Gas Injection System Research Articles

Rapid and massive throughput analysis of a constant volume high-pressure gas injection system

Abstract Fusion power shutdown system (FPSS) is a safety system to stop plasma in case of accidents or incidents. The gas injection system for the FPSS presented in this work is designed to research the flow development in a closed system. As the efficiency of the system is a crucial property, plenty of experiments are executed to get optimum parameters. In this system, the flow is driven by the pressure difference between a gas storage tank and a vacuum vessel with a source pressure. The idea is based on a constant volume system without extra source gases to guarantee rapid response and high throughput. Among them, valves and gas species are studied because their properties could influence the velocity of the fluid field. Then source pressures and volumes are emphasized to investigate the volume flow rate of the injection. The source pressure has a considerable effect on the injected volume. From the data, proper parameters are extracted to achieve the best performance of the FPSS. Finally, experimental results are used as a quantitative benchmark for simulations which can add our understanding of the inner gas flow in the pipeline. In generally, there is a good consistency and the obtained correlations will be applied in further study and design for the FPSS.

Combining atomic force microscopy and shear-force acoustic near-field microscopy to characterize confined mesoscopic fluids

An atomic force microscopy (AFM) cantilever is integrated into to a quartz tuning fork (QTF) to probe the viscoelastic properties of mesoscopic fluid layers confined between two solid surfaces under shear. Two procedures to fabricate the AFM/QTF probe are described herein. In the first, a nano-manipulator is used to transport a commercially available afm cantilever from its chip holder to the edge of a QTF tine. In the second, an afm cantilever is fabricated at the edge of the QTF tine itself. In both cases we exploit the capabilities of a dual-beam system (focused ion beam/scanning electron microscope), equipped with Omni-Probe nano-manipulator and a Gas Injection System (GIS). The new device improves the ability of shear-force acoustic near-field microscopy (SANM) to monitor the constraining normal and damping shear forces exerted by the solid boundaries, concurrently with the acoustic emission from the trapped fluid.

Overview of the J-TEXT progress on RMP and disruption physics

The J-TEXT tokamak has been operated for ten years since its first plasma obtained at the end of 2007. The diagnostics development and main modulation systems, i.e. resonant magnetic perturbation (RMP) systems and massive gas injection (MGI) systems, will be introduced in this paper. Supported by these efforts, J-TEXT has contributed to research on several topics, especially on RMP physics and disruption mitigation. Both experimental and theoretical research show that RMP could lock, suppress or excite the tearing modes, depending on the RMP amplitude, frequency difference between RMP and rational surface rotation, and initial stabilities. The plasma rotation, particle transport and operation region are influenced by the RMP. Utilizing the MGI valves, disruptions have been mitigated with pure He, pure Ne, and a mixture of He and Ar (9:1). A significant runaway current plateau could be generated with moderate amounts of Ar injection. The RMP has been shown to suppress the generation of runaway current during disruptions.

The Central Control System for KTX

The Keda Torus eXperiment (KTX) is a new medium-sized reversed-field pinch device designed and implemented jointly by the University of Science and Technology of China and the Institute of Plasma Physics at the Chinese Academy of Science. An important component of the KTX project is a central control system that is composed of six modules: 1) central console; 2) process control system; 3) central timing system; 4) safety and interlock system; 5) gas injection system; and 6) shot information server. The network and optical fiber infrastructures also provide great support for the stable operation of the experiment. This paper will describe the details about the system architecture and networks deployment.

Numerical study of gas injected heat pump using zeotropic R32/R1234ze(E) mixture: Comparison of two type economizers

Rare pure refrigerants can meet the environmental, thermodynamic, and safety requirements to new-generation refrigerants completely. R32/R1234ze(E) zeotropic mixture is a potential replacement in the field of air conditioning and heat pumps. At the same time, gas injection technology is considered as a good solution to increase the seasonal energy performance of heat pump system. Accordingly, a comprehensive model of gas-injected water-water heat pump with R32/R1234ze(E) is built in this paper. Based on it, the performance of the gas injected heat pump with flash tank economizer and intermediate heat exchanger economizer are researched. Finally, the effect of type of the economizer type on the performance is identified. Three potential key parameters affecting the performance of the gas injection system, including molar fraction of refrigerant, inlet temperature of heat transfer fluid in evaporator, mass flowrate of heat transfer fluid in evaporator, are investigated. As a result, both flash tank gas injection and intermediate heat exchanger injection can largely enhance the heating capacity and COP of water-water heat pump using R32/R1234ze(E) mixture. Intermediate heat exchanger injection promotes the heat pump with zeotropic mixture more effectively than flash tank injection.

