Development Of Langmuir Probe Diagnostic System And Experimental Study Of Heat&Particle Fluxes For The EAST Tungsten Divertor

The Experimental Advanced Superconducting Tokamak(EAST)has successfully installed the upper ITER-like tungsten divertor for the first time in the world,and planning to upgrade the lower graphite divertor to the tungsten divertor,which will provide the important support for the high-power long-pulse operation on EAST.In this paper,based on the EAST tungsten divertor,the divertor Langmuir probe(Div-LP)diagnostic system is developed,and the experimental studies on the H-mode high-density detachment and the particle flux control in the divertor region are carried out.Firstly,the structure of EAST tungsten divertor was analyzed,and the Div-LP diagnosis system suitable for the structure of EAST tungsten divertor was designed,especially the ceramic terminal and signal line switch cabinet.As the most critical component of the Div-LP system,two types of divertor probe structures for W/Cu Monoblock and W flat-tile divertor target plate structures are designed,respectively,as well as their poloidal and toroidal distributions on the EAST divertor.The thermal analysis of the kinds of Div-LP assemblies was carried out with the domed,roofed,and flush-mounted probe tip,respectively.The 3D finite element models were built and simulated on the platform of ANSYS finite element software.The results show that the flush-mounted probe tip should be used instead of the domed and roofed probe during the high power long-pulse plasma discharges with the steady state perpendicular heat flux over 10 MW/m2 on the divertor target surface,and the W flat-tile unit has better heat dissipation than the W/Cu monoblock.A data processing software for EAST Div-LP diagnosis system with visual interactive interface was designed by using the Matlab software,which greatly improved the efficiency of data analysis and data information mining for the EAST Div-LP system.Besides,some related measurement experimental researches were carried out for the EAST Div-LPs,the measurement results of different probe measurement methods on EAST were analyzed and compared,and the methods and conditions of measuring plasma parameters by single probe,double probe,triple probe and flush probe were determined.Futhermore,the H-mode high-density detachment with upper single null(USN)magnetic configuration was studies on EAST,and the H-mode detachment was firstly obtained with ITER-like tungsten divertor in USN,pure NBI heating discharges for the reversed Bt(B ×?VB ?).The detached divertor operation in EAST is accompanied by a rollover of particle flux to the target with the increasing of the plasma density,and the high particle flux to the targets significantly reduce the electron temperature(below 5eV close to the targets),which indicates the divertor plasma enters the detachment regime.Meantime,with the further increase of the plasma density,the detachment region will extend from the position near the strike point to the far-SOL zone along the target plate.The impact of heating scenarios on the divertor detachment has been assessed in EAST H-mode discharges.It is shown that the threshold of detachment is higher with the heating power(especially for RF heating)increasing.The detachment asymmetry can be significant observed in USN reversed B,.With toroidal field reversed,i.e.,the normal B,(B× VB ?),it is interesting to find that the particle flux near the outer strike point nearly maintain a constant when entering the detachment regime.The detachment onset between inner and outer divertor become nearly symmetric,and outboard divertor detachmentis achieved at a lower line-averaged density than that in the reversed B,direction.However,the threshold of the detachment at inner divertor is significantly higher than that in reversed B,.The electric drifts in divertor and SOL may qualitatively explain the appearance of the detachment asymmetry,which can drive the particle flux deposited at the inner and outer divertor targets,as the directions of the drifts are dependent on the direction of Bt.All these provide experimental data support and theoretical basis for further research on methods to reduce the heat and particle fluxes on the divertor target.Finally,the control mechanism of the particle flux on the divertor target plate was discussed,based on the EAST tungsten divertor,under the condition of USN,H-mode plasma discharge for the reversed Bt(B ×?B ?),the steady state particle flux control experiments on the divertor target plate were carried out by injecting working gas(D2)or impurity gas.The plasma density control method was successfully implemented for the first time to reduce and maintain the particle flux on the divertor target plate.At the same time,the control parameters of injecting impurity gas were discussed on EAST,then Ne impurity gas was applied to be the radiation source,and the ion saturation current density measured by the Div-LP diagnostic system was used as the control reference signal to carry out the experimental study on particle flux control.Besides,the influence of total radiated power on particle flux control was studied.The results indicates that the stability control of the total radiated power level and the detachment state are both crucial to achieve the reduction and sustainment of heat&particle fluxes during the high-performance,long time scale plasma discharge,which provides an important reference for the steady state particle flux control under high-parameter long-pulse plasma discharge in the future.