Showing papers on "Buffer gas published in 2005"

Atomic vapor cells for chip-scale atomic clocks with improved long-term frequency stability.

Abstract: A novel technique for microfabricating alkali atom vapor cells is described in which alkali atoms are evaporated into a micromachined cell cavity through a glass nozzle. A cell of interior volume 1 mm3, containing 87Rb and a buffer gas, was made in this way and integrated into an atomic clock based on coherent population trapping. A fractional frequency instability of 6 x 10(-12) at 1000 s of integration was measured. The long-term drift of the F=1, mF=0-->F=2, mF=0 hyperfine frequency of atoms in these cells is below 5 x 10(-11)/day.

High-flux beam source for cold, slow atoms or molecules.

Abstract: We demonstrate and characterize a high-flux beam source for cold, slow atoms or molecules. The desired species is vaporized using laser ablation, then cooled by thermalization in a cryogenic cell of buffer gas. The beam is formed by particles exiting a hole in the buffer gas cell. We characterize the properties of the beam (flux, forward velocity, temperature) for both an atom (Na) and a molecule (PbO) under varying buffer gas density, and discuss conditions for optimizing these beam parameters. Our source compares favorably to existing techniques of beam formation, for a variety of applications.

Temperature and Pressure Dependent Rate Coefficients for the Reaction of Hg with Cl and the Reaction of Cl with Cl: A Pulsed Laser Photolysis-Pulsed Laser Induced Fluorescence Study

Abstract: A pulsed laser photolysis-pulsed laser induced fluorescence technique has been employed to study the recombination of mercury and bromine atoms, Hg + Br + M → HgBr + M (1) and the self-reaction of bromine atoms, Br + Br + M → Br2 + M (2). Rate coefficients were determined as a function of pressure (200−600 Torr) and temperature (243−293 K) in nitrogen buffer gas and as a function of pressure (200−600 Torr) in helium buffer gas at room temperature. For reaction 1, kinetic measurements were performed under conditions in which bromine atoms were the reactant in excess concentration while simultaneously monitoring the concentration of both mercury and bromine. A temperature dependent expression of (1.46 ± 0.34) × 10-32 × (T/298)-(1.86±1.49) cm6 molecule-2 s-1 was determined for the third-order recombination rate coefficient in nitrogen buffer gas. The effective second-order rate coefficient for reaction 1 under atmospheric conditions is a factor of 9 smaller than previously determined in a recently published ...

Cooling of radioactive ions with the Penning trap REXTRAP

Abstract: Cooling of radioactive ion beams in a Penning trap is an essential component of the post-accelerator REX-ISOLDE at CERN. Prior to their charge-breeding and acceleration, ions from the on-line mass separator ISOLDE are accumulated, cooled and bunched with REXTRAP. This beam preparation provides short ion pulses with low emittance, key ingredient for a high efficiency of REX-ISOLDE. Two different cooling techniques have been investigated with REXTRAP. Both rely on the use of a buffer gas as the coolant but differ in the way the transversal compression of the stored ion cloud is achieved. Sideband cooling with a light buffer gas as coolant is the standard technique used at REXTRAP so far. With this technique an efficiency of about 45% for the injection, cooling, and extraction process has been obtained for stable and radioactive ions. For about 10 5 simultaneously stored ions the resulting emittance of the extracted ion pulses is about 10 π mm mrad at 30 keV beam energy. For much larger numbers of ions shifts of the resonance frequency of the sideband excitation are observed together with an emittance growth. As an alternative to sideband cooling a “rotating wall” technique was tested. First results with rotating dipole as well as quadrupole fields are presented.

Gas-phase electronic spectra of C18 and C22 rings.

Abstract: The electronic spectra of C18 and C22 in the 15150–36900cm−1 range have been detected in the gas phase by a mass-selective resonant two-color two-photon ionization technique coupled to a laser ablation source. The spectra were assigned to several electronic systems of monocyclic cumulenic isomers with a D9h symmetry for C18 and D11h for C22, based on time-dependent-density-functional calculations and reactivity with respect to H2. The best cooling conditions were achieved with Kr as the buffer gas, and the origin of the A1A2″←X1A1′ transition of C18 at 592.89nm shows a pair of 1cm−1 broadbands spaced by 1.5cm−1. The next electronic transitions exhibited much broader, ∼30 (in the visible) to 200cm−1 (in ultraviolet range), features. The spectrum of C22 exhibits an absorption pattern similar to C18, except that the narrow features to the red are missing; the oscillator strength of the A←X transition is predicted to be low.

