Abstract: Advances in understanding and modelling kinetic electrons in tokamak exhaust
Electrons play a crucial role in transporting energy leaving the core of tokamaks to the divertors; the component responsible for absorbing the charged-particle, power outflows. This parallel transport of highly magnetized electrons along the open magnetic field lines in the scrape-off layer (SOL) sets the fastest timescale for determining temperature and pressure profiles along the field lines, which in turn sets the environment in which SOL ion turbulence occurs. The collisionality of electrons can be low, such that Braginskii transport and heat flow is inaccurate and kinetic corrections are crucial. This will only become more so moving to reactor scale. However, the bulk of exhaust system design is conventionally performed with fluid codes.Developments in SOL kinetic modelling via Vlasov-Fokker-Planck (VFP) codes and understanding gained from them will be discussed. Codes include SOL-KiT [1] originally developed at Imperial and its successor ReMKiT1D [2] at UKAEA. Recent progress in improving the magnetic topology supported by our kinetic codes will be presented. Advances in physics understanding include the influence of electron kinetic effects on SOL profiles and sheath boundary conditions [3] particularly during transients such as ELMs [4]. The non-Maxwellian electron distributions that arise also affect the interaction of plasma with the cloud of “recycled” neutral deuterium atoms emitted from divertor surface and even more so, higher-Z impurities [5]. The implications of these findings on detachment will be discussed.