Hydrogen isotope ratios measurements by Penning gauge spectroscopy of molecular Fulcher-α band

Penning gauge spectroscopy of Balmer-α lines of hydrogen isotopes is widely used in fusion experiments to determine the hydrogen isotope ratios and the partial pressures in the pump duct. The Balmer-α line isotopic shifts are very small < 0.176 nm and the lines partially overlap because of the presence of energetic atoms produced by molecular dissociation. The ro-vibrational emission bands of each hydrogen isotopomer consist of many narrow spectral lines, covering a wide wavelength span and have an unique signature. To investigate the capability of the hydrogen molecular spectroscopy for the isotopic ratio determination, an Alcatel-type Penning gauge was coupled by the optical fiber to the Echelle spectrometer having 365–715 nm spectral range and the spectral resolving power above 20,000. The intensities of both atomic Balmer-α lines and molecular Fulcher-α bands were measured in the range of 6·10−6 – 4·10-3 mbar. The rotational and vibrational populations were almost independent of the gas pressure below 2·10-4 mbar. The total intensities of the Fulcher-α molecular bands were linearly proportional to the gas pressure. The H2 and D2 molecular emission in 599–639 nm spectral range were in a good agreement with the isotopic composition of the used gas mixtures

Short-term retention in metallic PFCs: modelling in view of mass spectrometry and LIBS

Based on the conventional model of hydrogen retention in plasma-facing components, the question of hydrogen outgassing during and after plasma exposure is addressed in relation to mass spectrometry and laser-induced breakdown sprectroscopy (LIBS) measurements. Fundamental differences in retention and release data acquired by LIBS and by mass spectrometry are described analytically and by modelling. Reaction-diffusion simulations are presented that demonstrate possible thermal outgassing effects caused by LIBS. Advantages and limitations of LIBS as a tool for analysis of short term retention are discussed

Improving accuracy of Penning gauge spectroscopy for the determination of hydrogen isotope H/D ratios

Atomic spectral lines emitted from a Penning discharge are often used to quantify partial pressures and isotopes ratios in gases. To identify the potential of this method for thermal desorption studies, the hydrogen emission spectrum lines (Hα and Dα) were examined by an Alcatel Penning gauge. The hydrogen/deuterium pressures were measured by both a capacitive vacuum gauge and the Penning gauge. Different gas mixtures were produced by varying of hydrogen/deuterium flows. The Balmer-alpha lines intensities were recorded with help of a high etendue spectrometer coupled to the Penning gauge using relay optics together with fiber bundle and equipped with Peltier cooled CCD camera. Subsequent measurements using hydrogen and deuterium gases revealed for identical pressures in the range of 10−6–10−3 mbar that the Hα line intensities are systematically higher the Dα line intensities by a factor of 1.28 ± 0.01. This observation can be explained by the dissociative excitation of the molecular hydrogen by electron impact. In addition the Hα line intensity for the H2 gas having constant partial pressure is slightly increased with total gas mixture pressure. Taking into account of both effects essentially improves the accuracy of the determination of partial pressures and isotope H/D ratios

Analysis and removal of ITER relevant materials and deposits by laser ablation

The analysis of the deposition of eroded wall material on the plasma-facing materials in fusion devices is one of the crucial issues to maintain the plasma performance and to fulfill safety requirements with respect to tritium retention by co-deposition. Laser ablation with minimal damage to the plasma facing material is a promising method for in situ monitoring and removal of the deposition, especially for plasma-shadowed areas which are difficult to reach by other cleaning methods like plasma discharge. It requires the information of ablation process and the ablation threshold for quantitative analysis and effective removal of the different deposits. This paper presents systemic laboratory experimental analysis of the behavior of the ITER relevant materials, graphite, tungsten, aluminum (as a substitution of beryllium) and mixed deposits ablated by a Nd:YAG laser (1064 nm) with different energy densities (1–27 J/cm2, power density 0.3–3.9 GW/cm2). The mixed deposits consisted of W–Al–C layer were deposited on W substrate by magnetron sputtering and arc plasma deposition. The aim was to select the proper parameters for the quantitative analysis and for laser removal of the deposits by investigating the ablation efficiency and ablation threshold for the bulk materials and deposits. The comparison of the ablation and saturation energy thresholds for pure and mixed materials shows that the ablation threshold of the mixed layer depends on the concentration of the components. We propose laser induced breakdown spectroscopy for determination of the elemental composition of deposits and then we select the laser parameters for the layer removal. Comparison of quantitative analysis results from laboratory to that from TEXTOR shows reasonable agreements. The dependence of the spectra on plasma parameters and ambient gas pressure is investigated