R&D Of A Comprehensive Monitoring And Diagnostic System For The Divertor Components

The divertor works in a very harsh environment in current magnetic confined tokamks,and future tokamak type fusion devices.And safe operation of the divertor is necessary to achieve long-pulse H-mode plasmas.Therefore it is very important and meaningful to develop a comprehensive component monitoring and edge plasma diagnostic system for the divertor.In this dissertation,an innovative comprehensive component monitoring and diagnostic system for the divertor,consisting of the electric resistance strain gauge(ERSG)based strain monitoring system,fiber Bragg grating(FBG)based strain monitoring system,FBG based temperature monitoring system and a new actively water-cooled Langmuir probe system,has been proposed,and relevant R&D activities conducted for probable applications in the future.Firstly,an ERSG based strain monitoring system was introduced to monitor the strain distribution of a tungsten divertor cassette of the EAST during the baking simulation experiment.The strain evolution were obtained and compared with finite element analysis(FEA)simulations,validating reliability of the system,and providing valuable experience for the future application of the system on the divertor.Secondly,a bare FBG based strain measurement system was introduced to measure the strain distribution of the same cassette as above mentioned.The experiment proves the feasibility of the application of the FBG system in the strain monitoring of the divertor.However,some shortcomings of the bare FBG system were also observed in comparison with the ERSG system.Then a series of R&D on the encapsulation and welding of the FBG were carried out to cope with those problems,and successfully improved the performance of the FBG based strain monitoring system.In view of the features of the ERSG and the FBG,a combination of the two methods is proposed to achieve better monitoring of the strain in divertor.Next,a string of femtosecond laser inscribed FBG(fs-FBG)was used to monitor the temperature distribution of a tungsten mono-block mock-up during an electron beam gun based high heat flux(HHF)testing.The str:ing of fs-FBG temperature sensors was succeeded measuring temperatures above 1000℃ under 10MW/m2 absorbed power density on the tungsten surface.And the fs-FBG temperature sensors showed equivalent measurement accuracy and even better sensitivity compared to thermocouples,which demonstrated the superiority of this fs-FBG based temperature monitoring system.This system has been listed as a new diagnostic to monitor the new lower tungsten divertor on EAST to be finished in 2020.Last,a newly-designed actively water-cooled Langmuir probe was introduced in the thesis to tackle the problem for current divertor probes,i.e.,easily damaged and even melting with exposure to the divertor plasmas with high thermal and particle loads.The new probe was testified with FEA simulations and HHF testings,showing good thermal removal capability.Several structural parameters of the probe were optimized with FEA method and the following HHF test:ings.Combination of the four systems constitutes a comprehensive monitoring and diagnostic system for the divertor:the actively water-cooled probe system for edge plasma diagnosis;the FBG temperature system for monitoring the temperature of PFC;and the ERSG and the FBG strain sensor for monitoring the stress-status of the divertor during machine operation.They have independent functions but supplement each other at the same time.In summary,the research work conducted in this dissertation focuses on some of very significant topics in the field of fusion engineering.The comprehensive monitoring and diagnostic system proposed here will be quite useful to guarantee safe operation of fusion devices and helpful to understand what happened inside.