Measurement Of Helium Distribution In The First Wall Material And Its Effect On Deuterium Retention

The first wall material is a structural material directly facing the plasma irradiation environment in the nuclear fusion device.Tungsten is known as a candidate material for the first wall material of the fusion reactor due to its high melting point,high sputtering threshold,and low fuel retention.The radiation damage and retention caused by the fusion reaction product helium on the wall material and the effect on the hydrogen isotope retention are also not conducive to the performance and service life of the fusion material.The study of helium retention behavior and depth distribution in the material is helpful for understanding the interaction between helium and wall materials.Therefore,this paper mainly uses magnetron sputtering and ion implanter to prepare films with controllable helium content and the first wall overall material,combined with rutherford backscatter spectrometry(RBS),scanning electron microscope(SEM),transmission(TEM),thermal desorption spectroscopy(TDS),SRIM software simulation and glow discharge optical emission spectroscopy(GDOES),established GDOES to analyze the helium concentration distribution in different materials(helium-tungsten film,tungsten,copper and EUROFER97 steel),quantitative study of helium retention in first wall materials and the effect of helium retention on the surface morphology and deuterium-helium retention behavior of the material after subsequent deuterium plasma irradiation.The main research results are as follows:(1)A tungsten film with controlled helium content was prepared by magnetron sputtering a tungsten target in an argon-helium mixed atmosphere.The surface of the prepared tungsten and helium film is smooth and dense,and the cross-sections have a columnar structure.In the thermal desorption spectrum of tungsten-helium film,helium has a helium desorption peak in a high temperature region(1300 K).Most of the helium desorption behavior in the high temperature region is related to the formation of helium vacancy complexes,clusters and bubbles.The 1200 nm thickness of helium-tungsten film does not have obvious desorption peaks,which may be due to the high helium desorption temperature or helium is an inert element.The helium ion energy during the preparation of the tungsten-helium film is low,has no implantation effect,and does not interact with tungsten co-deposition.(2)The first wall material containing helium was prepared by implanting helium ion into tungsten,copper and EUROFER97 steel materials,and the depth and concentration of helium in the material were calibrated and analyzed by SRIM,TEM and GDOES analysis methods.The results showed that after 400 keV helium ion implantation of tungsten and copper,a large number of helium bubbles were formedin the regions of 0.7 μm and 0.8 μm to 1.3 μm,respectively.The helium distribution is consistent with the SRIM simulation.GDOES and step instrument were used to analyze the depth of the erosion hole.The sputtering rates of tungsten,copper and EUROFER97 steel were 18.3 nm/s,31.5 nm/s and 12.0 nm/s,respectively.When the helium ion concentration exceeds 0.01 at.fr,GDOES measures the peak helium concentration more accurately.The total helium retention was calculated by integrating the TDS and GDOES curve.It was found that the total helium retention amount in the tungsten sample measured by the TDS method was lower than the calculated value of GDOES.This was mainly due to the limitation of the heating temperature in the thermal desorption experiment.The total helium value in copper or EUROFER97 steel tested by GDOES and TDS is basically the same,which is slightly higher than the helium retention amount calculated by SRIM simulation,which is effected by helium diffuses in the material.(3)The service behavior of tungsten materials after high-energy helium ion implantation was further investigated,and the surface profile,deuterium thermal desorption behavior,and depth distribution of deuterium and helium after the irradiation of deuterium plasma with tungsten were analyzed.The results showed that high density helium bubbles exist at the peak position of helium concentration in tungsten observed by TEM.GDOES measured the deuterium retention concentration in the helium ion-implanted damaged area of tungsten increased significantly.The TDS test found that the release peak of deuterium in tungsten after helium ion pre-implantation was significantly enhanced and extended to the low temperature region,indicating that helium ion pre-implantation caused a large number of dislocations such as deuterium to capture low-energy deuterium sites in tungsten and increased high-energy capture sites such as vacant clusters.