Numerical Simulation Of Heat Flux On The CFETR First Wall And Divertor

The high heat flux deposited on the first wall and divertor targets is always one of the critical issues threatening the safe run of magnetic confinement nuclear fusion device.During the CFETR design phase,using revelent modelling tools to estimate the heat flux on the first wall and divertor is necessary and essential for optimizing the design parameters and components design of the first wall and divertor.An optimization procedure about computating the heat flux on the first wall is performed.The coupling of SOLPS-ITER and PFCFlux code achieved by the optimization work can calculate the complete heat flux deposited on the CFETR first wall.The impact of magnetic equilibria designs on the plasma heat flux deposited on the CFETR first wall is also explored.Based on the modelling results from SOLPS-ITER,with different Ne seeding rates the distributions of heat flux on the CFETR divertor targets are analyzed.Combining with the electron density shoulder present in EAST experiments,the effect of shoulder structure on the heat flux deposition onto the first wall and divertor is further investigated by using effective diffiusion transport coeffecients in SOLPS-ITER.Firstly,the SOLPS-ITER and PFCFlux modelling has complished the calculation of complete heat flux deposited on the CFETR first wall,considering the modelling scenario of 1 GW H-mode steady state.By introducing the relevant physics models and assumptions of blob and considering the radiative divertor operation,the distributions of complete heat flux on the first wall is computed with different Ne seeding rates.The modelling results indicates that the peak heat flux occurs on the inboard module 9#,and evidently an asymmetry distribution of heat flux on the inboard and outboard first wall is observed,more heat flux is deposited on the inboard of the CFETR first wall.The main contribution to the complete heat flux is from the plasma heat flux,the heat flux from neutrals is alomost neglectable.Compared with the results from ITER and EU DEMO,the radial arrangement between SND equilibria design and the CFETR first wall determines the different location of peak heat flux from ITER’s and EU DEMO’s.Analyzing the heat flux distributions with different Ne seeding rates,it can be found that Ne seeding is favorable for reducing the heat flux on the first wall to the engineering limit of 1 MW/m2.Secondly,the impact of CFETR promising magnetic equilibiria designs on the plasma heat flux deposition onto the first wall is assessed,including QSF+(quasisnowflake-plus)and SND(single null divertor)baseline equilibrium.The modelling results reveal that three EHFMs will be appeared,if CFETR is operated with the QSF+design.In view of protecting the first wall from high heat flux,this result may suggest the SND baseline design is more suitable for CFETR.Adjusting the radial distance ΔRsep between the first and second separatices of SND equilibrium design,can obtain the differtent relative position relationship between the second separatrix and the CFETR first wall.After the compution of the plasma heat flux with SND equilibria of differenΔRsep,it turns out that the peak plasma heat flux occurs on the top of the main chamber when ΔRsep=4 cm,which is consitent with the results from ITER and EU DEMO.On the perspective of peak plasma heat flux on the CFETR first wall,this modelling has validated that the SND of ΔRsep=6 cm is reasonable to be selected as the baseline magnetic equilibrium design.Scaning the plasma heat flux on the CFETR first wall with a series of potential power decay lengths in the far SOL,has confirmed that the sensitivity of plasma heat flux on the first wall to the power decay length will not threaten the safety of the CFETR first wall.The stationary heat flux on the CFETR radiative divertor targets is also calculated and analyzed.If no mitigation method is considered,the peak heat flux on both inner and outer target will reach above 20 MW/m2,which is much higher than the current engineering limit of 15 MW/m2.Then,the mitigation effect of varied Ne seeding rates on the heat flux on the CFETR divertor is studied.Combined with the radiation and Ne ions distributions in the divertor region,the heat flux distributions on the inner and outer targets can be explained.Furthemore,in order to meet the requirment on impurity concentration in the pedestral region,the suitable range of Ne seeding rate for the CFETR radiative divertor operation should be 1 ×1020 s-1 to 5 × 1020 s-1.The flattening of electron density in the far SOL is the density shoulder,which is has been observed in many devices,including EAST.In order to study the impact of density shoulder on the heat flux deposition onto the first wall and divertor,the density shoulder measured in EAST experiment has been simulated by using effective diffusion transport coeffecients in SOLPS-ITER.After analyzing the simulation results,it is found out that the existence of density shoulder can strengthen the radial transport in SOL and bring more energy and particle flux onto the first wall,the modeling results in this work will quantify the study of heat flux deposition and material damage on the first wall.For the divertor,the main plasma paramters near the strike points are reduced due to shoulder structure,but the parametes away from the strike points is slightly increased,such impact on targets may be favorable for the detachment process.In this thesis,SOLPS-ITER and PFCFlux are used to simulate the heat flux deposition on the CFETR first wall and divertor targets,and the impact of density shoulder on the heat flux deposition onto the first wall and divertor is further investigated by using modelling method.All these results will provide some key data and design references for the future CFETR blanket design,magnetic equilibria design and radiative divertor operation.More researches about the enhancement of radial transport in the SOL should be performed to minimize the uncertenties from the physical model and assumptions.