokamak where the magnetic configuration is 2D. Recently, it was upgraded to model toroidal variations of the magnetic field strength, and applied to study effects of ripple in a “quasi-2D” configuration. In a stellarator, the magnetic configuration is fully 3D. The goal of this project is to take a step towards full-3D geometry by incorporating in the code a magnetic strength that depends on the three dimensions in space, in a way as close as possible to that of typical stellarators, while the vector itself will remain 2D. Full 3D modelling will be left for future work. The outputs of the code will be benchmarked on the very few codes capable to handle full 3D geometries, notably the local code NEO devoted to neoclassical transport.

Using the Gysela code, which has the advantage of being global and flux-driven, could shed light on the following:

• Steady-state or quasi-steady-state modeling of the impurities: density and temperature profiles of lithium, tungsten, alpha and Helium ashes.
• Quantification of diffusivities and other impurity transport coefficients.
• Modeling and parametrizing their dependence on field, density, and aspect ratio.

The research will combine numerical simulations, theoretical analysis, and experimental validation:

• Numerical simulations: use the state-of-the-art plasma simulation code GYSELA to model impurity transport in stellarator-like configurations. Incorporate 3D magnetic field magnitude configurations and plasma profiles.
• Theoretical analysis: develop analytical models to gain insights into the fundamental physics governing impurity transport and identify key parameters influencing impurity behavior.
• Experimental validation: collaborate with experimental stellarator facilities to compare simulation results with observations, validating the accuracy and reliability of the developed model.

The candidate has knowledge and experience in tokamak plasma physics – in particular regarding neoclassical transport, gyrokinetic theory and the use of high performance computing numerical codes. Knowledge in stellarator physics is desirable although not mandatory.

She/he is able to work in collaboration with several researchers of different expertise, including other physicists, applied mathematicians, numerical developers and experts in parallelization.

In line with CEA's commitment to the integration of disabled people, this position is open to all. The CEA offers accommodation and/or organizational possibilities for the integration of disabled workers.