Numerical Simulation Research On Turbulence In Tokamak Plasmas

Turbulence can lead to the particle transport perpendicular to the magnetic fields in plasmas and destroy the confinement of particles by magnetic fields in Tokamak,which is bad for the sustained burning of plasmas and also harmful to the device itself.The Ion Temperature Gradient(ITG)mode and Trapped Elec-tron Mode(TEM)turbulence are believed to be two important plasma turbulence.In D?-D Tokamak,the ITG and TEM turbulence are observed in the#142358 and#142371 discharges,respectively.The radial correlation lengths of the tur-bulence,the relative electron density fluctuation intensities,and the energetic particle transport induced by the turbulence are almost the same in the two shots.The electrons were heated through the Electron Cyclotron Resonance Heating in the later shot,leading to the electron temperature about two times larger than that in the former shot with the other plasma parameters almost the same.To explain the experimental results,large-scale parallel Gyrokinetic Toroidal Code(GTC)is applied to carry out the simulations to do comparisons with the experimental re-sults.Two groups of experimental equilibrium data are loaded in GTC to carry out the numerical simulations,respectively.The main contents are as follows.1.In the first step,the numerical simulations with and without collisions are compared in the lower and higher Te plasmas to analyse the collisional effects on the turbulence.In the linear simulations,the growth rates of the drift waves are decreased by the collisions compared to the collision-less simulations in the two simulations.And the collisions can induce the transition of the drift wave regime from the TEM-dominant instability to the ITG-dominant instability in the lower Te plasma.The zonal flows are excited by the microturbulence and act as a modulation mechanism for the microturbulence in the nonlinear simulations.Microturbulence can excite high frequency zonal flows in the collisionless plasmas,which is in agreement with the theoretical work.In the lower Te plasma,the colli-sions decrease the microturbulence in the nonlinear saturated stage com-pared to the collisionless simulations,which is beneficial for the plasma confinement.In the higher Te plasma,the final saturated microturbulence shows almost no change.2.Furthermore,ITG and TEM microturbulence are compared in the lower and higher Te plasmas,which are also compared and analyzed with the experimental results.The dominant mode wavelengths of the perturbed potential increase when evolving from the linear to nonlinear stages in both simulations,with the fluctuation energy transferring from the lin-early dominant modes to the nonlinearly dominant modes.The turbu-lence intensities,the relative electron density fluctuation intensities,the radial correlation lengths,and the energetic particle transport induced by the turbulence are almost the same in the nonlinear saturated stages in the two simulations,which are consistent with the experimental result-s.The radial correlation lengths are about 3.8pi(2.3cm)for the ITG mi-croturbulence and 4.3pi(2.6cm)for the TEM microturbulence,which are consistent with the experimental results of the radial correlation length?c(?=0.65cm)>2cm in both cases.The electron density fluctuation intensities in the radial domain are around the same in the lower and high-er Te plasmas,which are also agreeable with the experimental values.