Numerical Study On Plasma Response To The 3-dimension Magnetic Perturbation Field Due To Fishtail Divertor In EAST

The Edge Localized Modes(ELMs)have to be controlled(within the mitigation or suppression)in the advanced tokamak devices operating the H-mode,specially for the future tokamak devices with huge size,such as ITER.Although the energy released by each crash of the type-III ELMs is lower than the one by type-I ELMs,it is still potentially dangerous to the materials of the plasma facing components,such as the divertor,if the heating flux released from ELMs loads the same and small region on divertor.This can cause severe erosion of the plasma facing components,and shorten the life of them.On the other hand,the high-Z impurity can be produced and recycled into the plasma region,which may lead to the loss of H-mode operation and even the disruptions of discharges.A new type of divertor – Fishtail Divertor(FTD)has been used in EAST at 2019,with a coil located outside but near the lower divertor.The footprint will be oscillated when an AC current is applied in FTD coil.Therefore,the averaged heating flux on the divertor will be reduced.However,different with the classical resonant magnetic perturbed(RMP)coils in tokamak devices,the FTD is produced by a single wire but not a saddle coil.In addition,the FTD coil only cover 2? 3 along the toroidal angle.The MARS-F code has been used to investigate the plasma response to RMP fields in many tokamak devices,as well as benchmarked with other codes.However,the lasted version of MARS-F still cannot describe the FTD coil in EAST.In this work,the key technical problem is to upgrade MARS-F code,in order to describe the FTD coil and compute the 3-D magnetic perturbed fields produced by it,as well as the plasma response to this fields.For benchmark the new version of MARS-F code,the Wesson's equilibria and one experimental equilibria in EAST is taken into account.We build computational models with various coils.Compared with the old version of the MARS-F code,the results are very well.By using the upgraded MARS-F code,we focus on the investigate on the 3-D magnetic perturbed fields due to the FTD in EAST.Several interesting points can be observed in our work.First and most important is that RFA effect for the sidebands of n(28)2,4,5 harmonic,can be found in the edge plasma region.However,the largest contribution of the 3-D magnetic perturbed fields due to the FTD comes from the n=2 harmonic.In addition,we also compute a special case,with assuming the plasma shape of the lower single null but the upper FTD,based on the corresponding experiments in EAST.Interesting conclusion is that the plasma response to this 3-D magnetic fields is quite similar to the one with the previous assumption.This conclusion can provide some explanations of the experimental results in EAST.