Showing papers on "Chamber pressure published in 2004"

Method and apparatus for substrate temperature control

Abstract: A method and apparatus for gas control is provided. The apparatus may be used for controlling gases delivered to a chamber, controlling the chamber pressure, controlling the delivery of backside gas between a substrate and substrate support and the like. In one embodiment, an apparatus for controlling gas control includes at least a first flow sensor having a control valve, a first pressure sensor and at least a second pressure sensor. An inlet of the first flow sensor is adapted for coupling to a gas supply. A control valve is coupled to an outlet of the flow sensor. The first pressure sensor is adapted to sense a metric indicative of the pressure upstream of the first flow sensor. The second pressure sensor is adapted to sense a metric indicative of the pressure downstream of the control valve.

Side-Load Phenomena in Highly Overexpanded Rocket Nozzles

Abstract: The operation of rocket engines in the overexpanded mode, that is, with the ambient pressure considerably higher than the nozzle exit wall pressure, can result in dangerous lateral loads acting on the nozzle. These loads occur as the boundary layer separates from the nozzle wall and the pressure distribution deviates from its usual axisymmetric shape. Different aerodynamic or even coupled aerodynamic/structural mechanic reasons can cause an asymmetric pressure distribution. A number of subscale tests have been performed, and three potential origins of side loads were observed and investigated, namely, the pressure fluctuations in the separation and recirculation zone due to the unsteadiness of the separation location, the transition of separation pattern between free-shock separation and restricted-shock separation, and aeroelastic coupling, which indeed cannot cause but do amply existing side loads to significant levels. All three mechanisms are described in detail, and methods are presented to calculate their magnitude and pressure ratio at which they occur.

Atomization characteristics on the surface of a round liquid jet

Abstract: Fundamental mechanisms of liquid jet breakup are identified and quantified. The quality of the atomization of liquids is an important parameter of many technological processes and is, e.g. for fuels and propellants critical in defining engine performance. This investigation takes a look at the jet behavior for a single injector element to determine the influence of the injection conditions on a round liquid jet. The study focuses on the atomization of a liquid forming a classical spray. To adjust the relative velocity between the liquid jet and the gaseous ambient a wind tunnel-like coaxial flow configuration was used. This made it possible to distinguish between effects of aerodynamic forces, chamber pressure and jet velocity, which determine the liquid Reynolds number and thereby the internal jet turbulence. Shadowgraphy and a novel image-processing approach was used to determine the jet surface characteristics: wavelength and amplitude. The absolute injection velocity of the jet seems to affect the structures the most with an increasing velocity causing the wavelengths to be smaller. An increase in chamber pressure seemed to have little influence on the jet with no relative velocity between the gas and liquid jet, but increased the amplitude and drop formation frequency at other testing conditions with relative motion. The wave amplitude trends provide information about the likelihood of drop formation but are limited in maximum size due to this breakup phenomenon of the jet. The study of the direction of the relative velocity demonstrated that injector performance cannot simply be described by scalar geometrical and operational injection parameters (e.g., We , Re or Oh), but has to include the injection direction of the atomizing fluids in relation to each other and to the ambient (e.g., combustion chamber). The undisturbed jet length and the spread angle were investigated, and a correlation for the droplet separation position was proposed. The data led to an extended classification of liquid jet breakup regimes. Large wave instabilities were experimentally analyzed and compared with linear stability theory.

Plasma etching of high dielectric constant materials on silicon in halogen chemistries

Abstract: Plasma etching of ZrO2 and HfO2 was studied in BCl3/Cl2 plasmas, as functions of the ion energy, chamber pressure, microwave power, and gas compositions. MClx is found to be the major etching product in Cl2 plasmas while MBxCly is the major etching product in BCl3 plasmas. The etching selectivity to Si is increased at lower ion energies and higher electron temperatures. Increasing microwave powers and reducing chamber pressures in BCl3/Cl2 plasmas increased the Cl and BCl2+ densities in the gas phase and consequently increased the metal oxide etch rate. A phenomenological model that takes into account the Cl density, BCl2+ density, and metal oxygen bond strength is proposed to describe the etch rate of ZrO2 and HfO2 in pure BCl3 plasmas as functions of the ion energy, microwave power, and chamber pressure. More accurate Cl flux measurement is needed to improve the model predictions.

