Helium Gas Atmosphere Research Articles

The influence of plasma shielding effect on laser-ablated copper samples: a focus on signal-to-background ratio and plasma expansion

AbstractThe influence of plasma shielding effect induced by ambient gas pressure and laser intensity on the laser-produced Cu plasma parameters, signal-to-background ratio (S/B) and expansion are experimentally and numerically investigated. A Q-switched Nd:YAG laser at 1064 nm at various intensities ranging from 2 to 7.1 GW/cm2 intensity (40–150 mJ) is used to produce Cu plasma in air, argon (Ar), helium (He), and neon (Ne) ambient gas at various pressures ranging from 5 to 1000 mbar. Laser-induced breakdown spectroscopy reveals that spectral radiation, S/B, electron temperature, number density, and front edge velocity of the plasma have an increasing trend up to a certain value of laser intensity and gas pressure. Afterwards, a saturation trend is achieved, which is attributed to the shielding and self-regulation effect. The numerical modeling of the laser-produced Cu plasma in the presence of air at atmospheric pressure is carried out using the MULTI radiation hydrodynamics code. We have shown that the feature of plasma shielding effect observed in the experiments can be reproduced using a continuum hydrodynamics model. Laser intensity at about 3.5 GW/cm2 is found to produce the highest S/B at 1000 mbar air. He, Ne, air, and Ar show the best S/B, respectively and the best S/B is found for air, Ar, He, and Ne at 10, 5, 10, and 20 mbar, respectively. The expansion of plasma plume is studied using a simple and effective technique based on probe laser absorption and scattering method. The plasma plume expansion through He, Ne, air, and Ar at 1000 mbar pressure has the highest velocity, respectively. The simulated results of strong shock wave model and Rankine–Hugoniot jump condition are fitted to the experimental data, which are then used to estimate the values of the ablation parameters.

Prediction of thermal behavior and trajectory of stratospheric airships during ascent based on simulation

For designers, operators and users, the ability to accurately predict thermal behavior and trajectory of stratospheric airships is very important. Thermal models and dynamic models of stratospheric airships during ascent are developed, including solar radiation, infrared radiation, convection heat transfer and gas expulsion equation. Based on the model, performance parameters of a stratospheric airship during ascent are obtained, including film temperature, helium gas temperature, air temperature, pressure differential, altitude and ascent velocity, changing regulation for these parameters are discussed, and influence of initial helium gas volume and film radiation properties on thermal behavior is analyzed. Simulation results show that, (1) stratospheric airships experience supercooling during ascent, the maximum value is about 30K, supercooling causes loss of net buoyancy, and affects ascent velocity and trajectory in the end, (2) stratospheric airships experience superheating at the floating altitude, and the maximum value is about 51K, (3) initial volume ratio of helium gas and the solar radiation absorptivity of film have important effect on thermal behavior and trajectory during ascent, the larger the initial volume ratio is, the faster the ascent velocity will be, and the bigger the solar radiation absorptivity of film is, the smaller the temperature differential between helium gas and outside atmosphere will be.

CO$_{2}$ adsorption behavior and kinetics on chemically modified activated carbons

CO$_{2}$ adsorption capacities of activated carbon-based adsorbents subjected to different treatments, such as HNO$_{3}$ oxidation, air oxidation, alkali impregnation, and heat treatment under helium gas atmosphere, were determined by gravimetric analyses and reported previously by our group. In the current work, the experimental adsorption isotherms of these modified activated carbon samples were fitted to Langmuir, Freundlich, and Dubinin--Radushkevich (D-R) models. The best fits were obtained to the D-R equation, indicating competitive or multilayer CO$_{2}$ adsorption occurring in the micropores of the adsorbents. Air oxidation followed by alkali impregnation led to the highest micropore volume, ranging between 0.259 and 0.298 g.CO$_{2}$/g.adsorbent, which resulted in the highest CO$_{2}$ adsorption capacity of 8.87{\%} at 1 atm and 25 $^{\circ}$C. The CO$_{2}$ adsorption kinetic plots revealed a two-step adsorption process for all the adsorbents: a relatively fast kinetic region phase followed by a slow one until reaching the equilibrium. Pseudo-first and pseudo-second order kinetics explain adsorption for the kinetic region for most of the samples. When the whole adsorption data range is considered, the adsorption cannot be explained by any model at 25 $^{\circ}$C due to the complex nature of the adsorbents, but the adsorption behavior fits rather well to pseudo-first order kinetics at 120 $^{\circ}$C for the alkali-impregnated samples.

