Argon-based Gas Mixtures Research Articles

Primary Ionization Simulation for Different Gas Mixtures

The primary ionization in a gas mixture is crucial in nuclear and particle physics experiments. In many particle physics experiments, the primary ionization is utilized in understanding the charge density and discharge formation studies. We present the simulation of primary ionization in argon based gas mixtures to get the number of primaries, energy and spatial information with geant4 and heed++ toolkits that have been used to simulate the passage of particles through the matter. The geant4 toolkit has an advantage of obtaining the particle information like energy deposition and position co-ordinates after each step i.e., at which the particle has done some interactions in a complex, realistic, three-dimensional geometry. These steps generate each interactions after computing the cross-sections of physics processes that were taken into account for this simulation in a gas volume. The number of primaries generated with the geant4 toolkit were also compared with those obtained using heed+ +. Alpha and muons were simulated to study the primary ionization. A similar study of primary ionization was carried out with 55Fe which is radioactive in nature and captures electron. 55Mn (X-rays), νe, auger electrons and gammas were produced in this process. Gamma simulation has also been carried out. The responses of alpha, muon, 55Fe and gamma in the argon based gas mixtures were found to be distinct due to their different properties.

Long term stability study of triple GEM detector using different Argon based gas mixtures: an update

The long-term stability in terms of gain and energy resolution of a prototype triple Gas Electron Multiplier (GEM) detector has been investigated with high rate X-ray irradiation. Premixed Ar/CO2 (80:20) and (90:10) gases have been used for this stability study. A strong Fe55 X-ray source is used to irradiate the chamber. The uniqueness of this work is that the same source has been used to irradiate the GEM prototype and also to monitor the spectra. This arrangement is important since it reduces the mechanical complexity of using an X-ray generator as well as the cost of the setup. A small area of the chamber is exposed continuously to the X-ray for the entire duration of the operation. The effect of temperature and pressure on the gain and energy resolution is monitored. The result of the long-term stability test for a triple GEM detector using Ar/CO2 (70:30) gas mixture has been reported earlier [1]. The results with Ar/CO2 (80:20) and (90:10) gas mixtures for the same chamber are presented in this article.

Investigation of UV laser ionisation in argon-based gas mixtures with a Triple-GEM detector

In the gas detectors, the ionisation mechanisms of the charged particles and X-ray/γ-photons are well studied by theory and experiment. However, on the experimental measurements of the ionisation ability of the lasers, publications only give the estimation results. This study aims to fill the gap and measures the laser ionisation precisely. A GEM detector and an optical system have been set up to measure the laser ionisation. The purity of each component of the gas mixtures is indicated in this study. Our research shows that a pulsed laser with a wavelength of 266 nm can generate 100–200 electrons per centimeter, which equals to the ionisation produced by 1–2 Minimum Ionising Particles (MIPs) in argon-based mixtures. Furthermore, this study gives an experimental reference to select the laser energy density in argon-based gas mixtures when applying lasers to calibration in the gaseous detectors. We have also studied the impacts of different vendors and gas flow rates on the ionisation created by UV laser pulses.

Comparison of bulk Micromegas with different amplification gaps

The bulk Micromegas detector is considered to be a promising candidate for building TPCs for several future experiments including the projected linear collider. The standard bulk with a spacing of 128μm has already established itself as a good choice for its performances in terms of gas gain uniformity, energy and space point resolution, and its capability to efficiently pave large readout surfaces with minimum dead zone. The present work involves the comparison of this standard bulk with a relatively less used bulk Micromegas detector having a larger amplification gap of 192μm. Detector gain, energy resolution and electron transparency of these Micromegas have been measured under different conditions in various Argon-based gas mixtures to evaluate their performance. These measured characteristics have also been compared in detail to numerical simulations using the Garfield framework that combines packages such as neBEM, Magboltz and Heed. Further, we have carried out another numerical study to determine the effect of dielectric spacers on different detector features. A comprehensive comparison of the two detectors has been presented and analyzed in this work.

