Gas Injection Valve Research Articles

Real-time density feedback control in ADITYA-U Tokamak

A real-time density feedback control system with a 100 GHz heterodyne interferometer has been designed, developed, and commissioned in ADITYA-U tokamak. It consists of three subsystems i.e. density measurement, feedback control, and gas fuelling. A proportional feedback controller is configured in voltage amplitude mode to operate the piezo valve for gas injection. Experiments are performed during plasma discharges to achieve a predefined density evolution as well as constant density. Stickiness of the piezo valve restricts the temporal response of the valve. It is required to minimize during the plasma discharge for a fast density response which is achieved by a short preceding voltage pulse known as a stick pulse. This paper describes the implementation of a real-time density feedback control system which is successfully validated using another existing 140 GHz interferometer system in ADITYA-U. Moreover, the developed system consumes low power, is cost-effective and re-programmable, can be easily upgraded, and provides interlock with plasma parameters.

Behavior of micro pillar array column in high pressure gas chromatography

Micro pillar array column with interpillar distance of 2.5 µm for pillars diameter of 5 µm has been introduced in high pressure gas chromatographic systems for online industrial analysis. Separation of gas mixtures have been performed under carrier gas pressure as high as 60 bar using rotating valve for gas injection without sample decompression stage prior to injection. A very low intrinsic height equivalent to a theoretical plate value of 14 µm has been obtained in few seconds. Instead of conventional gas chromatography, carrier gas nature such as helium, argon and carbon dioxide and pressure can be used to tune the selectivity. Liquid hydrocarbon samples have been successfully introduced in the column using a septum based split/splitless injector modified to work up to 40 bar. Separations of VOCs and gasoline samples have been successfully performed.

Dissipation of runaway current by massive gas injection on J-TEXT

Plasma disruption is one of the major challenges for ITER. A large fraction of runaway current may be formed due to the avalanche generation of runaway electrons (REs) in disruptions. Current researches find that the generation of REs may be hard to totally suppress during the disruptions, and lead to the formation of large runaway current in future fusion devices. Runaway currents carry huge magnetic and kinetic energies that need to be dissipated safely. Runaway current dissipation by high-Z impurities has been performed on J-TEXT. Runaway currents are formed by an injection of ∼1019 argon atoms, and then large quantities of argon or krypton impurities are injected by the massive gas injection valve to dissipate the runaway current during the runaway current plateau phase. The dissipation efficiency increases with the increase of injected impurity quantity. When the injected impurity quantity exceeds 2 × 1021, the dissipation efficiency becomes saturated. Up to a 28 MA s−1 runaway current dissipation rate and a 15% energy dissipation rate can be achieved. Analysis shows that the saturation of dissipation efficiency is caused by the decrease of impurity assimilation rate with the increase of total injected impurity quantity. The decrease of impurity assimilation rate may be caused by the saturation of impurity density growth rate during the short dissipation phase. A simple estimate also shows that the increase of internal inductance leads to the slowing down of the growth of runaway current dissipation rate during the runaway current decay phase. The results may have important implication for ITER disruption mitigation.

TCV heating and divertor upgrades

The operational range and the reactor relevance of the TCV experiments are being enhanced by two sets of major upgrades. The first includes the installation of neutral beam injection (NBI) and new electron cyclotron (EC) auxiliary heating sources, to reach ITER relevant beta values and vary the electron to ion temperature ratio. A 15–30 keV, 1 MW tangential NBI system has been operational on TCV since 2015. A second beam of 1 MW, 50–60 keV ion energy, also aligned tangentially but opposite to the first beam, is foreseen to approach beta limits, vary the applied torque through zero and probe suprathermal ion physics. For the EC power, two 0.75 MW gyrotrons at the second harmonic have been installed. The next step will add two 1 MW dual frequency gyrotrons, one of which is currently being commissioned. These heating upgrades will increase the total available power for high-density plasmas from 1.25 MW to 5.0 MW. The rest of the upgrade consists of installing an in-vessel structure to form a divertor chamber of increased closure, to reach higher neutral divertor densities and impurity compression and thereby extend TCV divertor regimes toward more reactor relevant conditions for conventional and advanced divertor configurations. Graphite gas baffles will be installed inside the TCV vessel to delineate divertor and main chamber regions. The first set of baffles features 32 tiles on the high and 64 tiles on the low-field side, with geometry guided by simulations performed using the SOLPS-ITER code. The baffles are expected to be effective for a wide range of divertor configurations, including snowflake and super-X divertors, yet maintain plasma close to the inner wall for improved passive stabilization. The baffle dimensions may be varied in the future to modify the divertor closure. Control of the plasma, neutral and impurity densities will be achieved by a combination of toroidally distributed gas injection valves and impurity seeding, and a possible addition of cryo-condensation pumps. Significant diagnostic developments will be undertaken, to better characterize the divertor plasma, measure power and particle deposition at the strike points, and, specifically, improve our physics understanding of the detachment process.

