Study On Fatigue Damage And Lifetime Of W/Cu Divertor Target

With fusion science and technology development,plasma parameters of magnetic confinement fusion have been progressed step by step in many tokamak devices.But there are still numerous challenges in the course of progress moving from laboratory basic research to pre-commercial development.And for the next-step tokamak devices or future fusion power reactors,long pulse and high confinement plasma regime(H mode)is considered to be a preferable scenario to get high fusion power amplifications.During H mode,because of the magnetohydrodynamics(MHD)instability,a regular and approximatively periodic flow of energy and particles will travel into scrape-off layer and then transport into divertor along magnetic line,which results in a large transient heat flux to the divertor targets.And it will damage the divertor targets.The divertor is one of the most important in-vessel components in tokamak due to its man missions being related to impurity control as well as energy and ash exhaust.In order to improve the capacity of the divertor and study the performance and behavior of the advanced tungsten divertor which will be installed in the ITER,the upper divertor of the EAST was upgraded into ITER-like in 2014.And prior to the high confinement experiment,it is necessary to assess the potential damage which is expected in the experiment of a high performance plasma regime.The conclusion could offer a pertinent guideline on the maintenance and replacement of the divertor in service and would also be helpful to provide some suggestions in the divertor design.Meanwhile,it can assist the physical experiment carried out successfully and improve the efficiency of the tokamak.Based on the characteristics of heat flux summarized from the experiments in EAST and other tokamaks around the world,.this dissertation studies the thermal and structure behavior of the W/Cu divertor target with the heat flux in H mode and develops a response model which can obtain the fatigue damage from the characteristic parameters of the heat flux on the divertor target detected in the tokamak directly.Then we can assess and monitor the fatigue damage of the divertor targets in real time and estimate whether the divertor targets will failure.Firstly,the response of the divertor target with excessive heat flux induced by the edge localized modes(ELMs)in the H mode has been analyzed.To make a visible outcome of the ELMs impact on the target,a preliminary evaluation system with three indices to exhibit the macro-and microcosmic effect has been developed.The indices contain temperature evolution,thermal penetration depth and crack initiation life.And the relationship between the indices and heat flux has been investigated respectively.Then,the response of the divertor target during whole H mode has been studied.In this part,the temporal evolution of the heat flux at the striking point in the discharge has been defined.And four characteristic parameters which include steady state heat flux,transient heat flux,rise time and frequency of ELMs have been extracted to analyzed the response.After that,the monoblock structure of the divertor target has been divided into four parts according to the response behavior and structure characteristics.And then the response behavior model related to the different heat flux parameters for each part has been established.Ultimately,based on the aforementioned results and combined with rain flow counting method,Neuber and Miner-Palmgren linear damage cumulative rule,fatigue damage and lifetime prediction models for plasma facing surface and cooper alloy tube of the W/Cu divertor target during H mode have been organized respectively.It is realizable to predict the fatigue damage of the divertor target with these models and then a suitable maintenance plan for the divertor can be developed according to the results.