How to prepare the GYSELA-X code to future exascale edge-core simulations

Grandgirard, V.*; Asahi, Yuichi   ; Bigot, J.*; Bourne, E.*; Dif-Pradalier, G.*; Donnel, P.*; Garbet, X.*; Ghendrih, P.*

Core transport modelling in tokamak plasmas has now reached maturity with non-linear 5D gyrokinetic codes in the world available to address this issue. However, despite numerous successes, their predictive capabilities are still challenged, especially for optimized discharges. Bridging this gap requires extending gyrokinetic modelling in the edge and close to the material boundaries, preferably addressing edge and core transport on an equal footing. This is one of the long term challenges for the petascale code GYSELA [V. Grandgirard et al., CPC 2017 (35)]. Edge-core turbulent plasma simulations with kinetic electrons will require exascale HPC capabilities. We present here the different strategies that we are currently exploring to target the disruptive use of billions of computing cores expected in exascale-class supercomputer as OpenMP4.5 tasks for overlapping computations and MPI communications, KOKKOS for performant portability programming and code refactoring.