Amount Of SF6 Research Articles

Tracking and Reducing SF6 Usage in Radiation Oncology: A Step Toward Net-Zero Health Care Emissions

Sulfur hexafluoride (SF6) is a widely used insulating gas in medical linear accelerators (LINACs) due to its high dielectric strength, heat transfer capabilities, and chemical stability. However, its long lifespan and high Global Warming Potential (GWP) make it a significant contributor to the environmental impact of radiation oncology. SF6 has an atmospheric lifespan of 3200 years and a GWP 23,000 times that of carbon dioxide. The amount of SF6 that can be emitted through leakage from machines is also concerning. It is estimated that the approximate 15,042 LINACs globally may leak up to 64,884,185.9 carbon dioxide equivalent per year, which is the equivalent greenhouse gas emissions of 13,981 gasoline-powered passenger vehicles driven for 1 year. Despite being regulated as a greenhouse gas under the United Nations Framework Convention on Climate Change, SF6 use within health care is often exempt from regulation, and only a few states in the United States have specific SF6 management regulations.This article highlights the need for radiation oncology centers and LINAC manufacturers to take responsibility for minimizing SF6 emissions. Programs that track usage and disposal, conduct life-cycle assessments, and implement leakage detection can help identify SF6 sources and promote recovery and recycling. Manufacturers are investing in research and development to identify alternative gases, improve leak detection, and minimize SF6 gas leakage during operation and maintenance.Alternative gases with lower GWP, such as nitrogen, compressed air, and perfluoropropane, may be considered as replacements for SF6; however, more research is needed to evaluate their feasibility and performance in radiation oncology. The article emphasizes the need for all sectors, including health care, to reduce their emissions to meet the goals of the Paris Agreement and ensure the sustainability of health care and our patients.Although SF6 is practical in radiation oncology, its environmental impact and contribution to the climate crisis cannot be ignored. Radiation oncology centers and manufacturers must take responsibility for reducing SF6 emissions by implementing best practices and promoting research and development around alternatives. To meet global emissions reduction goals and protect both planetary and patient health, the reduction of SF6 emissions will be essential.

Development of Combined Instrument Transformer for Gas-Insulated Switchgears

Accurate measurement of current and voltage information is essential to the safe reliable operation of railway substations. This paper dealt with a combined instrument transformer (CIT) built in a spacer for the purpose of miniaturization and eco-friendliness of a GIS, rated 72.5 kV and 2,000 A. A D-dot sensor and a Rogowski current sensor were applied to voltage and current measurement, respectively, to secure the insulation of the CIT in high-voltage and high-current conditions. As a result of an evaluation based on IEC 60044-7 and IEC 60044-8, the performance of the prototype CIT was found to sufficiently satisfy Class 0.5. When the CIT proposed in this paper was applied to a GIS of rated 72.5 kV, it was possible to reduce the size by 33% in length, 11% in height and 90% in weight per bay of the GIS compared to conventional iron-core transformers. In addition, since the amount of SF6 will be reduced by 15% in terms of volume, it is expected that this method can be used for the digitization, miniaturization and eco-friendliness of railway substations.

Performance studies of RPC detectors with new environmentally friendly gas mixtures in presence of LHC-like radiation background

RPC detectors are widely used at the CERN LHC experiments as muon trigger thanks to their excellent time resolution. They are operated with a Freon-based gas mixture containing C2H2F4 as well as some amount of SF6. Both C2H2F4 and SF6 are greenhouse gases with a very high global warming potential. The search of new environmentally friendly gas mixtures is necessary to reduce greenhouse gas emissions and costs as well as to optimize the RPC performance. Several recently available gases with low global warming potential have been identified as possible replacements for C2H2F4 and SF6. More than 60 environmentally friendly gas mixtures have been investigated on 2 mm single-gap RPCs. The RPC detectors have been tested in laboratory conditions and at the CERN Gamma Irradiation Facility, which provides a high energy muon beam combined with an intense gamma source allowing to simulate the background expected at HL-LHC . The performance of RPCs were studied at different gamma rates with the new environmentally friendly gases by measuring efficiency, streamer probability, rate capability, induced charge, cluster size and time resolution. To finalize the studies, the RPCs are now operated under gas recirculation with the selected new gas mixture and exposed to the intense gamma radiation of GIF++ for evaluating possible long-term aging effects, gas damage due to radiation and compatibility of LHC gas system with new gases.

Gravimetric Standard Gas Mixtures for Global Monitoring of Atmospheric SF6.

