Hydrogen Glow Discharge Research Articles

Laboratory studies of H retention and LiH formation in liquid lithium

Laboratory experiments on H/D retention on liquid lithium followed by thermal desorption spectrometry (TDS) have been performed at Ciemat. Two different experimental set ups were used in order to expose liquid Li to hydrogen gas or to hydrogen glow discharge plasmas at temperatures up to 673K. In the present work the results concerning the gas phase absorption are addressed. Two different kinetics of absorption were identified from the time evolution of the uptake. Alternate exposures to H2 and D2 were carried out in order to study the isotope exchange and its possible use for tritium retention control in Fusion Reactor. Although important differences were found in the absorption kinetics of both species, the total retention seems to be governed by the total sum of hydrogenic isotopes, and only small differences were found in the corresponding TDS spectra, on which evidence of some isotope exchange is observed. The results are discussed in relation to the potential use of liquid lithium walls in a Fusion Reactor.

Study of a continuous spectrum of low pressure glow discharge in hydrogen and helium in a longitudinal magnetic field

The influence of a longitudinal magnetic field on electron temperature and density and on the continuous spectral radiance of a negative glow discharge in the visible spectrum range was studied. The electron temperature and density were determined by the double probe method. It was found that the discharge is compressed to a narrow column under the action of the magnetic field and its glow intensity increases by ∼100 times. This is accompanied by an increase in the electron temperature and density. The total voltage at the discharge decreases by two or three times. The study of the influence of a longitudinal magnetic field on the spectral radiance of the continuous spectrum is of greatest interest in this work. For the given conditions of the studied glow discharge (low pressure and small degree of ionization ∼10−6), bremsstrahlung radiation was shown to make the largest contribution to continuous spectral radiance upon electron scattering on a neutral particle. The measured quantity of the continuous spectral radiance of the discharge was compared with the calculated quantity of bremsstrahlung radiation for neutral particles. The measured quantity was found to be larger than the calculated one by 102–103 times, and the largest discrepancy was observed in the absence of the magnetic field. A hypothesis is proposed to explain such a strong discrepancy between the measured and calculated spectral radiance of the continuum spectrum.

Excitation and transition rate diagrams of singly ionized iron in analytical glow discharges in argon, neon and an argon–hydrogen mixture

Excitation and ionization processes of iron ions in argon-, neon- and argon–hydrogen glow discharges are described based on transition rate diagrams.

Comparative Study on the Use of Different Metal Electrodes in Low-Pressure Glow Discharge Plasma Sterilization

The sterilizing efficacy of low-pressure direct current glow discharge hydrogen peroxide (H2O2) plasma generated by a planar parallel plate plasma source using the plasma enhanced chemical vapor deposition (PECVD) facility was tested. This study compares the effect of using different metals (copper, stainless steel, and aluminum) as electrodes in plasma sterilization of stainless steel dishes. Test samples were exposed to H2O2 plasma under different sets of discharge currents and exposure times. Bacillus subtilis was used as the test organism and microbial analysis was made by means of the standard plate count method of serial dilution and pour plating. Evaluation of microbial death was done using survival curves, percent reduction, and decimal reduction value. Results showed that sterilization using copper electrodes exhibited the highest decimal reduction value (D-value) and percent reduction among the three electrodes. However, statistical analysis using multivariate analysis of variance (MANOVA) at 0.05 significance level assessed that the type of electrode material is not a significant factor in the H2O2 plasma sterilization of Bacillus subtilis cells.

Chemical corrosion by chlorides on ancient-like bronzes and treatment by hydrogen glow discharge plasma

Three representative ancient-like bronzes are employed for the chemical synthesis of Cu2(OH)3Cl rich patinas in order to study the influence of the alloying elements in the evolution of the chloride attack and to further conduct stabilization treatment via Hydrogen Glow Discharge Plasma (HGDP) at low temperature and pressure. The corrosion behavior of specimens having Sn and Pb as main alloying elements is governed by a decuprification mechanism and by the formation of Sn–Pb–O enriched barrier layers. In the case of the Zn containing alloy, dezincification is more pronounced at the corrosion initial stages, and copper species predominate the corrosion products evolution. A three-hour HGDP treatment leads to Cu+ production and metallic Cu, Sn, Zn, and Pb redeposition, as a result of metal cation reduction. This process is accompanied by partial removal of Cl species, O diminution, and change in coloration. The further increase of the Cl/O atomic ratio measured on the post-treated surfaces leads to the formation of nantokite and thus to the conclusion that the stabilization of objects with extensive Cl attack is not feasible by HGDP without preliminary chemical treatment.