Pressure-volume-temperature gauging method experiment using liquid nitrogen under microgravity condition of parabolic flight

Measuring an exact amount of remaining cryogenic liquid propellant under microgravity condition is one of the important issues of rocket vehicle. A Pressure-Volume-Temperature (PVT) gauging method is attractive due to its minimal additional hardware and simple gauging process. In this paper, PVT gauging method using liquid nitrogen is investigated under microgravity condition with parabolic flight. A 9.2 litre metal cryogenic liquid storage tank containing approximately 30% of liquid nitrogen is pressurized by ambient temperature helium gas. During microgravity condition, the inside of the liquid tank becomes near- isothermal condition within 1 K difference indicated by 6 silicon diode sensors vertically distributed in the middle of the liquid tank. Helium injection with higher mass flow rate after 10 seconds of the waiting time results in successful measurements of helium partial pressure in the tank. Average liquid volume measurement error is within 11% of the whole liquid tank volume and standard deviation of errors is 11.9. As a result, the applicability of PVT gauging method to liquid propellant stored in space is proven with good measurement accuracy.

Thermal decomposition of tetraethyl ammonium tetrafluoroborate

Thermal decomposition of tetraethyl ammonium tetrafluoroborate has been studied employing simultaneous techniques of TG–DTG–DSC—quadrupole mass spectrometric techniques in an inert atmosphere of pure Helium gas at a sample heating rate of 5 K min−1 employing a platinum crucible. The observed decomposition paths are the most commonly expected Hofmann elimination and substitution reactions paths.

헬륨 가스 플로우와 가스 펄스 젯에서 할로겐족 원소들의 레이저유도 플라즈마 방출 스펙트럼

할로겐족 원소들의 강한 원자 방출선들은 진공자외선 영역에 존재하여, 공기 중에서 레이저 펄스를 시료에 집속하여 플라즈마 방출 스펙트럼을 얻어 원소 분석을 수행하기 매우 어렵다. 또한 근적외선 영역에 할로겐족 원소들의 들뜬 전자 상태들 사이의 전이에 의한 원자 방출선들이 존재하는데, 이들은 스타크 효과에 의한 선폭 넓어짐 현상이 매우 커서, 공기 중에서 원소 분석에 충분한 신호 대 잡음비를 얻기 어렵다. 헬륨 가스 플로우를 이용하여 근적외선 영역의 할로겐족 원소들의 원자 방출선들은 레이저유도 플라즈마로부터 관측하였다. 특히, 804.374 nm와 905.833 nm의 아이오딘 원자 방출선들은 레이저유도 플라즈마에서 처음으로 관찰된 것이다. 헬륨 분위기에서 스타크 효과에 의한 선폭 넓어짐 현상과 연속 배경복사의 세기는 현저히 억제되었다. 헬륨 가스 플로우의 유량에 따른 원자 방출선의 세기, 플라즈마 온도, 전자 밀도의 변화를 조사하였다. 이 방법을 이용하여 고무의 난연제 성분에 포함된 염소와 불소를 레이저유도 플라즈마 분광법을 이용하여 검출하였다. 마지막으로 레이저유도 플라즈마 분광법을 이용하여 할로젠 원소들을 검출하는데 헬륨 가스 소모량을 줄일 수 있는 가스 펄스 젯 장치를 제안한다. Detection of halogens using laser-induced breakdown spectroscopy (LIBS) in open air is very difficult since their strong atomic emission lines are located in VUV region. In NIR region, there are other emission lines of halogens through electronic transitions between excited states. However, these lines undergo Stark broadening severely. We report the observation of the emission lines of halogens in laser-induced plasma (LIP) spectra in NIR region using a helium gas flow. Particularly, the emission lines of iodine at 804.374 and 905.833 nm from LIPs have been observed for the first time. In the helium ambient gas, Stark broadening of the emission lines and background continuum emission could be suppressed significantly. Variations of the line intensity, plasma temperature, and electron density with the helium flow rate was investigated. Detection of chlorine and bromine in flame retardant of rubbers was demonstrated using this method. Finally, we suggest a pulsed helium gas jet as a practical and ecomonical helium gas source for the LIBS analysis of halogens in open air.

