Bounce-averaged gyrokinetic simulation of trapped electron turbulence in elongated tokamak plasmas

Plasma elongation effects on turbulence and zonal flow are explicitly investigated for the first time with global bounce-averaged gyrokinetic simulations for a collisionless trapped electron mode (CTEM). As the most efficient steady state turbulence simulation scheme for this problem, bounce-averaged gyrokinetic simulation provides deeper insights into nonlinear physics separated from the linear effects in the investigation. Based on studies for a limited range of parameters, our results show that shorter radial scale zonal flows which are prominent for CTEM are more enhanced with higher elongation leading to reduced transport. According to the single time radial correlation function, potential fluctuation exhibits two radial characteristic scales similar to previous gyrokinetic simulation and experimental measurements. A dual mode propagating in counter directions is observed with a stronger sheared zonal flow for higher elongation.