Structural integrity analysis for final design of ITER gas fueling manifold

The Gas Fueling (GF) manifold is a major subsystem of the ITER gas injection system and it is designed to deliver fueling gases from tritium plant for initiating, maintaining or controlling plasma. According to the load specifications, the detailed structural analysis of ITER GF manifold have been performed to assess the design and structural integrity. The results show that the GF manifold is safe under all load combinations and the structural integrity requirements are well satisfied. This paper provides briefly the results of structural analysis for ITER GF manifold final design review.

Smallest microhouse in the world, assembled on the facet of an optical fiber by origami and welded in the μRobotex nanofactory

In this study, the authors have demonstrated that it is possible to realize several three-dimensional (3D) micro- and nanostructures, by the fabrication of the smallest microhouse using a dual beam scanning electron microscope (SEM)/focused ion beam (FIB) Auriga 60 from Zeiss together with a six degree of freedom robot built with SmarAct components. In this new type of nanolab, cutting, etching, folding, assembling, and then welding thin membranes of silica on top of a cleaved optical fiber SMF28, or production of micro- and nanostructures, like the microhouse, are possible. The authors have experimentally shown that FIB can be used, in this new generation of micro/nanofactory, in combination with SEM, and gas injection system, in order to fabricate three-dimensional microstructures: a microhouse in this study, with ultrahigh accuracy assembly down to 10 nm. By using the theory of sputtering, the authors are able to propose a model of folding thin membranes of numerous materials such as metals, polymers, or crystals, i.e., silica, silicon, potassium tantalite, or lithium niobate. This method is usually described as origami in the literature [W. J. Aroa, H. I. Smith, and G. Barbastathis, Microelectron. Eng. 84, 1454 (2007); W. J. Aroa et al., J. Vac. Sci. Technol., B 25, 2184 (2007); and K. Chalapat et al., Adv. Mater. 25, 91 (2013)]. The experimental results indicate that the introduction of a microrobot inside the SEM vacuum chamber will provide the means to enlarge the scope of clean room facilities to build complex and smart 3D microsystems with heterogeneous materials, especially on the facet of an optical fiber in the lab on fiber new field. The authors propose a new way to easily manufacture many kinds of optical functions for light trapping based on nanoantennas, nanophotonic crystal, axicon or lattice, 3D biosensor with origami, and nanopatterning surfaces or carbon nanotubes, etc.

Initial implementation of helium Gas into the SNS mercury target for mitigation of fatigue and cavitation damage

The short-pulse, 60 Hz beam used at the Spallation Neutron Source (SNS) initiates pressure waves in the mercury target with each pulse that 1) lead to huge numbers of fatigue stress cycles in the target vessel, and 2) pitting / erosion damage to the target vessel caused by mercury cavitation. Both phenomena can lead to target leaks and interruption of neutron production.The number of beam pulses expected over a successful target life is on the order of 109; the number of response stress cycles at a vessel position can exceed 1 per pulse. This number is even beyond the regime typical of high-cycle fatigue. It is important to be aware that contemporary knowledge fatigue damage includes probabilistic behavior for many materials, and that for many materials a true endurance limit does not exist. Obtaining data in the giga-cycle regime is difficult, particularly repeatable data. In this regime, the effects of very small material defects, inclusions and inhomogeneity become relevant as their size approaches that of the material microstructure. Detecting and controlling such defect sizes is problematic in the SNS mercury target module weld assembly.While considerable efforts are being made to improve the robustness of the SNS target, one thing that can be assuredly stated is that reducing high-cycle fatigue stress magnitude will add margin to its fatigue life. Injecting gas into the target mercury is one way to accomplish this. The degree of pulse stress reduction to be expected from a given gas condition is difficult to predict. There are SNS experimental data and JPARC target gas injection experience to expect stress reduction to ½ ~ ¼ of that without gas throughout much of the target mercury vessel.As a first step towards reduction of cyclic stresses and mitigation of cavitation damage, SNS will implement gas injection in its mercury target module beginning in the fall of 2018. The project is known as Gas Injection Initial Implementation, or GI3. GI3 will comprise of a once-through system. That is, the injected helium will be processed through the Mercury Off-gas Treatment System (MOTS) rather than recycled for re-injection. GI3 will employ relatively low flow rate of up to 1 slpm of helium gas through a total of sixty orifices, each with a diameter of 8 microns. The upstream supply pressure will be approximately 6.9 atm.GI3 in envisioned as a first step towards a more complete and complex gas injection system that would include much higher flow rates, gas re-circulation, and the potential combination of small gas bubble and gas wall supplies. Despite this reduced scope, there are significant design, installation, operational, and safety related challenges associated with the project. This paper and presentation will describe these challenges and the strategies employed to overcome them.

