Helium Gas Atmosphere Research Articles

LIBS plasma in atmospheric pressure argon, nitrogen and helium: Spatio-temporal distribution of plume emission and Hα linewidth

Laser Induced Breakdown Spectroscopy (LIBS) method is considered for assessing the retention of hydrogen isotopes in the ITER plasma-facing components during the maintenance breaks when the reactor is filled with near atmospheric pressure nitrogen or inert gas. At these conditions, the broadening of the spectral lines of hydrogen isotopes and the reduction of line intensities complicates the distinguishing of hydrogen isotopes. The aim of the present study was to investigate the effect of atmospheric pressure nitrogen, argon and helium ambient gas on the spatio-temporal distribution of the LIBS plasma plume emission and linewidths of Hα line, representing the hydrogen isotopes. Nd:YAG laser with 8 ns pulse width was used to ablate the molybdenum (Mo) target with hydrogen impurity. The development of the formed plasma plume was investigated by time and space-resolved emission spectra in the 20 nm range around the 656.28 nm Hα line. For all gases used in the experiments, the intensity and linewidth of Hα line decreased with the delay time between the laser pulse and the spectral registration. At the same linewidth values, the highest intensities were obtained in the helium atmosphere while the lowest intensity was obtained in nitrogen. According to spatially resolved spectral measurements, the Hα line was most intense near the Mo target while the Mo lines peaked farther away. In the case of the helium atmosphere, the plasma plume emission was observed at a longer distance from the target and it decayed faster than in argon and nitrogen atmospheres. According to these results, helium is the most beneficial ambient gas for hydrogen isotope detection by atmospheric pressure LIBS. The use of argon ambient gas may be required when LIBS is used for the simultaneous determination of fuel and He retention in the wall material.

Experimental study on influence of shielding gas pressure on the quality of pulsed laser welding of thin walled T91 steel clad tube with end plug

Fabrication of metal fuel pins for test irradiation in fast breeder test reactor requires welding of thin wall clad tube with solid end plug of modified 9Cr-1Mo steel material under high pressure helium atmosphere. Autogenous pulsed Gas Tungsten Arc Welding [GTAW] technique is currently used for end cap welding of metal fuel pins inside the glove box. Pulsed laser welding of end plug with clad tube of modified 9Cr-1Mo steel material under inert atmosphere at 1.2 bar gas pressure is under development.Pulsed laser beam welding [PLBW] is considered as alternate welding technique to replace the pulsed tungsten inert gas welding.In the current study the influence of shielding gas pressure on the weld joint characteristics like depth of penetration, bead width, and heat affected zone were investigated to optimize laser welding parameters. Initially experiments were conducted under helium gas at atmosphere pressure to optimize the process parameters to obtain the desired depth of penetration and then repeated the experiment with the optimized parameters at 0.5 bar pressure to study the effect of shielding gas pressure. Laser beam welding parameters like peak power − 1800 to 2400 W, pulse frequency – 5 to 8 Hz and pulse duration – 6 to 10 ms were varied during welding sample coupons. Welded sample coupons were subjected to various NDT techniques and subsequently metallographic examination was carried out to measure the bead width, depth of penetration and delta ferrite distribution in the weld metal. Laser beam welding parameters were optimized at atmosphere pressure to meet the stringent acceptance criteria. Further study was carried out under helium gas atmosphere at 0.5 bar using optimized welding parameters and it reveals that the drastic reduction in heat input due to laser beam attenuation and absorption by quartz window.

Numerical study on uniformity of atmospheric helium gas dielectric barrier discharge on non-smooth surface regulated by sinusoidal clipping voltage

In practical applications of dielectric barrier discharges under atmospheric pressure, plasma usually acts on non-smooth surfaces. The electric field distortion and uneven surface charge distribution caused by its surface morphology will create an adverse effect on the uniformity and stability of the discharge. In this paper, we establish a simulation model of atmospheric pressure helium dielectric barrier discharge on a wavy lower dielectric plate, and use a sinusoidal clipping voltage to regulate the discharge uniformity. The results show that the discharge uniformity is improved compared with the unclipped case, and the discharge mode is changed from columnar mode to quasi-uniform mode. This can be attributed to the incomplete discharge dissipation caused by the reduction of air gap voltage; the subsequent electron backflow process neutralizes the the residual space electrons with the surface charge, which limits the accumulation of surface charges. With the increase of clipping ratio, the surface charge distribution becomes more uniform, and the radial fluctuation of electric field distribution weakens. In addition, the discharge efficiency is improved in a certain clipping range. This study reveals the mechanism of clipping voltage influence on non-smooth surface discharge, and provides a new idea for regulating the uniformity of dielectric barrier discharge.

