Pulsed Valve Research Articles

Characterization of a cryogenic, high-pressure gas jet operated in the droplet regime

We report on the characterization of a cryogenically cooled high-pressure pulsed valve for laser–droplet interaction experiments. The gas jet can produce liquid droplets of a variety of gases over a wide range of temperature (100–300±0.25 K). Measurements of total mass flow for argon and krypton are presented as well as droplet size distributions obtained via dark-field shadowgraphy. Using light scattering, the temporal behavior of the valve is also investigated and the droplet flow speeds measured. The results are explained in terms of the phase diagrams for these gases and the dynamic operation of the valve. This characterization allows for properly interpreting yields of extreme ultraviolet emission from laser-irradiated droplet plasmas.

An Electrodynamic Pulsed Valve for Molecular Beams

The pulsed valve with an electromagnetic drive, based on a permanent magnet and a movable coil, is intended to obtain pulsed molecular beams. It is controlled by small currents of a few amperes and, thus, does not produce considerable electrodynamic disturbances. An electric control circuit of the valve provides for reduced mechanical stress on the movable coil. The frequency of the valve actuation is controlled in a range of 5–50 Hz; the gas pulse duration is regulated within the limits of 0.2–4 ms (FWHM). This device is suggested for application in the spectroscopy of complex molecules in molecular beams.

Time response of protection in event of vacuum failure based on Nude ionization gauge controller

This article describes the design and application of fast-response vacuum protection sensor module, based on the Nude ionization gauge and a homemade controller named GH07X. A simulative test indicated that the controller’s response time was less than 200 μs when 1 atm air rushed into the vacuum system through a pulsed valve with 0.8 mm orifice nozzle and the emitting current of the Nude gauge was 4 mA. The experiment result showed that the response time mainly depended on the gas density as well as the electron emitting current of the Nude gauge filament. Compared with the vacuum protection sensors based on sputter ion pump and cold-cathode gauge, GH07X is faster and reliable besides, GH07X can be used as an ultrahigh-vacuum slow valve interlock controller with response time of 100 ms, which is faster than other gauge controllers. The widely used field–bus interface CAN and common serial interface RS232/RS485 are embedded in GH07X controller system.

A pulsed mixing valve for generating reactive complexes in a supersonic expansion

A pulsed source for producing clusters of reactive species in a supersonic expansion has been successfully implemented. The design utilizes two commercial pulsed valves to mix cluster components directly in the expansion, forming cold complexes and minimizing or eliminating the complications due to prereaction of the sample. The duty cycle of the source is well matched to pulsed laser probe techniques and minimizes gas loading on the vacuum system. The source has been tested with an unreactive system and also employed to produce strongly interacting aliphatic–I2 species.

High harmonic generation at 1 kHz repetition rate with a pulsed valve

High harmonic generation at 1 kHz repetition rate is reported. A piezoelectric pulsed valve together with a femtosecond Ti:Sapphire laser both operating at 1 kHz are employed to generate high harmonic radiation in xenon and argon. The characteristics of the valve have been analyzed by using a fast ion gauge and a time-of-flight mass-spectrometer.

Epitaxial growth and electronic structure of a C60 derivative prepared by using a solution spray technique

We demonstrate and analyze the epitaxial film formation of a molecular material that cannot be evaporated in vacuum due to thermal decomposition. A solution of the material is sprayed onto single crystalline van der Waals surfaces using a pulse valve under controlled vapor pressure of the solvent. Monolayer epitaxial films are obtained and we propose that the growth is mediated by liquid ultrathin films formed on the surface. Molecular arrangement and electronic structure of C60(CH3)5H films are studied by reflection high energy electron diffraction and ultraviolet photoelectron spectroscopy, respectively. The present technique will be useful to study the electronic structure of recently synthesized molecular materials.

Millimeter-wave intracavity-jet OROTRON-spectrometer for investigation of van der Waals complexes

A highly sensitive intracavity millimeter-wave spectrometer was developed for the investigation of the absorption spectra of van der Waals complexes in a supersonic jet. The key element of the spectrometer is a tunable oscillator, called OROTRON, which generates the millimeter-wave radiation through the interaction of an electron beam with the electromagnetic field of a high quality (Q≈104) Fabry–Perot resonant cavity. This cavity consists of a movable spherical mirror and a fixed planar mirror with the periodic structure imprinted on its surface. The electron beam moves along the periodic structure of the plane mirror. This part separated from the rest of the resonator by a mica foil is kept under ultrahigh vacuum conditions. The molecular jet is injected by a pulsed valve into the other part of the resonator. The absorption in the jet is sensitively detected by measuring the electric current in a special collector circuit of the OROTRON. The spectral purity of the OROTRON radiation is 10–15 kHz providing the capability of sub-Doppler spectral resolution without phase locking. An increase in sensitivity of a factor of about 100 in comparison with the usual single pass arrangement was evaluated from the measurements of the absorption lines of the CO rare isotopomers, the Ar–CO and Ne–CO van der Waals complexes. The high sensitivity, wide spectral range, and simple tunability of the spectrometer make it a very efficient tool for the searching of weakly absorbing species in a jet.