Stress-tuned, single-layer silicon nitride film

Abstract: We have discovered that is possible to tune the stress of a single-layer silicon nitride film by manipulating certain film deposition parameters. These parameters include: use of multiple (typically dual) power input sources operating within different frequency ranges; the deposition temperature; the process chamber pressure; and the composition of the deposition source gas. In particular, we have found that it is possible to produce a single-layer, thin (300 Å to 1000 Å thickness) silicon nitride film having a stress tuned to be within the range of about −1.4 GPa (compressive) to about +1.5 GPa (tensile) by depositing the film by PECVD, in a single deposition step, at a substrate temperature within the range of about 375° C. to about 525 ° C., and over a process chamber pressure ranging from about 2 Torr to about 15 Torr.

Time-Resolved Fuel-Grain Port Diameter Measurement in Hybrid Rockets

Abstract: A novel technique is presented for determining the instantaneous spatially averaged port diameter of solid-fuel grains in hybrid rocket motors. This technique requires measurement of the frequency of the Helmholtz oscillation of the motor and is based on the principle that this frequency is inversely proportional to the square root of the chamber volume. This technique was applied to a hybrid rocket motor burning paraffin wax with gaseous oxygen. The calculated variation of port diameter agreed well with the correlation for average regression rate, determined from mass loss during operation. A major advantage is that the only instrumentation required for implementing this technique is a high-speed pressure transducer or a photomultiplier tube.

Study of dry etching for GaN and InGaN-based laser structure using inductively coupled plasma reactive ion etching

Abstract: Dry etching of undoped, n-GaN, p-GaN and InGaN laser structure was investigated by inductively coupled plasmas reactive ion etching (ICP-RIE) using Ni mask. As Cl 2 /Ar gas flow rates were fixed at 10/25 sccm, the etched surface roughness has the lowest value of 0.2 nm at constant ICP/bias power=300/100 W and 5 mTorr chamber pressure for undoped GaN. The highest etching rate of 12,000 A/min for n-GaN was achieved at 30 mTorr, 300 W ICP, 100 W bias power using low Cl 2 flow rate (Cl 2 /Ar=10/25 sccm) gas mixtures. The surface roughness was dependent of bias power and chamber pressure, and shows a low root mean square (rms) roughness value of about 1 nm at 50 W of bias power for n-GaN and p-GaN. For etching of InGaN laser structure using high Cl 2 flow rate (Cl 2 /Ar=50/20 sccm) and low chamber pressure 5 mTorr, a smooth mirror-like facet of InGaN laser diode structure was obtained. Using these etching parameters, mirror-like facets can be obtained which can be used for the fabrication of nitride-based laser diodes. Moreover, at the fixed Cl 2 /Ar flow rate of 10/25 sccm, ICP/bias power of 200/100 W and chamber pressure of 30 mTorr, the InGaN-based materials nanorods were fabricated with a density of about 10 8 cm −2 and dimension of 50–100 nm.

Ionized physical vapor deposition apparatus using helical self-resonant coil

Abstract: Provided is an ionized physical vapor deposition (IPVD) apparatus having a helical self-resonant coil. The IPVD apparatus comprises a process chamber having a substrate holder that supports a substrate to be processed, a deposition material source that supplies a material to be deposited on the substrate into the process chamber, facing the substrate holder, a gas injection unit to inject a process gas into the process chamber, a bias power source that applies a bias potential to the substrate holder, a helical self-resonant coil that produces plasma for ionization of the deposition material in the process chamber, one end of the helical self-resonant coil being grounded and the other end being electrically open, and an RF generator to supply an RF power to the helical self-resonant coil. The use of a helical self-resonant coil enables the IPVD apparatus to ignite and operate at very low chamber pressure such as approximately 0.1 mtorr, and to produce high density plasma with high efficiency compared to a conventional IPVD apparatus. Accordingly, a high efficiency of ionization of deposition material is achieved.

