Author: Javier Maurino
Requested Type: Consider for Invited
Submitted: 2022-03-09 09:23:18
Co-authors: F.I. Parra, M. Barnes, I. Calvo, S.L. Newton
University of Oxford
Beecroft Building, Parks Road,
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 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. Furthermore, we show that this turbulent redistribution of momentum induces a current in up-down asymmetric geometries.
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. In up-down asymmetric geometries we are able to quantify the impact of the turbulence on current drive and show a small, but beneficial, increment to the total current. The examination of the evolution of the phase space under scans of the turbulent characteristics gives an intuitive understanding of the phenomena involved.
This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 — EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them.