Aerodynamic Window Research Articles

Vacuum‐ultraviolet‐photoionization chamber for the investigation of ion‐based surface treatment and thin film deposition at atmospheric pressure

AbstractThe vacuum‐ultraviolet‐photoionization chamber was constructed to allow controlled ion generation and well‐defined surface treatment with these ions at atmospheric pressure. It utilizes atmospheric helium plasma as a photon source and separates the ion generation from the plasma by an aerodynamic window. The ions are guided to the grounded substrate by a weak electric field, while the diffusive transport of neutrals is reduced by a helium gas flow along the substrate. Ionic species and the absolute ion flux were determined in the substrate region. Ion‐based thin film deposition using a precursor was investigated as a model process. The proposed system enables future investigation of e.g. the isolated interaction of ions with biological substrates.

Aerodynamic Window Sealing of a Large-Aperture Channel for High-Power Laser Transmission

In this study, the sealing of a large-aperture channel for high-power laser transmission is achieved using an aerodynamic window. Further, a numerical model of the gas and dust particle motion in the channel is established under three different blowing schemes, and the sealing performance of the large-aperture channel is analyzed and compared under different blowing schemes. The results indicate that the larger the proportion of purge gas volume flows in the axial direction, the better the sealing effect of the channel. More importantly, the axial blowing scheme can ensure that the large-aperture channel maintains the relative positive pressure to the external environment, effectively blocking the ambient gas and dust particles blowing in. The axial blowing scheme can achieve the sealing requirements of the large-aperture channel in an environment where the ambient wind speed is less than 20 m/s, and the dust particle mass concentration is less than 8×10−3 kg/m3. In this case, the minimum non-zero z-directional wind speed is stable and positive at a position 100 mm away from the port in the channel, and the particle mass concentration is zero.

Investigation of UV filaments and their applications

UV laser pulses at 266 nm with 170 ps duration and up to 300 mJ energy create UV filaments. The effects of different beam preparation scenarios on UV filamentation are discussed. Beam preparation by focusing in vacuum and launching into the atmosphere through an aerodynamic window establishes the existence of filaments as self-guided non-diffracting entities. In addition, focusing through the aerodynamic window converts the initial super-Gaussian into a parabolic beam profile at the edge of the nonlinear medium (air). The shock-wave generated by the UV filament is investigated via shadowgraphy techniques. The shock-wave is cylindrically symmetric, leaving a low density channel behind, which is well-sustained for 1 ms, as it propagates outward. This low density channel is a waveguide that can be used for guiding purposes. Applications of UV filaments including guiding, remote sensing, and drag reduction for supersonic aircrafts are discussed.

Measuring Method of Slit Free-Vortex Aerodynamic Window Optical Quality

Measuring Method of Slit Free-Vortex Aerodynamic Window Optical Quality

Vacuum ultraviolet spectroscopy of cold atmospheric pressure plasma jets

AbstractDue to elevated pressure, cold atmospheric pressure plasmas generate excimer species, which can emit highly energetic photons, thus transferring energy inside the discharge and to treated substrates. However, they are difficult to assess, as they are absorbed by air or window material. Here, we present a method to measure vacuum ultraviolet photons using a monochromator with an aerodynamic window. The emission spectra of a radiofrequency‐excited atmospheric plasma jet were analyzed for typical gas mixtures. The data indicate that helium excimers contribute notably to the excitation of molecular and atomic species. The emission intensities do not follow densities of ground‐state species, underlining the variety of excitation channels and the change of the electron energy distribution function under changing gas composition.