High-performance serial block-face SEM of nonconductive biological samples enabled by focal gas injection-based charge compensation.

A longstanding limitation of imaging with serial block-face scanning electron microscopy is specimen surface charging. This charging is largely due to the difficulties in making biological specimens and the resins in which they are embedded sufficiently conductive. Local accumulation of charge on the specimen surface can result in poor image quality and distortions. Even minor charging can lead to misalignments between sequential images of the block-face due to image jitter. Typically, variable-pressure SEM is used to reduce specimen charging, but this results in a significant reduction to spatial resolution, signal-to-noise ratio and overall image quality. Here we show the development and application of a simple system that effectively mitigates specimen charging by using focal gas injection of nitrogen over the sample block-face during imaging. A standard gas injection valve is paired with a precisely positioned but retractable application nozzle, which is mechanically coupled to the reciprocating action of the serial block-face ultramicrotome. This system enables the application of nitrogen gas precisely over the block-face during imaging while allowing the specimen chamber to be maintained under high vacuum to maximise achievable SEM image resolution. The action of the ultramicrotome drives the nozzle retraction, automatically moving it away from the specimen area during the cutting cycle of the knife. The device described was added to a Gatan 3View system with minimal modifications, allowing high-resolution block-face imaging of even the most charge prone of epoxy-embedded biological samples.

Development of a High Performance Natural Gas Engine with Direct Gas Injection and Variable Valve Actuation

Natural gas is a promising alternative fuel for internal combustion engine application due to its low carbon content and high knock resistance. Performance of natural gas engines is further improved if direct injection, high turbocharger boost level, and variable valve actuation (VVA) are adopted. Also, relevant efficiency benefits can be obtained through downsizing. However, mixture quality resulting from direct gas injection has proven to be problematic. This work aims at developing a mono-fuel small-displacement turbocharged compressed natural gas engine with side-mounted direct injector and advanced VVA system. An injector configuration was designed in order to enhance the overall engine tumble and thus overcome low penetration. Gas injection, interaction thereof with charge motion and geometrical bounding walls, and the resultant mixture formation process was investigated in detail by the combination of planar laser-induced fluorescence (LIF) in an optical engine and computational fluid dynamics (CFD) analysis with moving injector model to verify the design of the injector and combustion chamber. Then a prototype engine was tested to compare the rated torque against target performance. The planar LIF investigation underlined the influence of the Coandǎ effect whereby the gas jet was deflected to the adjacent injector niche and then to the combustion chamber roof. Such effect was inhibited at early injection timings due to strong intake air flow. CFD analysis confirmed this behavior and pointed out that the mixing process is dominated by the gas jet during injection and flow patterns promoted by it. It was concluded that the principal mixing mechanism is the jet-promoted tumble and elliptical swirl motion, and the mixing rate is thereby scaled with absolute time, rather than crank angle degree, and mainly determined by the strength of these two motion patterns. It was in addition found that the injection contributes to combustion-relevant turbulence mainly by intensifying the large-scale charge motion. Overall high mixing capacity was observed, and the injector and combustion chamber design deemed efficacious. The engine design has been successfully accomplished and the prototype multi-cylinder engine (MCE) is ready for extensive performance and emission analysis on the test rig.

