Showing papers on "Buffer gas published in 2006"

Cesium vapor laser pumped by a volume-Bragg-grating coupled quasi-continuous-wave laser-diode array

Abstract: The experimental demonstration of a broad-area Quasi-continuous-wave (QCW) laser-diode array pumped cesium vapor laser is reported in this letter according to our experimental results. We used a volume-Bragg grating to narrow the spectral linewidth for acquirement of enough resonance transitions. A glass cylindrical cell filled with cesium/buffer gas was set in an end-pumped flat-concave cavity and the gas pressure was set lower than 1atm. Using the QCW drive mode with the repetitive rate and pulse width of 1kHz and 50μs, respectively, 13.45μJ pulse energy has been achieved with the slope efficiency of about ∼1.8%.

The ion-catcher device for SHIPTRAP

Abstract: An ion-catcher device consisting of a buffer-gas stopping cell and a radio-frequency quadrupole (RFQ) has been built for the SHIPTRAP facility at GSI. Results of characterisation measurements with the buffer-gas cell and the extraction RFQ performed at GSI in Darmstadt and at the MLL (Maier-Leibnitz-Laboratory) in Garching are presented. The set-up was tested off-line using laser-produced ions and on-line using stable beams and fusion–evaporation products. During the on-line measurements the ions with total energies of around 200 keV/u were thermalised in helium buffer gas at 40–60 mbar. In the following they were guided by a combination of electric RF- and DC-fields until they were transported by the gas flow through the extraction nozzle. After being extracted by a supersonic gas jet the ions were separated from the buffer gas and guided by the extraction RFQ towards subsequent detection systems. Depending on the electric-field strength average extraction times of around 10 ms and an overall efficiency (including stopping and extraction) between 4% and 8% have been achieved.

Comparison of atmospheric-pressure helium and argon plasmas generated by capacitively coupled radio-frequency discharge

Abstract: In this paper, the electrical discharge characteristics of plasmas generated in coaxial cylindrical electrodes capacitively powered by a radio-frequency power supply at atmospheric pressure are investigated with respect to helium and argon gases. The electrical discharge parameters, voltage (V), current (I), and power (P), are measured for both helium and argon plasmas, and the electron temperatures and electron densities for them are evaluated by means of the equivalent circuit model and the power balance equation. By comparison of the discharge characteristics of the helium and argon plasmas, it is found that the discrepant macroscopic characteristics of helium and argon plasma, viz., current and voltage characteristics and current and power characteristics, are owed to their own intrinsic microscopic parameters of the helium and argon atoms, such as the first excited energy, the ionization energy, the total cross section, and the atom mass. Furthermore, the influences of the additive gas, oxygen gas, on the electrical discharge characteristics are also investigated in the helium and argon plasmas, which are closely related to the electron temperature of plasmas.

Study of the transport of titanium neutrals and ions in the post-discharge of a high power pulsed magnetron sputtering device

Abstract: This paper deals with the diagnostics of a high power pulsed magnetron sputtering device (HPPMS). The HPPMS plasma was spatially and temporally characterized in the post-discharge using optical absorption spectroscopy and Langmuir probe time resolved measurements. A circular titanium target was used, the buffer gas was argon and the pressure was fixed at 4 Pa. The titanium densities (neutrals and ions) were measured by a pulsed resonant absorption spectroscopy technique. We found an ionization degree higher than 0.5. Comparison beetween the experimental results and a simple one-dimensional model of diffusion shows that in these conditions, the transport of neutral and ionized sputtered atoms is mainly controlled by diffusion (ambipolar diffusion for ions).

IonCool¿A versatile code to characterize gas-filled ion bunchers and coolers (not only) for nuclear physics applications

Abstract: A Monte-Carlo simulation package is presented which has primarily been used to characterize ion bunching devices based on gas-filled (linear) Paul traps and Penning traps. The code calculates the motion of ions in the presence of arbitrary electric and/or magnetic fields modeling the effect of the buffer gas by realistically simulating collisions between ions and buffer gas molecules. A summary of the algorithm is presented. Examples of applications of the code are discussed, which include the ion beam bunchers of ISOLTRAP, REXTRAP, LIST and LEBIT.

Method and arrangement for the suppression of debris in the generation of short-wavelength radiation based on a plasma

Abstract: The invention is directed to a method and arrangements for the suppression of debris in short-wavelength radiation sources based on a plasma, particularly for EUV sources for semiconductor lithography. The object of the invention is to find a novel possibility for suppressing the particle flow (debris) from a plasma which keeps the debris away from primarily optical components located downstream without excessive attenuation of the desired radiation emitted from the plasma. According to the invention, this object is met in that a buffer gas is injected inside the filter structure of the debris filter lateral to openings that are provided for passing the radiation. The filter structure generates a flow resistance in direction of the plasma and in direction of propagation of the radiation so that an increased gas pressure of buffer gas remains limited to a defined volume layer in the debris filter relative to the pressure in the vacuum chamber, and the buffer gas exiting from the filter structure of the debris filter is sucked out of the vacuum chamber by vacuum pumps.

Performance of the MLL-IonCatcher

Abstract: The MLL-IonCatcher is a new setup for the thermalization of fusion-evaporation reaction products in highly pure helium with subsequent extraction of the stopped, singly charged ions. The setup consists of a buffer-gas stopping cell and a radio frequency quadrupole (RFQ)-based extraction system and is placed at the Tandem accelerator facility of the MLL in Garching. Test experiments were performed using the α emitter Er152 with total kinetic energies of around 180keV∕u, produced via the reaction Sb121(Cl35,4n). During the on-line measurements the number of ions entering the stopping chamber through the entrance window was determined via the detection of their specific α-decay energy. After being thermalized in the helium buffer gas at 40–140mbar the ions were guided by a combination of electric rf and dc fields towards the extraction nozzle where the ion transport was taken over by the gas flow. Subsequent to the extraction by a supersonic gas jet the ions were separated from the buffer gas and guided by t...

