Hydrogen Glow Discharge Research Articles

A dual-route optical emission spectroscopy diagnostic with wide spectral range and high wavelength resolution on HL-2A tokamak

A dual-route optical emission spectroscopy (D-OES) diagnostic is newly developed to monitor the optical emission from the X-point plasma region on the HL-2A tokamak. This diagnostic is composed of an imaging system, a beam-splitting system for dual-route measurements, fiber bundles, a spectrometer system, and a control and acquisition system. One route is used to obtain wide-spectral-range spectra, and the other route is used to acquire high-wavelength-resolution line shapes. The spectral resolution of the wide-range spectrometers is 0.8 nm with a coverage of 800 nm (@200–1000 nm). The spectral resolution of the high-resolution spectrometer is 0.01 nm with a coverage of 6 nm (@200–660 nm). The spatial resolution of each route of D-OES is about 4 cm with 11 channels. The temporal resolution is 16 ms at maximum in the single-channel mode. Wide-range spectra (containing Balmer series and a Fulcher band) and highly resolved line shapes are obtained by D-OES in the hydrogen glow discharge in the lab. D-OES measurements are carried out in the high-density deuterium experiments of HL-2A. The electron density and deuterium temperature in the X-point multifaceted asymmetric radiation from the edge (MARFE) region are derived simultaneously by fitting the measured shape. The density is observed to increase from ~ to ~ , and the temperature drops from ~14.4 eV to ~2.3 eV after the onset of MARFE in the discharge #38260.

Ultra-sensitive determination of mercury in flue gas by atmospheric pressure glow discharge atomic emission spectrometry coupled with gold amalgam enrichment

In this work, a highly sensitive procedure for the determination of mercury in flue gas was developed, based on direct-current atmospheric pressure glow discharge in hydrogen and helium (H2-He) atomic...

Lithium wall conditioning techniques in ADITYA-U tokamak for impurity and fuel control

In fusion devices, various techniques are employed for coating the plasma facing components (PFCs) including the vessel wall with low-Z material like lithium, boron, and silicon in order to enhance the plasma parameters and control. In ADITYA-Upgrade tokamak, different techniques of lithium wall conditioning are developed and implemented to obtain uniform and sustainable coating of Li on PFCs and the vessel wall. In this paper, two techniques used to generate Li from the source are reported. In one of the technique, a heated (fixed temperature of ∼120 °C) Li-rod is placed inside the hydrogen glow discharge cleaning (H-GDC) plasma and the sputtered Li by hydrogen (H) ions and atoms coats the wall and periphery. In the second technique, the Li is vapourized using a high-temperature Li-evaporator and released into the H-GDC plasma for uniform coating of Li on the PFCs and vessel. Significantly enhanced plasma parameters are obtained after Li coating by both techniques, with the evaporated Li performed better than the Li rod case. With the Li coating obtained with evaporated Li at 600 °C (550 mg Li) with H-GDC, the Li wall conditioning has been observed to be sustaining for in a larger number of plasma discharges in comparison to non-H-GDC assisted Li deposition. As the melting temperature of lithium hydride (LiH) is much higher (688.7 °C) than that of lithium (180.5 °C), this enhance the longer Li-coating lifetime relatively due to the formation of Li–H molecules on the vessel wall and PFCs. In ADITYA-U the carbon impurity and hydrogen recycling, due to relatively high surface area of graphite PFCs as well as their proximity to the plasma, limits the plasma performance and effective controls. Hence, H-GDC, H-GDC with Li-rod sputtering or Li evaporation, helium-GDC, argon–hydrogen mixtures-GDC in particular sequence are carried out to obtain better plasma discharges. The Li coating techniques and their effect on tokamak plasma discharges of ADITYA-U are discussed in this paper.

The effect of UV and glow-discharge hydrogen plasma irradiation on the crystalline structure and efficiency of CdTe/CdS thin film solar cells prepared by the quasi-closed volume method

The effect of UV and glow-discharge hydrogen plasma irradiation on the crystalline structure and efficiency of CdTe/CdS thin film solar cells prepared by the quasi-closed volume method