Anodically bonded cell, method for making same and systems incorporating same

Abstract: A cell suitable for use with an atomic clock and a method for making the same, the cell including: a silicon wafer having a recess formed therein; at least one amorphous silicate member having an ion mobility and temperature expansion coefficient approximately that of silicon sealing the recess; and, an alkali metal containing component and buffer gas contained in the recess. The method includes: providing a silicon wafer; forming a cavity through the silicon wafer; introducing an alkali metal containing component and buffer gas into the cavity; and, anodically bonding at least one amorphous silicate member having an ion mobility and temperature expansion coefficient approximately that of silicon to the wafer to close the cavity.

EIT and diffusion of atomic coherence

Abstract: We study experimentally the effect of diffusion of Rb atoms on electromagnetically induced transparency (EIT) in a buffer gas vapour cell. In particular, we find that diffusion of atomic coherence in and out of the laser beam plays a crucial role in determining the EIT resonance lineshape and the stored light lifetime.

Hydrocarbon nanoparticles as a diffuse ISM analogue: morphology and infrared absorption in the 2000?500?cm?1 region

Abstract: In this paper, we analyse the morphology and chemistry of carbonaceous dust particles previously proposed as a candidate analogue material for dust in the diffuse interstellar medium (ISM). The particles were polymerized in a low pressure capacitively coupled radiofrequency discharge in mixtures of argon/acetylene and helium/acetylene. Infrared (IR) spectra of our dust particles reveal the strong presence of aliphatic features, both stretching and bending modes, which are very similar to astronomical data from diffuse interstellar dust. A comparison between the IR spectra obtained using argon or helium as buffer gases reveals the strong presence of C = C double bonds (skeletal modes) when helium is used. The presence of these skeletal modes is clearly visible through the broad absorption feature at 1600 cm−1 (6.25 µm). The origin of this feature in our laboratory analogue is related to the change in the plasma parameters due to the variation of the buffer gas used under the same discharge conditions. Observational data of interstellar polycyclic aromatic hydrocarbons also exhibit a feature at this wavelength.

Influence of a buffer gas on nonlinear magneto-optical polarization rotation

Abstract: We show experimentally that the presence of a buffer gas in a rubidium vapor cell modifies significantly the nonlinear magneto-optical rotation of polarization of near-resonant light propagating through the cell. We observe not only the well-known narrowing of the nonlinear magneto-optical resonances, but also changes in their shape and visibility. We explain these effects in terms of coherence-preserving, velocity-changing collisions between rubidium and buffer gas atoms.

Nitrogen: a possible substitute for mercury as a UV-emitter for mercury-less low-pressure discharge fluorescent lamps using Penning-like energy transfer

Abstract: Nitrogen is well known as a UV-emitter because of its 2nd positive band lying around 350 nm. However, it is a molecular gas and when energy is stored in rotational or vibrational levels, the gas temperature can become high enough to melt even the glass tube. To avoid such problems the authors tried to use the Penning-like effect between the argon metastables and nitrogen C 3Πu states with very low partial pressure of nitrogen compared with that of the argon. By adding a very small amount of nitrogen to argon, the discharge changes drastically. Though pure argon discharge and pure nitrogen discharge are both unstable and easy to constrict, a small amount of nitrogen improves the stability of the discharge and emits the nitrogen 2nd positive band UV light by energy transfer from the argon metastable to the nitrogen molecule C 3Πu state. Nitrogen-added argon fluorescent lamps operated at 30 kHz of alternative square voltage wave achieve about 4500 cd m−2 at 3.75 W and at 9.3 kPa of pressure with good dimming characteristics. The maximum luminance should be higher than this because the input power is limited by the power supply. At this condition the luminous efficacy achieves 7.1 lm W−1. These results show a possibility of argon–nitrogen fluorescent lamps as mercury-less fluorescent lamps.