In this study, standard gas mixtures of SF6 in synthetic air were gravimetrically developed as a suite consisting of 6 mixtures with mole fractions of SF6 ranging from 5 to 15 pmol/mol. For precision in weighing the gas fills, an automatic weighing system coupled with a high sensitivity mass balance was used and a gravimetry precision of 3 mg (2σ) was achieved. Impurity profiles of the raw gases were determined by various analyzers. In particular, sub pmol/mol levels of SF6 in the matrix components (N2, O2, and Ar) were carefully measured, since the mole fraction of SF6 in the final step can be significantly biased by this trace amount of SF6 in the raw gases of the matrix components. Gravimetric dilution of SF6 by purity-assessed N2 was performed in 6 steps to achieve a mole fraction of 440 pmol/mol. In the final step, O2 and Ar were added to mimic the atmospheric composition. Gravimetric fractions of SF6 and the associated standard uncertainty in each step were computed according to the ISO 6142 and JCGM 100:2008, respectively, and validated experimentally. Eventually, the SF6 fraction uncertainty of the standard gas mixtures combined by uncertainties of gravimetric preparation and verification measurements were found to be nominally 0.08% at a 95% confidence interval. A comparison with independent calibration standards from NOAA shows agreement within 0.49%, satisfying the extended WMO compatibility goal, 0.05 ppt.

Electrostatic Neutralization Characteristics of an AC‐Corona‐Discharge‐Type Ionizer in Mixed N2‐O2, N2‐SF6 Atmosphere

SUMMARYWe are developing an electrostatic neutralizer operating in an atmosphere without oxygen for the organic electronics fabrication industry. As a part of the study, we investigated ion generation and neutralization characteristics of an ac‐corona‐discharge‐type ionizer in different atmospheric gases such as ambient air, pure nitrogen, and mixed N2‐O2 and N2‐SF6 gases, with changing the partial pressure of O2 and SF6, respectively. The I–V characteristic of the emitter shows that the negative current in N2 gas is significantly greater than the positive one; thus, the product final voltage VPF gives a significant deviation to a negative value (about –2 kV). However, by introducing SF6 gas by 0.01%, VPF reduces to about 0 V as that in ambient air. The amount of SF6 needed to improve the ion balance is three orders of magnitude smaller than that of O2, due to higher electronic affinity that a SF6 molecule has.

N<sub>2</sub>-O<sub>2</sub>, N<sub>2</sub>-SF<sub>6</sub>混合ガス雰囲気でのACコロナ放電型イオナイザの静電気除電特性

We are developing an electrostatic neutralizer operating in an atmosphere without oxygen for the organic electronics fabrication industry. As a part of the study, we investigated ion generation and neutralization characteristics of an ac-corona-discharge-type ionizer in different atmospheric gases such as ambient air, pure nitrogen, mixed N2-O2 and N2-SF6 gases, with changing the partial pressure of O2 and SF6, respectively. The I-V characteristic of the emitter shows that the negative current in nitrogen gas is significantly greater than the positive one; thus the product final voltage VPF gives a significant deviation to a negative value (about -2 kV). However, by introducing SF6 gas by 0.01 %, VPF reduces to about 0 V as that in ambient air. The amount of SF6 needed to improve the ion balance is three orders of magnitude smaller than that of O2, due to higher electronic affinity that a SF6 molecule has.

The Effect of SF6 on Ozone Generation using Dielectric Barrier Discharge

This paper reports the results of an experimental study of effect of SF6 on ozone generation within a Dielectric Barrier Discharge (DBD) fed by both pure oxygen and dry air. The chemical reaction mechanisms relevant to the process of ozone generation (and destruction) are discussed. The experimental results show the oxygen source should avoid the presence of SF6 but the addition of a small amount of SF6 in an air discharge can improve ozone concentration and ozone produce efficiency.

Pure SF6 and SF6−N2 Mixture Gas Hydrates Equilibrium and Kinetic Characteristics

Sulfur hexafluoride (SF6), whether pure or mixed with inexpensive inert gas, has been widely used in a variety of industrial processes, but it is one of the most potent greenhouse gases. For this reason, it is necessary to separate and/or collect it from waste gas streams. In this study, we investigated the pure SF6 and SF6-N2 mixture gas hydrates formation equilibrium aswell asthe gas separation efficiency in the hydrate process. The equilibrium pressure of SF6-N2 mixture gas was higher than that of pure SF6 gas. Phase equilibrium data of SF6-N2 mixture gas was similar to SF6 rather than N2. The kinetics of SF6-N2 mixture gas was controlled by the amount of SF6 at the initial gas composition as well as N2 gas incorporation into the S-cage of structure-II hydrate preformed by the SF6 gas. Raman analysis confirmed the N2 gas incorporation into the S-cage of structure-II hydrate. The compositions in the hydrate phase were found to be 71, 79, 80, and 81% of SF6 when the feed gas compositions were 40, 65, 70, and 73% of SF6, respectively. The present study provides basic information for the separation and purification of SF6 from mixed SF6 gas containing inert gases.

