Multiscale Modelling of Large-Amplitude Fluctuations in Tokamak Edge Plasmas
Examensarbete för masterexamen
Physics and astronomy (MPPAS), MSc
For the efficient and safe operation of magnetic confinement fusion reactors, reliable theoretical descriptions of the dynamic behaviour of the confined plasma are required. One proven, highly successful description is gyrokinetics, which describes small amplitude turbulence in the core plasma. However, this description is expected to break down in the plasma edge, in the presence of large fluctuations and an extremely steep pressure gradient. Attempting to capture these edge conditions, in this thesis we use multiscale analysis to produce a new set of equations we collectively refer to as Toroidal Kinetic Reduced MHD (TKRMHD). These equations, suitable for describing ITG-like turbulence, are fully kinetic, applicable in general field confinement configurations, and capable of describing the collisional to weakly-collisional transition. As such this description constitute a first step towards a first-principle description of L-mode tokamak edge turbulence. In this thesis we furthermore demonstrate that the TKRMHD equations can be smoothly matched onto gyrokinetics through an intermediary set of equations, derived from suitable subsidiary multiscale expansions. This is important because gyrokinetic tokamak transport simulations strongly depend upon density and temperature edge boundary conditions. This new matching may make it possible to choose these conditions reliably, instead of relying on ad-hoc assumptions.
Fysik , Physical Sciences