Numerical Study On Edge Localized Mode Control And Error Field Correction In Tokamaks

The plasma response to 3D magnetic fields is an important research topic in fusion research,including the edge localized modes(ELMs)control using the resonant magnetic perturbations(RMPs),the error field correction(EFC),the plasma flow damping,the resonant field amplification of high pressure plasmas,the active control of the resistive wall mode(RWM)and other magneto-hydrodynamics(MHD)instabilities.It has recently been realized that,even a small amount of the external 3D fields,of the 3-4 orders smaller than the background(equilibrium)magnetic field,can have profound influence on the stability and confinement of the otherwise 2D axi-symmetric tokamak plasmas.The external 3D fields manifest themselves in controlling various MHD instabilities.During recent years,it has been realized that large ELMs instability,the so-called type-I ELMs,can pose significant danger to the material walls in future tokamak devices.For ITER,the plasma facing components and divertor can only bear 20%of heat loads associated with edge localized mode events.So studies in ELMs mitigation and suppression are important research topics in fusion research.So far the most mature and reliable technique,is the application of RMPs.The RMPs technique has been extensively employed in DIII-D,JET.MAST,ASDEX Upgrade,and recently in KSTAR as well as EAST.ELMs control has been achieved in these devices.Due to various physics mechanisms,which are not fully clear yet at the moment,the ultimate cause and the necessary conditions for ELMs suppression are still open questions.The non-axisymmetric magnetic field perturbations inevitably exist in the tokamak device design and construction due to various sources.In particular,the n=1 error field(EF)can induce mode locking,and the locked mode often leads to the plasma disruption.The EFC using external magnetic perturbation fields in tokamaks is an important research topic in fusion research.The EFC experiments have been carried out in many tokamaks,e.g.DIII-D,JET,MAST,EAST,KSTAR,etc.Despite extensive experimental efforts in understanding the EFC using additional magnetic coils,modelling work is so far limited.This is probably because the EFC modelling is critically involves the geometery.A full toroidal geometry is essential,in order to provide useful recommendations for the optimal correction of the EF in a given device.ELMs control and EFC,using the external magnetic perturbation,are important topics.Simulations are carried out to compare with the experiments.Analyse the results of experiments deeply,and try to understand the physics of ELMs control and EFC.In chapter I,the variety of fusion devices and ITER plan are introduced.The progress of the ELMs.ELMs control using RMPs and EFC are reviewed.In chapter Ⅱ,the MARS code and models are described.The computational tool is the state-of-the-art codes suite MARS-F,MARS-K and MARS-Q.And how to use the MARS code to model the response of the plasma to the external magnetic field in toroidal geometry is introduced.In chapter Ⅲ,we have computationally simulated plasma response to the n=2 even parity RMP in DⅢ-D.using the MARS-F code.This study is based on the linear plasma response,using both the resistive,rotation plasma and ideal,static plasma response models.This work focuses on understanding how the edge safety factor affects computed plasma response.We find that both the resistive,rotation plasma and ideal,static plasma response models show a jump in low field side,high field side-A and high field side-B pickups in(q95,qa)space.It is also shown that transition is more smoothly with ideal,static plasma response model.Furthermore,large edge-peeling component is responsible for both large pickup fields and large plasma displacement near X-point,and the reason of the jump.In chapter Ⅳ,we carry out a modelling of plasma response to 3D external magnetic field perturbations in EAST,using MARS-F code.The modelled results,takeing into account the plasma response,agree well with the experimental observations in terms of the coil phasing for both the mitigated and the suppressed ELMS cases in EAST experiments.Another important finding from the present study is that the field and plasma-displacement-based criteria,derived from the MARS-F model,seem to work not only for ELMs mitigation,but also for ELMs suppression.In chapter Ⅴ,we carry out a modelling of EFC in EAST,using MARS-F code.Assumed n=1 intrinsic vacuum EF with multiple poloidal spectra,the compass scan predicted 2/1 EF,based on minimizing the computed resonant electromagnetic torque,can be made to match well with that of the EFC experiments using both even and odd parity coils.Moreover,the compass scan predicted vacuum EFs are found to be significantly differing from the true intrinsic EF used as input to the MARSF code.While the puzzling result remains to be fully resolved,the results from this study offer an improved understanding of the EFC experiments and the compass scan technique for determining the intrinsic EF.Finally,the summary of this thesis and the future work are presented.