Cubic Nonlinearity of Tellurite and Chalcogenide Glasses: Terahertz-Field-Induced Second Harmonic Generation vs. Optical Kerr Effect

Third-order nonlinear susceptibilities χ3−2ω;ω,ω,0 and χ3−ω;ω,−ω,ω responsible for electric-field-induced second harmonic generation and the optical Kerr effect were measured and directly compared for tellurite and chalcogenide glasses. The nonlinear coefficients were found by measuring the second harmonic radiation from samples under the action of an external field of terahertz pulses and by the classical z-scan technique, respectively. The influence of ambient air and helium gas on second harmonic generation was analyzed. It was demonstrated that both susceptibilities χ3−2ω;ω,ω,0 and χ3−ω;ω,−ω,ω have close absolute values, which shows the dominant role of nonresonant electronic nonlinearity in the studied glasses.

Helium sealed hard disk drive

Cloud data services started to expand rapidly about 10 years ago and it became increasingly important for storage devices to provide higher capacities with lower power consumption. To meet this demand, Hard Disk Drives (HDDs) were introduced that operated with a sealed atmosphere of helium gas. The helium greatly reduced the power dissipation and allowed the number disks in the HDD to be increased. The concept of a helium sealed drive was not new, but helium is a notoriously difficult gas to contain and there were major challenges along the path to commercialization. This paper describes the history of the development of helium-sealed HDDs, the design of the world's first successful helium-sealed HDD, and the significant advantages that were realized. Future prospects for sealed-drive technology are also discussed.

Effect of CuO on Electrical Property, Seebeck Coefficient and Power Factor of CuGd2O4

The effect of increasing molar ratio for the concentration of CuO in the compound xCuO:1Gd2O3 (x = 2.0, 2.5, 3.0 and 3.5 mol) produced by solid state reaction method was investigated in this study. Thermoelectric properties such as Seebeck coefficient, the electrical resistivity and power factor were investigated in the temperature range of 400 − 800 K using the instrument, ZEM-3 Series under helium gas atmosphere. Through the inspection, the following results were reported: the electrical resistivity drops as the temperature increases, indicating the semiconductor's characteristic behavior. Seebeck coefficient shows a negative value throughout the temperature range used in the investigation. The power factor can be calculated from the relation of P = S2/ρ (where S is Seebeck coefficient and ρ is electrical resistivity) with the highest value of 4.65 µW−1m−1K−2 at 570 K.

Study Ratio Between the CuO and Eu2O3 Concentrations on Electrical Resistivity, Seebeck Coefficient and Power Factor of CuEu2O4

This work, to study ratio between the CuO and Eu2O3 concentations better than to study the effect of CuO content, xCuO: 1Eu2O3 (x = 2, 2.5, 3, 3.5). All of samples were prepared by conventional solid-state reaction method. The electrical resistivity, Seebeck coefficient and power factor were measured by ZEM-3 series under helium gas atmosphere at temperature ranges of 400 − 800 K. They were found that, the electrical resistivity of all samples were decrease with increasing of measurement temperature. Seebeck coefficient are negative in whole temperature range. The power factor was calculated by P = S2/⟩ (where S is Seebeck coefficient and ⟩ is electrical resistivity) and exhibited highest value about 20 W−1m−1K−2 at 775 K.

Effect of a helium gas atmosphere on the mechanical properties of Ti-6Al-4V alloy built with laser powder bed fusion: A comparative study with argon gas

In metal additive manufacturing, the microstructures and associated mechanical properties of metal specimens can be controlled over a wide range. Although process parameters are considered important in the fabrication of functional parts, the effect of atmospheric gas has not been comprehensively documented. In laser powder bed fusion (LPBF), gas flow is used to eliminate fumes generated by laser irradiation. Simultaneously, the gas removes heat from the laser-irradiated part, which is exposed to high temperature. In this study, we investigated the capacity of helium as an alternative to argon, which is conventionally used as the LPBF atmosphere gas. He has a higher thermal conductivity and lower gas density than Ar, which may result in enhanced heat removal from the Ti-6Al-4V alloy during fabrication. Numerical simulations suggest a greater cooling rate under He flow. Further, the material built under He flow contained finer α' martensite grains and showed improved mechanical properties compared to those fabricated under Ar flow, despite the identical laser irradiation conditions. Thus, He gas is advantageous in LPBF for fabricating products with superior mechanical performance through microstructural refinement, and this is a result of its capacity for cooling and fume generation inhibition. Therefore, this study reveals the importance of the choice of atmospheric gas because of its effects on the characteristics of metallic specimens fabricated using LPBF.

