A gyrokinetic model for the tokamak periphery

Despite significant development over the last decades, a model able to describe the tokamak periphery region extending from the edge to the far scrape-off layer is still missing. In this work, we present a new gyrokinetic model that retains the fundamental elements of the plasma dynamics at the tokamak periphery, namely electromagnetic fluctuations at all scales, comparable amplitudes of background and fluctuating components, and a large range of collisionality regimes. Such model is derived within a gyrokinetic full-F approach, describing distribution functions arbitrarily far from equilibrium, and projecting the gyrokinetic equation onto a Hermite-Laguerre velocity space polynomial basis, obtaining a gyrokinetic moment hierarchy. This extends a previously derived electrostatic drift-kinetic moment hierarchy to the electromagnetic gyrokinetic regime. The treatment of arbitrary colisionalities is performed by expressing the full Coulomb collision operator in gyrocentre phase space coordinates, and providing a closed formula for its gyroaverage in terms of the gyrokinetic moments. In the electrostatic high collisionality regime, the novel hierarchy reduces to an improved set of drift-reduced Braginskii equations which have been widely used in scrape-off layer simulations.