A mass spectrometer with a custom sampling system comprising one fixed and one variable orifice is presented. The custom sampling system allows the determination of the gas composition in the pressure range from 5 mbar to 1000 mbar, with low gas-demixing (<1.5%). A case study of mass spectrometer optimization and calibration for the measurement of relative concentration of CO2, CO, O2, and N2 gases is presented, together with an example of the CO2 conversion at a microwave plasma torch. The absolute error of the measured conversion of CO2 in CO is found to be less than 1.6% in the complete pressure range. The conversion determination routine presented here allows us to determine relative molar flows of CO2, CO, O2, and N2 and to distinguish between CO and N2 gases, which is important for the determination of the CO2 conversion in the case of air impurities or in the case of CO2/N2 mixtures.

Impurity seeding will be mandatory for ITER to protect the divertor files from excessive heat loads. Nitrogen seems to be a possible candidate due to its good radiation properties. The N content in the divertor plasma is crucial for cooling by radiation but is difficult to characterize. To assess the nitrogen fluence from the divertor plasma in nitrogen seeded discharges of ASDEX Upgrade (AUG), the concentration of two nitrogen containing molecules, ammonia and molecular nitrogen (N-2) was measured. The N-2 measurements were strongly affected by local effects which indicates that a significant fraction of the puffed N-2 did not enter the plasma. In contrast, the measured ammonia fluence is proportional to the integrated nitrogen core density. This leads to the possibility of gaining the nitrogen fluence of the plasma, with the help of the created ammonia, for nitrogen seeded discharges. In discharges where the wall inventory was the only source of nitrogen in the plasma, 50% of the nitrogen was converted to ammonia, in the inner divertor. This allowed for the assessment of the nitrogen atom fluence from the plasma based on the detected ammonia in N-2-seeded discharges.

Nitrogen seeding, necessary for divertor heat-load mitigation in ITER, has been shown to lead to ammonia formation which would be a severe operational and safety issue in ITER. Predictions of ammonia production in ITER are based on data from present day fusion devices. Ammonia is mainly detected by residual gas analysis (RGA). Detection of ammonia is impeded by the presence of water and methane which, in a mixed H-D system, leave signatures in the same range of the mass spectra. A statistical model is used to ascribe an average isotope ratio to each gaseous species. The model is tested with simulated RGA recordings with varying concentration of ammonia to evaluate the sensitivity to fitting parameter boundaries, noise in the recordings and mis-matching cracking patterns. The analysis shows that the fitting procedure may in some occasions substitute species among each other, resulting in faulty concentrations. Nevertheless, the right choice of parameter boundaries ensures correct fitting results. Finally, the fitting procedure is applied to experimental data from nitrogen-seeeded discharges at AUG and JET. (C) 2017 Published by Elsevier B.V.

Amorphous hydrogenated carbon (a-C:H) deposits were eroded in the afterglow of a NH3 plasma, created with an inductively coupled RF generator in pure NH3 at the gas pressure of 50 Pa. The plasma system was characterised by optical emission spectroscopy and mass spectrometry, and the erosion process was monitored in-situ with a laser interferometry system. Based on the mass spectrometry measurements, the degree of dissociation of the NH3 molecules was estimated at 90% at the highest generator forward power in the discharge region, however the densities of N and H atoms were significantly smaller at the location of the sample holder. The erosion rates were found to increase with surface temperature and forward generator power. In the high dissociation regime, the composition of the afterglow and the reaction products highlight the role of N atoms in the erosion process. (C) 2016 Published by Elsevier B.V.

The ASDEX Upgrade (AUG) system for glow discharge (CD) has been revised comprehensively. This was necessary due to technical as well as operational requirements. The available space with in the low field side of the vacuum vessel is strongly limited because it's the preferred place for diagnostics. The new development based on the design of the W7-X anode now has a smaller footprint, is long term reliable and easier maintainable. Additionally each of the anodes is equipped with a separate starting device. The use of this device now allows the fast ignition of GD at operational pressure without the need of a short-term pressure increase. With the change from carbon to tungsten plasma-facing components (PFCs) an enhanced Helium (He) content at plasma discharges was observed for unboronized walls and the implantation of He during GD could be identified as source. For this reason the use of He GD has to be strongly reduced. It turned out that pulsed GDs of about 10 s length followed by a pumping down phase are sufficient to clean the wall. This mode of operation requires a reliable breakdown of the GD at operating pressure. This paper gives an overview of the technical setup and first measurement results. (C) 2017 Elsevier B.V. All rights reserved.