Hydro-pneumatic suspension system

Abstract: A hydro-pneumatic suspension system includes one or more hydraulic suspension cylinders mounted between the vehicle body and the axle. Each cylinder includes a piston chamber and rod chamber, each of which are connected to an accumulator and which can be connected to a pressure source and a tank by valve systems. The valve system for the rod chamber includes a first solenoid valve and a hydraulically and electrically actuated proportional pressure adjusting valve. The proportional valve is exposed to rod chamber pressure and to tank pressure. The rod chamber pressure can be applied on the proportional valve either directly as control pressure or can be detected with a sensor, and can be used to control the proportional valve. Such a system can influence the dependency of the suspension stiffness on the axle load and can be used to adjust the stiffness to ballast conditions and operating or driving states.

Control of the Ceramic Erosion by Optical Emission Spectroscopy: Parametric Studies of SPT-100ML

Abstract: In this contribution, we present a real time optical method to control the ceramic erosion of the thruster channel inner walls. OES measurements were performed on a SPT100-ML (laboratory model) during tests using permanent magnets instead of magnetic coils in the PIVOINE french facility. Different magnet/coil configurations was studied for different discharge parameters as discharge voltage, mass flow rate, chamber pressure, and coil current. Join to LIF and Fabry-Perot ion velocity measurements very helpful informations has been obtained about potential map evolution with discharge parameters.

Vacuum Chamber Pressure Maps of a Hall Thruster Cold-Flow Expansion

Abstract: TECHNICAL NOTES are short manuscripts describing new developments or important results of a preliminary nature. These Notes cannot exceed 6 manuscript pages and 3 figures; a page of text may be substituted for a figure and vice versa. After informal review by the editors, they may be published within a few months of the date of receipt. Style requirements are the same as for regular contributions (see inside back cover).

The Thermodynamic and Fluid Dynamic Functions of a Pulsed Detonation Engine Nozzle

Abstract: The design and analysis of a Pulsed Detonation Engine, PDE, nozzle creates new and unique technical challenges. These challenges involve both the thermodynamic and the fluid dynamic functions that the PDE nozzle serves. Thermodynamically, the nozzle controls the detonation chamber pressure and converts the hot chamber flow into thrust. Fluid dynamically, the PDE nozzle controls the engine's operating frequency. The contraction ratio of the PDE nozzle is designed to maintain pre-detonation chamber pressure and to control engine operating frequency. In practice, the functions of chamber pressure control and frequency control are synergistic. The expansion ratio of the PDE nozzle is a compromise, which covers the broad nozzle pressure ratio ranges imposed by the dynamic operation of the PDE, as well as the typical Mach number influence. This paper explains these functions and suggests analysis techniques.

Incorporation of Nonlinear Capabilities in the Standard Stability Prediction Program

Abstract: Predictive algorithms now in general use cannot characterize high-amplitude pressure oscillations that are frequently observed in solid propellant rocket motor combustion chambers. In fact, programs such as the Standard Stability Prediction (SSP) code are based on a linear theory, which has serious shortcomings. Therefore, it is necessary to address both correction of the flawed linear theory and incorporation of models to allow prediction of important nonlinear effects. These include: 1) limit cycle behavior in which the pressure fluctuations may dwell for a considerable period of time near their peak amplitude, 2) elevated mean chamber pressure (DC shift), and 3) a triggering amplitude above which pulsing may cause an apparently stable system to transition to violent oscillations. Culick’s wellestablished nonlinear model provides useful guidance in dealing with the system limit cycle transition. It is demonstrated in this paper that his calculations represent the classical steepening mechanism by which the wave system evolves from an initial set of standing acoustic modes into a shock-like, traveling, steep-fronted wave. However, a very important missing element is the ability to predict the accompanying mean pressure shift; clearly, the program user requires information regarding the maximum chamber pressure that might be experienced during operation of the motor, as well as the peak amplitudes reached by the pressure oscillations. Recent theoretical work has resulted in a firm foundation upon which to build the required predictive capabilities. These are described in detail, and it is demonstrated that the new theory yields results that are in excellent agreement with experimental data.

