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任洋研究员报告
2017-04-03
聚变理论与模拟中心
title about: Exploring the Regime of Validity of Global Gyrokinetic Simulation with Spherical Tokamak Plasmasspeaker: Dr. Yang RenTime: Thursday, April 6th, 02:00 pmVenue: Rm. 413, Bld. 11#, Yuquan Campus题目：Exploring the Regime of Validity of Global Gyrokinetic Simulation with Spherical Tokamak PlasmasAbstract Plasma turbulence is considered one of the main mechanisms for driving anomalous thermal transport in magnetic confinement fusion devices. Based on first-principle model, gradient-driven gyrokinetic simulations have often been used to explain turbulence-driven transport in present fusion devices, and in fact, many present predictive codes are based on the assumption that turbulence is gradient-driven. However, using the electrostatic global particle-in-cell Gyrokinetic Tokamak Simulation (GTS) code [1], we will show that while global gradient-driven gyrokinetic simulations provide decent agreement in ion thermal transport with a set of NBI-heated NSTX H-mode plasmas, they are not able to explain observed electron thermal transport variation in a set of RF-heated L-mode plasmas, where a factor of 2 decrease in electron heat flux is observed after the cessation of RF heating. Thus, identifying the regime of validity of the gradient-driven assumption is essential for first-principle gyrokinetic simulation. This understanding will help us more confidently predict the confinement performance of ITER and future magnetic confinement devices. The work is supported by DOE and computational resource is provided by NERSC.[1] W.X. Wang et al., Phys. Plasmas 17, 072511 (2010)
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李罗权院士报告
2017-04-03
聚变理论与模拟中心
Title about: Generation of helium and oxygen EMIC waves by the bunch distribution of oxygen ions associated with fast magnetosonic shocks in the magnetosphere Speaker: 李罗权院士,Institute of Earth Science, Academia Sinica, Nankang, Taiwan Time: Thursday, April 6th, 3:30pmVenue: Rm. 413, Bld. 11#, Yuquan CampusAbstract: Electromagnetic ion cyclotron (EMIC) waves are often observed in the magnetosphere with frequency usually in the proton and helium cyclotron bands and sometimes in the oxygen band. The temperature anisotropy, caused by injection of energetic ions or by compression of magnetosphere, can efficiently generate proton EMIC waves, but not as efficient for helium or oxygen EMIC waves. Here we propose a new generation mechanism for helium and oxygen EMIC waves associated with fast magnetosonic shocks, which are observed in the magnetosphere. These shocks can be associated with either dynamic pressure enhancement or shocks in the solar wind and can lead to the formation of a “bunch” distribution in the perpendicular velocity plane of oxygen ions. The oxygen bunch distribution can excite strong helium EMIC waves and weak oxygen and proton waves. The dominant helium EMIC waves are strong in quasi-perpendicular propagation and show harmonics in frequency spectrum of Fourier analysis. The proposed mechanism can explain the generation and some observed properties of helium and oxygen EMIC waves in the magnetosphere.