NMR measurements of hyperpolarized 3He gas diffusion in high porosity silica aerogels.

Abstract: Hyperpolarized He3 is used to nondestructively probe by NMR the structure of custom-made and commercial silica aerogels (97% and 98.5% porous). Large spin-echo signals are obtained at room temperature and very low magnetic field (2mT) even with small amounts of gas. Attenuation induced by applied field gradients results from the combined effects of gas diffusion and confinement by the porous medium on atomic motion. Nitrogen is used as a buffer gas to reach equivalent He3 pressures ranging from 5mbarsto3.5bars. The observed pressure dependence suggests a nonuniform structure of the aerogels on length scales up to tens of micrometers. A description by broad phenomenological distributions of mean free paths is proposed, and quantitatively discussed by comparison to numerical calculations. The investigated aerogel samples exhibit different effective diffusion characteristics despite comparable nominal porosities.

Ammonia gas sensor method and device

Abstract: A mixed potential sensor device and methods for measuring total ammonia (NH3) concentration in a gas is provided. The gas is first partitioned into two streams directed into two sensing chambers. Each gas stream is conditioned by a specific catalyst system. In one chamber, in some instances at a temperature of at least about 600°C, the gas is treated such that almost all of the ammonia is converted to NOx, and a steady state equilibrium concentration of NO to NO2 is established. In the second chamber, the gas is treated with a catalyst at a lower temperature, preferably less than 450°C such that most of the ammonia is converted to nitrogen (N2) and steam (H20). Each gas is passed over a sensing electrode in a mixed potential sensor system that is sensitive to NOx. The difference in the readings of the two gas sensors can provide a measurement of total NH3 concentration in the exhaust gas. The catalyst system also functions to oxidize any unburned hydrocarbons such as CH4. CO, etc., in the gas, and to remove partial contaminants such as SO2.

Effect of hydrogen on the average output power of the UV Cu/sup +/ Ne-CuBr laser

Abstract: The effect of different additives-air, synthetic air, N/sub 2/, O/sub 2/, CO/sub 2/, He, Ar, Xe, and H/sub 2/, to the neon buffer gas on the average output power of a UV Cu/sup +/ Ne-CuBr is investigated. It is found that the addition of small amounts of hydrogen, 0.02-0.04 torr, leads to an increase by more than twice of the average output power for simultaneous laser oscillation at the five Cu/sup +/ lines-248.6, 252.9, 259.7, 260.0, and 270.3 nm.

Amplitude- versus frequency-modulated pumping light for coherent population trapping resonances at high buffer-gas pressure

Abstract: Coherent population trapping (CPT) signals can be optimized with amplitude-modulated pumping light. As shown theoretically and experimentally in this paper, the optimum wave forms produce strong CPT signals at both low buffer-gas pressures, where the hyperfine structure (HFS) splitting of the optical absorption lines is well resolved, and also at high buffer-gas pressures, where the HFS is no longer optically resolved due to pressure broadening. On the other hand, CPT resonances from frequency-modulated waves are severely degraded for these high-pressure conditions. High buffer-gas pressures may offer advantages for miniature frequency standards and magnetometers, including suppression of diffusion losses in miniature cells, suppression of light shifts, and less stringent requirements for frequency stability of the pumping light sources.

Recombination of polycyclic aromatic hydrocarbon photoions with electrons in a flowing afterglow plasma.

Abstract: A new technique, flowing afterglow with photoions (FIAPI), has been developed to measure the rate coefficient for the recombination of complex ions, and, in particular, polycyclic aromatic hydrocarbon (PAH) cations with electrons. The method is based on the flowing afterglow Langmuir probe - mass spectrometer apparatus at the University of Rennes I. A helium plasma is generated by a microwave discharge in a He buffer gas and downstream, a small amount of argon gas is injected to destroy any helium metastables. A very small amount of neutral PAH molecules is added to the afterglow plasma by evaporation from a plate coated with the PAH to be studied. PAH ions are then produced by photoionization of the parent molecule using a pulsed UV laser (157 nm). The laser beam is oriented along the flow tube and so a constant spatial concentration of photoions is obtained. The electron concentration along the flow tube is measured by means of a movable Langmuir probe. Ion concentration decay in time is measured at a f...