On the expansion dynamics of plasma plume produced by laser ablation of LiYF4 crystal in a helium atmosphere

The effect of helium ambient gas on the expansion dynamics of plasma plume produced by ablating the LiYF4 crystal with 355 nm laser pulses is investigated. To study the expansion dynamics, the time-resolved optical signals from the plume constituents, either neutral or ionized, were recorded as a function of various experimental parameters, including laser fluency, at different distances, d, from the target along the expansion direction of the plume and at various angles with reference to the target normal. The analysis of the plume constituents at different distances from the target was used to derive the expansion velocities of the species. Depending on the species and on d, the shifted Maxwell–Boltzmann distribution component of the fit gave the values of the expansion velocities in the range 1.0 × 104 m s−1–4.0 × 104 m s−1. The effect of laser fluency on the expansion velocities of the plume species was also investigated. With the exception of Y and Y+, the expansion velocities of all the plume species, increased linearly with increasing laser fluency up to ∼8 J cm−2. Beyond this value, a saturation regime is observed. The angular distribution of the plume constituents in 1 Pa of He evidenced that all the plume species were focused along the target normal, and the FWHM of the angular distribution curve resulted reduced when compared with the vacuum.

Rapid powder analysis with laser-induced breakdown spectroscopy at low pressure ambient helium gas employing bamboo charcoal as a sample holder

Several experiments are performed to explore the possible benefits of using bamboo charcoal as a sample holder for rapid powder analysis using laser-induced breakdown spectroscopy at low-pressure helium ambient gas. Standard powdered samples such as ZnS and CuSO4 are used to demonstrate the feasibility of using cheap and widely available bamboo charcoal as a sample holder. A commercial baby milk powder and several sets of soil samples with a tiny amount of impurities are also introduced to show the potential application of bamboo charcoal as a powder holder. By appropriately adjusting the laser pulse energy and the thickness of the powder layer, we successfully obtained a spectrum that is free from the undesirable matrix effect. A remarkable result was obtained, even using a tiny amount of the powder sample. This proposed method is considered notably promising for the rapid analysis of the powder sample, especially with a very limited amount.

Low Power Cuk Inverters

The paper describes a low power cuk inverter for atmospheric Helium plasma (He). A high frequency was used in order to drive the pulse width modulation circuit. The average output current consumption (AOCC) was modified from (10A) up to (20A) by increasing the duty ratio from (0.10) up to (0.30) for the atmospheric Helium gas plasma. The switching frequency of the cuk inverter was fixed at (25KHz).

Truncation of a nanosecond CO2 laser pulse by following of the temporal characteristics of the plasma parameters in laser ablation model

The evolution of laser-induced plasma for an aluminum target in a helium ambient gas at different pressures of 100, 300, 500, 700, and 1000 mbar is numerically studied. A thermal model of laser ablation is utilized for calculation of plasma parameters which comprise heat conduction, Euler equations, Saha–Eggert equations, Knudsen layer boundary condition, mass and energy balance relations, and optical shielding effects. In addition, in order to determine the temporal parameters of aluminum's plasma, the hydrodynamic equations are computed for calculation of the plasma absorption due to inverse Bremsstrahlung and photoionization. A CO2 laser pulse at a wavelength of 10.6 μm with different pulse durations of 50 and 100 ns is irradiated on laser induced Al plasma for truncation of the transmitted CO2 laser pulse. The laser intensities irradiated on the Al sample for producing plasma and generation of a shortened pulse are considered as 1016, 1017, and 5 × 1017 W/m2. Furthermore, for validation of the theoretical calculations, some experimental results are presented. Results showed that higher helium gas pressures caused the critical density attained at earlier delay times which caused the CO2 laser beam became efficiently truncated. Moreover, it is concluded that pulse duration has an inverse relation with ambient gas pressure and laser intensity which means that the higher gas pressure or laser intensity induces less pulse duration.