Numerical study of transient flow in the preliminary design of fusion power shutdown system

The FPSS (fusion power shutdown system) provides a safety emergency shutdown system terminating the ITER (international thermonuclear experimental reactor). It has a reservoir of impurity gas and a dedicated tube for the impurity gas injection. In the preliminary design stage, the FPSS is studied as a sealed gas injection system, it is a supersonic and high pressure flow field. The transient flow of the system is analyzed with a commercial CFD code, ANSYS® FLUENT in this paper. To satisfy the functional requirement, the injected gas volume of the VV (vacuum vessel) is predicted from a series of tank pressures in 3s. The influence of initial tank pressures, vessel pressure and flow times of the FPSS is quantified. CFD data is compared with the experimental activities and the discrepancy is acceptable. All the results will be used for optimized design of the FPSS.

Rubidium distribution at atomic scale in high efficient Cu(In,Ga)Se2 thin-film solar cells

The introduction of a rubidium fluoride post deposition treatment (RbF-PDT) for Cu(In,Ga)Se2 (CIGS) absorber layers has led to a record efficiency up to 22.6% for thin-film solar cell technology. In the present work, high efficiency CIGS samples with RbF-PDT have been investigated by atom probe tomography (APT) to reveal the atomic distribution of all alkali elements present in CIGS layers and compared with non-treated samples. A Scanning Electron Microscopy Dual beam station (Focused Ion Beam–Gas Injection System) as well as Transmission Kikuchi diffraction is used for atom probe sample preparation and localization of the grain boundaries (GBs) in the area of interest. The analysis of the 3D atomic scale APT reconstructions of CIGS samples with RbF-PDT shows that inside grains, Rb is under the detection limit, but the Na concentration is enhanced as compared to the reference sample without Rb. At the GBs, a high concentration of Rb reaching 1.5 at. % was found, and Na and K (diffusing from the glass substrate) are also segregated at GBs but at lower concentrations as compared to Rb. The intentional introduction of Rb leads to significant changes in the chemical composition of CIGS matrix and at GBs, which might contribute to improve device efficiency.

A low pressure direct gas injection system for a four stroke LPG: Diesel dual fuel engine

ABSTRACTInternal combustion engines running on gaseous fuels produce low torque because the inducted gaseous fuel displaces air and reduces the volumetric efficiency. This can be overcome by injecting the gaseous fuel directly into the cylinder after the intake of air is completed. This work is a step in developing and demonstrating a cost effective system, as such systems are not readily available for small applications. A low-pressure gas injector was mounted on the cylinder barrel of a fully instrumented dual fuel engine. Its location is such that the injector will be exposed to the cylinder gases about 65.5 degrees before bottom dead center, where the cylinder pressure and temperature will be relatively low. An electronic controller was also developed to time the injection process to occur after the intake valve closes and also to control the duration of injection (quantity). Experiments were conducted with LPG (Liquefied petroleum gas) as the primary fuel that was injected with this new system and diesel as the pilot fuel at the rated speed of 1500 rpm with different amounts of LPG at 80% and 100% load. Comparisons of performance, combustion and emissions with the conventional manifold injection of LPG were done. The system allowed greater amounts of LPG to be used without knock as compared to manifold injection. On the whole the developed system has potential for application in small dual fuel and spark ignited gas engines and can be taken up for further optimization.

Organic ice resists for 3D electron-beam processing: Instrumentation and operation

Organic vapors condensed into thin layers of ice on the surface of a cold substrate are exposed with an electron beam to create resist patterns for lithography applications. The entire spin- and development-free lithography process requires a single custom instrument. We report the design, material choice, implementation and operation of this apparatus. It is based on a scanning electron microscope fitted with an electron beam control system that is normally used for electron beam lithography in a multi-user open-access laboratory. The microscope was also equipped with a gas injection system, a liquid nitrogen cooled cryostage, a temperature control system, and a load-lock. Three steps are required to initialize the apparatus for organic ice resist processing, and two steps are required to restore the apparatus for routine multi-user operations. Five steps are needed to create organic ice resist patterns. Finally, by stacking nanoscale patterns made in organic ice we created 3D structures using two complementary cyclic condense, expose and sublimate processes.

