Research On Reliability Of EAST Divertor Targets

As one of the important parts in Tokamak,the divertor bears energy impact and particles bombardment under strong magnetic fields,which is the energy and particles channel out of the vacuum and also has the role of controlling impurity.During the operation of Tokamak,the plasma facing divertor targets,under great thermal loads and electromagnetic loads,encounter various failure modes which are likely to cause standstill of the plasma test,even cause damage to the machine.Therefore,it is necessary to research on reliability of EAST divertor targets.By describing the current situation of energy utilization,controlled nuclear fusion and Tokamak are introduced,in addition to development process of the divertor.Then,research history of reliability and general concept of reliability are described,and current mainstream research approaches are given.Failure modes of divertor targets,which consist of failures due to material and function,are summarized based on the survey of reliability of EAST divertor targets,and there is analysis of causes of divertor targets failure modes.Taking EAST lower divertor as an example,statistics and distribution of divertor targets failure modes are shown.After setting up the Gaussian Mixture Model of Halo currents peak distribution through EAST upper divertor targets,the failure probability and reliability probability of upper divertor targets are calculated using the Exception Maximization Algorithm,which is integrated with the Limit State Function derived from the equivalent model and design parameters of upper divertor targets,and the results show upper divertor targets have extremely high reliability under Halo currents.On basis of the current status of operation of EAST upper divertor targets,the calculated results of structural reliability are analyzed.Using IDEF(?)method,the functional analysis of EAST lower divertor targets is carried out in the bottom-up way.Based on the scale for occurrence and severity of failure modes,the parameter estimation of reliability is proposed,and failure modes of lower divertor targets are qualitatively and quantitatively evaluated.Risk mitigation actions are taken according to the risk scale of different failure modes.On this foundation,the initial and expected reliability and availability of lower divertor targets are calculated using the BlockSim code.Compared with the initial availability and reliability,the expected reliability and availability of EAST lower divertor targets are improved.On basis of the current status of operation of EAST lower divertor targets,the calculated result of reliability and availability is analyzed.Research on reliability of EAST divertor is in a development stage,and the work already been completed in this dissertation is able to provide the reference for the coming upgrade of EAST divertor and the fusion reactor in the future.