Structure, phase analysis and component composition of multilayer films depositing in tokamak T-10

Full text: Two types of deuterocarbon films (homogeneous and globular) differing in their structure were found inside the T-10 tokamak vacuum chamber. Other films similar in microstructure to the homogeneous ones have formed on the smooth plasma facing surfaces of the 04Kh16N11MCT stainless steel mirror-specimens located inside the upper stub pipe of the vacuum chamber. Both types of the homogeneous films have been studied using X-ray diffraction analysis, Rutherford backscattering spectroscopy, scanning electron microscopy and elastic recoil detection method. The films formed on the chamber walls were reddish- brown and yellow. Those on mirrors were thinner, semitransparent and had a play of green, yellow and pink colors. The surface of the films was smooth, without any signs of physical sputtering. The films had a multilayer structure. Few hundreds of thin (<100 nm) layers were detected in cross sections of reddish-brown, ∼0.1 mm thick, films, while ∼10 layers formed on mirrors during a campaign. X-ray diffraction analysis indicates that all the films have crystalline structure and represent compounds of C and D. Both types of films have close values of the Wulf-Bragg diffraction angles and of lattice constants. These facts suggest that the film formation in both cases has the same mechanism. Measurements of refractive indices of the films in the ultraviolet range suggest that the films contain compounds of D with fullerens. At the same time, the two film types essentially differ in D-content. Films formed on the chamber walls are 'soft' with the D/C atomic ratio varying from ∼0.6 to 1.4. In the films on mirrors D/C = 0.2 - 0.35. D is distributed uniformly across the film thickness, except a narrow near-surface layer of films on mirrors where its concentration abruptly decreases. The difference in the amount of accumulated D in the films is determined by different conditions of the deuterocarbon molecules condensation. Simulation of the formation of hydrocarbon films having microstructure and internal texture similar to those in films formed in tokamaks was performed in the accelerator VITA and have shown that formation of the 'soft' films is not observed at temperature of 673 K. Our studies suggest that, in principle, it is possible, to suppress formation of 'soft' carbon films with high hydrogen isotope content in tokamaks, containing carbon plasma facing elements. (author)