Non-perturbative effects of EP on mode structure Symmetry breaking and EP transport——讲座通知

2022-12-06 14:47




Abstract: Energetic particles (EPs) are known to change the properties of shear Alfvén waves in tokamaks, and for this reason non-perturbative models have to be used to describe their linear and non-linear evolution. In this work, mode structures distortion with symmetry breaking properties featured by a finite radial wave phase velocity due to EP effects are considered. A mode structure of the form A(s) = exp[-σ (s-s0)^2] with complex parameters σ and s0 is used, to describe not only the width (∝ 1/√Re{σ}) and the mean location (Re{s0}) of the bell-shaped radial structure, but also the radial phase variations (Im{σ}, Im{s0}), where s is the normalized radial coordinate. The values of (σ, s0) are fitted from the results given by the gyrokinetic eigenvalue code LIGKA. The impact on EP transport is investigated using the drift-kinetic code HAGIS. The effects of the mode structure symmetry breaking on the mode saturation level and the EP transport are analysed. In the presence of mode structure symmetry breaking which is relevant to the simulation and experimental observations, the growth rate as well as the particle and energy transport level can vary by ~10%. The velocity-space averaged parallel velocity of EPs in the inner region s = 0.2-0.5 can change its sign for different mode structures, demonstrating the importance of the mode structure symmetry breaking on EP toroidal velocity reversal. This large effect (~100%) on the mean parallel flow could have implications for EP current drive and the transport in the burning plasmas.

The more self-consistent simulations are carried out following, the gyrokinetic eigenvalue code LIGKA, the drift-kinetic/MHD hybrid code HMGC and the gyrokinetic full-f code TRIMEG-GKX are employed to study the mode structure details of reversed shear Alfvén eigenmodes (RSAEs). Using the parameters from an ASDEX-Upgrade plasma, a benchmark with the three different physical models for RSAE without and with EPs is carried out. Reasonable agreement has been found for the mode frequency and the growth rate. Mode structure symmetry breaking (MSSB) is observed when EPs are included, due to the EPs' non-perturbative effects. It is found that the MSSB properties are featured by a finite radial wave phase velocity, and the linear mode structure can be well described by the analytical complex Gaussian expression Φ(s) = exp[-σ (s-s0)^2] with complex parameters σ and s0. The mode structure is distorted in opposite manners when the EP drive shifted from one side of ${q}_{\min }$ to the other side, and specifically, a non-zero average radial wave number 〈ks〉 with opposite signs is generated. The initial EP density profiles and the corresponding mode structures have been used as the input of HAGIS code to study the EP transport. The parallel velocity of EPs is generated in opposite directions, due to different values of the average radial wave number 〈ks〉, corresponding to different initial EP density profiles with EP drive shifted away from the ${q}_{\min }$.


报告人:孟果,北京大学博士,期间在PPPL联合培养访问一年半。现德国马克斯普朗克等离子体物理研究所博士后。主要从事托卡马克中高能量粒子物理方面的研究。国际托卡马克ITPA高能粒子物理专题组expert,参与Eurofusion enabling Research项目MET, ATEP