A molecular beam study of water–methanol clusters

Clusters generated by injecting vapor from water–methanol liquid mixtures of varying compositions through a pulsed valve, have been analyzed using a time-of-flight mass spectrometer. Neat clusters of water and methanol as well as mixed species have been observed, the relative populations varying with composition. The mole fractions in the vapor deviate significantly from the values calculated assuming ideality of the liquid except at water mole fraction of 0.67, the composition around which the excess enthalpy is minimum. An anomaly observed in the cluster populations at this composition is related to an extended hydrogen bonded interaction of molecules in the liquid.

Valve makes filter cleaning a blast

Air jet cleaning is the widely accepted cleaning method for fabric filters in dust control applications. The blast of air required to do this is generated by valves, and the design of these valves is largely responsible for the intensity of the air pulse. Here, Asco/Joucomatic, The Netherlands, explains why the Power Pulse valve is the next generation valve for this application.

ABSORPTION OF FEMTOSECOND LASER PULSES BY ATOMIC CLUSTERS

Energy absorption by Xe,Ar,He atomic clusters are investigated using laser pulses with 5mJ energy in 150fs duration.Experimental results show that the size of cluster and laser absorption efficiency are strongly dependent on several factors,such as the working pressure of pulse valve,atomic number Z of the gas.Absorption fraction of Xe clusters is as high as 45% at a laser intensity of 1×1015W/cm2 with 20×105Pa gas jet backing pressure.Absorption of the atomic clusters is greatly reduced by introducing pre-pulses.Ion energy measurements confirm that the efficient energy deposition results in a plasma with very high ion temperature.

Application of pulse combustion technology in spray drying process

The paper presents development of valved pulse combustor designed for application in drying process and drying tests performed in a specially built installation. Laser technique was applied to investigate the flow field and structure of dispersed phase during pulse combustion spray drying process. PDA technique was used to determine initial atomization parameters as well as particle size distribution, velocity of the particles, mass concentration of liquid phase in the cross section of spray stream, etc., in the drying chamber during drying tests. Water was used to estimate the level of evaporation and 5 and 10% solutions of sodium chloride to carry out drying tests. The Computational Fluid Dynamics technique was used to perform theoretical predictions of time-dependent velocity, temperature distribution and particle trajectories in the drying chamber. Satisfactory agreement between calculations and experimental results was found in certain regions of the drying chamber.

Conformation and stability of the hydrogen-bonded complex 6-oxabicyclo

The hydrogen-bonded complex between 6-oxabicyclo[3.1.0]hexane and hydrogen chloride was investigated by microwave spectroscopy in a supersonic jet. A dual flow pulsed valve was used to preclude chemical reaction between the monomers. Only the equatorial conformer was observed and the spectra of three isotopomers, (C5H8O, H35Cl), (C5H8O, H37Cl) and (C5H8O, D35Cl), were measured. The derived structure of the complex has Cs symmetry with the hydrogen chloride pointing to the domain of the equatorial lone pair of electrons at the oxygen atom. The three atoms involved in the hydrogen bond adopt a bent arrangement with a O...H distance of 1.77(4) A, a (O...H-Cl) angle of 115(4)degrees, and a deviation of 15.4(14)degrees of the hydrogen bond from collinearity. In agreement with the experimental results, ab initio calculations predict the equatorial form to be the most stable one.

Nuclear spin–rotation interaction in CF 2 ( [formula omitted]) observed by Fourier transform microwave spectroscopy

The rotational spectrum of difluoromethylene (CF 2) in its X ̃ 1A 1 ground electronic state has been observed using molecular beam–Fourier transform microwave spectroscopy. CF 2 was produced in a free jet expansion in Ar as inert carrier gas by ArF excimer laser photolysis of CF 2Cl 2, CF 2CHCl, or CF 2CHBr or by flash pyrolysis of CF 2Br 2 in the high-pressure region directly behind a pulsed molecular beam valve. Rotational transitions were observed in the frequency range from 8 to 40 GHz in the CF 2 (000) ground vibrational state and in the (100), (010), and (001) excited vibrational states. Several observed lines were split due to the hyperfine interaction between the 19 F nuclear spin and the overall rotation of the molecule. The results were used to determine the nuclear spin–rotation interaction parameters for CF 2.

Cooling of large molecules below 1 K and He clusters formation

We present here the design details of a high-pressure pulsed valve that generates intense supersonic jets. The measured rotational contours of Aniline indicate that temperatures lower than 0.5 K can be achieved before the formation of clusters with the He carrier gas. The spectral shifts and vibronic structure of Anthracene–Hen clusters (n=1–6) are showing some surprising features.