Investigation of Hydrogen Glow Discharge Cleaning Side Effects on Tungsten

Hydrogen glow discharge cleaning (H-GDC) is a routine conditioning procedure for the modern tokamaks and the future fusion machines, including ITER. Due to the low energy of hydrogen ions in glow discharge plasmas, the probability of any considerable damage to the plasma-facing components was mainly ignored. In this work, Tungsten, as the primary candidate for the plasma-facing materials in tokamaks, is considered for studies regarding effects of the H-GDC procedure on the material during a routine vacuum vessel conditioning in Damavand tokamak. After performing routine H-GDC using pure hydrogen, the formation of loosely attached nanostructured bundles (NSBs) on the surface of the tungsten samples was observed. The presence of the NSBs, which can be a source of dust, would be significant due to their possible effects on the functionality of the future fusion plasma devices. The NSBs are observed on the tungsten samples with the surface temperature of <370 K after 2.5–4 hours of hydrogen ion bombardment with incident energy of ≈120 eV and fluence of ≈(2–3.5) × 1022 m–2. The surface modifications of specimens exposed to H‑GDC were examined using a material probe experiment and several surface analysis techniques such as SEM, EDX, XRD, and ERDA. Therefore, the formation of loose nanostructures on the wall of plasma confinement vessels due to H-GDC draws attention to probable damaging effects of this phenomenon upon functionality and outcomes of tokamaks.

Etching Characteristic of Graphite and Metal Substrates by Hydrocarbon Plasma in Closed Cavity

Plasma can be used to effectively remove coke from a metal surface. The plasma etching conditions of coke and emission spectrum characteristics on the metal surface in a complex structure can be determined in real-time using the flexible optical fiber of an emission spectrometer. In this study, the glow discharge hydrogen plasma etching characteristics of a graphite sheet covering Cu and Fe electrodes were investigated. Methane plasma and a bare Cu electrode without graphite were used to conduct experiments for comparison. The cathode was heavily etched owing to the chemical and physical reactions of abundant H and other active species. Many hydrocarbon particle shells with fuzzy boundaries of multilayer graphite were observed on the ground electrode as black dots with diameters less than 1 micron. The cracking reaction of etching process in the case of hydrogen plasma with graphite electrodes plays a leading role, but polymerization reaction is dominant for the methane plasma with bare Cu electrodes. Significant excitation peaks of the emission spectrum are observed in regions centered at 388 and 776 nm for the etching of carbon-rich electrodes in hydrogen-rich plasma. Different hydrocarbon and metal substrate bonds can exist even under strong etching conditions.

Application of classical models to high resolution electric field strength falls in a hydrogen glow-discharge

This paper presents the application of two classical models to high-resolution electric field measurements carried out in a hollow cathode discharge operated in pure hydrogen plasma. The electric field determination has been done via the Stark shifting and splitting of the 2S level of hydrogen, followed by optogalvanic detection. Two classical models, Rickards' and Wroński's, are applied to these measurements with the objective of obtaining a first estimation on the discharge dynamics. The chosen models provide an idea of the ions movement, their energy and their mean free path at the cathode fall region, as well as the electric field strength behaviour depending on the discharge characteristics.

Improvement of catalytic activity of graphene oxide by plasma treatment

A considerable enhancement of the catalytic activity of graphene oxide (GO) was achieved as a result of plasma treatment in a hydrogen glow discharge. The results obtained for the hydroisomerization of 1-octene, together with the catalyst characterization showed that plasma exposure leads to the formation of defects in the material and of surface acidic species. Optical emission spectroscopy diagnostics of the plasma revealed that the electron temperature and the dissociation of molecular hydrogen are important parameters that can be tuned for optimization of the treatment process.

Q-branch of fulcher-α diagonal bands for determination of the axial temperature distribution in the cathode sheath region of hydrogen and hydrogen-argon abnormal glow discharge

In this paper, we present results of rotational, vibrational, and gas temperature distribution study in the cathode-sheath region of an abnormal glow discharge in hydrogen and hydrogen-argon mixture. For this purpose, we used Q-branch of the Fulcher-α diagonal bands d3Π−u, ν′=0, 1, 2, 3→ a3Σ+g, ν″=0, 1, 2, 3. The boundary between the cathode sheat and negative glow region is determined as the position where the electric field strength falls to zero. For the electric field measurement Stark polarization spectroscopy of hydrogen Balmer alpha line was employed and the thickness of cathode sheat is estimated by fitting the experimentally obtained distribution of electric field strength to a suitable model function.The temperature values, measured in the cathode sheath from different vibrational bands, decrease with vibrational quantum number v′ increase. The vibrational temperature is determined from the relative intensities of vibrational bands of the Fulcher-α system (d3Π−u→ a3Σ+g electronic transition; Q-branch v′= v″=2 and v′= v″=3). Temperature distributions along the axis of the cathode sheath are also reported and discussed. The distributions of rotational temperature show that all three temperatures (gas, rotational and vibrational) vary along the cathode sheath region of discharge and that all four bands give consistent values for the rotational temperature. The measurements performed with high spectral resolution provide further insight into understanding or modelling the DC glow discharge. The reported results represent the contribution to the development of the spectroscopic method for gas temperature measurement.