Initial stages of Inconel 625 superalloy (Ni60Cr30Mo10Ni4Nb1) oxidation upon short treatment with gaseous plasma at different temperatures up to about 1600 K were studied. Samples were treated for different periods up to a minute by oxygen or hydrogen plasma created with a microwave discharge in the standing-wave mode at a pressure of 40 Pa and a power 500W. Simultaneous heating of the samples was realized by focusing concentrated solar radiation from a 5 kW solar furnace directly onto the samples. The morphological changes upon treatment were monitored using scanning electron microscopy, compositional depth profiling was performed using Auger electron spectroscopy, while structural changes were determined by X-ray diffraction. The treatment in oxygen plasma caused formation of metal oxide clusters of three dimensional crystallites initially rich in nickel oxide with the increasing chromium oxide content as the temperature was increasing. At about 1100K iron and niobium oxides prevailed on the surface causing a drop of the material emissivity at 5 pm. Simultaneously the NiCr2O4 compound started growing at the interface between the oxide film and bulk alloy and the compound persisted up to temperatures close to the Inconel melting point. Intensive migration of minority alloying elements such as Fe and Ti was observed at 1600K forming mixed surface oxides of sub-micrometer dimensions. The treatment in hydrogen plasma with small admixture of water vapor did not cause much modification unless the temperature was close to the melting point. At such conditions aluminum segregated on the surface and formed well-defined Al2O3 crystals. (C) 2014 Elsevier B.V. All rights reserved.

Dusty plasma has traditionally been considered as pollutant species in plasma processes. However, lately it is being regarded as an interesting way of producing nanocomposite thin films. In this paper, the basics of dusty plasma physics are presented. Discussed is the nucleation and growth, which can be either a consequence of homogeneous plasma reactions, heterogeneous reactions on the plasma-surface interface or they can be injected externally into the plasma. The particles are negatively charged, which strongly influences their movement. The most important interaction is the repelling force in the plasma sheath which confines the particles to the plasma volume. Also presented in this paper are the basic properties of nanocomposite thin films and their application in modern technological and industrial applications. Examples of dusty plasma produced nanocomposite thin films are given in the final chapter.

Composite thin films are deposited from acetylene in a microwave multipolar plasma excited at distributed electron cyclotron resonance in one single process. The composite consists of carbon-based nanoparticles embedded in a hydrogenated amorphous matrix. Effects of plasma duration and microwave power on the composite thin film are described along with the powder growth mechanisms. Indeed, two types of nanoparticles are formed: pure graphite-like and graphite-like shell with a metallic core. The first type grows from recombinations in the plasma phase, while core-shelled starts from a metallic core generated from the reactor walls. These metallic clusters can be heated while immersed in the plasma which leads to catalytic growth of powders.

Dissociation fraction of CO2 molecules was measured in an early afterglow of microwave plasma by catalytic probes. The experiments were performed using the MESOX facility at the focus of the 5 kW solar furnace of PROMES-CNRS. Plasma was created in a quartz tube within a microwave cavity powered with a generator with adjustable power between 200 and 1200 W and frequency of 2450 MHz. The dissociation fraction was measured by catalytic probes at different flows of carbon dioxide gas up to 20 l h−1 corresponding to different pressures up to 150 Pa. The dissociation fraction reached 13% at the pressure of about 20 Pa. The density of O atoms at the probe position was increasing with discharge power and was almost 1021 m−3 at the highest power. A broad maximum in the O-atom density versus pressure was observed. The results were explained by gas-phase and surface reactions.

In the search for a sustainable energy source for future generations, thermonuclear fusion should not be left unconsidered. One of the important problems of current and near-future fusion devices is the formation of amorphous hydrogenated carbon deposits (a-C:H), which have to be removed regularly. Removal of a-C:H by atomic oxygen seems like a suitable candidate for a cleaning method. Efficiency of the cleaning method will depend on the efficiency of atomic oxygen delivery. This in turn will depend on the atom loss on reactor walls, which is predominantly governed by recombination. An experiment was performed to measure the recombination coefficient of a-C:H for neutral oxygen atoms. The source of atomic oxygen was an inductively coupled RF discharge, created in pure oxygen. The oxygen densities were measured by a nickel tipped FOCP. The a-C:H sample was prepared by thermionic arc sputtering of a graphite target in a mixed argon / acetylene atmosphere. The recombination coefficient was found to be of the order of 10(-3). Moreover, it was discovered that the a-C:H deposition was eroded by O atoms during the experiment. In a rough estimate, the probability of oxidation was found to be two orders of magnitude lower than the probability of recombination.