Spatial characterization of an IPVD reactor: neutral gas temperature and interpretation of optical spectroscopy measurements

Abstract: This paper deals with the characterization of an ionized physical vapour deposition (IPVD) reactor using an additional microwave plasma. The IPVD reactor was spatially characterized using optical emission spectroscopy, optical absorption spectroscopy and Langmuir probe measurements. A rectangular titanium target was used, the buffer gas was argon and the pressure was fixed at 4 Pa. The influence of the microwave power (between 0 and 900 W) and the magnetron discharge current (0.5 and 2 A) on the densities of the titanium species (neutral and ionic), argon emission line intensity and titanium and argon temperature variations was investigated. The titanium temperature and densities were measured using the pulsed resonant absorption spectroscopy technique. The neutral and ion fluxes on the substrate were deduced from these measurements. It was found that the ratio (Ti+)/(Tin) increases by a factor of 30 when additional microwave plasma is used. Moreover, we point out the temperature as a key parameter in plasma diagnostic interpretations.

Highly efficient cw chemical oxygen?iodine laser with transsonic iodine injection and a nitrogen buffer gas

Abstract: Methods of increasing the efficiency of low-pressure chemical oxygen?iodine lasers (COILs) with transsonic injection of molecular iodine, in which nitrogen is used as a buffer gas, are studied. A two-layer gas-dynamic model is used for a parametric analysis of physicochemical processes occurring in the transsonic iodine injector and in the COIL resonator, including mixing and generation of radiation. The 3D-RANS computer simulation software is used to study the flow structures resulting from an injection of iodine-containing flow into the transsonic zone of the oxygen nozzle. Experiments with a 10-kW modified laser have resulted in a chemical efficiency of 31.5% for a lasing power of 13.5 kW. The results of experimental studies of the cryosorption COIL exhaust system are presented.

Method for Producing Hydrogen and Power from a Synthesis Gas

Abstract: The invention relates to a method for producing hydrogen and power from a synthesis gas (4) that contains CO, H2 and H2S. The synthesis gas is separated into two partial streams (9, 27), vapor (11) is added to the first partial stream of synthesis gas, out a CO conversion (13) is carried out at a temperature of 220 °C to 500 °C, pure hydrogen (16) is obtained from the converted synthesis gas in a pressure swing absorption device (15) and a residual PSA gas (18) is produced. The second partial stream of synthesis gas is fed to a power-generating gas turbine for combustion, H2S and optionally other sulfur-containing components are removed in one or more separators that are arranged in any position in the process, however, before entry into the gas turbine, the residual PSA gas is mixed with nitrogen (20), the gas mixture so obtained is compressed and the compressed gas mixture is admixed to the partial stream of synthesis gas that is fed to the power-generating gas turbine (32).

Liter sized ion clock with 10/sup -15/ stability

Abstract: We have recently completed a breadboard ion-clock physics package based on Hg ions shuttled between a quadrupole and a 16-pole rf trap. With this architecture we have demonstrated short-term stability ~2-3times10-13 at 1 second, averaging to 10-15 at 1 day. This development shows that H-maser quality stabilities can be produced in a small clock package, comparable in size to an ultra-stable quartz oscillator required for holding 1-2times10-13 at 1 second. This performance was obtained in a sealed vacuum configuration where only a getter pump was used to maintain vacuum. We have selected materials for the vacuum tube, ion trap and UV windows that will allow a 450 C tube bake-out to prepare for tube seal-off. This approach to the vacuum follows the methods used in flight vacuum tube electronics, such as flight TWTA's where tube operation lifetime and shelf life of up to 15 years is achieved. We have made a thorough study of residual gas shifts of the ion-clock frequency and a study of alternate noble gasses as a buffer gas within the sealed tube. We find that neon is more suitable than the traditional use of helium, with 2-3 times less pressure induced frequency pulling. Since neon is heavier than helium, negligible diffusion losses will occur over the operation lifetime. We have developed a modular optical system that integrates lens, mirrors, 202Hg lamp and exciter, photomultiplier tube and pulse generation electronics, all into a small package that attaches to the vacuum tube, aligned with its optical ports and ion trap inside. Similarly, the reference magnetic field coil, an inner layer magnetic shield and a 40.5 GHz microwave feed with window have been incorporated into this breadboard

