A Study On Deuterium Retention In Carbon-tungsten Composite Material

Carbon(graphite and composite materials) and tungsten are used as plasma facing materials in the existing Tokomak reactors(such as JT-60U in Japan, ASDEX-U in Germany, DIII-D in America, etc.), as a result of the characteristic of thermodynamic property, high sublimation temperature and good compatibility with plasma in C and high melting point, poor sputtering yield and inert with D in W. In the future, the safety and stable operation of ITER and commercial fusion reactor requires only a little retention of hydrogen isotope, therefore, the digital analogy and experimentation research of hydrogen isotope retention has been carried out in the world.In recent years, the study of deuterium retention in carbon flakes and tungsten flakes are more than that in carbon-tungsten mixed flakes in the world and there exists difference for achieving the research conclusions in carbon-tungsten mixed flakes, so the co-deposited C-W layers were produced by RF magnetron sputtering in D2/Ar plasma. The layers were characterized by ion beam analysis (IBA), Raman spectra (RS), scanning electron microscopy (SEM) and thermal desorption spectrum (TDS). First of all, thickness, ingredients and D concentration were analyzed by IBA. Then, the structure and surface morphology of them were analyzed by RS and SEM respectively. Finally, we made a further study on the peak of D desorption and D concentration by TDS. Some valuable conclusions that have been obtained by our study are as follows:1. It was found that D atoms in C-W layers are mainly trapped by the trapping site of C atoms and only few of them arrested by W atoms or defects. The increase of W concentration will significantly lead to the decrease of D concentration. D concentration in the C-W layers deposited at5.0Pa with a fixed flow rate ratio QD2/QAr=2.5decreased slightly with increasing temperature.2. D concentration increased with the gas pressure from zero Pa to5Pa and then decreased from5Pa to10Pa when the other conditions remain unchanged.3. RS revealed that the crystal structure of the C-W flakes became graphite-like and the structure became more amorphous with increasing temperature.4. SEM images showed that the caves disappeared and convex bodies were dotted on the surfaces when the temperature increased.5. XRD patterns indicated that there are no obvious W and W2C phases in the near surface of the deuterated C-W layers and the crystal structure of the C-W flakes became graphite-like with increasing temperature. The latter conclusion further confirmed the phenomenon showed in Raman spectra.6. It was showed by TDS that the retained deuterium was desorbed mainly in the forms of D2, HD, HDO and D2O/CD4. The images also indicated that D concentration in the C-W layers decreased slightly with increasing temperature and it further confirmed the analysis by IBA.