Oxidation Performance Test of Detritiation System Under Existence of SF6

To obtain performance data of atmosphere detritiation system at the off normal events such as SF6 release for the safety of ITER, the detritiation experiment was planned and performed at Tritium Process Laboratory (TPL) in Japan Atomic Energy Agency (JAEA) using a small scaled detritiation system for the oxidation performance test which can process gas flow rate of 0.06 m3/hr in once through. The detritiation system consists of two oxidation catalyst beds (473K and 773K) for converting hydrogen isotopes and tritiated methane in compounds to water vapor and a bubbler for removing water vapor. SF6 gas is used as an electric insulation gas of Neutral Beam Injection system (NBI) in ITER, and is expected to be released in an accident such as fire. In this time, the performance of oxidation catalyst bed of the detritiation system for hydrogen under existence of SF6 which are released from NBI was investigated.The SF6 gas was notably decomposed in the case of the catalyst bed temperature higher than 623K. In addition, when 0.05% or more of SF6 was introduced with 1% of hydrogen, a part of the water produced by the 473K catalyst bed was reduced to hydrogen due to the reaction with the decomposed gas in SF6. Consequently, the detritiation factor (D.F.) of the detritiation system was decreased to less than 50 from > 10000 of its initial value. Since the effect of SF6 depends on its concentration closely, the amount of SF6 released into the tritium handling area in an accident should be reduced by some ideas of the arrangement of components using SF6 in the buildings.

Inversion of the Electron Energy Distribution in Hollow-Cathode Glow Discharge in Nitrogen–Sulfur Hexafluoride Gas Mixture

The electron energy distribution function (EDF) in a hollow-cathode glow discharge in nitrogen-sulfur hexafluoride (N2-SF6) gas mixture has been studied by experimental and theoretical methods. On adding a small amount of SF6 to N2, the density of electrons in the energy interval (2−4 eV) of the EDF inversion increases by approximately one order of magnitude.

Measurement of electron drift, diffusion, and effective ionization coefficients in the SF6–CHF3 and SF6–CF4 gas mixtures

The electron drift velocity, the longitudinal diffusion coefficient, the effective ionization coefficient and the limiting field strength for mixtures of SF6 with CHF3 and CF4 have been measured with a pulsed Townsend technique. The overall density-reduced electric field strength, E/N, could be varied between 60 and 520 Td (1 Td = 10−17 V cm2), while the SF6 content in the gas mixtures was varied over the range 1–50%. We have found that the electron drift velocity and the density-normalized longitudinal diffusion coefficient vary weakly with the amount of SF6 in the mixture. In contrast, the effective ionization coefficient shows a strong dependence with the SF6 content, becoming more electronegative as the amount of SF6 is increased. The measured limiting field strength for these two mixtures is lower than those for SF6–N2. To our knowledge, no previous ionization or electron transport data for these mixtures have been published.

Dynamic current-zero behaviour of wall-stabilised arc in different arc-quenching media

SF6 gas is the medium currently used to quench the arc in gas circuit breakers (GCBs) and gas insulated switchgear (GIS). It has become increasingly necessary to look at alternatives to SF6 for the following reasons: (i) high cost, (ii) sensitivity to particle contamination, (iii) concerns regarding global warming and hence the possibility of imposed rules for decreased SF6 production. From a practical standpoint, the complete elimination of SF6 as an arc-extinguishing medium is improbable. On the other hand, a reduction in the amount of SF6 and the inclusion of a buffer gas is worthy of consideration. In order to determine the suitability of a buffer gas, it is necessary to understand the buffer gases' fundamental plasma properties. A comparative prediction of the thermal breakdown strengths of the following gases: SF6, N2, O2, air, CO2, H2, He and N2–PTFE after current-zero is presented. The thermophysical properties of a N2–PTFE mixture are also calculated. A one-dimensional wall-stabilised arc model is solved numerically to determine the thermal breakdown strength of the aforementioned buffer gases in the presence of a uniform electric field intensity having a certain rate of rise. Calculations are done for two typical arc radii: 2.5 and 1.5 mm. Predictions confirm the suitability of He, CO2, N2 and air as a buffer gas to SF6 and helium is found to be the best buffer choice.