Efficient production of vibrationally excited NO using a pulsed molecular beam discharge source

An efficient way of producing vibrationally excited, but rotationally cold NO molecules is described. A dc-discharge is incorporated into a piezoelectric pulsed molecular beam valve of the Gerlich design. Efficiencies larger than 10% are achieved for the production of vibrationally excited NO( v′′=1) characterized by a rotational temperature of 4 K. At lower backing pressures, a population ratio NO( v′′=1)/NO( v′′=0)=0.5 is found with rotational temperatures around 30 K. Population of NO in higher vibrational states, e.g. v′′=2, is generated with smaller but still significant density. Even highly vibrationally excited NO molecules with 7⩽ v′′⩽19 have been detected.

Generation of metal–ligand cluster ion beams through pulsed discharge ionization and ablation

Pulsed capacitor discharge ionization in supersonic expansions was investigated for the production of intense beams of molecular cluster ions from seeded and ablated compounds. A pulsed discharge based on a triggered spark gap switch was designed and used as a method for ionization and ablation. Several combinations of nozzle geometry and electrode arrangement in front of a pulsed valve, were made to optimize the intensity of the ion beam as well as its composition. The cationic metal–ligand complexes Cu +–(methanol) n , Cu +–(acetone) n , Cu +–(toluene) n , Cu +–(water) n , and Al +–(water) n were synthesized by ablation of the metal from metallic discharge electrodes in a discharge gas mixture of helium seeded with the ligand of choice. The cluster mass spectra of the expanded plasmas show little background ion signal besides the metal–ligand species. Charge exchange processes in the expansion guarantee high ionization yields of the desired species and account for low backgrounds. Changes in the successive binding energy of Cu +–(water) n clusters n = 1–4 are clearly observed in the cluster mass spectra as step formation. A similar pattern found in Cu +–(acetone) n suggests the same trend in the successive binding energy as known for water.

Gas-phase basicity of (CH3)3N+-C6H4-COO- zwitterions: a new class of organic super bases.

Gas-phase basicity of (CH3)3N+-C6H4-COO- zwitterions: a new class of organic super bases.

SiC Epitaxial Growth by Vertical Hot-Wall Type Chemical Vapor Deposition.

Epitaxial growth of silicon carbide (SiC) by “Vertical hot-wall type chemical vapor deposition (CVD)” has been investigated. Higher growth rates over 10μm/h has been realized at a growth temperature of 1700oC. The surface morphology has been observed by atomic force microscopy to examine formation of macroscopic steps. In addition to conventional (0001) face, 6H- and 4H-SiC epitaxial layers with smooth surfaces have been realized on (11-20) and (1-100) faces. Crystallographical quality of epitaxial layers has been evaluated by X-ray diffraction. Furthermore, we developed a novel doping method, “Pulse doping”, during epitaxial growth for a well-controlled doped layer. A pulse valve that could open and close within a very short period less than 10 μs was used in this study to supply the dopant gases. Carrier concentrations of the doped layers have been precisely controlled, and their abrupt doping profiles have been achieved.

Optical Properties of Manganese Doped Amorphous and Crystalline Aluminum Nitride Films

An aluminum nitride (AlN) film deposited on silicon (100) was used as the substrate for growing manganese (Mn) doped AlN film by metal organic chemical vapor deposition (MOVCD). The (15.78 µm) under layer of AlN was grown at 615°C at a pressure of 10−4 Torr. The (2.1 µm) top layer of Mn-AlN was grown at the same temperature and pressure but doped with pulse valve introduction of the manganese decacarbonyl (100 ms on, 100 ms off). The film was then characterized ex situ with IR reflectance microscopy, X-ray diffraction, scanning electron microscopy imaging, cathodoluminescence, and X-ray fluorescence. The IR reflectance measurements showed a strong (A1) LO mode for AlN at 920 cm−1 and 900 cm−1 with a shoulder at 849 cm−1. X-ray Diffraction yielded three diffraction peaks at a 2θ position of 33, 36 and 38 degrees corresponding to 100, 002, and 101 lattice planes respectively. Cathodoluminescence results show strong visible emitted light from incorporated manganese. The relative percentage of manganese to aluminum was below the detection limit (0.01 %) of the X-ray fluorescence spectrometer. Amorphous Mn doped AlN films have also been grown using a low temperature atomically abrupt sputter epitaxial system. The amorphous Mn doped AlN showed no cathodoluminescence.

Peaking the current of a microsecond generator operating into a plasma load

A configuration of a plasma flow switch intended for peaking the current of a capacitor bank operating into a liner load has been proposed and tested where the current bridge and the liner are formed with the help of a single pulsed gas valve. The design of the load unit has been optimized for the efficiency of the energy transfer from the energy store to the liner. The peaker was tested in experiments on generation of soft x-radiation and K-radiation of neon. High efficiency of conversion of the magnetic energy of the primary store to x-radiation has been demonstrated.