The growth of dust particles in electron cyclotron resonance plasma is highly related to the confinement of species in the magnetic field. Nanoparticles formed in these regions draw curved trajectories observable by naked eyes, related to their velocity, mass, and charge.

Results on chemical removal of oxygen from thin tungsten oxide films with hydrogen plasma are presented. Tungsten foils were oxidized in a furnace at 400 °C for 1 h, so a compact oxide film with the thickness of about 160 nm was formed. The samples were then exposed to hydrogen plasma created in a microwave discharge at the power of 1000 W and a hydrogen pressure of 90 Pa. The plasma density was estimated to the order of 1016 m−3, whereas the density of neutral hydrogen atoms was 2.5 × 1021 m−3 measured by a fiber optics catalytic probe. Samples were exposed to hydrogen plasma for different time. The evolution of the reduction process was monitored by measuring the AES depth profiles on samples exposed to plasma for different time. The results showed that the oxide film was reduced in about 10 s of plasma treatment. The average removal rate was thus about 16 nm s−1. Such a high reduction rate cannot be explained by the interaction of hydrogen ions, because the ion flux onto the sample surface is orders of magnitude too low, but rather by the interaction of neutral H‐atoms with the oxide film. Taking into account the known reduction rate and H‐atom density, one can estimate the reaction probability to about 3 × 10−4. Copyright © 2010 John Wiley & Sons, Ltd.

A density of neutral hydrogen atoms was systematically measured in the MESOX solar plasma reactor at different MW powers and flow rates. The H-atom density was measured by a gold fibre optics catalytic probe. The H-atom density was in general increasing with increasing MW power. At a pressure of 40Pa and a power of 500W it was about 3.5×1021m−3 and at a power of 1000W it was about 4.1×1021m−3. A degree of dissociation of hydrogen molecules was between 3% and 20% depending on pressure and power. A maximum degree of dissociation was obtained at a pressure of 40Pa and 1000W, while the lowest one at 130Pa and 500W.

Surface oxidation of the duplex stainless steel DSS alloy 2205 was studied by X-ray photoelectron spectroscopy (XPS) and SEM imaging. The experiments were performed on the alloy after controlled oxidation with oxygen atoms created in an inductively coupled plasma. Experiments were performed at temperatures from room temperature up to 700°C. Compositions of the modified oxidized surfaces were obtained from XPS survey scans, and the chemistries of selected elements from higher energy resolution scans of appropriate peaks. The morphologies of the surfaces were obtained using field emission scanning electron microscopy at different magnifications, up to 10,000×. Different Fe/Cr/Mn oxidized layers and different oxide thicknesses were observed and correlated with temperature.

A study on surface oxidation of AISI316L stainless steel surface was performed. Stainless steel was oxidized in air plasma with a high degree of dissociation of oxygen molecules of about 70%. The resultant flux of oxygen atoms to the surface was about 1×1024m−2s−1. The oxidation was performed at high temperatures ranging up to 1250K. The oxidation time was 5min. After oxidation the surface of the samples was analyzed by different methods including Auger electron depth profiling (AES), X-ray photoelectron spectroscopy (XPS), scanning electron spectroscopy (SEM) and X-ray diffraction (XRD). The microstructure and composition of the surface were temperature dependent. In all cases high Cr concentration was observed on the surface after oxidation at a temperature above 600K. With increasing temperature Mn concentration at the surface increased as well. Below 1000K the oxide film was uniform, while above 1000K islands with large spinel particles were observed to appear.

The response of an originally developed catalytic sensor with a Nb2O5 nanowire array at its outer surface to the varying density of O atoms is experimentally and numerically studied. This technique can be used to measure one order of magnitude lower densities of O atoms and achieve a stable linear response in a significantly broader pressure range compared to conventional catalytic probes with a flat surface. The nanostructured outer surface also acts as a thermal barrier against sensor overheating. This approach is generic and can be used for reactive species detection in other reactive gas environments.

