Simulating The Asymmetries Of Divertor Power And Particle Fluxes In EAST Using SOLPS

Divertor power and particle fluxes asymmetries are key issues for high-power long-pulse discharges of the future devices such as ITER and CFETR.They can affect the control of detachment,heat and particle fluxes.The simulated and experimental results have demonstrated that the drifts including diamagnetic and electric drifts are the main factors for inducing the divertor power and particle fluxes asymmetries.So far,the physical mechanism for it is not well understood.There still exists an interrogation.Some authors found that the radial electric drift can play a leading role in inducing the asymmetries.In contrast,other authors' work indicated the poloidal electric drift can play a main role in determining the asymmetries.The asymmetries have been observed in EAST,and the experimental results showed that the asymmetries can become more and more obvious with the increment of upstream plasma density.Other authors also have studied the asymmetries in EAST by considering drifts using SOLPS.But,the simulated asymmetries were not as distinct as the experimental observations.The detailed reason is not clear.Besides,the asymmetries of power and particle fluxes also affect impurity transport,and induce the impurity particle asymmetry,so that impurity particle can very easily penetrate into the core plasma by density diffusion.Based on the above questions,the two dimension edge plasma fluid code SOLPS was employed to investigate the physical mechanism of the divertor power and particle fluxes asymmetries.The first chapter introduces the background,motivation.Chapter 2 illustrates divertor plasma physics and modeling code SOLPS.Chapter 3 shows the systematic study on which component of electric drift can play a leading role in inducing the asymmeltry in different discharge regimes(low,high recycling and detachment)and modes(L-mode and H-mode).The simulated results show that the radial electric drift plays a main role in inducing the asymmetries during L-mode partial detachment,rather than poloidal electric drift.On the contrary,the poloidal electric drift also can play a main role in inducing the asymmetries during H-mode high recycling regime,instead of radial electric drift.In addition,both radial and poloidal electric drifts also can simultaneously play a key role in inducing the asymmetries during H-mode partial detachment.Their synergistic effects can make the in-out asymmetries much more obvious than any one component.This conclusion can well solve other authors,divergence on which electric component can play a key role in determining the asymmetry.The simulated results also show that the synergistic effect of poloidal and radial electric drifts can drag impurity particle from outer target region into inner target region along private flux region flux tubes.On the contrary,any one component alone can not induce the much obvious impurity asymemrty,especially,radial electric drift.Besides,in this chapter the effect of ballooning transport on the asymmetries also has been assessed.The modeling results reveal that the ballooning transport also can produce the obvious in-out asymmetries.The combined effect of ballooning and drifts can make the asymmetries become much stronger.Chapter 4 presents the effect of upstream plasma density on the in-out asymmetries arising from drifts.The simulated results show the in-out asymmetries are not obvious under the condition of low upstream plasma density.However,the simulated in-out asymmetries can become much more obvious with the increment of upstream plasma density,which can well reproduce the experimental measurements.The main reason is contributed to the SOLhigh and low field sides plasma density asymmetry in upstream region with drifts.Moreover,the plasma density relation between upstream and downstream target plate region is verydifferent during different discharge regimes,e.g.linear relation during low recycling regime and exponential relation during high recycling regime.Besides,the gradients of temperature and pressure along poloidal flux tube,which are completely different under the condition of different upstream plasma density,can have a great influence on the radial electric drift.Chapter 5 estimates the effect of drifts on impurity transport and detachment obtained by injecting argon impurity.The simulated results reveal that the detachment order completely depends on drifts,instead of the locations of gas puffing,which is in good agreement with the experimental result.The reason is due to that the electric and diamagnetic drifts flows can reverse the background plasma parallel flow,which can drive more particles into upper divertor region.Besides,argon impurity transport mainly depends on background plasma parallel flow,which can drag argon impurity into upper divertor region.The asymmetrical distribution of impurity particles can make impurity particles easily penetrate into core plasma region with amount of radiation loss.The modelling results show the speed matching relation between gas puffing and pumping is very important for impurity transport to maintain the impurity particles balance.