Gyrokinetic flux-driven simulations in mixed TEM/ITG regime using a delta-f PIC scheme with evolving background

TL;DR

This paper introduces an adaptive delta-f PIC scheme for gyrokinetic simulations that uses a time-evolving background to accurately model plasma turbulence over long periods, reducing noise and computational cost.

Contribution

The paper presents a novel adaptive background scheme in delta-f PIC simulations that maintains low noise and improves convergence in long-term turbulence modeling.

Findings

Adaptive scheme reduces sampling noise over long simulations.

Allows convergence with fewer markers.

Maintains accuracy in quasi-steady state profiles.

Abstract

In the context of global gyrokinetic simulations of turbulence using a Particle-In-Cell framework, verifying the delta-f assumption with a fixed background distribution becomes challenging when determining quasi-steady state profiles corresponding to given sources over long time scales, where plasma profiles can evolve significantly. The advantage of low relative sampling noise afforded by the delta-f scheme is shown to be retained by considering the background as a time-evolving Maxwellian with time-dependent density and temperature profiles. Implementation of this adaptive scheme to simulate electrostatic collisionless flux-driven turbulence in tokamak plasmas show small and non-increasing sampling noise levels, which would otherwise increase indefinitely with a stationary background scheme. The adaptive scheme furthermore allows one to reach numerically converged results of quasi-steady state with much lower marker numbers.