Wave numbers and Ar pressure-induced shifts of 198Hg atomic lines measured by Fourier Transform Spectroscopy

Abstract: Wave numbers and argon-pressure-induced shifts of mercury emission lines were measured using a UV/visible Fourier transform spectrometer (FTS). The observations were made with electrodeless lamps containing isotopically pure 198Hg and argon buffer gas at pressures of 33 Pa (1/4 Torr), 400 Pa (3 Torr), 933 Pa (7 Torr) and 1333 Pa (10 Torr). Calibration of the FTS wave number scale was obtained from the four most prominent 198Hg lines (6p 3P2–7s 3S1 at 546.2 nm, 6p 3P1–7s 3S1 at 436 nm, 6p 3P0–7s 3S1 at 404.8 nm and 6p 3P2–6d 3D3 at 365.1 nm), enabling measurements of wave numbers and argon pressure shifts of other UV and visible mercury transitions with high accuracy. Our measurements provide new data for the wave numbers and pressure-induced shifts of 20 mercury lines. The wave numbers of mercury lines emitted from the 400 Pa (3 Torr) lamp can be used as standards for wavelength calibration in inductively coupled plasma (ICP) spectrochemical analysis or in experiments where medium-resolution monochromators are used. The pressure-induced shifts of the 198Hg emission lines are in reasonable agreement with theoretical predictions and could be of interest for validating calculations of mercury–argon interactions.

Rubidium dimer destruction by a diode laser

Abstract: We observed rubidium dimer destruction by excitation of rubidium vapor with diode laser light tuned across the Rb D{sub 2} resonance line in a 2400 GHz tuning interval. The destruction was measured for rubidium atom concentrations in the (1-9)x10{sup 16} cm{sup -3} range, pump beam power up to 43 mW, and with a 5 Torr of the helium buffer gas. We discuss the physical mechanisms involved and specify the molecular pathways which may effectively lead to the observed dimer destruction.

Experimental Study on the Effect of Different Noble Gas Admixtures on the Gas Temperature of Oxygen Plasma

Abstract: Abstract We measured rotational temperature of oxygen plasma by optical emission spectroscopy (OES) in order to examine approximate value of its gas temperature. We generated microwave discharge oxygen plasma in a cylindrical quartz tube whose inner diameter 26 mm with its discharge pressure 0.5 - 2.0 Torr. We measured the band spectrum of radiative transition A 2Σ+ → X 2∏i , of OH radical to obtain rotational temperature in the present study. In order to obtain the rotational temperature, first we calculate the above OH band spectrum with the change in vibrational quantum number Δv = 0, for given vibrational and rotational temperatures. After that, we compare the experimentally measured spectrum with the calculated one to determine the real rotational and vibrational temperatures of the generated plasma. The rotational temperature observed ranges between 0.08 - 0.18 eV. Consequently, it is found that the rotational temperature in the oxygen plasma gradually decreases as the plasma flows to the downstream region of the discharge tube, and that higher discharge pressure makes the rotational temperature lower. We also examine the effect of admixture of noble gases with the oxygen discharge on its rotational temperature. It becomes remarkably lower when neon or argon is mixed more than 80% in the volumetric ratio. On the other hand, it becomes higher when krypton is mixed. The difference in the temperature change is discussed from several physical viewpoints.

