In this paper we described new experimental data on hydrogen interaction with the first wall of a nuclear fusion reactor. By applying a very sensitive method we were able to measure most relevant parameters which govern hydrogen transport through tungsten films. Combined Magnetron Sputtering and Ion Implantation (CMSII) technology was used for W coating of Eurofer substrates. Double layered membrane was then investigated in permeation experiment with gaseous hydrogen at 400 °C. Measured diffusivity is several orders of magnitude lower compared to the average of published data for tungsten, while the measured solubility is several orders of magnitude higher. The explanation is given in terms of hydrogen trapping that has significant impact on hydrogen migration.
COBISS.SI-ID: 24636967
Highly symmetric ring-shaped field emission patterns were observed from broad-area flat cathodes prepared by growing a film of vertically aligned carbon nanotubes (CNTs) on TiN coated Si substrates. The images were obtained utilizing a luminescent screen of a specially designed triode cell composed of parallel electrodes. The emission rings sporadically appeared during voltage scans in which the emission patterns and cathode currents were recorded. The fine structure and stability of the rings suggests that their formation is due to an emission state of an individual CNT. The observed patterns are consistent with models that predict the formation of emission rings produced by the inhomogeneous electron emission from CNTs. The macroscopic value of the electric field when the rings were observed was between 0.7 and 2.5 V/µm, and the emission current corresponding to individual rings was estimated to be in the range of 2–4 µA. Numerical simulation of electron trajectories for sidewall emission from similar shaped metallic structures is in qualitative and quantitative agreement with the experimentally observed ring-shaped field emission patterns
COBISS.SI-ID: 24646183
In our work, long-term hydrogen outgassing and permeation studies of structurally highly disordered ungsten films, deposited on 40 mm diameter highly permeable Eurofer substrates, using the Pulsed Laser Deposition technique have been realized. Permeability of W films having different thicknesses (1 and 10 micrometers) was initially extremely low, and was gradually increasing over a several-day campaign. The final values at 400 °C, lying between P = 1.46x10-15 mol H2/(m s Pa^0.5) and P = 4.8x10-15 mol H2/(m s Pa^0.5), were substantially lower than those known for well-ordered films. Surprisingly, the 10 micrometer thick W film initially contained a very high amount of hydrogen, ~ 0.1 H/W, which was gradually releasing during the twenty-day campaign.
COBISS.SI-ID: 25908263
Melamine-formaldehyde fibres were synthesised from a meltable prepolymer of etherified melamine-formaldehyde in the form of a low-density fleece, subsequently thermally cured in a conveyor belt oven at temperatures of up to 200 °C and post-heated at 260 °C. High thermal stability and small fibre diameter below 5 µm made it a serious candidate as a novel core material for vacuum thermal insulation panels. Two most crucial core properties, thermal conductivity and outgassing rate, were investigated in thin-walled stainless steel envelopes, enabling thermal processing combined with a pump-out procedure. A base thermal conductivity of ~2.3 mW m-1 K-1 was achieved with randomly oriented fibres at a density of ~250 kg m-3. The long-term pressure-rise measurements revealed extremely low specific outgassing rates, q ~ 10-15 mbar L s-1 cm-2. Additional measurements of thermal conductivity in a wide pressure range from 10-3 mbar to the atmosphere indicate that these melamine-formaldehyde fibres could be claimed as the first organic candidates applied as the core material in vacuum insulating panels with an adequate service lifetime. Their performance is comparable to selected inorganic core materials like glass fibres.
COBISS.SI-ID: 27183911
The vacuum problem in sealed off chambers of VIGs type has been solved. The solution is based on two innovations. The first one is the usage of activationless getters in a form powders or granules of the composition Ca0.35Li0.45Mg0.20 instead of barium. The second one – the changed sequence of assembling the vacuum window at which the getter is introduced into the window under vacuum but after the thermal outgassing and edge sealing of the VIG. A mathematical model of the sorption process for getter powders or granules, which follow the parabolic sorption law, has been built. The model analysis leads to an easy method of calculating the lifetime of the vacuum window, when the thermal-insulating properties are maintained by the getters of the class of reactants. Also a criterion of usefulness of technical solutions as applied to VIGs is provided
COBISS.SI-ID: 1449386
Quantification accuracy of nitrogen and carbon monoxide in argon used as the matrix gas was studied by quadrupole mass spectrometers (QMS) at very low partial pressures when no interference between ions was expected. The effect of mutual ion interactions within the ionization cell is well recognized, but it arises at much higher pressures. Our measurements were performed in an UHV system designed for pressure gauge calibrations. In two in situ calibrated QMSs with different ion source designs, the argon leak rate noticeably increased the QMS signal of a trace gas: at low leak rates, nitrogen was increased for a factor of up to ~3, and carbon monoxide signal for a factor of up to ~2.8 at the first QMS, while this effect was much smaller in the other QMS. The anomaly was not observed at high leak rates of trace gases. The underlying physical process seems to be the argon-assisted charge transfer to nitrogen and carbon monoxide molecules adsorbed on the quadrupole rods in the filter section. Despite the fact that this physical effect is manifested as an instrumental error, the accuracy of quantification of unknown gas mixtures containing these gases can be substantially improved after numerical correction factors for particular QMS device have been determined.
