Dissipative Trapped Electron Mode Simulation In Tokamak

The gyrokinetic simulation using GTC is carried out for the dissipative trapped electron mode(DTEM),which is an important source for the electrostatic turbulence in the pedestal of tokamak plasmas.The DTEM instability is identified for the edge plasmas,and its dependence on the wavelength and collisional frequency is obtained by both simulation and theory.It is shown for the first time that the linear gyrokinetic simulation results are fully consistent with that from the analytic theory with edge parameters.This suggests that the GTC code can simulate accurately the DTEM instability in the pedestal.It provides a useful benchmark for verifying gyrokinetic simulation of edge plasmas.Electron turbulence induced by trapped electron mode has been widely studied.The dissipative trapped electron mode(DTEM)is an important candidate for tokamak edge turbulence.Nonlinear gyrokinetic particle simulations based on edge parameters are carried out to investigate the collisional effects on the nonlinear transport of DTEM turbulence.It is found the collisions can induce a low level radially inward electron transport for the DTEM turbulence,which is closely related to the phase difference between the radial turbulent motion and perturbed density fluctuation induced by collisional dissipation.We observe an inverse spectral cascade of the turbulence during the nonlinear DTEM saturation,which is caused by quasimode scattering induced by trapped electrons and important for determining the magnitude of turbulent transport.The nonlinear decorrelation time is found to be inversely proportional to the collisional frequency by gyrokinetic simulation,which is consistent with the predication of quasilinear theory.