Collisional-radiative recombination of Ar+ions with electrons in ambient helium at temperatures from 50 K to 100 K

Ternary electron-assisted collisional radiative recombination (E-CRR) and neutral-assisted radiative recombination (N-CRR) have very strong negative temperature dependencies and hence dominate electron recombination in some plasmas at very low temperatures. However, there are only few data for molecular ions and almost none for atomic ions at temperatures much below 300 K. In this experimental study we used a cryogenic afterglow plasma experiment (Cryo-FALP II) at temperatures from 50 K to 100 K to measure ternary recombination rate coefficients for ${\mathrm{Ar}}^{+}$ ions in ambient helium gas. The measured magnitudes and the temperature dependencies of the ternary recombination rate coefficients for electron-assisted and neutral-assisted collisional radiative recombination agree well with theoretical predictions (${K}_{\mathrm{E}\ensuremath{-}\mathrm{CRR}}\ensuremath{\sim}{T}^{\ensuremath{-}4.5}$ and ${K}_{\mathrm{He}\ensuremath{-}\mathrm{CRR}}\ensuremath{\sim}{T}^{\ensuremath{-}2.5}$ to ${T}^{\ensuremath{-}2.9}$) over a broad range of electron and He densities.

CO2 adsorption on chemically modified activated carbon

CO2 adsorption capacity of a commercial activated carbon was improved by using HNO3 oxidation, air oxidation, alkali impregnation and heat treatment under helium gas atmosphere. The surface functional groups produced were investigated by diffuse reflectance infrared Fourier transform spectrometer (DRIFTS). CO2 adsorption capacities of the samples were determined by gravimetric analyses for 25–200°C temperature range. DRIFTS studies revealed the formation of carboxylic acid groups on the HNO3 oxidized adsorbents. Increased aromatization and uniform distribution of the Na particles were observed on the samples prepared by Na2CO3 impregnation onto HNO3 oxidized AC support. The adsorption capacities of the nonimpregnated samples were increased by high temperature helium treatments or by increasing the adsorption temperature; both leading to decomposition of surface oxygen groups, forming sites that can easily adsorb CO2. The adsorption capacity loss due to cyclic adsorption/desorption procedures was overcome with further surface stabilization of Na2CO3 modified samples with high temperature He treatments. With Na2CO3 impregnation the mass uptakes of the adsorbents at 20bars and 25°C were improved by 8 and 7 folds and at 1bar were increased 15 and 16 folds, on the average, compared to their air oxidized and nitric acid oxidized supports, respectively.

Pore formation and compressive deformation in porous TiAl–Nb alloys containing directional pores

Porous Ti–xAl–8Nb (x=45, 48, and 49at%) alloys (i.e., intermetallic TiAl–Nb compounds) with cylindrical pores oriented along a single direction were prepared via unidirectional solidification in a hydrogen and helium gas atmosphere, while making use of the differences in the hydrogen solubilities of the liquid and solid phases of the alloys. The microstructures and pore morphologies of the alloys revealed that pore formation in the alloys was closely related to their solidification processes. In the case of the alloy with x=45at%, a primary solidified β (bcc) phase with high hydrogen solubility suppressed the formation of pores during solidification. On the other hand, in the case of the alloy with x=49at%, the formation of the primary β phase was suppressed, leading to the formation of elongated pores along the solidification direction. After being heat treated, the porous TiAl–Nb alloys exhibited a fully lamellar structure composed of α2-Ti3Al and γ-TiAl phases. These porous TiAl–Nb alloys with lamellar structures and directional pores exhibited superior compressive properties parallel to the direction of the pores.