Influence of Wall Conditioning on ADITYA Plasma Discharges

ADITYA (R0 = 75 cm, a = 25 cm), an ohmically heated circular limiter tokamak is regularly being operated to carry out several experiments related to controlled thermonuclear fusion research. In recent operational campaign, various experiments have been carried out to enhance the discharge performance as well as improve the plasma parameters. A comparative plasma discharges study with SiC and Graphite limiter was carried out to increase the plasma heating and reduce runaways. Excellent plasma heating has been observed in many discharges using Graphite limiter. Good repeatability of low hard X-rays, high temperature discharges was obtained. The control of plasma impurities and hydrogen recycling is very much essential for high performance discharges. The wall conditioning in ADITYA tokamak is carried out by hydrogen glow discharge cleaning (GDC), Pulse discharge cleaning and electron cyclotron resonance (ECR) discharge cleaning techniques with and without lithium wall coating. GDC assisted Lithiumization was found to be the most effective technique for substantial reduction in Ha and low Z (CIII & O-I) impurities. The partial pressure of mass number 18 (H2O) and 28 (N2/C2H4/CO) were regularly monitored before plasma discharge operation. Furthermore, experiment on optimization of pulse gas feed was helped in reducing wall loading and recycling. However, hard X-rays suppression with the application of multiple gas puff has been successfully achieved during negative converter operation, which led to the extension of plasma pulse length up to ∼ 250 ms. All the supporting facts and operation aspects are reported.

Using vacuum ultraviolet sources in the design of a fluorescence hygrometer

This paper describes a fluorescence hygrometer for measuring the microconcentration of water vapor in the stratosphere. The vacuum ultraviolet sources to be used in the hygrometer are considered. Questions of the temperature dependence of the characteristics of hydrogen and krypton glow-discharge lamps are discussed, as well as the operation of the lamps in the modulation regime. The results of laboratory and field tests of the hygrometer are presented.

Electric field distribution in the cathode-fall region of an abnormal glow discharge in hydrogen: experiment and theory

We present the results of an experimental and theoretical study of the electric field distribution in the cathode-fall (CF) region of an obstructed abnormal glow discharge in hydrogen. The distribution of electric field strength was measured using an improved Stark polarization spectroscopy technique of the hydrogen Balmer beta line profile. The developed technique extends field measurements to the low-field region while remaining in good agreement at larger field strengths with the well established Stark polarization peak separation electric field measurement technique. The experimental electric field distribution is modeled by a simple analytical formula, adopted after consideration of elementary processes relevant in the CF. It fits the experimental distribution within error bars and consequently enables determination of the CF parameters such as its thickness and the mean free path for electrons in the CF region.

Low-temperature synthesis of microcrystalline 3C-SiC film by high-pressure hydrogen-plasma-enhanced chemical transport

The synthesis of microcrystalline 3C-SiC films on glass substrates at relatively low temperatures (⩽600 °C) by the plasma-enhanced chemical transport method was carried out using a high-pressure pure hydrogen glow discharge. This method used the chemical erosion products of graphite and silicon in the hydrogen plasma as the deposition source. The temperature dependence of the etching rate of graphite and the generated volatile C-species were investigated by exposing sintered graphite to a pure hydrogen plasma at 100 Torr. Infrared absorption gas analysis indicated that the C-related film precursor generated from the graphite was mainly CH4. The etch rate of graphite reached a maximum at a sample temperature of 200 °C. The deposition rate of the SiC film prepared at a hydrogen pressure of 200 Torr increased monotonically from 14 to 29 nm min−1 with an increase in substrate temperature (Tsub) from 100 to 600 °C. The Si/C composition ratio in the films was independent of Tsub and all the film compositions were nearly stoichiometric. The prepared SiC films were microcrystalline 3C-SiC. Raman spectroscopy indicated that the film quality significantly depends on Tsub. The electrical conductivity of the films at room temperature was found to increase exponentially from 3 × 10−4 to 1.7 S cm−1 with Tsub.

The influence of longitudinal magnetic field on recombination radiation of low-pressure glow discharge in hydrogen and helium

We study the influence of longitudinal magnetic field on the radiation of low-pressure glow discharges in hydrogen and helium. We conducted experiments under a pressure in a discharge chamber of 10–20 Pa and a discharge current of 10–20 mA. A 0–1600 G magnetic field influenced only the cathode parts of the discharge, negative glow, and the dark Faraday space. The electron temperature and density were measured by the two-probe method as a function of magnetic field. We studied the dependence of the intensity of radiation in the spectral lines and continuous spectrum on magnetic field induction. We discovered that, under the action of magnetic field, discharge in hydrogen and helium is compressed and its glow volume increases by a factor of 20–25. In contrast, the radiation intensity in the lines and continuous spectrum increase by a factor of 100–200. We found a strong discrepancy in the measured intensity of the continuous spectrum into spectral ranges with calculation of electron-ion recombination.