Optimization of the performance of injection cooling system using genetic algorithm

Injection cooling is a method to reduce the boil-off loss of cryogenic liquids, and has been applied in space launch vehicles. In this, subcooling due to liquid evaporation into the gas bubble causes a reduction in the liquid boil-off. Extent of evaporation depends on the gasliquid interfacial area, and heat and mass transfer rates. Hence, gas flow rate, gas injection temperature and system configuration have profound effect on liquid subcooling. Optimum values of process variables are needed to maximize the process performance. The present study involves the development of an optimization strategy to minimize the evaporative loss of cryogenic liquid in injection cooling. Genetic Algorithm (GA) has been applied for this purpose as it enables the determination of global optimum values of various process variables. An in-house code has been developed to carry out optimization studies on the injection cooling.

Effect of Separation Angle and Nozzle Radial Position on Mixing Time in Ladles with Two Nozzles

Chemical, thermal and mechanical homogenization of both slag and steel during the ladle furnace process depends on the design of the gas injection system in gas bottom stirred ladles. In the past, a large number of variables have been investigated, nevertheless due to the importance of the slag layer during the process, it has been incorporated in water modeling studies in more recent investigations. In large industrial size ladles is common to use two porous plugs. The configuration of the injection system with two porous plugs requires optimization of both nozzle radial position and nozzle separation angle. In this work the effect of nozzle radial position, nozzle separation angle, gas flow rate and slag thickness on mixing time has been investigated using a water model. The effect of tracer concentration on mixing time was also explored. It is shown that a separation angle of 60 degrees provides the best mixing efficiency.

Preliminary study of a fast massive gas injection system for plasma disruption mitigation

In fusion experiments, and for future international thermonuclear experimental reactor-like fusion reactors, the mitigation of plasma disruptions is a key issue to reduce the severe damage that can be caused to the machine by high heat loads and runaway electrons. Pellet injection (PI) and massive gas injection (MGI) are present among the most promising candidate techniques to mitigate disruption effects. PI consists of injecting into the plasma solid cryogenic pellets, while MGI involves the injection of large amounts of different species of noble gases by means of a fast valve. In present day facilities, a suitable fast disruption mitigation valve (FDMV) typically must be able to deliver [Bozhenkov et al., Rev. Sci. Instrum. 78, 033503 (2007)] about 10 bar × l of a noble gas in 10 ms (although this figure depends on the plasma stored energy). An almost unique know-how has been developed in the Special Technologies Laboratory, at ENEA Frascati, concerning high-speed cryogenic pellet injectors based on two-stage pneumatic light-gas guns [Frattolillo et al., Rev. Sci. Instrum. 67, 1834 (1996).]. The possible use of the fast valve, integrated inside the first stage of the gun driver, as a FDMV, is proposed in this article. Preliminary laboratory tests, conducted using an existing device, demonstrate the considerable potential of this particular fast valve concept, which is actuated by a difference in pressure exerted on the opposite sides of the valve shutter. Although the equipment used in these preliminary laboratory tests was not specifically designed for this purpose, its performances (about 20 bar × l of He injected in the test volume in roughly 10.5 ms) are comparable with those of other FDMV concepts; moreover, it proved to be reliable, flexible, and repeatable, allowing an accurate control of the amount of gas released by the valve. The results of these exploratory experiments are reported and compared with other FDMV concepts.

Field-reversed configuration formed by in-vessel θ-pinch in a tandem mirror device.

We describe a field reversed configuration (FRC) experiment featuring in-vessel θ-pinch coils and open-field-line plasmas confined in a tandem mirror. Two FRCs, formed near the west and the east mirror throats of a central cell, are ejected toward the mid-plane for colliding and merging. Each FRC consists of four groups of pulsed power supplies and four groups of coils, having diameters 35, 35, 40, and 45 cm. The rise time of the main reversal field is 7.15 μs, and the maximum voltage is 40 kV with total currents of 416 kA, corresponding to a magnetic field of 1690 G. The total capacitive stored energy is 115.2 kJ. A fast pulse gas injection system was designed and tested to inject neutral gas into the FRC formation region with controlled directions. The successful installation of the θ-pinch coils inside the vacuum vessel offers greater freedom for diagnostics and control instruments as well as preserving magnetic tandem mirror configuration. The magnetic field reversal is confirmed by internal magnetic field measurements. The plasma temperature, density, and lifetime are, respectively, ∼100 eV, ∼3.0 × 1018 m-3, and ∼300 μs for the current operating conditions.

