Locking of Tearing Modes by the Error Field

The locking of tearing modes by the error field is studied by nonlinear numerical modeling.The threshold of mode locking for J-TEXT tokamak plasmas is found.

Investigation of turbulence rotation in the SOL and plasma edge of W7-X for different magnetic configurations

The W7-X stellarator is optimized with respect to neoclassical transport.Therefore turbulent transport plays an important role.It is equipped with an inertial cooled graphite divertor which intersects the island chain at the plasma edge depending on the magnetic configuration.Additional control coils and the plasma current modify the iota profile at the plasma edge and shift the position of the island chain.To monitor the effects on the poloidal propagation velocity in the scrape-off layer(SOL)and the plasma edge,an O-mode Poloidal Correlation Reflectometer(PCR)is used which simultaneously monitors the propagation of low-k turbulence.Operating in the density range of 0.6?×?1019 m-3 to2?×?1019 m-3 it covers a large part of the SOL and the plasma edge and allows for the experimental determination in the last closed flux surface(LCFS)and the associated shear layer in low to middensity discharges.In this paper it is shown that the propagation in the shear layer and its vicinity is determined best,when based on an elliptical model.Different magnetic configurations with magnetic edge topology of five independent islands forι?=?1 and six linked islands forι?=?0.81 are investigated.Also the effects of the plasma current and additional control coils on the edge magnetic topology are studied.The coherence spectra of antenna pairs for different poloidal separations is investigated.Using a decomposition method for the measured coherence spectra the characterization of turbulence spectra is possible with respect to e.g.broad band turbulence and quasi coherent modes.A strong reduction of the broad band turbulence is observed in the vicinity of the LCFS which is evidence for the suppression of low-k turbulence at the shear layer.

Mode structure symmetry breaking of reversed shear Alfvén eigenmodes and its impact on the generation of parallel velocity asymmetries in energetic particle distribution

In this work,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 ASDEXUpgrade plasma,a benchmark with the three different physical models for RSAE without and with energetic particles(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 an analytical complex Gaussian expressionФ(s)=e^(-σ(s-s_(0))^(2))with complex parametersσand s_(0),where s is the normalized radial coordinate.The mode structure is distorted in opposite manners when the EP drive shifted from one side of qminto the other side,and specifically,a non-zero average radial wave number 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,corresponding to different initial EP density profiles with EP drive shifted away from the qmin.