New installation of in-vessel Non Evaporable Getter (NEG) pumps for the divertor pump in the LHD

A case of the application of Non Evaporable Getter (NEG) pumps to fusion devices is discussed. Compared with other pumping technologies used in fusion devices, the NEG pumps have advantages in terms of operation temperature at 100–200 °C (in which there is a high tolerance of the temperature increase due to a plasma radiation and/or an unexpected heat load from heating devices), low power consumption and compactness. Moreover, in the case of a power outage getters continue pumping and do not release hydrogen and its isotopes. The NEG pumps have been installed as an in-vessel pump into the divertor region in the Large Helical Device (LHD) for the first time. The pumping performance test shows that the effective pumping speed is 10 m3/s in hydrogen, which is close to the target value. In addition, the exposure of the NEG pumps to boronization and glow discharge treatments have been tested. While the boronization and glow discharge under noble gases do not show effect on the pumping performances of the NEG pumps, the establishment of an operational scenario including hydrogen and deuterium glow discharges consistent with other pumping facilities is still an aspect to be refined. However, the use of NEG pumps in LHD divertor is a milestone for the possibility of using this technology in future fusion devices.

Effect of Glow-discharge Hydrogen Plasma Treatment on Zinc Oxide Layers Prepared through Pulsed Electrochemical Deposition and via SILAR Method

Effect of Glow-discharge Hydrogen Plasma Treatment on Zinc Oxide Layers Prepared through Pulsed Electrochemical Deposition and via SILAR Method

Theoretical simulation of hydrogen glow discharge in the positive column of plasma sources

Direct current (DC) glow discharge positive column has played an important role in the field of plasma material surface modification. In this kinetic study of hydrogen glow discharge in the positive column, it is found that electron energy distribution function (EEDF) obviously departs from Maxwell distribution. The EEDF tail moves to higher energy when the ratio between electric field E and density of neutral species N (E/N) increases and the tail moves toward higher energy if hydrogen atom proportion increases at the same E/N. It is also shown that electron temperature augments with the increase of E/N. Additionally, the dissociation ratio percentage of H2 rises with the increase of E/N.

Analysis of applicability of triplet-state emission of molecular hydrogen for spectral diagnostics of a DC discharge

The applicability of emission of the N 3Λσ triplet states of molecular hydrogen for spectral diagnostics of the positive column of a dc glow discharge in hydrogen at translational gas temperatures of 360–600 K, specific absorbed powers of 0.8–4.25 W/cm, gas pressures of p = 0.3–15.0 Torr, reduced fields of E/N = 30–130 Td, and electron densities of n e = 4.0 × 109–6.5 × 1010 cm–3 is analyzed by using an advanced level-based semi-empirical collisional−radiative model. It is found that secondary processes make the main contribution to the population and decay of the N 3Λσ = a 3Σ+ g , c 3Π u , g 3Σ+ g , h 3Σ+ g , and i 3Π g triplet states. The dipole-allowed transitions e 3Σ+ g → a 3Σ+ g , f 3Σ+ g → a 3Σ+ g , g 3Σ+ g and k 3Π u → a 3Σ+ g can be used for spectral diagnostics of a dc discharge within a simplified coronal model.

Study of the interaction between molten indium and sub-atmospheric pressure hydrogen glow discharge for low-temperature nanostructured metallic particle film deposition

Indium (In) evaporation is enhanced by high-pressure hydrogen glow plasma, and a sponge-like In film containing submicron pores is prepared on the substrate. The glow plasma is generated at a total pressure of 13.3 kPa (100 Torr) as a capacitively coupled plasma. When the process atmosphere is diluted by He and Ar, the In evaporation rate increases by increasing the hydrogen concentration and no evaporation is observed without H2 gas. The In deposition rate exhibits no dependence on the In temperature in the range from 300 °C to 600 °C. However, the In deposition rate increases linearly by increasing the input power. The obtained deposition rate reaches 7.5 mg/s with an input power of 800 W even at an In temperature of 450 °C. The obtained weight deposition rate is equivalent to the thickness deposition rate of 1.6 μm/s. The prepared In film on the Si substrate is composed of a porous foam-like structure. The particle diameter distributes from 40 nm to a few tens of micrometers. The particles with diameters above a few micrometers reveal a porous structure with a pore size of less than 100 nm. The obtained In film consists of crystalline In. Thermal desorption measurements of the prepared In film reveal that a large amount of H2 gas is confined in the In film relative to the hydrogen solubility in solid In. The obtained results suggest that the excess hydrogen solubility in the liquid metal induced by H2 plasma is an important factor for the enhancement of In evaporation.