Recombination studies in a He-Ar-H 2 plasma

Abstract: The recombination of H+3 ions with electrons has been studied in afterglow plasma in three different experiments. In two experiments, using the Variable Temperature Stationary Afterglow (VT-AISA) and the Variable Temperature Flowing Afterglow (VT-FALP) techniques, a decay of the electron number density was measured by an electrostatic Langmuir probe to determine the recombination rate coefficient. In the third experiment a near infrared Cavity Ring-Down Absorption Spectrometer (CRDS) was used to monitor the decay of the H+3 (v = 0) ion density during the afterglow. Measurements were carried out in helium buffer gas with small admixtures of argon and hydrogen at total pressures ranging from 150 up to 1200 Pa and at buffer gas temperatures ranging from 100 up to 330 K. In the experiments the partial number density of hydrogen was varied from 5 × 1010 up to 1 × 1016 cm−3 and for this broad range of hydrogen number densities effective recombination rate coefficients were obtained, which varied over three orders of magnitude from 2 × 10−9 cm3s−1 at [H2] = 5 × 1010 cm−3 up to 3 × 10−6 cm3s−1 at [H2] = 1 × 1016 cm−3. Using our experimental results we discuss possible mechanisms of recombination in hydrogen plasma in a very broad range of several parameters: buffer gas pressure, temperature, electron number density, hydrogen number density and internal excitation of recombining ions.

Helical lobe compressor for hydrogen water spray cooled

Abstract: The invention provides a water-spray cooling type hydrogen gas screw compressor, including cylinder body, gas suction end seat, gas exhaust end seat, open screw, secret screw, synchronous gear, sealing component and water spray mechanism. The sealing component includes a labyrinth sealing structure, a band buffer gas sealing structure and a floating ring sealing structure installed in turn at two shaft ends of the two screws. The water spray mechanism is installed on the cylinder body. It can reduce the raised temperature with hydrogen gas compression and controls the gas temperature at about 70 deg.C; the sprayed-in water can form a liquid membrane in the gap between the two screws and on their gas exhaust end surfaces, thus playing the role in sealing, improving the air tightness and inner compression volumetric efficiency of the compressor, and simultaneously strengthening the safety of the compressor. It can be widely applied to the hydrogen gas compressors in petrochemical enterprises.

Magnetic trapping of an atomic 55Mn-52Cr mixture

Abstract: Atomic manganese {sup 55}Mn and chromium {sup 52}Cr are simultaneously loaded and confined in a magnetic trap Using a cryogenic {sup 3}He buffer gas, 10{sup 11} manganese and 10{sup 12} chromium atoms are trapped at an initial temperature of 600 mK The buffer gas is then pumped away, thermally isolating the sample The Mn-Cr interspecies inelastic rate constant is measured to be {gamma}{sub Mn,Cr}=15({+-}02)x10{sup -13} cm{sup 3}/s

Gas absorption column and a method of chemically treating an acid gas using such a gas absorption column

Abstract: A method of chemically treating an acid gas, includes the steps of immersing a micro-porous membrane having a plurality of micro-pores in a liquid containing a reactant chemical and passing a gas stream containing an acid gas under pressure through the micro-porous membrane. The acid gas passes through the micro-pores to form micro-bubbles which float up through the liquid and react with the reactant chemical. A number of configurations of gas absorption columns are described as being suitable for use in accordance with the teachings of this method.

Atmospheric-pressure plasma treatment of gaseous effluents

Abstract: The invention relates to a method for the conversion of a gas or gas mixture and, in particular, a fluorinated gaseous effluent. According to the invention, at least one bond between two atoms of at least one molecule of the gas or gas mixture is broken under the influence of an electric and/or magnetic field to which the gas or gas mixture is subjected. The gas or gas mixture stream is injected through the electric and/or magnetic field in a non-rectilinear manner in order to increase the distance travelled by the gas molecules through the field and, in this way, increase the effectiveness of the conversion of the gas or gas mixture molecules.

Hyperpolarized 3 He gas production by metastability exchange optical pumping for magnetic resonance imaging

Abstract: A portable 3 He gas polarizer based on metastability exchange optical pumping is described. It produces 75 ml of highly polarized 3 He gas at the pressure of 100 mbar, by implementing a non-magnetic peristaltic compressor, which transfers the 3 He gas from the low-pressure optical pumping cell to the storage cell. About 30% polarization at 1 mbar is achieved in the optical pumping cell in a single run, and 20 compression cycles are needed to reach the final pressure in the storage cell. After adding a buffer gas up to the atmospheric pressure, the mixture is used in magnetic resonance imaging (MRI) experiments. Preliminary images of phantoms and of the rat lungs in vivo confirm the usefulness of the 3 He gas polarizer in MRI applications.