| To achieve the ignition of nuclear fusion,a higher temperature,density and fusion gain are desired.Under a certain condition,fusion gain is proportional to the normalized beta(beta,the ratio of pressure to magnetic pressure),?N.The achievement of high ?N(?N>1.5)discharge benefits to the future high-performance plasma operation of ITER.Researchers have been dedicated to improving ?N.The feasible ways to increase ?N are the optimization of controlling the core transport,the formation of internal transport barrier(ITB)and the improvement of a fraction of bootstrap current.A study on EAST shows that high and stable power injection,the control of impurity radiation and ITB dynamics are pivotal to the sustainment of high ?N discharge.A large amount of heat and particles from the main plasma region in a long-pulse and high-power plasma pass through the last closed magnetic surface and are guided forward to the first-wall of tokamak and the divertor target plate along the open mag-netic lines.The high heat load in the divertor target plate and the strong plasma-wall interaction are serious challenges to the steady-state operation of future fusion reactors.Therefore,the heat load in the high ?N discharge is required to be evaluated for the first-wall and the divertor target.Based on the database of high-?N discharges in EAST,the effect of the core and edge plasma activities on the divertor particle flux,heat flux and SOL width are studied as follows:(1)The characteristics of the divertor particle flux and their responses to ITB dy-namics have been studied.In order to describe the characteristics,the ITB duration is divided into two phases:phase ?(i.e.ITB formation)and phase ?(i.e.ITB degrada-tion),according to the variation of plasma stored energy.In phase I,the particle flux near the inner strike point(SP)is continuously enhanced during the inter-edge-localized mode(ELM)phase in both the lower single-null and upper single-null configurations.The total particle flux in the scrape-off layer(SOL)region reveals a similar trend with an increase of the flux near the SP.However,in the private flux region(PFR)the total particle flux shows a reduction.Meanwhile,a movement of the SP away from the di-vertor corner is also observed during the ITB formation.In phase ?,the particle flux near the inner SP,the total particle flux in the inner SOL and PFR region recover to their initial level before ITB formation,respectively.Additionally,the particle decay length is obviously reduced in phase ? and then gradually enhanced in phase ?.The continuous variation of the particle flux at the inner divertor target is in accordance with a compres-sion of the magnetic flux surfaces due to ITB formation,which increases the gradient of electron density in the edge region.It is indicative that the ITB has a feasible impact on the behavior of divertor plasmas by means of increasing the Shafranov shift during the inter-ELM phase.(2)The coherent mode(CM)effected by the kinetic ballooning mode in the high-?N discharge generally appears in the pedestal region.The effect of CM on the divertor plasma behaviors has been studied.The CM can introduce a strong outward transport at the low magnetic filed side and cause a significant increase of particle flux and heat flux at the divertor target.Since CM limits the increase of growth rate of density and pressure pedestal,the pedestal pressure during an inter-ELM keeps stable and possibly affect the collapse of pedestal and the ELM burst.Based on this regime,firstly,the effect of CM amplitude during inter-ELM and During ELM periods has been analyzed.Compared without CM,CM can introduce a more particle flux and heat flux from main plasma region.Experimental study shows with an increase of the CM amplitude,particle flux increase in the inter-ELM and During ELM.In addition,the entire profile of particle flux with CM becomes higher than the profile without CM.Under a different amplitude of CM,particle flux decay length does not change much at the inner divertor target. |
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