"Nonlinear Gyrokinetic Simulation of Zonal Fields and TAE in Fusion Plasmas"

 

 

ABSTRACT:  

 

Zonal electrostatic fields and corresponding zonal flows have been widely observed in experiments. It is believed that microscopic turbulence (usually electrostatic) can self-regulate itself through the nonlinear generation of zonal flows. Meanwhile, zonal magnetic fields and corresponding zonal currents have only been observed recently in experiments in the compact helical system (CHS), although a number of theoretical analyses have predicted its existence.  

The nonlinear simulation model of GTC has been revisited in order to make sure we are using the correct model. After comparison with three major nonlinear gyrokinetic frameworks, including Frieman-Chen's work (Frieman1982), White-Chance's work (White1984) and Brizrad-Hahm's work (Brizard2007), we found that there is a missing nonlinear term in the current GTC formulation, which is important especially to the calculation of zonal currents. 

Nonlinear simulation results with the corrected model confirms its influence on the zonal currents. In our simulation, zonal fields (both electric and magnetic) are nonlinearly forced driven, but not spontaneously excited by parametric instability predicted in a recent theory work (Chen2012). Zonal flow plays an important role in the nonlinear saturation mechanism of TAE, while zonal current is several order of magnitude smaller, thus has negligible effects. Simulation also shows an interesting nonlinear frequency chirping of TAE,  which is not observed in the experiment.