Effect of turbulence on the neoclassical momentum fluxes*

Although the origin of the phenomenon is not fully understood, several experimental tokamak plasmas have been observed to rotate toroidally without any external input of parallel (i.e. approximately toroidal) momentum. This self-induced rotation can bring positive aspects to the tokamak design, such as the stabilisation of MHD tearing modes or the generation of an intrinsic current.

In this work, we study how parallel momentum fluxes can be driven by the effect of turbulence on neoclassical transport. We base our work on the path set by Parra and Barnes 2015, who proposed a form of the gyrokinetic equation which can account for characteristic eddies sizes ranging from the ion gyroradius to the ion poloidal gyroradius. This renders the equation self-consistent for neoclassical formulations and allows us to produce analytical predictions for the parallel momentum flux driven by the turbulence.

 

Our model has been implemented into a code that couples STELLA, a local δf gyrokinetic code, to SFINCS, a drift kinetic solver. The numerical results hold a significant resemblance to our analytical predictions. The examination of the evolution of the phase space under scans of the turbulent characteristics give further intuitive understanding of the phenomena involved.