An estimation of the effective number of electrons contributing to the coordinate measurement with a TPC: II

For time projection chambers (TPCs) the accuracy in measurement of the track coordinates along the pad-row direction deteriorates with the drift distance (z): σX2∼D2·z/Neff, where D is the diffusion constant and Neff is the effective number of electrons. Experimentally it has been shown that Neff is smaller than the average number of drift electrons per pad row (〈N〉). In the previous work we estimated Neff by means of a simple numerical simulation for argon-based gas mixtures, taking into account the diffusion of electrons only in the pad-row direction (Kobayashi, 2006 [1]). The simulation showed that Neff could be as small as ∼ 30% of 〈N〉 because of the combined effect of statistical fluctuations in the number of drift electrons (N) and in their multiplication in avalanches. In this paper, we evaluate the influence of the diffusion normal to the pad-row direction on the effective number of electrons. The de-clustering of the drift electrons due to the diffusion makes Neff drift-distance dependent. However, its effect was found to be too small to explain the discrepancy between the values of Neff measured with two TPC prototypes different in size.

The simulation results of signal fluctuation for micromegas-like gaseous detector

In the present paper, the mean signal value and its fluctuations were investigated for the well known Micro-Mesh Gaseous Structure (Micromegas) filled with argon-based gas mixtures. The number of primary electrons and ions in the conversion gap were calculated using the FLUKA code for incoming electrons. The signal resolution is a function of the energy loss or the number of produced primary electrons and its fluctuation in the detector volume. The signal generations were made with a Single Particle Monte Carlo simulation technique in the amplification gap region. We assumed a homogeneous electric field inside both the conversion and the amplification gap because the electric field shows only a small change near the openings of the microgrid. Based on the simulation, we discuss the signal fluctuations that affect the work performance of the Micromegas for different argon-based gas mixtures.

Penning transfer in argon-based gas mixtures

Penning transfers, a group of processes by which excitation energy is used to ionise the gas, increase the gas gain in some detectors. Both the probability that such transfers occur and the mechanism by which the transfer takes place, vary with the gas composition and pressure. With a view to developing a microscopic electron transport model that takes Penning transfers into account, we use this dependence to identify the transfer mechanisms at play. We do this for a number of argon-based gas mixtures, using gain curves from the literature.

INFLUÊNCIA DA PRESSÃO NA ABSORÇÃO DE OXIGÊNIO

Few technological data are available concerning operational limits of shielding gases aiming the application of the GMAW process in hyperbaric welding. In order to contribute to this knowledge, this paper presents results correlating the pressure and the oxygen content in the shielding gas to the weld metal chemical composition. The welding of bead on plate and multipass test joints was performed in the hyperbaric simulator of the GKSS Forschungszentrum Geesthacht GmbH, in Germany. The absolute pressures of 5,1 MPa (51 bar); 7,1 MPa (71 bar); 9,1 MPa (91 bar) e 11,1 MPa (111 bar) were applied in combination with the following Helium and Argon based gas mixtures: He-0.1%O2, He-0.5%O2, Ar-0.3%O2, Ar-0.6%O2 Ar-1.0%O2. The welding consumable was a low alloy steel wire containing 1% Ni and 0.4% Mo. Considering the high partial pressures attained the oxygen contents in the weld metals were unexpectedly low. In addition, increasing the oxygen partial pressure, small variations on the contents of Mn, Si and C in the weld metal were observed. These results do not follow the corresponding tendency reported in the literature for welding under the room pressure. To explain such behaviour it is suggested that under high pressures the oxygen partial pressure does not play an important role anymore. The oxygen diffusion throughout the metallic vapour which emerges from the molten metal surfaces is claimed to be a new mechanism to be considered and probably it becomes the most important controlling mechanism in the oxygen absorption by the weld metal.

"The Role of Gases in Welding and Cutting Processes"

From the time that Edmond Fouche and Charles Picard developed the first oxy-acetylene torch, which gave a flame hot enough to melt steel in 1900, gases have played a very important role in the development of welding and cutting processes. In the early 1900s it was gas welding which laid the foundation for the commercial application of welding as a repair and joining process for steel and other metals, till the development of the coated electrode and shielded metal arc welding process by Oscar Kjellberg. Gas cutting, first introduced commercially in 1907, has however continued to be the backbone cutting process for the fabrication industry till today. Arc welding in a shielding gas atmosphere was patented by C.L.Coffin in 1890. However it was only in the 1940s that commercial use of inert gases Argon and Helium for shielding of the arc in the Gas Tungsten Arc and Gas Metal Arc welding processes was developed. The use of carbon dioxide and later argon based gas mixtures further enhanced the productivity and performance of Gas Metal Arc welding so that it has become the dominant welding process today. Gases and gas mixtures have also played a crucial role in the development of more advanced welding and cutting processes such as plasma and laser and today they play a very significant part in controlling the quality and cost effectiveness in any welded fabrication. The paper attempts to review the history and role of gases in the development of the welding and cutting processes through the years till the modern times.