Suppression of runaway current generation by supersonic molecular beam injection during disruptions on J-TEXT

The suppression of disruption-generated runaway electrons (REs) by supersonic molecular beam injection (SMBI) has been investigated on the J-TEXT tokamak. Experimental results demonstrate that the hydrogen injected by SMBI during plasma current flattop phase can provoke magnetic perturbations, which increase RE losses rapidly. The effective radial diffusion coefficient of REs due to SMBI is estimated as Dr ≈ 16 m2 s−1. Based on this benefit, the SMBI has been used to explore the suppression of disruption-generated REs. In J-TEXT, RE current is created with rapid argon injection by a massive gas injection valve. It is found that hydrogen SMBI before disruption efficiently suppresses the generation of RE current.

Spring-driven high speed valve for massive gas injection in tokamaks.

A new high speed gas valve was developed for disruption mitigation studies in the tokamak ASDEX Upgrade. The valve was designed to operate inside the vacuum vessel to reduce the time of flight of the injected gas and to prevent dispersion of the gas cloud before the gas reaches the plasma. A spring-driven mechanism was chosen for the valve as it is robust against the high magnetic fields and electromagnetic disturbances inside the vessel. The internal gas reservoir (128 cm3) of the valve, which holds the mitigation gas, is opened within 1.5 ms, and the maximal stroke between the valve plate and nozzle (diameter 13 mm) is 4.5 mm. This allows a peak flow rate of 72 kPam3/s after 1 ms which was determined both analytically and numerically. The highest gas velocity (approximately 560 m/s) is reached 0.6 ms after the valve is opened. The gas cloud expands in a pear shape with an opening angle of 49°.

Massive Gas Injection Valve Development for NSTX-U

NSTX-U research will offer new insights by studying gas assimilation efficiencies for massive gas injection (MGI) from different poloidal locations using identical gas injection systems. In support of this activity, an electromagnetic MGI valve has been built and tested. The valve operates by repelling two conductive disks due to eddy currents induced on them by a rapidly changing magnetic field created by a pancake disk solenoid positioned beneath the circular disk attached to a piston. The current is driven in opposite directions in the two solenoids, which creates a canceling torque when the valve is operated in an ambient magnetic field, as would be required in a tokamak installation. The valve does not use ferromagnetic materials. Results from the operation of the valve, including tests conducted in 1-T external magnetic fields, are described. The pressure rise in the test chamber is measured directly using a fast time response Baratron gauge. At a plenum pressure of just 1.38 MPa ( $\sim 200$ psig), the valve injects 27 Pa $\cdot \text{m}^{\mathrm {\mathbf {3}}}$ ( $\sim 200$ torr $\cdot $ L) of nitrogen with a pressure rise time of 3 ms.

The optimization approach of casing gas assisted rod pumping system

The free gas evolved in the pump chamber results in a low rod pump working efficiency, and it can even lead to a failure. A common and effective solution is to install a downhole gas separator before fluid entering the chamber, which can divert the free gas to the annulus. If we can re-inject the diverted gas back to the tubing at a shallower depth above the pump, the flowing gas is then re-combined with the liquid and decreases fluid density. Consequently, the injected gas also creates additional lifting drive for the liquid. A new technology based on this concept has been developed and called Casing Gas Assisted Rod Pumping (CGARP). This paper firstly presents an analytical model to optimize the overall lifting performance and minimize the operating expenditure. It is especially useful in producing hydrocarbon at high GOR.As the gas is re-combined with the liquid above the pump installation depth, the hydrostatic pressure gradient is reduced consequently. However, if the gas reinjection valve is placed at a shallow depth, the well segment at reduced fluid density is subsequently short, so the contribution of gas lift is restricted. Vice versa, if the gas reinjection valve is placed at the depth close to the pump, it requires high pressure to open the gas injection valve, so the gas reinjection can happen infrequently and the production rate is unsfplease. This paper has proposed a genetic optimization method to maximize the overall production system efficiency. A multi-variable vector has been defined, which includes pumping speed and depth, mechanical power, rod string diameter and length, surface stroke length, downhole separator efficiency, as well as gas reinjection valve depth. The optimized object can be the system lifting efficiency or Net Present Value, which must be a function of this vector in the constraint of mass and momentum conservations.This work has been applied as the primary guide for four oil producers with rod pump installed in Jilin field, China. The average system lifting efficiency and production rate have been increased by 20% and 15% respectively. This analytical model has enhanced the field performance. Most importantly, the same concept can be applied for other pump-assisted wells.

