(TH/P8-30) Global Nonlinear Simulations of Ion and Electron Turbulence Using a Particle-In-Cell Approach

S. Jolliet1), B.F. McMillan1), T.M. Tran1), X. Lapillonne1), L. Villard1), A. Bottino2), P. Angelino3)
 
1) Centre de Recherches en Physique des Plasmas, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
2) Max Planck Institüt für Plasmaphysik, IPP-EURATOM Association, Germany
3) DRFC, Association EURATOM, CEA Cadarache, 19018 Saint-Paul-Lez-Durance, France

Abstract.  Understanding turbulence driven by micro-instabilities such as Ion Temperature Gradient (ITG) or Trapped Electron Modes (TEM) is one of the key issues to accurately predict the performance of future Tokamak devices such as ITER. Simulations with gyrokinetic codes require extremely large computer resources, especially for TEM turbulence where the fast electron time scale needs to be resolved simultaneously with the ions time scale. So far, physical studies of TEM turbulence have been essentially obtained using the flux-tube approach but very little is known on global TEM turbulence. This work presents global nonlinear simulations performed with the Particle-In-Cell code ORB5. In order to counteract profile relaxation due to the turbulent transport, a heat source in combination with a noise control algorithm has been implemented in the code, which restricts the accumulation of numerical noise in the system, and allows long simulations to be run which reach a quasi-steady state. The electron model retains kinetic trapped electrons but considers Boltzmann passing electrons. The reliability of TEM simulations will be addressed both numerically and physically by a careful look at the numerical noise and the late time fluxes. While in ITG turbulence, the main saturation mechanism is the E×B shearing due to the zonal flow, the main saturation mechanism for TEM turbulence is still unclear and, according to flux-tube simulations, seems to depend on the physical parameters. Global simulations of TEM turbulence at moderate rho-star with Cyclone-like parameters will be presented. Results will be compared with GENE flux-tube simulations for different equilibrium gradients values. The second part of this work will focus on the rho-star scaling for ITG turbulence. Gyrokinetic simulations predict a transition of the transport from Bohm to Gyro-Bohm, but results are still controversial. With the help of the noise control algorithm, nonlinear simulations with heat sources and noise control are performed in which quasi-steady state values of the ion diffusivity and temperature gradients are obtained in order to study such transition.

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