System having device for preventing air bubbles in a hybridization chamber and corresponding method

Abstract: The present invention relates to a system (1) having hybridization chambers (5) for hybridizing nucleic acid samples, proteins, or tissue sections immobilized on slides (27), each hybridization chamber (5) being defined as an essentially gap-shaped chamber, which is essentially fillable with a liquid, between one of these slides (27) and a cover (26), and the cover (26) being positioned in relation to the slide (27) in such a way that the hybridization chamber (5) is sealed to the surrounding air, the system (1) including a device for preventing air bubbles in the hybridization chambers (5). The system according to the present invention is distinguished in that this device for preventing air bubbles in the hybridization chambers (5) is implemented as a pressure device to build up a chamber pressure in the hybridization chambers (5), this chamber pressure lying above the normal atmospheric pressure existing in the surrounding air. The present invention additionally relates to a method for preventing air bubbles in the hybridization chambers (5) of such a system (1) and is distinguished in that, using a pressure device of this system (1), a chamber pressure is implemented in the hybridization chambers (5) which lies above the normal atmospheric pressure existing in the surrounding air.

Method of improving the wafer-to-wafer thickness uniformity of silicon nitride layers

Abstract: Wafer-to-wafer thickness uniformity may be improved significantly in a process for depositing a silicon nitride layer in that the flow rate of the reactant and the chamber pressure are varied during a deposition cycle. By correspondingly adapting the flow rate and/or the chamber pressure before and after the actual deposition step, the process conditions may be more effectively stabilized, thereby reducing process variations, even after non-deposition phases of the deposition tool, such as a preceding plasma clean process or an idle period of the tool.

Measurements of temperature and electron number density in a dc argon-nitrogen plasma torch: Supersonic operation

Abstract: The diagnostics study on supersonic argon/nitrogen plasma jets expanded into a low-pressure test chamber is carried out by means of emission spectroscopy and enthalpy probe measurement techniques. The spatial distributions of electron density, temperatures, and associated shock structure effects in plasma jets are investigated in conjunction with their direct dependency upon the chamber pressure. The experimental results show the occurrence and the position of different zones; i.e., supersonic expansion, stationary shock waves and subsonic jet at pressures below 51 kPa. Flow fluctuations due to the oblique shock wave at 39 kPa background pressure are observed and discussed. The electron density profiles show variations along the plasma axis that coincide with the position of the shock waves. The experimental results show the transition from the moderately under-expanded to the strongly under-expanded jet structure induced by lowering of the chamber pressure.

Ultrasonic Measurement of the Pressure-Coupled Response Function for Composite Solid Propellants

Abstract: Transient phenomena associated with solid-propellant combustion are examined by means of an oscillatory burner designed to create pressure oscillations through the use of a rotary nozzle. The oscillatory burner is designed to operate at pressures up to 20.7 MPa (3000 psi), with the target operating pressure achieved through prepressurization with an inert gas (helium) and manipulation of constant and variable-area nozzle diameters. A spherically focused 1-MHz ultrasound transducer is pulsed at 2.5 kHz through the bottom of the propellant to obtain the thickness-time profile of the propellant, which is then converted to a burning rate by taking the time derivative. Two piezoelectric pressure transducers simultaneously record the pressure-time history of each experiment. The burning rate and pressure are then used to calculate the pressure-coupled response of each test. The experiments presented here were motivated by three primary goals. The first was to investigate the effect of propellant composition on the response function. The second was to evaluate effect of mean pressure on the response of propellants, and the third was to investigate the response of a propellant within a plateau region. These experiments targeted mean pressures of 2.0, 5.0, and 12.5 MPa at frequencies ranging from 20-200 Hz.

