| Neutron yield of deuterium-deuterium(DD)and deuterium-tritium(DT)fusion is a significant parameter to evaluate the control and the heating of the plasma in Magnetic confinement fusion research.The neutron activation method uses the activation reaction of neutrons and specific materials to measure the neutron yield of DD and DT fusion,it has been developed and applied as a standard neutron diagnostic method in Tokamak devices.The neutron activation diagnostic method will also be employed in fusion reactors in the future due to its high accuracy,wide measurement range,strong anti-interference and well radiation resistance.This thesis presents the employment and study of neutron activation method in the measurement of neutron yield in EAST.A neutron activation system has been designed and constructed on EAST based on the discharge parameters and neutron yield level.The calibration of the efficiency and the correction of the parameters of the neutron activation system has been accomplished,and the measurement of DD and DT neutrons and the research of the triton burn-up were performed.The EAST neutron activation system is mainly composed of activation samples,pneumatic transfer system and activation products measurement system.High purity(99.999%)indium and silicon with a dimension of ?20 × 1mm were served as activation sample which was applied in the measurement of DD and DT neutron respectively.The pneumatic transfer system uses a single transmission pipeline(?63mm)and several check valves to achieve the bidirectional transmission of activation sample between the activation measurement laboratory and the activation terminal which is located in G port.A high purity germanium spectrometer with a relative efficiency of 30%was used in the activation products measurement system.The detection efficiency of neutron activation system was calibrated by accelerator-based DD and DT neutron sources,the function between the net counts of characteristic gamma rays and the irradiated neutron flux of indium and silicon samples were obtained,and the detection efficiency of the samples with different thickness was calibrated as well.The characteristic pameters of high purity germanium detector was corrected with an 152Eu source,and it can be used to simulate the detection efficiency of activation samples.During the deuterium plasma experiment of EAST,the DD and DT neutron flux in the irradiation terminal during the discharge can be obtained by the measurement of full-energy peak of neutron activated indium and silicon samples respectively,and then the DD and DT neutron yield of the plasma can be calculated by combining the neutron transport coefficient which was simulated by MCNP.The EAST neutron activation diagnostic system was built in 2018 and put into experiment to measure the accumulated DD and DT neutron yield in each shot.The measurement range of DD and DT neutron yield is 1.9×1012?8.4×1014n/shot and 8.4×1010?2.2×1012n/shot respectively.The neutron flux correction function with dead-time less than 20%was obtained by analyzing the relative error of neutron flux under different dead-time of the gamma spectrometer.In addition,the gamma counts produced by interference reaction of indium samples were effectively reduced by using a 1mm cadmium shielding layer,and the precision of the result was improved as well.The study of DD neutron yield under neutral beam injection(NBI)was performed in EAST,the results show that the heating efficiency of different beam line of NBI is as follows:left source of line 1>right source of line 1>right source of line 2,the emissivity of DD neutron is approximately linear with the high voltage of NBI and the plasma current.The triton burn-up ratio of deuterium plasma was investigated by measuring the DD and DT neutron yield simultaneously.The results shows that the DT neutron yield increases with the DD neutron yield,the burn-up ratio of triton ranges from 6.2×10-4 to 5.0×10-3 in EAST,and the triton burn-up ratio increases with the DT neutron yield. |
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