10月23日 Anomalous emission and absorption of microwaves in ECRH experiments at toroidal machines

报告题目：Anomalous emission and absorption of microwaves in ECRH experiments at toroidal machines 

报告时间：10月23日（星期四）上午9:30-12:00

报告地点：4号楼-601会议室

报告人：Prof.Gusakov E.Z.,Popov A.Yu

主持人：张洋 研究员

报告人简介：Prof.  Gusakov E.Z is with the Division of Plasma Physics,Atomic Physics,and Astrophysics,IOFFE Physical Technical Institute,St. Petersburg,Russia,where he is the Head of the High Temperature Plasma Physics Laboratory. His interests include parametric decay instabilities,wave propagation in inhomogeneous turbulent plasmas,nonlinear wave-plasma interaction,RF heating,and microwave plasma diagnostics.

报告简介：

Electron cyclotron resonance heating (ECRH) and current drive is widely used in toroidal plasmas and is considered for application in ITER for heating and neoclassical tearing mode control. Nowadays an abrupt increase of the ECRH power from 20 MW up to 60 MW is decided by the ITER team. According to the predictions of the theory developed in 80th nonlinear effects and first of all parametric decay instabilities (PDIs),which can accompany the ECRH experiments, were believed to be deeply suppressed by huge energy loss of daughter waves from the decay region. However, during the last 15 years many experiments have demonstrated excitation of the anomalous nonlinear phenomena in the 1 MW level ECRH experiments. The clearest evidence of the nonlinear effects onset was obtained first at TEXTOR and then at ASDEX-UG and W-7X, where the strong microwave emission down–shifted in frequency was observed. At ASDEX-UG and recently at TCV the emission of the half harmonic of the pump wave was also observed. A convincing demonstration of the fast ion generation during the ECRH pulse under conditions when the energy exchange between the ion and electron components is negligible was reported at TCV and TJ-II. Besides this a substantial broadening of the power deposition profile was observed at L-2M,T-10 and DIII-D in the second harmonic ECRH experiments. The missing power effect was reported as a result of the energy balance study at T-10 and TJ-II.

In this talk a review of the anomalous phenomena experimental observations is presented and a theoretical model taking into account,as distinct from the standard theory,trapping of the decay waves due to non-monotonous features of the density profile,which always exist on the discharge axis or may be present due to the magnetic island, the density pump-out effect or ELM filaments and blobs is developed. We interpret the anomalous microwave emission and the ion acceleration, as a result of secondary nonlinear processes that accompany a primary low–threshold PDI leading to excitation of trapped waves. The primary PDI growth is saturated in our model due to both the secondary decays of the daughter waves, the pump wave depletion or the daughter wave nonlinear Landau damping. The coupling of different daughter waves and the pump is responsible in the model for the microwave emission, which is a spurious signal for a tokamak microwave diagnostics.  This mechanism appears capable of reproducing the fine details of the frequency spectrum and the absolute value of the emitted radiation. It also predicts substantial anomalous absorption in the range of 10% - 70% in the electron channel, which could be responsible for the broadening of the ECRH power deposition profile, and explains the anomalous fast ion production by the generation of the secondary ion modes,which directly transfer the pump power to ions. Results of theoretical analysis of anomalous emission at TEXTOR and W-7X as well as of anomalous absorption reported by L-2M,TJ-II,T-10 and TEXTOR where broadening of the power deposition profile and/or missing power effect were observed will be presented.

当天下午14：00在4号楼-3楼中间会议室和Gusakov教授讨论，欢迎感兴趣的老师和同学参加！