题 目：Effects of zonal structures on the nonlinear saturation of energetic particle driven Alfven eigenmodes
报告人：陈杨 (美国科罗拉多大学研究员，APS fellow)
时 间：2017年3月17日（星期五） 10:00—11:00
Zonal flow is known to play an important role in drift-wave turbulence, but its effect on energetic particle (EP) driven Alfven eigenmodes (AE) is yet to be understood. For near-marginal Alfven instabilities it is widely believed that the dominant nonlinear effect is the trapping of resonant particles in the wave field and the flattening of the EP distribution function in the resonance region. As the instability becomes stronger, zonal structures are expected to be more important. Here we use the gyrokinetic Particle-in-Cell code GEM to study the interaction between a driving EP driven n=4 instability and the n=0 mode. Ions are gyrokinetic, but a fluid model is used for electrons. The trapping scaling of the n=4 mode amplitude A, sqrt(A)~growth rate, is observed as the growth rate decreases, indicating that the zonal structure is not important. However, it is important to include the zonal structures in the simulation. Excluding the n=0 mode altogether from the fields leads to wrong scaling. This paradoxical observation is explained with the collisionless damping of the zonal flows. Results with kinetic electrons will also be reported.