Supersonic jet and nozzle flows in uniform-flow and free-vortex aerodynamic windows of gas lasers

The mathematical models and computational tools for design, analysis and predictions of supersonic jet and nozzle flows in the aerodynamic windows of high-power gas lasers are considered. The steady-state Euler equations describing strong shock waves, contact discontinuities, rarefaction waves and their interactions are solved with the finite-volume solver and space-marching method. The results of numerical simulation of steady-state supersonic flows of inviscid compressible gas in nozzles and under- and over-expanded jets are obtained and analyzed for different pressure ratios in the laser cavity and ambient atmosphere. The flowfields corresponding to the uniform velocity profile and free-vortex velocity profile in the outlet nozzle boundary are compared. Nozzle profiling tools are developed on the basis of numerical solution of a sequence of direct problems. The aerodynamic performance of the window is evaluated in terms of the simulated laser cavity pressure and plenum pressure of the free-vortex supply nozzle. The pressure support characteristic for the aerodynamic window is established by determining the ambient to cavity pressure ratio over a range of aerodynamic window supply pressures.

Development of low vacuum laser welding technique using an aerodynamic window

Development of low vacuum laser welding technique using an aerodynamic window

自由旋涡气动窗口全流场的数值模拟

自由旋涡气动窗口全流场的数值模拟

High Temperature Flow Visualization and Aerodynamic Window Protection of a 100-kWth Solar Thermochemical Receiver-reactor for ZnO Dissociation

Abstract A 100-kWth receiver-reactor designed for the thermal dissociation of ZnO into metallic Zn is separated from atmosphere by use of a transparent quartz window, through which concentrated solar radiation is admitted. Protection of such windows from reactant and product particle deposition is critical for successful reactor operation. Usingin-situ visualization techniques, the effectiveness of an auxiliary flow of inert gas in aerodynamically protecting a 600-mm-diameter quartz window mounted on the receiver-reactor has been directly assessed during high-temperature experimentation. This work has shown that: (i) high-temperature, in-situ flow visualization is possible and effective in assessing flow patterns developed inside the reactor;(ii) there exist three characteristic flow patterns inside the reactor that can be dynamically controlled by use of a set of tangential and radially oriented jets; and (iii) a region of stable protective flow, under a wide range of experimental and operational conditions, is capable of repeatedly and fully suppressing detrimental particle depositions on the quartz window.

Experimental Investigation of Vortex Flow in a Two-Chamber Solar Thermochemical Reactor

Recent advances in the field of large-scale solar thermochemical processing have given rise to substantial research efforts and demonstration projects. Many applications of high-temperature solar-thermal technology employ an enclosed cavity environment, thus requiring a transparent window through which concentrated solar energy can enter. One configuration employed is a two-cavity reactor connected by a narrow aperture, where solar flux entering through the window is focused at the aperture plane before diverging into the lower chamber, where the chemical reaction occurs. For the Zn/ZnO thermochemical cycle where Zn is solar-thermally reduced from ZnO in a high-temperature cavity environment, effective removal of the product gas stream containing zinc vapor is of paramount importance to prevent fouling by condensation on the reactor window. Two argon-jet configurations, tangential and radial, located around the circumference of the upper chamber are used to control the gas flow within the reactor cavity. First, the tangential jets drive a vortex flow, and second, the radial wall jet travels across the window before converging at the reactor center line and turning downward to create a downward jet. The tangential jet-induced flow creates a rotating vortex, contributing to overall flow stability, and the radial jet-induced downward flow counters the updraft created by the vortex while actively cooling and sweeping clear the inner surface of the window. Flow visualization in a full-scale transparent model of the reactor using smoke and laser illumination is employed to characterize the effectiveness of aerodynamic window clearing and to characterize the processes by which a vortex flow develops and breaks down in a two-chamber solar reactor geometry. Based on a large dataset of flow visualization images, a metric is developed to define vortex stability over a wide range of flow conditions and identify an ideal operating range for which a vortex formation path is established that maintains stable flow patterns and removes product gases while minimizing the use of argon gas. The predominant influence of vortex instability and breakdown is identified and examined for the case of a beam-down, two-chamber solar reactor geometry.

The effect of propagation in air on the filament spectrum

Filamentation studies traditionally start from letting a beam focus in air. We present filament studies with control over the preparation propagation, in air or vacuum, using an aerodynamic window. The spectral content of the filament strongly depends on its preparation medium.

