Study Of Divertor Heat Flux Distribution With Auxiliary Heating On EAST

Experimental advanced superconducting tokamak(EAST)was designed for the long pulse steady-state divertor operation.The intense interactions between the plasma and the divertor make the divertor target plate exposed to high temperature and high heat flux risks.The temperature and the heat flux distribution of the divertor target plate are influenced by many factors,such as the heating mechanism,the magnetic configuration and the structure of the divertor target plate.Studies of these effects on the divertor temperature and the heat flux not only help the understanding of the physical mechanisms,but also provide a certain guarantee for the safe operation of the device,and provides the necessary reference for the next step of the engineering design.The infrared temperature measurement is the main method in this thesis,the temperature data were extracted,and the heat flux of the divertor target plates were calculated by the DFLUX code and ANSYS.The main research results are:1.Experimental study of the influence of heating mode on the heat flux distribution of the divertor target plate.In the lower single null(LSN)configuration with lower hybrid current drive(LHCD)only,when the frequency of ELMs less than 50Hz,a wider poloidal distribution of heat flux was produced on the lower outer(LO)divertor target plate,with the full width at half maximum(FWHM)two times more than that neutral beam injection(NBI)combined with LHCD under the same condition.If the lower hybrid wave(LHW)power exceeds 1.2MW in the LSN configuration discharges,a very wide distribution of heat flux was produced in the target plate at the beginning of LHCD,however that kind of wide distribution does not appear if the NBI has already working,indicating that the NBI affects the heat flux distribution caused by the LHW.Local energy deposition will occur on the upper outer(UO)divertor target plate with large NBI power.The poloidal temperature/heat flux distribution of the divertor target plate is related to the frequency of edge localized modes(ELMs):A wider distribution of heat flux/temperature was produced on the divertor target plate under the dominant condition of LHW than that of LHCD combined with NBI when the frequency of ELMs less than 50Hz;the result is opposite when the frequency of the ELMs is about 150Hz.The analysis of the temperature/heat flux distribution of the lower target plate in the H-mode discharge with LHCD shows the toroidal asymmetry.At the low temperature region of the toroidal direction,with the increase of the peak temperature/heat flux,the FWHM of the radial distribution curve of the temperature/heat flux decreases rapidly;however at the high temperature region of the toroidal direction,the FWHM did not change that much with the increase of the peak temperature.The temperature in the high temperature area increased as a whole,so extremely high heat flux will not formed in a small region.2.Experimental study of the influence of magnetic configuration on the heat flux of the divertor target plate.The magnetic configuration affects the heat flux of the target plate,mainly due to the direction of B×?B.The temperature distribution of the UO and LO target plate in the DN discharge with lower hybrid wave was analyzed.It is found that the temperature of the UO target plate is higher than that of the LO target plate,and the temperature distribution of the UO target plates is wider.That was caused by the magnetic configuration,but also included the effect of the structure of the target plate and the auxiliary heating.Under the same conditions of the upper and lower divertor structure and materials,the heat flux distribution of the target plate in the LSN,USN and double null(DN)configuration discharges with ion cyclotron resonance heating(ICRH)was analyzed respectively.The heat flux on the outer target plate was larger than that on the inner target plate.The heat flux on the upper target plate is larger than that on the lower target plate.Especially in the DN configuration,the peak heat flux on the UO target plate reaches about 4 times that on of the UI target plate,and 6 times of that on the LO target plate.3.Study of the effect of the divertor structure on the temperature and heat flux of the divertor target plate.The disruptive heat flux on the divertor target plate under DN configuration was simulated by TSC.The results show that the heat flux on the UO target plate is the highest,reaching 7.94MW/m,1.6 times of that on the UI target plate and 1.33 times of that on the LO target plate.The result indicated that the influence of the divertor structure asymmetry on the heat flux is significant.The characteristic time of heat balance of the upper and lower target plates were analyzed and compared in the discharges over 60s.It is found that the temperature of the graphite divertor target plate is constantly rising in the whole discharge until the auxiliary heating was stopped.Whereas,the temperature of the tungsten target plate reaches quasi steady state about 8-13s after the auxiliary heating starting work.The actual time is about 2 times that of the engineering analysis.The ITER-like W-Cu divertor has good thermal conductivity compared with the graphite divertor.4.High pulse heat flux calculation for upper and lower target plates in high power operation.In the LSN configuration discharges with auxiliary heating power about 4MW,in both case with the LHCD only and the LHCD combined with the NBI,the transient heat flux of about 4MW/m2 was produced on the divertor target plate by ELMs.In the USN configuration discharge with the same auxiliary heating power,the transient heat flux on the UO divertor targer plate produced by ELMs was more than 10 MW/m2.The peak heat flux is much larger than that of the LO target plate,which is caused by a variety of reasons,including the magnetic configuration,and the target plate structures and materials.