In gyrokinetic plasma simulations, such as those performed with the GyselaX code [1,2], a Poisson-type equation must be solved on poloidal cross-sections of tokamak geometries. The presence of curved boundaries poses challenges for both geometric accuracy and solver efficiency. A natural modeling approach relies on curvilinear meshes; however, this requires transforming the Poisson operator into curvilinear coordinates, which typically introduces strong anisotropies and complicates the design of efficient multigrid solvers [3]. In this work, we investigate an alternative approach based on unstructured discretizations posed on tokamak cross-sections, combined with a multigrid solver enhanced by an implicit extrapolation technique. The method relies on a linear finite element discretization, while the linear system and right-hand side are modified according to an extrapolation rule. For elliptic finite element systems on polygonal domains, this approach can be interpreted as a defect-correction multigrid scheme that mimics a higher-order discretization when using appropriate quadrature rules. To further improve geometric consistency on curved domains, we incorporate isoparametric mappings into the extrapolation procedure. This approach avoids the implementation complexity of fully optimized higher-order isoparametric finite element discretizations, while preserving multigrid efficiency and improving solution accuracy on non-polygonal domains. REFERENCES [1] V. Grandgirard, J. Abiteboul, J. Bigot, T. Cartier-Michaud, N. Crouseilles, et al. A 5D gyrokinetic full-f global semi-lagrangian code for flux-driven ion turbulence simulations. Computer Physics Communications (2015) pp. 35-68, doi: 10/1016/j.cpc.2016.05.007 [2] E. Bourne, V. Grandgirard, Y. Asahi, J. Bigot, P. Donnel, et. al.. Gyselalib++: A portable c++ library for semi-lagrangian kinetic and gyrokinetic simulations. J. Open Source Software, 10 (2025), pp. 8582-8582. Doi: 10.21105/joss.08582 [3] M.J. Kuehn, C. Kruse, U. Ruede. Implicitly extrapolated geometric multigrid on disk-like domains for the gyrokinetic Poisson equation from fusion plasma applications. Journal of Scientific Computing 91.1 (2022), pp. 1–27. doi: 10.1007/s10915-022-01802-1.