Auger electron spectroscopy (AES) depth profiling was used to study the oxidation phenomena of AISI316L stainless steel during treatment with oxygen plasma. Samples were exposed to low-pressure RF plasma with a high dissociation degree, so that the flux of oxygen atoms onto the sample surface exceeded 1024m−2s−1. A set of samples was oxidized 4min at different temperatures up to 1300K during plasma treatment. AES measurements showed that the oxide film thickness increased with the increasing temperature. The thickness of the oxide film on the samples oxidized in plasma at 300K was nearly the same as for the untreated sample. The thickness of the oxide film of the samples which were oxidized at 1000K was about 170nm and it consisted of iron oxide. The thickest oxide film of about 350nm was found on the samples heated in oxygen plasma to 1300K. Depth profiling showed the uppermost layer of manganese oxide, followed by a mixture of chromium oxide and iron oxide. The scanning electron microscope analyses showed a dramatic increase of the surface roughness.

Surface effects during plasma activation of poly(p-phenilene sulphide)—PPS have been studied. Samples that were exposed to weakly ionized highly dissociated oxygen plasma created an inductively coupled radiofrequency discharge with the power of 100W. The electron density and temperature were measured with a double Langmuir probe and were 4×1015m−3 and 3eV, respectively, while the neutral atom density was measured with a fiber optics catalytic probe and was 4×1021m−3. The surface tension was determined by measuring the contact angle of deionized water, while the appearance of surface functional groups was detected by XPS. The surface tension of untreated PPS was 7×10−3N/m or/and increased to 7×10−2N/m in few seconds of plasma treatment. It remained fairly constant for longer plasma treatments. The XPS survey spectrum showed little oxygen on untreated samples, but its concentration increased to about 20at.% in few seconds. Detailed high resolution XPS C 1s peak showed that the carbon was left fairly stable during plasma treatment. The main functional groups formed were rather sulphate in sulphite groups, as determined from high resolution S 2p peak. Namely, a strong transition from sulphide to sulphate state of sulfur was observed. The spontaneous deactivation of the polymer surface was measured as well. The deactivation was fairly logarithmic with the characteristic decay time of several hours.

Density of neutral oxygen atoms in the ground state has been measured during treatment of wool fabric samples. Samples were placed in an afterglow reactor with a volume of about 5 l, which was pumped with a two stage rotary pump with the nominal pumping speed of 28 m3/h. The source of the oxygen atoms was a microwave discharge operating in the surfatron mode at 2.45 GHz and adjustable output power up to 300 W. The density of O-atoms in the afterglow chamber was measured with a fiber-optics catalytic probe. For the empty reactor, the O density depended on discharge parameters and was between 0.8 and 2.8 × 1021 m−3 at 40 and 50 Pa respectively. During the treatment of wool, the O density depended largely on the exposure time. For untreated samples, the O density was below the detection limit of the probe, while prolonged treatment allowed for recovering the O density. The recovery always occurred after having submitted wool samples to the dose of the order of 1023 atoms/m2. The results were explained by oxidation of the thin lipid layer on the surface of the wool fibres.

The removal of organic contaminants from porous Al2TiO5 during treatment in oxygen plasma was studied by optical emission spectroscopy (OES). The samples of Al2TiO5 were immersed into water emulsion of mineral oil for 3 h to get soaked. Then, they were thoroughly cleaned in ultrasound to remove oil from the surface. Samples were later exposed to RF oxygen plasma at the pressure of 75 Pa. The plasma density was about 2 × 1016 m−3, the electron temperature was about 6 eV and the density of neutral oxygen atoms was about 2 × 1021 m−3. Optical emission spectra between 200 and 1,000 nm were measured continuously during plasma treatment. The CO peak resulting from oil oxidation reached a well-pronounced maximum between 100 and 150 s of plasma treatment. The maximum in CO corresponded well with a minimum in O peaks. Concentration of oil in the samples was estimated by energy dispersion X-ray analysis. Initially the samples showed high concentration of carbon (about 38 at.%), while after plasma treatment the carbon concentration decreased below the detection limit. The cleaning efficiency was explained by diffusion of oil towards the surface where it was removed by oxidation with oxygen radicals.