Direct evidence of mismatching effect on H emission in laser-induced atmospheric helium gas plasma

A time-resolved orthogonal double pulse laser-induced breakdown spectroscopy (LIBS) with helium surrounding gas is developed for the explicit demonstration of time mismatch between the passage of fast moving impurity hydrogen atoms and the formation of thermal shock wave plasma generated by the relatively slow moving major host atoms of much greater masses ablated from the same sample. Although this so-called “mismatching effect” has been consistently shown to be responsible for the gas pressure induced intensity diminution of hydrogen emission in a number of LIBS measurements using different ambient gases, its explicit demonstration has yet to be reported. The previously reported helium assisted excitation process has made possible the use of surrounding helium gas in our experimental set-up for showing that the ablated hydrogen atoms indeed move faster than the simultaneously ablated much heavier major host atoms as signaled by the earlier H emission in the helium plasma generated by a separate laser prior to the laser ablation. This conclusion is further substantiated by the observed dominant distribution of H atoms in the forward cone-shaped target plasma.

Mechanical tests of the conduit tubes of a conductor for the Toroidal winding of the International Thermonuclear Experimental Reactor (ITER)

Extremely stringent requirements, which include the impact toughness at the liquid-helium temperature, are imposed on the material of the conduit tubes for International Thermonuclear Experimental Reactor (ITER) Toroidal Field (TF) conductors. Modified 316LN-IG stainless steel is recommended as the conduit tube material. Steel 316LN-IG tube samples (both full-size samples and sub-sized samples) are subjected to mechanical tests at various stages of the process of conductor production: in the as-recieved state and after compacting, preliminary elongation by 2.5% at room temperature, and annealing at 650°C for 200 h in a pure helium gas atmosphere. The tests are carried out at room, liquid nitrogen, and liquid helium temperatures and satisfy the standards of the American Society of Mechanical Engineers (ASME and ASTM). The results of sub-size and full-size samples testing show that the last one gives more representative results to qualify the weld joints in liquid nitrogen. When the temperature decreases or the strain increases, the magnetization of the samples increases, especially in the weld area. Strain measurements with an extensometer demonstrate that the intracrystal processes occurring at the liquid-helium temperature can lead to a significant change in the local load, up to complete unloading in a deformation zone. Unusual local serrated deformation is observed with an extensometer installed in the weld area during tests in liquid helium: this deformation is the result of compressive jumps opposite to the loading direction.

Quantitative Analysis of Deuterium in Zircaloy Using Double-Pulse Laser-Induced Breakdown Spectrometry (LIBS) and Helium Gas Plasma without a Sample Chamber

A crucial safety measure to be strictly observed in the operation of heavy-water nuclear power plants is the mandatory regular inspection of the concentration of deuterium penetrated into the zircaloy fuel vessels. The existing standard method requires a tedious, destructive, and costly sample preparation process involving the removal of the remaining fuel in the vessel and melting away part of the zircaloy pipe. An alternative method of orthogonal dual-pulse laser-induced breakdown spectrometry (LIBS) is proposed by employing flowing atmospheric helium gas without the use of a sample chamber. The special setup of ps and ns laser systems, operated for the separate ablation of the sample target and the generation of helium gas plasma, respectively, with properly controlled relative timing, has succeeded in producing the desired sharp D I 656.10 nm emission line with effective suppression of the interfering H I 656.28 nm emission by operating the ps ablation laser at very low output energy of 26 mJ and 1 μs ahead of the helium plasma generation. Under this optimal experimental condition, a linear calibration line is attained with practically zero intercept and a 20 μg/g detection limit for D analysis of zircaloy sample while creating a crater only 10 μm in diameter. Therefore, this method promises its potential application for the practical, in situ, and virtually nondestructive quantitative microarea analysis of D, thereby supporting the more-efficient operation and maintenance of heavy-water nuclear power plants. Furthermore, it will also meet the anticipated needs of future nuclear fusion power plants, as well as other important fields of application in the foreseeable future.

