| Properties of plasma transport and confinement in tokamak devices have been a longstanding issue in the research field of magnetically confined fusion plasmas.It is well-known that turbulence and turbulent transport are deleterious for plasma confinement,while zonal flows on the other hand play beneficial roles in improving confinement by two means.One is that the zonal flow itself does not induce radial transport owing to its poloidal/toroidal homogeneous mode structure,and the other is that the zonal flow extracts energy from ambient turbulence via nonlinear coupling and therefore reduces the turbulence power.Thus,study on turbulence and associated transport is always the focus of transport physics in fusion plasmas.Resonant magnetic perturbation（RMP）has been widely applied for the control of the edge localized mode（ELM）in H-mode experiments,in which the plasma instability and confinement characteristics are closely related to local parameters and the magnetic topology at the pedestal region of the edge transport barrier.In contrast,the RMP used in ohmically heated plasmas reflects more the changes of fundamental features of edge turbulence and associated transport in the stochastic area induced by the RMP.Meanwhile,in recent years,a large amount of experiment in tokamaks/stellarators has demonstrated the importance of isotopic mass in affecting plasma transport and confinement properties,which in many cases has even been out of gyro-Bohm theoretical expectations.Hitherto,the mechanisms governing the isotope effect are not fully understood although possible influence of isotopic mass on the shear flow rate and zonal flows has been proposed.In this perspective,it is of paramount importance to investigate the impact of the resonant magnetic perturbation and isotope effects on turbulence and zonal flows in order to unravel underlying mechanisms responsible for turbulence-driven transport and plasma confinement.This doctorial research work has been focused on above topics,i.e.,executed experimental studies of the impact of RMP and isotope effects on turbulence and zonal flows in the TEXTOR tokamak and the HL-2A tokamak,respectively.In the TEXTOR tokamak,the influence of the8)8)?9)9)=6/2 RMP on multi-scale turbulence and improved particle confinement in the Ohmically heated plasmas has been detailedly surveyed,using multiple Langmuir probe array systems.The investigation includes:（i）impact of RMP on edge magnetic topology;（ii）impact of RMP on edge equilibrium parameters;（iii）impact of RMP on edge plasma potential and the mean radial electric field;（iv）impact of RMP on propagation properties of edge turbulence;（v）impact of RMP on turbulent transport in distinguished ergodic zones;（vi）impact of RMP on multi-scale turbulence,including small-scale turbulence and large-scale geodesic acoustic mode（GAM）zonal flows as well as turbulence-driven transport and（vii）nonlinear interaction between GAM and ambient turbulence across RMP-induced confinement improvement.The results indicate that in Ohmically heated plasmas at TEXTOR,with RMP the large-scale zonal flows and small-scale ambient turbulence are both significantly reduced.At high RMP currents,a reduction of edge transport can be realized due to primarily decline of small-scale ambient turbulence and turbulent transport in the ergodic zone,where the turbulence eddy size is largely decreased.Investigation on the dynamic process of fluctuation quantities during the perturbation current ramp-up phase further shows that the GAM zonal flows and their nonlinear interaction with background turbulence decrease incessantly with increasing perturbation current.The reduction of edge transport and confinement improvement do not occur until the micro-scale turbulence starts to be suppressed by the RMP when the perturbation current reaches a certain threshold value.The results provide new experimental evidence for understanding the impact of the RMP on multi-scale turbulence dynamics and associated transport in the stochastic region of plasma boundary in fusion devices.In the HL-2A tokamak,the influence of the mass isotope on plasma confinement and transport properties has been investigated in Ohmically-heated hydrogen（H）and deuterium（D）majority plasmas,using multiple Langmuir probe arrays.The investigation includes:（i）comparison of edge equilibrium parameters and turbulence-induced transport between H and D plasmas;（ii）comparison of characteristics in the frequency spectra of edge fluctuating quantities between H and D plasmas;（iii）comparison of interplay between GAM zonal flows and ambient turbulence in H and D plasmas;（iv）comparison of spatial structures of turbulence eddies and their features between H and D plasmas.The results show that under similar discharge conditions the D majority plasma has better confinement and lower turbulent transport than the H one,and concomitantly,it is found that the magnitude of GAM zonal flows,the tilting angle of the Reynolds stress tensor and the turbulence correlation lengths are all larger in the edge region of the D plasma.A possible explanation is that the larger correlation length in D plasmas is closer to the typical radial scale of×sheared flows,leading to an increase of Reynolds stress tilting and nonlinear energy transfer between GAM zonal flows and background turbulence,and consequently,a reduction of turbulence power and an enhancement of plasma confinement.The results provide direct experimental evidence on the importance of the nonlinear energy coupling between ambient turbulence and zonal flows for governing the isotope effects in fusion plasmas.The novelties of present research work provide（i）the first observation on the dynamic evolutions of edge turbulence and zonal flows as well as their nonlinear coupling during the ramp-up phase of the RMP current,and found that the confinement improvement takes place only when the perturbation strength reaches a certain threshold value to suppress small-scale turbulence;（ii）direct experimental evidence showing that the better confinement in D majority plasmas arises mainly from larger Reynolds stress tilting and stronger nonlinear energy transfer between GAM zonal flows and ambient turbulence than those in H plasmas. |
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