Characterization of supersonic low pressure plasma jets

Abstract: Low Pressure Plasma Spraying (LPPS) processes use a DC plasma jet expanding at low pressure for fast deposition of dense coatings in a controlled atmosphere. The LPPS technology is widely used industrially in particular in the aeronautics and medical industries among others. Unlike atmospheric pressure plasma jets, which have been extensively studied experimentally and theoretically, the interest in low pressure DC plasma jets only occurred recently. However, the process development has been mainly based on empirical methods and the basics of the physical mechanisms that govern them still remain to be investigated. Further improvement of the processes requires, in particular, the knowledge of physical properties of the plasma jet such as the temperature, flow velocity and plasma density. Low pressure plasma jets present unconventional properties such as low collisionality, large dimensions and supersonic flow. Therefore specific diagnostics have to be adapted to these conditions. In this study, argon plasma jets at pressures between 2 and 100 mbar are investigated. Imaging has been used to allow a qualitative description of the plasma jet topology for different pressures and torch parameters. Low pressure plasma jets are most of the time supersonic, compressible and in an aerodynamic non-equilibrium, which results in visible successive compression and expansion zones corresponding to a variation of the local pressure, temperature and density. Imaging, combined with pressure measurements inside the plasma torch, has evidenced three different types of flow regimes with respect to the chamber pressure. For chamber pressures below 45 mbar, the flow is under-expanded and is characterized by an exit pressure higher than the chamber pressure. For pressures above 45 mbar, the plasma jet is over-expanded, in this case the exit pressure is lower than the chamber pressure. When the exit pressure is equal to the chamber pressure, the plasma jet is in the so-called design pressure regime. A diagnostic tool, extensively applied on atmospheric plasma jets, the enthalpy probe system, has been modified in order to allow gas sampling from the plasma jet at low pressures. A shock wave appears in front of the probe when it is immersed in a supersonic plasma jet, making the interpretation of enthalpy measurements more difficult.The free-stream properties, like the Mach number, temperature and free-stream enthalpy have to be inferred from stagnation measurements. Two interpretations of enthalpy probe measurements are described in this study. The first method uses the energy conservation equation and LTE assumptions with calorically perfect gas and neglecting the aerodynamic non-equilibrium, whereas the second method, uses a complementary measurement of the static pressure just after the shock using a specially developed tool: the Post Shock Static Pressure Probe (PSSPP). This allows the use of the conservation equations to determine the free-stream properties of the plasma jet without the assumption of calorically perfect gas and aerodynamic non-equilibrium. Determination of the free-stream enthalpy, Mach number and temperature were possible on over-expanded jets for pressures higher than 40 mbar. At 100 mbar with torch parameters of 400 A and 40 SLPM argon flow, the temperature of the plasma jet reaches 10000 K and the velocity is about 3000 m/s on axis. Measurement of plasma jet properties such as the Mach number, electron density and temperature, were performed using double Langmuir probes and Mach probes. In particular, under-expanded jets are studied in detail by performing complete mappings of plasma jet properties at 10 and 2 mbar chamber pressure. These results show that the measured physical properties are consistent with the jet flow phenomenology such as the presence of periodic expansion and compression zones, the effect of the pressure and the location of the shocks. It is shown in particular that for highly under-expanded jets at 2 mbar, the Mach number reaches 2.8 in the first expansion zone followed by a strong drop to subsonic flow revealing the presence of a Mach reflection. The flow is accelerated further and a periodic structure of compression/expansion cells is observed until the local static pressure is in equilibrium with the surrounding pressure. Another diagnostic often used in plasma spraying is optical emission spectroscopy (OES) which is non-intrusive and gives information about the plasma excited species.However, the determination of the excitation temperature, obtained by the Boltzmann plot method, relies on the assumption of local thermodynamic equilibrium (LTE), which is no longer satisfied at low working pressures. The result of the deviation from LTE is that the heavy particle, electron and excitation temperatures are different. In this study, Boltzmann plots have been used to evaluate the deviation from LTE as a function of the working pressure and the location in the plasma jet. It has been shown that the plasma jet is closer to LTE in the compression zones and close to the axis. Measurements of spectral line broadening due to the Stark effect allowed to determine the electron density for under-expanded jets and give results similar than with electrostatic probe measurements.On the other hand, excitation temperatures are systematically lower than the electron temperature for the same plasma conditions. For a 10 mbar plasma jet, the excitation temperature of argon is between 0.73 and 0.78 eV whereas the electron temperature is between 0.7 and 1.2 eV. This shows that at low pressure the plasma jets are not in LTE.These results contribute to the understanding of the supersonic plasma jet behavior at low pressure and can be used to quantify the deviation from local thermodynamic equilibrium (LTE). The extensive mapping of the measured physical properties of the jet will also serve as input for modeling.

