The objective of the position is to address turbulent transport issues in non-axisymmetric configurations representative of current stellarators, in view of their better characterization and, ultimately, of their possible optimization. Very few first principle numerical codes can handle such complex geometries within the relevant 5-dimensional gyrokinetic description. The full-f and flux-driven code Gysela was initially developed to study turbulence and transport in the core of tokamak plasmas. Recently, simulations were extended to non-axisymmetric magnetic configurations by accounting for a sinusoidal perturbation of moderate magnitude in the toroidal direction of the magnetic field strength, its vector direction remaining axi-symmetric. The idea is to extend these types of simulations to account for a broad spectrum of magnetic perturbations of larger magnitude reminiscent of stellarators.

 In the proposed work, particular emphasis will be given to the two main characteristics of the stellarator project of Renaissance Fusion, namely the large magnetic field strengths permitted by high temperature superconductors and the relatively small aspect ratio geometry. As a side effect of the large B field, such plasmas are also expected to achieve high densities, regimes that should be therefore explored. A staged approach will be adopted for the work plan, so as to build up a comprehensive understanding of the role of the various scanned parameters:

• Experimental scaling laws of the energy confinement time in tokamak plasmas are inconclusive regarding the sign of the exponent of the aspect ratio R/a. Exploring the impact of R/a in axisymmetric configurations would already be instructive.
• Identify a few characteristic spectra of 3D magnetic perturbations that would be reminiscent of current stellarator configurations. Compare their turbulence characteristics and associated transport in various regimes, including simulations with fully adiabatic and hybrid (trapped kinetic) electron response.
• Perform a scan in magnetic field strength B and density N. The resulting transport level could be analyzed in terms of the critical dimensionless parameters rho*~1/B and nu*~N and compared to the international stellarator scaling law ISS04.

The candidate has knowledge and experience in tokamak plasma physics – in particular regarding neoclassical and turbulent 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.