Influence of treatment in the (O2,H2) plasma on the structure and physical properties of SnO x films

The influence of treatment in hydrogen and oxygen glow discharge plasmas on the structural and optical properties of 270- to 350-nm-thick SnOx films prepared using magnetron sputtering and the sol-gel method on the glass substrate has been considered. It has been demonstrated that the plasmas exert segregating and destroying effects on the structure of crystal grains, the transparency of films, and on their porosity. It has been established that treatment in the hydrogen glow discharge plasma makes it possible in principle to prepare crystal-amorphous nanostructures in which tin oxide nanocrystals of high quality alternate with tin oxide clusters.

Exchange and reduction of retained hydrogen isotope by glow discharges

Following hydrogen glow discharge of stainless steel, a deuterium glow discharge was conducted to exchange the retained hydrogen in the stainless steel for deuterium. During the deuterium discharge, about 60% of the retained hydrogen desorbed. The amount of retained deuterium was 1.5 times larger than that of desorbed hydrogen. After the deuterium discharge, glow discharge cleaning with inert gas was conducted and the amount of the removed hydrogen isotope was evaluated. The removal ratio of hydrogen isotopes in the stainless steel was the largest during He glow discharge, and the smallest during Ar glow discharge. The removal ratio of retained hydrogen isotope by neon discharge cleaning did not change although sequential discharges of deuterium and neon were conducted repeatedly.

Oriented carbon nanostructures grown by hot-filament plasma-enhanced CVD from self-assembled Co-based catalyst on Si substrates

We report the synthesis of coral- and caterpillar-like carbon nanostructures assemblies starting from cobalt nitrate ethanol solutions deposited by drop-casting onto blank or carbon nanoparticles film covered Si(100) substrates. The seeded films were pre-treated with glow discharge hydrogen plasma aided by hot-filaments at 550°C followed by introduction of acetylene at 700°C. The resultant carbon nanostructure assemblies contain a high density of aligned carbon nanotubes/nanofibers (CNTs/CNFs). The influence of the forces that act during liquid-mediated self-assembly of Co catalyst precursor is discussed.

Fuel removal from castellated structures by plasma discharges in hydrogen and oxygen

Removal of a-C:H layers from castellated structures of the ITER-like geometry by glow discharge and electron-cyclotron resonance plasmas in hydrogen and oxygen has been studied. The removal efficiency has been determined for gap widths of 1 and 2.5mm and sample temperatures of 470 and 620K. In general, the cleaning is more efficient (i) in oxygen- than in hydrogen-GDC, (ii) in ECR than in GDC, in terms of removal per unit time, (iii) for wider gaps, (iv) at higher sample temperatures, which is more pronounced for hydrogen, (v) at the upper edge of the gap side wall than deeper inside, (vi) at the bottom than at the adjacent side wall of a gap.

Fast H in hydrogen mixed gas microwave plasmas when an atomic hydrogen supporting surface was present

Atomic hydrogen is heated to temperatures of up to two orders of magnitude greater than the electron temperature or the temperature of any other species in certain hydrogen mixed gas RF or glow discharge plasmas. A crucial test of energetic hydrogen chemistry regarding a resonant energy transfer or rt-mechanism (RTM) versus field acceleration models (FAM) as the basis of this selective isotropic heating of a population of extraordinarily high-kinetic-energy hydrogen atoms is the observation of fast H in microwave cells proven to lack a high field as shown by the complete absence of fast H (∼0.08 eV) by Jovicevic et al. [S. Jovicevic, N. Sakan, M. Ivkovic, N. Konjevic, J. Appl. Phys. 105, 013306-1 (2009)]. The RTM predicts an enhancement in the production of fast H with the presence of a surface to support a high concentration of hydrogen atoms in order to initiate the energetic hot H source reaction that then propagates isotropically throughout the plasma. In contrast to the prior results, extraordinarily fast H of greater than 4 eV (50 times that observed and deemed possible in the Evenson microwave cell by FAM advocate Jovicevic et al.) and 50% fractional population was observed as predicted for RTM using the catalytic reaction systems of He/H 2, Ar/H 2, pure H 2, and water vapor microwave plasmas when an electrically insulating, but atomic hydrogen supporting material was placed in the plasma region. Increasing concentrations of Xe in the non-catalytic Xe/H 2 system results in a significant decrease in the energy and population of fast excited-state H atoms.