A new nanostructure consisting of nitrogen-doped carbon nanoonions for an electrochemical sensor to the determination of doxorubicin

Cancer is a serious disease and a significant cause of mortality in humans, so the determination of doxorubicin (DOX) as an important anticancer drug is significant in pharmaceutical samples. An electrochemical sensor for doxorubicin was designed by modifying a glassy carbon electrode (GCE) with the nitrogen-doped carbon nanoonions (N-CNOs). The N-CNOs from the fullerene family were prepared using a simple and cost-effective method using aminated nanodiamonds (AM-NDs) as a substrate. Nitrogen atoms were introduced into CNO cages during the preparation of these nanostructures by annealing AM-NDs under an inert helium gas atmosphere and decreased pressure. Under the optimal conditions, the sensor displayed a linear response for DOX detection ranging (from 0.2 nmol L−1 to 10.0 µmol L−1) with a detection limit of 60.0 pmol L−1 (an at S/N ratio of 3) and sensitivity 1.13 µA µmol L−1 cm−2 was calculated, at a typical working potential of −0.59 V vs. Ag/AgCl (3.0 M). The reliability of the sensor for DOX detection in serum samples as the real sample was successfully evaluated. The qualities of this novel sensor, including its high surface area, wide linear range, low detection limit, rapid-response, sensitivity and ease of use. May be beneficial for potential applications in detecting other targets.

Suppression of self-absorption effect in laser-induced breakdown spectroscopy by employing a Penning-like energy transfer process in helium ambient gas.

A unique approach for achieving total suppression of the self-absorption effect in laser-induced breakdown spectroscopy (LIBS) has been demonstrated employing a previously published technique of laser-induced plasma spectroscopy utilizing a helium (He) metastable excited state (LIPS-He*).This achievement was attained by the use of the He metastable excited state (He*) and a Penning-like energy transfer mechanism for the delayed excitation of the ablated analyte atoms. KCl and NaCl samples showed the disappearance of the self-absorption emission lines of K I 766.4 nm, K I 769.9 nm, Na I 588.9 nm, and Na I 589.5 nm, and the FWHM values of K I 766.4 and Na I 588.9 nm were found to be 0.8 nm and 0.15 nm, respectively, by LIPS-He* as compared to 4.8 nm and 1.4 nm, respectively, by single-laser operation. A standard Al sample also showed the total disappearance of the self-absorption emission lines Al I 394.4 nm and Al I 396.1 nm. The FWHM of Al I 396.1 nm was 0.12 nm when LIPS-He* was employed compared to 0.44 nm when a single laser was used. A remarkable linear calibration line with zero intercepts was also obtained for high-concentration Al samples (87.0%, 93.0% and 99.8%). Thus, it is established that the self-absorption effect can be completely neglected when excitation through He* is employed in LIBS.

<i>In situ</i> Neutron Diffraction on Ferrite and Pearlite Transformations for a 1.5Mn-1.5Si-0.2C Steel

The phase transformation behavior from austenite upon cooling in a 1.5Mn-1.5Si-0.2C steel was in situ monitored using dilatometry, X-ray and neutron diffractions. The starting temperature of ferrite transformation was in good agreement between dilatometry and neutron diffraction, whereas much higher in X-ray diffraction. Such a discrepancy in transformation temperature is attributed to the change in chemical composition near the surface of a specimen heated to elevated temperatures in a helium gas atmosphere for X-ray diffraction. In situ neutron diffraction enables us to investigate the changes in lattice constants of ferrite and austenite, which are affected by not only thermal contraction but also transformation strains, thermal misfit strains and carbon enrichment in austenite. Pearlite transformation started after carbon enrichment in austenite reached approximately 0.7 mass% and contributed to diffraction line broadening.

Enhancement of carbon detection sensitivity in laser induced breakdown spectroscopy with low pressure ambient helium gas

Carbon detection is usually difficult to carry out with high sensitivity and minimally destructive effect. While the conventional laser induced breakdown spectroscopy (LIBS) method operated with atmospheric ambient air is well known as a powerful and versatile analytical tool, it suffers nevertheless from the low sensitivity of C detection when measured in both atmospheric and low pressure ambient air with the more adverse effect found in the former case. This was shown to have its origin in the serious time mismatching effect between the formation of the shock wave plasma by the ablated major host elements and the premature fast passage of the much lighter ablated C atom. However, this study shows the result of high sensitivity C analysis of stone samples using LIBS technique with relatively low laser pulse energy of 60 mJ and low pressure He ambient gas without showing visible surface damage. The helium gas provides the additional delayed excitation by the He metastable excited states through the Penning-like ionization process. The C emission intensities measured from the jasper and black stone in 2.6 kPa He ambient gas are in general significantly higher than those measured in 0.5 kPa ambient air. The enhancement is shown to increase reaching an 8 fold enhancement with increased laser energy up to 60 mJ before undesirable surface damage is created. A further measurement of C emission using pelletized KBr mixtures with various CaCO3 concentrations reveals a straight calibration line of rather large slope with extrapolated zero intercept and estimated detection limit of around 0.6 ppm, demonstrating its potential application for highly sensitive quantitative analysis of C with minimal destructive effect.