Laser cutting using off-axial supersonic rectangular nozzles

Laser cutting is a well-established process in the industry, mainly for cutting metallic materials such as steels. However, the utilization of this laser technique to process advanced materials, such as ceramics or some aluminium alloys, is restricted due to the formation of a large heat affected zone (HAZ), rough cut edges, presence of dross, or thermal cracks. These defects are closely related to the performance of the assist gas during the removal of molten material. Previous works have demonstrated the impressive improvement in cut quality with the utilization of off-axial supersonic axisymmetric nozzles to inject the assist gas. This is due to the higher removal of molten material. However, these results can be even improved if the geometry of the gas jet is tailored to the cut kerf. In the present work, a cutting head with an off-axial supersonic rectangular nozzle was developed to improve the efficiency of the current assist gas injection systems. The performance of this system was compared with that of a converging (coaxial) nozzle, and an off-axial supersonic axisymmetric nozzle during the processing of Al2024-T3 sheets. Results demonstrated the superior performance of the new assist gas injection system in terms of cut quality and productivity (cut edge roughness was 6.5 times lower, and the cutting speed is 1.98 times higher as compared to the results found for a converging coaxial nozzle).

Modeling and designing a new gas injection diffusion system for metalorganic chemical vapor deposition

Metalorganic chemical vapor deposition (MOCVD) is a critical process and is widely used for the epitaxial growth of light-emitting diode (LED) wafers. The key component, a gas injection system, delivers the gas into the reactor by using a nozzle or showerhead. In this paper, the numerical simulation method was applied to investigate the thermal fluid field and to design a new gas injection system for MOCVD. In this study, we developed a new gas injection system with inlet barriers. The inlet barriers can separate the various reactive gases, reduce the prereaction, and prevent adducted particles from forming and blocking the inlet gas system. The barrier geometry, including the barrier length, the barrier inclination angle, and the V/III precursor ratio was systematically studied to determine the optimal design conditions. Higher growth rate and improved uniformity were demonstrated using the new optimal gas inlet barrier design.

The characteristic analysis of high-pressure gas jets for natural gas engine based on shock wave structure

High gas injection pressure leads to the formation of under-expanded gas jet at nozzle exit. The shock wave structure near the nozzle affects gas jet injection and mixing characteristics, which affects the combustion and emission performance of the engine. Gas jet injection process and shock wave structure evolution law under different nozzle pressure ratio (NPR) and orifice diameter have been investigated with the application of Schlieren imaging and numerical simulation. Results show that long injection duration exists in gas injection process after the end of injection. It is attributed to the slow pressure reduction velocity in the nozzle. This phenomenon is one of the key factors which influence the high HC emission of gas fuel port injection natural gas engines. The change of pressure inside the nozzle also affects the shock wave structure (Mach disk) near the nozzle. It is found that the increase of Mach disk width leads to a large jet near-field angle which promotes the spatial distribution and turbulent mixing of gas jet. In addition to experimental results, numerical simulation is used to analyze the injection characteristics of gas injection system. Increasing gas nozzle flow area and shortening gas nozzle length are regarded as effective ways to improve the responsiveness of gas injection system and reduce gas injection duration. The range of Reynolds number at exit of the nozzle is 0.5–2.5×105 under various gas injection pressures and orifice diameters. This presents that gas jet is easily influenced by air turbulence in intake manifold. Strong air turbulence in intake manifold is needed in a gas fuel port injection natural gas engine in order to obtain homogeneous gas/air mixture.

Surface heat flux feedback controlled impurity seeding experiments with Alcator C-Mod’s high-Z vertical target plate divertor: performance, limitations and implications for fusion power reactors

The Alcator C-Mod team has recently developed a feedback system to measure and control surface heat flux in real-time. The system uses real-time measurements of surface heat flux from surface thermocouples and a pulse-width modulated piezo valve to inject low-Z impurities (typically N2) into the private flux region. It has been used in C-Mod to mitigate peak surface heat fluxes >40 MW m−2 down to <10 MW m−2 while maintaining excellent core confinement, H98 > 1. While the system works quite well under relatively steady conditions, use of it during transients has revealed important limitations on feedback control of impurity seeding in conventional vertical target plate divertors. In some cases, the system is unable to avoid plasma reattachment to the divertor plate or the formation of a confinement-damaging x-point MARFE. This is due to the small operational window for mitigated heat flux in the parameters of incident plasma heat flux, plasma density, and impurity density as well as the relatively slow response of the impurity gas injection system compared to plasma transients. Given the severe consequences for failure of such a system to operate reliably in a reactor, there is substantial risk that the conventional vertical target plate divertor will not provide an adequately controllable system in reactor-class devices. These considerations motivate the need to develop passively stable, highly compliant divertor configurations and experimental facilities that can test such possible solutions.