The desorption and reactivity of butanol adsorbed on lithium iron phosphate (LISICON) activated in a hydrogen plasma

The reactivity and desorption of butanol-2 adsorbed on Li3Fe2(PO4)3 not subjected and subjected to treatment in a glow discharge hydrogen plasma were studied under flow conditions with a gas chromatographic analysis of products. X-ray photoelectron spectroscopy data showed that the number of phosphate groups on the surface of the phosphate was two times larger than the stoichiometric number and increased after plasma chemical treatment. The strength of butanol-phosphate bonds also increased, and the selectivity of alcohol decomposition with the formation of an olefin (dehydration) and ketone (dehydrogenation) changed. After plasma treatment, dehydrogenation centers were deactivated. The selectivities of alcohol transformations in the adsorbed state and under vapor phase conditions were different. Ketone was formed from adsorbed alcohol because the activation energies of dehydrogenation were equal for the two reaction variants.

Performances of inert gas glow discharges for reductions of fuel hydrogen retention and helium retention

In order to clarify the effects of inert gas discharges on the reduction of fuel hydrogen retention, the inert gas discharge has to be similarly conducted in the same apparatus with the same conditions. In the present experiment, first, the hydrogen glow discharge was conducted to measure the fuel hydrogen retention. During the discharge, the amount of retained hydrogen was measured by a technique of residual gas analysis. The inert gas discharges, He, Ne and Ar discharges, then, were carried out after the hydrogen discharge to measure the amount of removed hydrogen. The fractions of removed hydrogen after the He, Ne and Ar discharges were 0.8, 0.3 and 0.1, respectively. The projected range of helium ion is comparable with that of the hydrogen ion, so that the helium impact desorption well removed the hydrogen. The sputter-etching rate of argon is significantly high, so that the wall surface is quickly covered by the deposited layer. Thus, the removal ratio of the Ar discharge becomes lower than that of the He or Ne discharge. The H 2, Ne or Ar discharge was carried out after the He discharge to reduce the helium retention. It was found that the Ne and Ar discharges significantly reduced the helium retention, although the H 2 discharge little reduced the helium retention. The reduction of the Ne discharge was larger than that of the Ar discharge. The amounts of the retained He, Ne and Ar were a few times, two orders and three orders of magnitude smaller than that of hydrogen.

Hydrogen and helium removal retained in stainless steel by neon glow discharge

In order to examine the effect of neon glow discharge on hydrogen or helium removal, neon glow discharge was conducted for the stainless steel after the exposure to hydrogen or helium glow discharge, and then the amount of desorbed hydrogen or helium and retained neon were evaluated. Large hydrogen desorption was observed at the initial period of the neon discharge following the hydrogen discharge. The removal ratio of retained hydrogen by the neon discharge with 2 h was 1.3 times larger than that by the argon discharge, and a half of that by the helium discharge. In the case of the neon discharge following the helium discharge, the removal ratio of retained helium was 4 times larger than that by the argon discharge. The amount of retained neon was an order of magnitude smaller than that of helium retained in the stainless steel.

Excessive Balmer line broadening in a plane cathode abnormal glow discharge in hydrogen

Results of a Doppler spectroscopy study of the hydrogen Balmer alpha line in an abnormal glow discharge operated in pure hydrogen are reported. Measurements of line shapes are performed side-on to the discharge axis in a low electric field region of negative glow. The excessive Balmer alpha broadening is detected and its presence and linewidth is related to the collisions of fast hydrogen atoms with molecular hydrogen. The collision model enabled also an estimation of effective cross section data from the Balmer alpha axial intensity decay curves. Large excessive Balmer alpha line broadening in pure hydrogen and its dependence upon the direction of observation with respect to the electric field is in contradiction to the resonance transfer model, proposed byMills et al. in several publications [see, e.g., IEEE Trans. Plasma Sci. 31, 338 (2003)].

Retention and desorption of hydrogen and helium in stainless steel wall by glow discharge

In order to evaluate the retention of hydrogen and helium and the ion impact desorption in stainless steel, the hydrogen and helium glow discharge were alternately conducted in the glow discharge apparatus with a stainless steel liner. The retained amount of hydrogen or helium in the stainless steel wall was measured based upon a residual gas analysis. The wall temperature was taken in the range from room temperature to 473 K. The retained amount of helium was observed to be large, comparable with that of hydrogen. The helium ion impact desorption for the retained hydrogen was observed to be effective, and increased with the wall temperature. The fraction of desorbed hydrogen became approximately a half of the retained amount of hydrogen. The hydrogen ion impact desorption for the retained helium, however, was observed to be negligible small. The impurity desorption owing to the hydrogen or helium glow discharge increased with the wall temperature. For reduction of the surface impurities, the hydrogen glow discharge was more effective than the helium glow discharge. The present results are useful to understand the retention and desorption of helium and hydrogen in stainless steel wall.