Gyrokinetic simulations of turbulence in magnetic fusion plasmas using a delta-f PIC scheme with evolving background

Using the GKEngine code which simulates an electrostatic plasma with adiabatic electron response under a sheared-slab geometry, an attempt at developing a hybrid approach between the delta-f and full-f schemes to describe plasma profiles exhibiting high fluctuation amplitudes, where the assumption of the delta-f scheme breaks down will, be conducted. This is important as such a hybrid scheme has the flexibility to optimise noise reduction in the applicable plasma regimes, both in space (i.e. core or edge) and time (i.e. pre-burst or long-time relaxation). Accounting for a time-dependent background distribution function will modify the current linear quasi-neutrality equation, resulting in an additional non-linear term. Solution methods and optimised algorithms to do so will be tested. Next, a code to simulate the entire plasma profile should somehow merge both cases of open and closed field-lines. The code PICLS from IPP Garching was developed to describe a 1-dimensional plasma with open field-lines, solved using the full-f scheme with kinetic electrons. This is the code that will most probably be the base on which further features are to be added upon under the TSVV Task. The current work with the GKEngine which employs the delta-f scheme under closed field-lines configuration will serve as a test bed for new features, or could eventually be part of the final end-product. Features to be added that are relevant to this thesis include, firstly, the aforementioned delta-f to full-f transition mechanism. And secondly, the inclusion of both closed and open field-line regions in a simplified cylindrical geometry, with the goal of being able to simulate limiter configurations encompassing core and edge/SOL plasmas. Further features also include the GPU-enabling of PICLS for heavy computation, and the development of a non-linear polarisation equation solver. For the former, support will be searched from the future Advanced Computing Hub (ACH) of EUROfusion and, for the latter, the involvement of IPP Garching will be essential.