Two-dimensional electrodynamic structure of the normal glow discharge in an axial magnetic field

Results are presented from numerical simulations of an axisymmetric normal glow discharge in molecular hydrogen and molecular nitrogen in an axial magnetic field. The charged particle densities and averaged azimuthal rotation velocities of electrons and ions are studied as functions of the gas pressure in the range of 1–5 Torr, electric field strength in the range of 100–600 V/cm, and magnetic field in the range of 0.01–0.3 T. It is found that the axial magnetic field does not disturb the normal current density law.

Drift−diffusion model of normal glow discharge in an axial magnetic field

A two-dimensional axisymmetrical computing model is formulated with using of which the mathematical modeling of the normal glow discharge in molecular hydrogen is fulfilled in an axial magnetic field with the induction B = 0.1 T in the pressure range p = 1.25−5 Torr and the current-source electromotive force E = 1−3 kV.

Aspects of the practical application of titanium alloys after low temperature nitriding glow discharge in hydrogen- free -gas media

X-ray diffraction analysis, X-ray photoelectron spectroscopy, and Electron Auger-spectroscopy investigation of phase transformation on the surface of the VT8 titanium alloy after a low temperature hydrogen-free nitriding in a glow discharge.Operational characteristics of titanium alloys defined physical-mechanical characteristics of the surface and their phase composition, which depend on the process parameters of nitriding. Surface modification of titanium alloys were carried out by low-temperature nitriding in a glow discharge in hydrogen-free environment. The main advantage of this method lies in the absence of hydrogen embrittlement and complete environmental safety process. Application of the glow discharge can not only speed up the process by the order of the diffusion surface saturation with nitrogen, but also significantly alters the kinetics of the process and quality of the nitrided layer, in particular its physio-mechanical properties and phase composition. For research purposes, the standards from an α+β alloy Ti-Al6-Cr2-Mo2,5 (VT8) were used.Research into the phase composition was performed by X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Stratified analysis by AES was conducted by etching the surface of the samples’ argon ion beam with diameters of 1.5mm with an energy of 3000eV and a current density of 400mA/cm2.The above material shows the promise of the technology of low-temperature hydrogen-nitriding by glow discharge. This greatly expands the range of practical applications of titanium alloys. In addition, changing the technological mode allows you to manage a wide range of modified phase composition of the surface layer and as a result – to form the surface of titanium parts, taking into account the conditions of the subsequent operation.

Child–Langmuir law applicability for a cathode sheath description of glow discharge in hydrogen

The present paper reveals that the Child-Langmuir law version with the constant ion mobility has to be applied for the cathode sheath description of the glow discharge in hydrogen. Using the analytical model we demonstrate that even in a high electric field the constant mobility law version rather than that for the constant ion mean free path has to hold in the case of impeded charge exchange and the dominant effect of polarization forces on the ion motion through the cathode sheath.

Blister formation on 13Cr2MoNbVB ferritic-martensitic steel exposed to hydrogen plasma

The influence of pre-irradiation specimen deformation level on surface blister formation and sub-surface cracking of dual-phase 13Cr2MoNbVB ferritic-martensitic steel was studied using glow discharge hydrogen plasma with ion energy of 1 keV to fluences of 2 × 1025 H/m2. Protium was used for most studies, but deuterium was used for measuring the depth dependence of hydrogen diffusion. Formation of blisters was observed in the temperature range 230–340 K. It was found that pre-irradiation deformation caused changes in the threshold fluences of blister formation and also in blister size distribution. Subsurface cracks located on grain boundaries far beyond the implantation zone were formed concurrently with blisters, arising from hydrogen diffusion and trapping at defects. It was observed that cracks as long as 1 mm in length were formed in 95% deformed steel at depths up to 500 μm from surface.

Spectroscopic application of an iterative kinetic cathode sheath model to high voltage hollow cathode glow discharge in hydrogen

We present a simple one-dimensional iterative kinetic model of the cathode sheath region of high voltage, low-pressure hydrogen hollow cathode discharge. The model's convenience as a supplemental diagnostic tool is demonstrated by determining the most relevant discharge parameters through an analysis of the spectral shape of the hydrogen Balmer alpha line recorded along the axis of a cylindrically symmetrical high voltage low-pressure hollow cathode glow discharge in hydrogen. Thus, an effectively one-dimensional approach is tested and shown to give satisfactory spectral lines fits with reasonable values for discharge parameters, most notably the gas temperature.