Hydro-pneumatic spring support arrangement

Abstract: A hydro-pneumatic spring support arrangement, particularly for a vehicle axle with at least one hydraulic spring support cylinder arranged between vehicle chassis and vehicle axle, having a cylinder chamber and a rod end chamber each connected with at least one pressure accumulator and can be selectively connected by valve arrangements with a pressure source and a tank To influence the ratio of the square of the spring rate to the axle loading and to make the spring rate conform to ballasting, vehicle, or operating conditions, the valve arrangement associated with the rod end chamber is provided with at least one first electromagnetic valve which connects the rod end chamber with the pressure source and is provided with a second electromagnetic valve which connects the rod end chamber with the tank A pressure sensor is provided, particularly a rod end chamber pressure sensor, the signals of which are utilized for the control of the first and the second electromagnetic valves

Optimization and analysis of NF3 in situ chamber cleaning plasmas

Abstract: We report on the optimization and analysis of a dilute NF3 in situ plasma-enhanced chemical vapor deposition chamber cleaning plasma for an Applied Materials P-5000 DxL chamber. Using design of experiments methodology, we identified and optimized operating conditions within the following process space: 10–15 mol % NF3 diluted with helium, 200–400 sccm NF3 flow rate, 2.5–3.5 Torr chamber pressure, and 950 W rf power. Optical emission spectroscopy and Fourier transform infrared spectroscopy were used to endpoint the cleaning processes and to quantify plasma effluent emissions, respectively. The results demonstrate that dilute NF3-based in situ chamber cleaning can be a viable alternative to perfluorocarbon-based in situ cleans with added benefits. The relationship between chamber clean time and fluorine atom density in the plasma is also investigated.

Hydraulic-pneumatic suspension system

Abstract: A hydro-pneumatic suspension system includes one or more hydraulic suspension cylinders mounted between the vehicle body and the axle. Each cylinder includes a piston chamber and rod chamber, each of which are connected to an accumulator and which can be connected to a pressure source and a tank by valve systems. The valve system for the rod chamber includes a first solenoid valve and a hydraulically and electrically actuated proportional pressure adjusting valve. The proportional valve is exposed to rod chamber pressure and to tank pressure. The rod chamber pressure can be applied on the proportional valve either directly as control pressure or can be detected with a sensor, and can be used to control the proportional valve. Such a system can influence the dependency of the suspension stiffness on the axle load and can be used to adjust the stiffness to ballast conditions and operating or driving states.

Design and Performance of a Controlled Atmosphere Polisher for Silicon Crystal Polishing

Abstract: A controlled atmosphere polisher (CAP) was manufactured featuring a pressure-resistant chamber that hermetically contains the entire processing unit. The machine allows chamber gases to be changed. A vacuum pump or a compressor is used to maintain chamber pressure at a desired set point. When polishing under an air ambient, polish rates under partial vacuum or under pressurized conditions are significantly higher than those under conventional polishing conditions. Differences in polish rate are also seen depending on the type of gas used during polishing. This polishing method and tool have the potential of efficiently controlling and enhancing silicon polish rates.

