Calculation Of Hydrogen And Helium Concentrations And The Irradiation Simulation Study Of CSNS Target

China Spallation Neutron Source(CSNS) is the largest major scientific research devices in China, and it is currently under construction. CSNS is an accelerator-based facility to produce high intensity neutron by high energy protons bombarding heavy-metal targets, the beam power and energy of proton is 500 kW and 1.6GeV,respectively. In the process of high energy protons bombarding heavy-metal targets,the incident protons and spallation neutron interact with target will result in the displacement damage of target. Meanwhile the proton and neutron can lead to the formation of large amounts of helium and hydrogen in the form of transmutation products. These helium and hydrogen are insoluble in the matrix material. Hydrogen accumulations in the material will build up high hydrogen concentrations which induces hydrogen embrittlement, Helium accumulations in the materials would form helium bubble, which initiates helium embrittlement. Both of these effects esult in significant decrease in the macroscopic mechanical behavior and the service life of materials. Therefore, it is significant to study on hydrogen and helium concentrations in the target material and which induces the damage of material for assessment of the target material safety and service life.This paper focuses on the tungsten target of CSNS, by using the related physical model, it has carried out the following work: 1) According to the parameters of CSNS proton beam and the cross section of the interactions between proton and tungsten, we calculated the hydrogen and helium production rate in tungsten; 2) Then, based on the Fick’s second law and its solution in the steady-state pulse system, we obtained the hydrogen and helium background concentration of tungsten; 3) Finally, we got the highest concentrations of the hydrogen and helium by introducing the crack tip stress field theory and calculating the enhancement of hydrogen and helium concentrations near a crack. The results showed that the hydrogen background concentration is 3orders higher than that of the helium background concentration; The range of therelaxation time of hydrogen in the tungsten target is 10 days-50 days, and the helium is 7 hours-13 hours; The hydrogen and helium concentration near the tips of cracks present a different degree increased.Then we made some irradiation effect experiments of tungsten, tantalum and gold by the method of ion implantation. In this study, tungsten, tantalum and gold were irradiated to a total Si+3 does of 6.9345×1015 ions cm-2 and a total He does of3.57×1016 ions cm-2 at room temperature, the energy of Si+3 and He is 20 MeV and2MeV, respectively. Un-irradiated and irradiated samples were detected and analyzed by Nanoindentation, X-ray diffraction(XRD), Scanning Electron Microscope(SEM)and Transmission.Electron Microscope(TEM).Through the summarizing experimental data,the following main conclusions are got: 1) Compared with Un-irradiated samples,the hardness of irradiated samples about three materials are noticeably increasing, the tantalum showed the highest hardness increase, followed by the gold, the tungsten showed only a small increase; 2) Full width at half maximum(FWHM) of irradiated samples shows a broadened, it may be due to a great deal of dislocation and defects to form in the process of radiation; 3) Irradiation resulted in the grain refinement of tungsten; 4) A large amount of helium bubble were found in the irradiated samples by TEM, and compared with Un-irradiated samples, the number of dislocation and defects of irradiated samples are noticeably increasing.