Numerical Simulation Study Of Long-leg Divertor In CFETR Using SOLPS

The divertor,where the heat and particle flux from the core plasma is exhausted,is one of the most important internal components in the magnetic-confined fusion device.It is critical to control the extremely high heat load onto the divertor targets in the future fusion reactor for the aim of steady-state operation.The long-leg divertor is one kind of the advanced divertor proposed recently.By extending the length of the divertor leg at the low-field side(LFS),the connection length can be increased.As a result,the detachment for the LFS divertor target is expected to be promoted and the heat load should be mitigated.In this work,to explore the solution of the heat exhaust issue for China Fusion Engineering Test Reactor(CFETR),the numerical simulations are performed for the long-leg divertor to study the influence of the change in the geometry on the divertor plasma.According to the magnetic equilibrium configuration and the geometry of the vacuum vessel,the geometry configuration of the long-leg divertor is preliminary designed.Compared to the traditional geometry configuration of the ITER-like divertor,the LFS divertor target is settled as far from the X point as possible.Using SOLPS(Scrape-off Layer Plasma Simulation)code,the divertor plasma is simulated for the long-leg divertor.By changing the D2 puffing rate,the results of the density scan indicate that,when the D2 puff rate exceeds 1.5×1023 s-1,both the peak heat flux density onto the inner and outer divertor targets can be reduced to the level below 5 MW/m2.Compared to the ITER-like divertor,the peak heat flux density onto the outer divertor target decreases more rapidly with the increasing gas puffing rate,while the detachment for the inner target is achieved with higher gas puffing rate.The influence of the length of the outer reflection plate on the in-out asymmetry is further studied.By fixing the D2 gas puffing rate at 1.0×1023 s-1,the simulation results for the cases with different length of the outer reflection plate show that,with increasing outer reflection plate length,the peak heat flux onto the inner divertor target decreases from～11 MW/m2 to～4 MW/m2,while that onto the outer target keeps at the level of 4 MW/m2.According to the preliminary analysis,the main reason of the above phenomenon is the increase of the upstream electron density,which is caused by the worse closure for the neutrals with shorter outer reflection plate.The present work provides the physics basis for the long-leg divertor configuration design for CFETR,and can be considered as an important reference for solving the issue of the high heat load of the divertor target in the future reactor.