Disruption Mitigation System Developments and Design for ITER

A disruption mitigation system (DMS) is under design for ITER to inject sufficient material deeply into the plasma for rapid plasma thermal shutdown and collisional suppression of any resulting runaway electrons. Progress on the development and design of both a shattered pellet injector (SPI) that produces large solid cryogenic pellets to provide reliable deep penetration of material and a fast opening high flow rate gas valve for massive gas injection (MGI) is presented. Cryogenic pellets of deuterium and neon up to 25 mm in size have been formed and accelerated with a prototype injector and a full scale prototype MGI valve is now in testing. Implications of the design with respect to response time and reliability at the proposed injector locations on ITER are discussed.

Designing of the massive gas injection valve for the joint Texas experimental tokamak.

In order to mitigate the negative effects of the plasma disruption a massive gas injection (MGI) valve is designed for the joint Texas experimental tokamak. The MGI valve is based on the eddy-current repulsion mechanism. It has a fueling volume of 30 ml. The piston of the MGI valve is made by non-ferromagnetic material, so it can be installed close to the vacuum vessel which has a strong toroidal magnetic field. A diode is use to prevent current oscillation in the discharge circuit. The drive coil of the valve is installed outside the gas chamber. The opening characteristics and the gas flow of the MGI valve have been tested by a 60 l vacuum chamber. Owing to the large electromagnetic force the reaction time of the valve is shorter than 0.3 ms. Duration for the opening of the MGI valve is in the order of 10 ms.

Design and operation of a fast electromagnetic inductive massive gas injection valve for NSTX-U.

Results from the operation of an electromagnetic valve, that does not incorporate ferromagnetic materials, are presented. Image currents induced on a conducting disc placed near a pancake solenoid cause it to move away from the solenoid and open the vacuum seal. A new and important design feature is the use of Lip Seals for the sliding piston. The pressure rise in the test chamber is measured directly using a fast time response Baratron gauge. The valve injects over 200 Torr l of nitrogen in less than 3 ms, which remains unchanged at moderate magnetic fields.

Study of runaway current generation following disruptions in KSTAR

The high fraction of runaway current conversion following disruptions has an important effect on the first wall for next-generation tokamaks. Because of the potentially severe consequences of a large full current runaway beam on the first wall in an unmitigated disruption, runaway suppression is given a high priority. The behavior of runaway currents both in spontaneous disruptions and in D2 massive gas injection (MGI) shutdown experiments is investigated in the KSTAR tokamak. The experiments in KSTAR show that the toroidal magnetic field threshold, BT >2 T, for runaway generation is not absolute. A high fraction of runaway current conversion following spontaneous disruptions is observed at a much lower toroidal magnetic field of BT = 1.3 T. A dedicated fast valve for high-pressure gas injection with 39.7 bar is developed for the study of disruptions. A study of runaway current parameters shows that the conversion efficiency of pre-disruptive plasma currents into runaway current can reach over 80% both in spontaneous disruptions and in D2 MGI shutdown experiments in KSTAR.