Mechanically Induced Graphite-Nanodiamonds-Phase Transformations During High-Energy Ball Milling

Due to their unusual mechanical, chemical, physical, optical, and biological properties, nearly spherical-like nanodiamonds have received much attention as desirable advanced nanomaterials for use in a wide spectrum of applications. Although, nanodiamonds can be successfully synthesized by several approaches, applications of high temperature and/or high pressure may restrict the real applications of such strategic nanomaterials. Distinct from the current preparation approaches used for nanodiamonds preparation, here we show a new process for preparing ultrafine nanodiamonds (3-5 nm) embedded in a homogeneous amorphous-carbon matrix. Our process started from high-energy ball milling of commercial graphite powders at ambient temperature under normal atmospheric helium gas pressure. The results have demonstrated graphite-single wall carbon nanotubes-amorphous-carbon-nanodiamonds phase transformations carried out through three subsequent stages of ball milling. Based on XRD and RAMAN analyses, the percentage of nanodiamond phase + C60 (crystalline phase) produced by ball milling was approximately 81%, while the amorphous phase amount was 19%. The pressure generated on the powder together the with temperature increase upon the ball-powder-ball collision is responsible for the phase transformations occurring in graphite powders.

Laser-induced breakdown spectroscopy to monitor ion cyclotron range of frequency wall cleaning Li/D co-deposition in EAST tokamak

In this paper, laser-induced breakdown spectroscopy (LIBS) under magnetic field condition has been studied in laboratory and EAST tokamak. The experimental results reveal that in helium ambient gas, the magnetic field significantly enhances the LIBS signal intensity (∼3 times). The effect of time delay and laser fluence on the intensity of LIBS has been investigated for optimizing the signal to background ratio (S/B). The developed LIBS approach has been applied to monitor the cleaning performance of the first wall in the fusion device of EAST using the ion cyclotron range of frequency (ICRF). The experimental results demonstrate that the cleaning performance for Li/D co-deposition layer is effective under helium ambient gas. The removing rate of Li on the surface of W tile is faster than that on Mo tile in He-ICRF cleaning and the D/(D+H) ratio on Mo tile is higher by ∼1.2 times than that on W tile. This work would indicate the feasibility of using LIBS to monitor the wall cleaning processes in EAST tokamak.

Application of picosecond laser-induced breakdown spectroscopy to quantitative analysis of boron in meatballs and other biological samples.

This report presents the results of laser-induced breakdown spectroscopy (LIBS) study on biological and food samples of high water content using a picosecond (ps) laser at low output energy of 10mJ and low-pressure helium ambient gas at 2kPa. Evidence of excellent emission spectra of various analyte elements with very low background is demonstrated for a variety of samples without the need of sample pretreatment. Specifically, limits of detection in the range of sub-ppm are obtained for hazardous Pb and B impurities in carrots and meatballs. This study also shows the inferior performance of LIBS using a nanosecond laser and atmospheric ambient air for a soft sample of high water content and thereby explains its less successful applications in previous attempts. The present result has instead demonstrated the feasibility and favorable results of employing LIBS with a ps laser and low-pressure helium ambient gas as a less costly and more practical alternative to inductively coupled plasma for regular high sensitive inspection of harmful food preservatives and environmental pollutants.

Plasma jet seven-array discharge at atmospheric helium gas

A low temperature plasma jet array device using seven single electrodes surrounded with insulated organic glass is designed to study the discharge properties of atmospheric plasma jet. The ambient gas is atmospheric Helium gas, whose flow rate is controlled from 0 L/min to 10 L/min. This discharge device is driven by a sub-microsecond repetitive high voltage pulsed power with the pulse width about 230 ns, the rising edge about 120 ns. Using a repetitive frequency rate about 500 Hz, the high speed photographs are taken and the current pulse width is about 110 ns. The average jet length was measured under the conditions of changing gas flow rate and pulse voltage amplitudes in the experiment, in order to acquire the interactions of every plasma jet discharge. It is found that the average plasma jet length increases with the increasing voltage amplitude when the voltage amplitude is less than 20 kV and that it increases slowly when the voltage amplitude is higher, up to 35 kV. It is also found that the average jet length reaches the maximum when the gas flowrate is at a regular value, that is, the average length decreases if the gas flowrate is over or under the regular range. Besides, it is also discovered that the central electrode discharge is affected extremely by the gas flowrate. The central jet length is almost invisible when the gas flowrate is very high or very low, while the central jet with a weak discharge is longer than the surrounding jets when the gas flow rate is 1 L/min. The main reasons are that the air blocks the jet developing and the central electrode jet channel is impeded by the surrounding jets. It is easier for the surrounding electrode to develop jets.