Experimental study of gas mixtures in strong non-uniform electric fields

Argon-based gas mixtures of various concentration ratios at low pressures were studied in a gas proportional counter. Over-exponential increase of gas gain in mixtures with low partial pressure of any admixture was observed. The best energy resolution was measured at a gas gain of several hundreds for lower admixture concentrations, but at high gas gains R degraded very fast. The first Townsend ionization coefficient α/ P in low-pressure gases depended also on the gas pressure. The single-electron spectra had a peaked shape in mixtures with relatively high content of the molecular gas. In mixtures with lower molecular gas amount they changed the shape toward the over-exponential distribution. A partial pressure of 10 kPa was determined as a requirement for good quenching property of the mixture.

Effect of argon buffer and the UV preionization regime on the electric-discharge XeCl laser parameters

The gas discharge and output radiation parameters were studied in XeCl lasers with various buffer gas compositions (argon vs. neon) and different types of excitation regimes (fast vs. quasi-stationary) in the preionization source. The intervals of specific energy for the neon-and argon-based buffer gas mixtures are 10–125 and 45–360 J/(l atm), respectively. The specific parameters of radiation in the neon-and argon-based buffer gas mixtures depend on the energy required for the UV preionization. For high-power UV preionization sources, the output parameters of lasers using argon-based gas mixtures may exceed those obtained with neonbased mixtures.

Study of argon-based penning gas mixtures for use in proportional counters

Results from an experimental investigation of three Penning gas mixtures, namely argon-acetylene (Ar-C 2H 2), argon-xenon (Ar-Xe) and argon-xenon-trimethylamine (Ar-Xe-TMA), are reported. The measurements, carried out in cylindrical geometry as well as parallel plate geometry detectors, demonstrate that the Ar-C 2H 2 mixtures show a significant Penning effect even at an acetylene concentration of 10% and provide the best energy resolution among all the argon-based gas mixtures (≤13% FWHM at 5.9 keV and 6.7% at 22.2 keV). In the parallel plate detector the Ar-C 2H 2 fillings provide a resolution of ≈ 7% FWHM at 22.2 keV up to a gas gain of at least ⋍10 4 . The nonmetastable Penning mixture Ar-Xe provides the highest gas gain among all the argon-based gas mixtures and is well suited for use in long-duration space-based experiments. Best results are obtained with 5% and 20% Xe in Ar, the energy resolution being ⋍ 7% FWHM at 22.2 keV and ⋍ 4.5% at 59.6 keV for gas gain ⪅10 3. Addition of ≥1% TMA to an 80% Ar-20% Xe mixture produces a dramatic increase in gas gain but the energy resolution remains unaffected (≈ 7% FWHM at 22.2 keV). This increase in gas gain is attributed to the occurrence of a Penning effect between Xe and TMA, the ionization potential of TMA being 8.3 eV, just below the xenon metastable potential of 8.39 eV.

Measurements of the anisotropy ratio between longitudinal and transverse diffusion in argon based gas mixtures

A special drift cell with proportional wire readout has been constructed to make simultaneous measurements of the drift velocity, the longitudinal and this ratio with percentage of quencher used, and also compare favourably with existing Monte Carlo models. A simple method of parametrizing the data is suggested that should allow prediction of the diffusion properties given the drift velocity.

A study of the effect of methane and carbon dioxide concentration on gas amplification in argon based gas mixtures

Proportional counter gas amplification has been studied for argon based gas mixtures with methane and carbon dioxide as the quenching agent. Measurements of gas gain have been made using coaxial proportional tubes with different wire radii over a wide range of chamber voltages and pressures. The reduced gain function was found to be dependent on the reduced field E a P , and the fraction of the quenching minority gas and approximately independent of the choice of quencher in most of the proportional region. The full data sample for the ten different gas mixtures can be described by a function with only nine parameters.