Excitation Mechanism of H, He, C, and F Atoms in Metal-Assisted Atmospheric Helium Gas Plasma Induced by Transversely Excited Atmospheric-Pressure CO2Laser Bombardment

To clarify the excitation mechanism of hydrogen in transversely excited atmospheric-pressure (TEA) CO2 laser-induced helium gas plasma, atomic emission characteristics of H, C, F, and He were studied using a Teflon sheet (thickness of 2 mm) attached to a metal subtarget. The TEA CO2 laser (750 mJ, 200 ns) was focused on the Teflon sheet in the surrounding He gas at 1 atm. Atomic emissions of H, C, F, and He occurred with a long lifetime, a narrow spectrum width, and a low-background spectrum. The correlation emission intensity curves of H–He and F–He indicated a parabolic functions. To explain the emission characteristics, we offered a model in which helium metastable atoms (He*) play an important role in the excitation processes; namely, atoms collide with helium metastable atoms (He*) to be ionized by the Penning effect, and then recombine with electrons to produce excited states, from which atomic emissions occur.

Excitation Mechanism of H, He, C, and F Atoms in Metal-Assisted Atmospheric Helium Gas Plasma Induced by Transversely Excited Atmospheric-Pressure CO2 Laser Bombardment

To clarify the excitation mechanism of hydrogen in transversely excited atmospheric-pressure (TEA) CO2 laser-induced helium gas plasma, atomic emission characteristics of H, C, F, and He were studied using a Teflon sheet (thickness of 2 mm) attached to a metal subtarget. The TEA CO2 laser (750 mJ, 200 ns) was focused on the Teflon sheet in the surrounding He gas at 1 atm. Atomic emissions of H, C, F, and He occurred with a long lifetime, a narrow spectrum width, and a low-background spectrum. The correlation emission intensity curves of H–He and F–He indicated a parabolic functions. To explain the emission characteristics, we offered a model in which helium metastable atoms (He*) play an important role in the excitation processes; namely, atoms collide with helium metastable atoms (He*) to be ionized by the Penning effect, and then recombine with electrons to produce excited states, from which atomic emissions occur.

Dynamics of C2 formation in laser-produced carbon plasma in helium environment

We investigated the role of helium ambient gas on the dynamics of C2 species formation in laser-produced carbon plasma. The plasma was produced by focusing 1064 nm pulses from an Nd:YAG laser onto a carbon target. The emission from the C2 species was studied using optical emission spectroscopy, and spectrally resolved and integrated fast imaging. Our results indicate that the formation of C2 in the plasma plume is strongly affected by the pressure of the He gas. In vacuum, the C2 emission zone was located near the target and C2 intensity oscillations were observed both in axial and radial directions with increasing the He pressure. The oscillations in C2 intensity at higher pressures in the expanding plume could be caused by various formation zones of carbon dimers.

Energy transfer in O collisions with He isotopes and Helium escape from Mars

[1] Accurate data on energy-transfer collisions between hot oxygen atoms and the atmospheric helium gas on Mars, are reported. Anisotropic cross sections for elastic collisions of O(3P) and O(1D) atoms with helium gas have been calculated quantum mechanically and found to be surprisingly similar. Cross sections, computed for collisions with both helium isotopes, 3He and 4He, have been used to construct the kernel of the Boltzmann equation describing the energy relaxation of hot oxygen atoms. Computed rates of energy transfer in O+He collisions have been used to evaluate the flux of He atoms escaping from the Mars atmosphere. Atmospheric layers mostly responsible for production of the He escape flux are identified. Our results demonstrate that strong angular anisotropy of scattering cross sections increases the collisional ejection of light atoms and is critical in the evaluation of He escape from Mars, Venus and Earth.

Fabrication of U-Pu-Zr Metallic Fuel Elements for the Irradiation Test at Experimental Fast Test Reactor Joyo

The Central Research Institute of Electric Power Industry and Japan Atomic Energy Agency have fabricated the first sodium-bonded metallic fuel elements in Japan as a collaborative research for the irradiation test at the experimental fast test reactor Joyo. The U-20 wt.%Pu-10 wt.%Zr fuel slugs of 200 mm length and approximately 5 mm diameter were fabricated in a small-scale injection casting furnace using U metal, U-Pu alloy and Zr metal. The fuel slugs met the specifications determined on the basis of the specifications of the Experimental Breeder Reactor II driver fuels in the United States and the results of preliminary casting tests. Each fuel slug was loaded into a ferritic-martensitic stainless steel (PNC-FMS) cladding tube with a few pieces of sodium rods as thermal bonds, the U-10 wt.%Zr thermal insulator and the PNC-FMS reflector in a helium gas atmosphere glove box. After top-end plug welding to the cladding tube and the heat treatment of the welding area, each fuel element was subjected to sodium bonding to fill the annular gap between the fuel slug and the cladding with the melted sodium. After inspection, six metallic fuel elements were manufactured successfully and transferred to the Joyo site.

