In-situ measurements of low energy D plasma-driven permeation through He pre-damaged W

Experiments concerning the effect of helium (He) plasma exposure on deuterium (D) plasma-driven permeation (PDP) through tungsten (W) foils in a linear plasma facility has been performed. 0.05 mm thick W foils were exposed to ~2×1020 m-2s-1 He plasma with various fluences at 883 K. After He irradiating, D permeation tests were performed for the samples and retention was also measured by high-resolution thermal desorption spectroscopy (TDS). It was observed that He pre-irradiation resulted in a significant reduction of D permeation and retention in W. Microstructure observation indicated that the surfaces of samples after He irradiation turned rough and He nanobubbles were formed near the surface. The defective structure including He nanobubbles very likely enhances D reemission and accordingly reduces the permeation and retention in He pre-irradiated W.

Axial uniformity diagnosis of coaxial surface wave linear plasma by optical emission spectroscopy

The coaxial surface wave linear plasma with preeminent axial uniformity is developed with the 2.45 GHz microwave generator. By optical emission spectroscopy, parameters of the argon linear plasma with a length over 600 mm are diagnosed under gas pressure of 30 Pa and 50 Pa and different microwave powers. The spectral lines of argon and Hβ (486.1 nm) atoms in excited state are observed for estimating electron excitation temperature and electron density. Spectrum bands in 305–310 nm of diatomic OH (A2 Σ+-X2 Πi) radicals are used to determine the molecule rotational temperature. Finally, the axial uniformity of electron density and electron excitation temperature are analyzed emphatically under various conditions. The results prove the distinct optimization of compensation from dual powers input, which can narrow the uniform coefficient of electron density and electron excitation temperature by around 40% and 22% respectively. With the microwave power increasing, the axial uniformity of both electron density and electron excitation temperature performs better. Nevertheless, the fluctuation of electron density along the axial direction appeared with higher gas pressure. The axial uniformity of coaxial surface wave linear plasma could be controlled by pressure and power for a better utilization in material processing.

Fabricating tritium permeation barrier for PFC with a new non-coating strategy

Tritium (T) permeation through plasma-facing component (PFC) into the coolant is a major concern of fusion reactor operation. In this work, deuterium (D) permeation through CLAM steel, CLAM/CLAM and CLAM/Fe-Cr-Al samples prepared by hot isostatic pressing (HIP) are tested in a linear plasma device. Only the downstream surfaces of the samples are oxidized with controlled atmosphere to form permeation barrier. No significant effect on D diffusion and penetration can be observed for the joining interfaces, while the dense oxide layer at the downstream side plays an important role in suppressing D permeation. The downstream surface oxidization of CLAM/Fe-Cr-Al is found to effectively reduce D permeation flux by a factor up to 1000.