COBISS.SI-ID: 31154215
The flow of different gases in a long, circular tube was investigated with a focus on the influence of the surface condition on the conductance in the molecular regime. The measurements of conductance were made with an uncertainty below 0.5%. A stainless-steel tube with a uniform diameter and roundness was used. The precisely known geometry of the tube allows an accurate calculation of the conductance in the molecular regime under the assumption of a perfectly diffuse scattering of molecules on the surface. Any deviation from diffuse scattering on the surface influences the molecular conductance of the tube. A comparison of the measured and calculated conductance in the molecular regime allows an estimation of the effective tangential momentum accommodation coefficient (ETMAC) of the tube's surface. The tube was first measured in the as-received condition (electropolished surface), and after that exposed to different treatments that altered the surface condition and influenced the ETMAC. In addition, the same tube was chemically etched to increase the surface roughness. Both surface types were treated by heating in vacuum, oxygen and hydrogen. A large variation in the conductance of 10%–20% was observed after etching, depending on the gas (He, CH4, Ne, N2, Ar, Kr).
COBISS.SI-ID: 1453994
The development of a new primary interferometric liquid column manometer for measurement of absolute and gauge pressures in the range up to 2?kPa is an ongoing project at PTB, Germany. For measurements in this pressure range, liquids with a low density are advantageous because of a better pressure resolution determined through differential column height measurements. In addition, low vapor pressure is a precondition for an accurate measurement of absolute pressure. The choice of liquid is crucial for the accuracy of the new instrument. This paper discusses the effect of liquid properties such as vapor pressure, density, viscosity, surface tension and gas absorption capacity on the performance of the micromanometer. Seven liquids – all oils used in vacuum applications (vacuum oils) – representing different classes of chemical compounds were analyzed in respect to their viscosity, density, thermal expansion and compressibility. Detailed investigations were performed on three liquids out of seven to determine their density versus gas saturation, ab- and desorption kinetics and surface tension, as well as the wettability of the micromanometer’s materials. Results of the measurements and recommendations for the use of the liquids are presented.
COBISS.SI-ID: 1454250
Gas flow was measured by using constant volume-variable pressure method. The gas flow is measured by pressure rise method using spinning rotor gauge (SRG). The design is relatively simple and has no precisely movable parts compared to the constant pressure-variable volume method. Due to outgassing effect we used a non-evaporable getter pump in order to diminish the influence of hydrogen outgassing on measured gas flow. Lower limit of pressure rise method is 5 × 10-10 mbar l/s and this is extended to 3 × 10-12 mbar l/s by using constant conductance method. With this flow meter we generated a calibration pressure of Argon in our calibration system in the range from 8 × 10-13 mbar up to 2 × 10-7 mbar.
COBISS.SI-ID: 1378986
The spinning rotor gauge (SRG) is a common transfer standard in key comparisons (KCs) and other intercomparisons for pressures in the range of 1.0 x 10-4 Pa to 1.0 Pa. To make absolute pressure measurements using a SRG, a calibration factor, known as the accommodation coefficient, must be determined. Comparisons which utilize SRGs require each participant to determine the accommodation coefficient. The accommodation coefficient of an SRG is known to have excellent long-term stability ((0.1% over 1 year; k = 1) in a laboratory environment where the rotor remains undisturbed and attached to a vacuum standard, but the long-term stability of SRGs used in comparisons is often worse than what is observed in the participants own laboratory. Recently, the Bureau International des Poids et Mesures Consultative Committee for Mass and Related Quantities Working Group on Low Pressures held a workshop to discuss the stability of the accommodation coefficient in inter-laboratory comparisons. Here we summarize the data presented during the workshop and the ensuing discussions and give a list of recommended practices derived from the workshop.
COBISS.SI-ID: 1118634