Emission characteristics of hydrogen in atmospheric helium gas plasma induced by TEA CO2 laser bombardment on zircaloy sample containing hydrogen

The most difficult issue as regards hydrogen (H) analysis using the laser-induced plasma technique is the disturbance of H emission by H2O molecules. This problem is essentially solved in this paper by employing a novel technique that makes use of the specific characteristics of a TEA CO2 laser. Thus, a small helium gas plasma was produced by focusing a TEA CO2 laser onto a zircaloy surface containing H atoms. High-purity helium (He) gas was passed over the focusing point during the experiment so that the plasma was totally covered by the He gas and the H2O molecules remaining in the surrounding gas could not attack the plasma region. This technique ensures that only hydrogen atoms come out from the melted region of the sample surface, and are excited via metastable He atoms. This method has allowed us to confirm that H alpha (Hα), H beta (Hβ), H gamma (Hγ), and H delta (Hδ) emission can clearly be detected from a hydrogen-containing zircaloy sample with no interference from host emission lines or the H emission arising from H2O. The intensity ratio of Hα, Hβ, and Hγ was compared with that obtained for a low pressure hydrogen discharge lamp.

Purification of Single-Walled Carbon Nanotubes Generated in Helium Ambient Gas Atmosphere with Arc-Burning Apparatus by Utilizing Mono-Dispersion Technique

Raw soot containing single-walled carbon nanotubes (SWNTs), generated with arc-burning apparatus in helium gas atmosphere, was dispersed in 1 wt% sodium cholate (SC)/D2O solution. This solution was then used for successive ultracentrifugation procedure. After ultracentrifugation, UV-VIS and Raman spectra of the supernatant of the solution were investigated. The obtained spectra demonstrate that SWNTs generated with arc-burning method can be well mono-dispersed in surfactant solution, even though large amount of carbonaceous impurities were also included in the raw soot. This finding indicates that mono-dispersion technique can also be applied as the purification procedure for the raw soot including SWNTs of poor quality. Also, it was found that, although the yield of empty fullerenes (as byproduct) decreases as the helium gas pressure increases, that of SWNTs still increases, and shows a maximum at higher pressure. The diameter distribution of semi-conductive SWNTs included in the soot was compared with that generated in nitrogen atmosphere, based on the experimental results obtained by utilizing fluorescence mapping technique to mono-dispersed solutions.

Crater effects on H and D emission from laser induced low-pressure helium plasma

An experimental study has been performed on the effects of crater depth on the hydrogen and deuterium emission intensities measured from laser plasmas generated in low-pressure helium ambient gas from zircaloy-4 samples doped with different H and D impurity concentrations as well as a standard brass sample for comparison. The results show that aside from emission of the host atom, the emission intensities of other ablated atoms of significantly smaller masses as well as that of the He atom generally exhibit relatively rapid initial decline with increasing crater depth. This trend was found to have its origin in the decreasing laser power density arriving at the crater bottom and thereby weakened the shock wave generated in the crater. As the crater deepened, the declining trend of the intensity appeared to level off as a result of compensation of the decreasing laser power density by the enhanced plasma confinement at increasing crater depth. Meanwhile, the result also reveals the significant contribution of the He-assisted excitation process to the doped hydrogen and deuterium emission intensities, leading to similar crater-depth dependent variation patterns in contrast to that associated with the surface water, with growing dominance of this common feature at the later stage of the plasma expansion. Therefore, a carefully chosen set of gate delay and gate width which are properly adapted to the crater-depth dependent behavior of the emission intensity may produce the desired intrinsic emission data for quantitative depth profiling of H impurity trapped inside the zircaloy wall.