Gas and Pellet Injection Systems for JT-60 and JT-60U

Designs and operations of the gas system and pellet injection systems for JT-60 and JT-60U are described. A gas injection valve that is a key component of the gas injection system was developed using a multilayer piezoelectric element. The maximum flow rate of this system is 43.3 Pa⋅m3/s. The valve has mechanism for adjustment at atmospheric side meaning that a repair and an adjustment can be conducted without ventilation inside a vacuum vessel. It was confirmed that the effect of magnetic field and temperature change on the valves in the JT-60U environment was negligible.In JT-60U, two systems of pellet injector – a pneumatic drive and a centrifugal one – were developed. The pneumatic type attained a pellet velocity of 2.3 km/s, which was the world record at the time in 1988. On the other hand, the centrifugal one was developed in 1998. This injector can eject trains of up to 40 cubic (2.1 mm3) pellets at frequencies of 1 to 10 Hz and speed of 0.1 to 1.0 km/s. A guide tube for a magnetic high field side injection (HFS) (top) was also developed in 1999. The pellet injection experiment with the HFS system started in 2000. In addition, another guide tube for HFS(mid) injection was newly developed and installed in March 2001. These systems are working well.

Determination of partition coefficients by headspace gas chromatography

Air-water partition coefficients of ethylacetate are determined by analysis of the headspace vapor from a closed system containing ethyl acetate and sodium chloride solutions of various concentrations. Knowing the amount of ethyl acetate in the headspace, it is possible to calculate the partition coefficient. This paper describes a simple method of determining these values without gas injection valves or other specialized equipment. The values obtained are within 7% of previously published values.

ＪＴ‐６０ガス注入装置・予備電離装置の性能特性

Gas injection and pre-ionization systems of JT-60 require quick response and good controllability to produce and to control plasma discharge. Their components were installed near a vacuum vessel. Repeated operation with high reliability is needed under high temperature and strong magnetic field.The performance tests of gas injection and pre-ionization systems of JT-60 were carried out for 4 months, in advance of actual plasma experiments.Test results are concluded as follows. The throughput rate of piezoelectric gas injection valves from 0.533 to 53.3Pa·m3/s was obtained and the response time less than 5.0ms was achieved. The accuracy of throughput amount was less than 4.0%. Measured gas amount and response time of fast magnetic gas injection valves satisfied the design specifications which were in the range of 0.1-4.0Pa·m3 and less than 5.0ms, respectiveiy. The discharge current under magnetic field was measured. The emission currents of 280mA and 52A were obtained for the electron beam type and JXB gun type pre-ionization systems.

Pulsed gas injection for on-line calibration of residual gas analyzers

Pulsed gas injection valves have been developed which deliver highly repeatable single bursts of gas in the 10−7–1 Torr l range. Although originally intended for studying dynamic vacuum phenomena, these valves appear to have interesting possibilities for on-line checking of residual gas analyzer calibration. The work chamber is pumped continuously during calibration. The almost instantaneous and predictable pressure increase in a chamber of known volume allows direct sensitivity measurements to be made provided the analyzer has a sufficiently fast response. Experimental results showing reproducibility and pressure waveforms for a manually triggered valve are summarized. An outline is given of a calibration procedure using pulses of noble gases of differing molecular weights. Preliminary results obtained with a simple electromagnetic valve capable of up to 100 pulses s−1 are also discussed.

Fast-opening magnetic valve for high-pressure gas injection and applications to hydrogen pellet fueling systems

A fast, magnetically driven gas valve and its application to pneumatic-based solid hydrogen pellet injectors are described. The valve, which is equipped with a polyimide stem tip (hard seal) and a 5-mm-diam orifice, can open against working pressures up to 140 bar (2000 psi). Other unique features of this design include temperature- and radiation-resistant seals, a programmable output pressure pulse, and repetitive operation in excess of 20 Hz. A prototype valve has been used to propel frozen hydrogen isotope pellets to speeds of up to 1900 m/s.

Supersonic gas injection valve for beam neutralization from Applied-B pulsed ion diodes

In place of conventional sonic injection gas puff valves, a supersonic gas injection nozzle has been developed to neutralize the pulsed ion beams extracted from Applied-B magnetically insulated diodes. This valve is driven by the magnetic pressure produced by the diode field coil. The features of this nozzle are its simple geometry, repetition capability, and easy timeable operation. Amounts of gas introduced in the diode section depend on the plenum pressure. Preliminary results of beam neutralization are described briefly.