Air filaments and vacuum

The use of a new diagnostic tool combined with an aerodynamic window forming a boundary between vacuum and air provides differentiation between the “preparation phase” and the “confinement phase” of filaments.

利用N2/He混合气提高自由旋涡气动窗口的光学性能

利用N2/He混合气提高自由旋涡气动窗口的光学性能

扩压器入口面积比对自由旋涡气动窗口性能的影响

扩压器入口面积比对自由旋涡气动窗口性能的影响

Propagation of non-diffracting intense ultraviolet beams

Ultraviolet pulses of 200 ps duration are focused in vacuum, and launched into the atmosphere through an aerodynamic window. Instead of diffracting, above a threshold of 100 mJ, the beam propagates in a self-induced waveguide in air. The peak electric field and beam profile are consistent with the eigenfunction of a modified nonlinear Schrödinger equation. The evolution of the beam waist with distance is calculated by a combination of the nonlinear Schrödinger equation and an equation for the nonlinear losses.

UV filaments and their application for laser-induced lightning and high-aspect-ratio hole drilling

Experimental results pertaining to 1 ps pulse-width filaments at 248 nm are reviewed. The theoretical studies presented in this paper show that scaling those filaments to ns pulse-widths should enable us to trap up to 1 J in a single channel. We will show how the use of an aerodynamic window can lead to applications such as laser-induced lightning and high-aspect-ratio hole drilling.

Research of Supersonic Free-Vortex Aerodynamic Window. 1st Report. Design Procedure of Free Vortex Nozzle and Operating Condition.

In the development of continuous high-power gas laser systems, the supersonic free-vortex aerodynamic window is one of the key technologies for extracting a laser beam from the laser cavity. The present paper describes the design procedure of the two-dimensional supersonic free-vortex nozzle, and demonstrates the operating conditions of the window, taking into account the phase transition of the working fluid in the nozzle expansion process and the operating conditions of the supersonic diffuser. Generally, the high-power laser will be operated in the atmospheric environment without auxiliary equipment, i. e., a heater installed in the nozzle supply and/or a vacuum pump connected with the ventage of the supersonic diffuser. Therefore, the temperature of the working fluid at the nozzle supply is nearly 300 K, and the back pressure of the supersonic diffuser is inevitably atmospheric pressure. Hence, when using nitrogen gas as the working fluid in such an environment, the pressure ratio of the laser cavity to the atmosphere, which can be achieved with no phase transition, is about 20. In order to attain the higher pressure ratio of about 50, helium gas is required as the working fluid.

Aerodynamic window with a pressure separation ratio greater than 500

The possibility of creating a two-stage aerodynamic window with a high pressure drop is demonstrated. The window consists of two gas channels with free vortex flow in each of them. It is shown that the gas exchange between the stages can be used efficiently to increase the working pressure drop of the window.

Injection GaAs–(GaAI)As semiconductor lasers in hermetically sealed flat casings with coupling of radiation through a section of a fiber-optic cable Aerodynamic window

Injection GaAs–(GaAI)As semiconductor lasers in hermetically sealed flat casings with coupling of radiation through a section of a fiber-optic cable Aerodynamic window

Subsonic multiple-jet aerodynamic window

An experimental apparatus, which simulates a subsonic multiple-jet aerodynamic window, is fabricated and aerodynamic characteristics of the single-curved jet and the multiple-curved jets are studied. A nondimensional quantity ξ is introduced in order to represent the magnitude of the power consumption. Then, the effect of the window configuration on ξ is evaluated experimentally. Within the range of the present experiments, it is shown that the power consumption of the multiple-jet aerodynamic window can be made less than that of the single-jet scheme, if at least three stages of jets are utilized. It is also shown that the design of the window configuration is important to reduce the power consumption and to obtain the stable operation of multiple-curved jets.