Simulating plasma turbulence with the global Eulerian gyrokinetic code GT5D. Numerical aspects

The efficiency of future fusion devices such as ITER is strongly affected by plasma turbulence, which produces outwards particle, momentum and heat transport. The most advanced tools to study such problems are gyrokinetic codes, which solve the Boltzmann-Maxwell system in five-dimensional phase-space. In this work, the gyrokinetic global Eulerian code GT5D is presented, focusing on the different numerical schemes and on the parallelization. Weak and strong scaling shows excellent scalability up to 104 processors. Finally, a straight-field-line solver is presented, which, for large plasma size, reduces the total memory by two orders of magnitude. Using Fourier transforms, this solver takes advantage of the alignment of turbulence with the magnetic field lines to reduce 3D turbulent fields to quasi-2D by filtering out non-aligned components. This procedure does not affect the steady state of GT5D simulations. Then, the code is applied to study the influence of plasma size scaling on plasma turbulence: worse-than-Bohm scaling is found for the first time in gyrokinetic simulations. (author)