Investigation of GaAs Dry Etching in a Planar Inductively Coupled BCl3 Plasma

Abstract: We investigated dry etching of GaAs in a planar inductively coupled plasma (ICP) reactor with BCl 3 gas chemistry. The process parameters included planar ICP source power, chamber pressure, reactive ion etching (RIE) chuck power, and gas flow rate. The ICP source power was varied from 0 to 500 W. Chamber pressure was changed from 5 to 20 mTorr. RIE chuck power was controlled from 0 to 150 W. The gas flow rate was varied from 10 to 40 sccm. We found that a process condition at 20 sccm BCl 3 , 300 W ICP, 100 W RIE, and 7.5 mTorr chamber pressure gave an excellent etch result. The etched GaAs feature showed extremely smooth surface (rms roughness 3000 A/min) and good selectivity to a photoresist (>3:1). X-ray photoelectron spectroscopy study on the surface of processed GaAs proved a very clean surface of the material after dry etching. We also noticed that our planar ICP source was successfully ignited both with and without RIE chuck power, which was generally not the case with a typical cylindrical ICP source, where assistance of RIE chuck power was required for turning on a plasma and maintaining it. These results indicate that the planar ICP source could be a very versatile tool for advanced dry etching of damage-sensitive compound semiconductors.

Study of preferred orientation of zinc oxide films on the 64°LiNbO3 substrates and their applications as liquid sensors

Abstract: The preferred (002) orientation of zinc oxide (ZnO) films has been grown and demonstrated on 64°LiNbO3 substrates using a rf magnetron sputtering system. The film orientations and crystallinity are strongly dependent on the rf power, total chamber pressure, ratio of argon to oxygen, and substrate temperature. We investigated the crystalline structure of the films by x-ray diffraction and scanning electron microscopy. Highly oriented (002) films were obtained under a total chamber pressure of 1.33Pa, containing 40% oxygen and 60% argon, and a substrate temperature around 120°C. Love-wave devices based on this structure (ZnO∕IDTs∕64°LiNbO3) are presented.

Effect of arc power and gas flow rate on properties of plasma jet under reduced pressures

Abstract: DC plasma torch with argon-water stabilization of are was attached to vacuum chamber, in which pressure was varied from atmospheric down to 4kPa. Properties of the plasma jet were strongly affected by plasma generating conditions. Influence of plasma generation parameters, namely chamber pressure, are power and plasma gas flow rate on temperature and velocity profiles in plasma jet were studied. Present the measurements were performed using enthalpy probe connected to mass spectrometer. Such arrangement allows simultaneous measurement of the plasma temperature and velocity as well as composition of the plasma gas.

Combustion Oscillation Monitoring Using Flame Ionization in a Turbulent Premixed Combustor

Abstract: To achieve very low NOx emission levels, lean-premixed gas turbine combustors have been commercially implemented which operate near the fuel-lean flame extinction limit. Near the lean limit, however, flashback, lean blowoff, and combustion dynamics have appeared as problems during operation. To help address these operational problems, a combustion control and diagnostics sensor (CCADS) for gas turbine combustors is being developed. CCADS uses the electrical properties of the flame to detect key events and monitor critical operating parameters within the combustor. Previous development efforts have shown the capability of CCADS to monitor flashback and equivalence ratio. Recent work has focused on detecting and measuring combustion instabilities. A highly instrumented atmospheric combustor has been used to measure the pressure oscillations in the combustor, the OH emission, and the flame ion field at the premix injector outlet and along the walls of the combustor. This instrumentation allows examination of the downstream extent of the combustion field using both the OH emission and the corresponding electron and ion distribution near the walls of the combustor. In most cases, the strongest pressure oscillation dominates the frequency behavior of the OH emission and the flame ion signals. Using this highly instrumented combustor, tests were run over a matrix of equivalence ratios from 0.6 to 0.8, with an inlet reference velocity of 25 m/s. The acoustics of the fuel system for the combustor were tuned using an active-passive technique with an adjustable quarter-wave resonator. Although several statistics were investigated for correlation with the dynamic pressure in the combustor, the best correlation was found with the standard deviation of the guard current. The data show a monotonic relationship between the standard deviation of the guard current (the current through the flame at the premix injector outlet) and the standard deviation of the chamber pressure. Therefore, the relationship between the standard deviation of the guard current and the standard deviation of the pressure is the most promising for monitoring the dynamic pressure of the combustor using the flame ionization signal. This addition to the capabilities of CCADS would allow for dynamic pressure monitoring on commercial gas turbines without a pressure transducer.Copyright © 2004 by ASME