Formation of clusters through generation of free atoms

Abstract: We consider, from a general point of view, conversion of a supersaturated vapour of metal atoms located in a buffer gas into metal clusters. A simplified set of balance equations for the size distribution function of clusters allows us to describe the time evolution of its parameters for various methods of cluster generation, such as the laser method, evaporation of metal atoms from a heated metallic surface, and the magnetron method of cluster generation by cathode erosion. Parameters of the distribution function together with certain peculiarities of cluster growth can be used for the analysis of certain methods of cluster generation under given external conditions. We illustrate this on the analysis of generation of titanium clusters in magnetron discharge where metal atoms from the cathode are captured by a buffer gas flow and are transformed there into clusters. The buffer gas together with metal clusters passes through an orifice, so that clusters can attach to a substrate. The analysis of this method allows us to find optimal parameters of this process.

Electron attachment to POCl3: measurement and theoretical analysis of rate constants and branching ratios as a function of gas pressure and temperature, electron temperature, and electron energy.

Abstract: Two experimental techniques, electron swarm and electron beam, have been applied to the problem of electron attachment to POCl3, with results indicating that there is a competition between dissociation of the resonant POCl3-* state and collisional stabilization of the parent anion. In the electron beam experiment at zero electron energy, the fragment ion POCl2- is the dominant ion product of attachment (96%), under single-collision conditions. Small amounts (approximately 2% each) of POCl3- and Cl- were observed. POCl3- and POCl2- ion products were observed only at zero electron energy, but higher-energy resonances were recorded for POCl-, Cl-, and Cl2- ion products. In the electron swarm experiment, which was carried out in 0.4-7 Torr of He buffer gas, the parent anion branching ratio increased significantly with pressure and decreased with temperature. The electron attachment rate constant at 297 K was measured to be (2.5+/-0.6)x10(-7) cm3 s(-1), with ion products POCl2- (71%) and POCl3- (29%) in 1 Torr of He gas. The rate constant decreased as the electron temperature was increased above 1500 K. Theory is developed for (a) the unimolecular dissociation of the nascent POCl3-* and (b) a stepladder collisional stabilization mechanism using the average energy transferred per collision as a parameter. These ideas were then used to model the experimental data. The modeling showed that D0 o(Cl-POCl2-) and EA(POCl3) must be the same within +/-0.03 eV.

System and method for eliminating process gas leak in a solids delivery system

Abstract: A system for controlling gas leakage in a solids delivery system is provided. The system includes a bulk solids pump comprising an inlet for a particulate material and an outlet for discharge of said particulate material. The system also includes a buffer gas channel configured to impede backflow of process gas into the bulk solids pump, such as from a downstream system or process. The system further includes a pressure differential system configured to control a flow rate of the buffer gas and maintain a positive differential in pressure between the buffer gas and the process gas.

High resolution spectroscopy and potential determination of the (3)Π1 state of NaCs

Abstract: The (3)Π1 state of the NaCs molecule was studied by high resolution Fourier-transform spectroscopy. The (3)Π1→XΣ+1 laser induced fluorescence was excited by an Ar+ ion laser or by a single-mode frequency-doubled cw Nd:YAG laser. The presence of argon buffer gas yielded rich rotational relaxation spectra allowing to enlarge the data set for the (3)Π1 state term values, as well as to observe Λ splittings in a wide range of vibrational (v′) and rotational (J′) quantum numbers. The data field includes about 820 energy levels of (3)Π1 NaCs in the range from v′=0 to 37 and from J′=3 to 190, which corresponds to ca. 95% of the potential well depth. Direct fit of the potential energy curve to the level energies is realized using the inverted perturbation approach method; a set of Dunham coefficients is also presented.

Investigation of excimer ultraviolet sources from dielectric barrier discharge in krypton and halogen mixtures

Abstract: The characteristics of the emission spectra of Kr/Br2 and Kr/I2 mixtures driven by dielectric barrier discharge as a function of gas pressure were respectively investigated. It was found that the KrBr* excimer lamp provided an intense narrow band ultraviolet (UV) radiation at λ=207 nm, whose intensity was strongly influenced by gas pressure and buffer gas. The excimer radiation at λ=191 nm generated by the KrI* excimer lamp was very weak and less dependent on gas pressure due to predissociation which was confirmed by the strong emission of the atomic iodine line at λ=183 nm.

Classical and quantal studies of the satellite features in the absorption spectra of lithium „2s-2p… perturbed by helium

Abstract: This work reports a theoretical analysis of the Li(2s{yields}2p) photoabsorption spectra when the lithium atoms are evolving in a ground helium buffer gas. The influence of temperature on the far-line wing spectra is particularly examined by adopting classical and full quantum-mechanical approaches. The computations show the appearance, above approximately 1000 K, of satellite structures in the blue wing around the wavelength 536 nm. The data obtained in the range of temperature 500-3000 K agree very well with those already calculated with different theoretical methods.

Passive atomic frequency standard based on coherent population trapping in 87 Rb using injection-locked lasers

Abstract: We present a microwave frequency standard based on coherent population trapping (CPT) in the 87Rb D1 line. The CPT spectrum is obtained using two Raman lasers with a 6.8 GHz frequency offset by injection locking of a master laser to a slave laser. We have constructed an atomic clock employing a 5 cm long Rb vapor cell confined with 6.67 kPa neon buffer gas at 70 °C. Using this system, we improve the CPT contrast through the elimination of undesired off-resonant fields created by the direct modulation method. We measured the frequency shift of the CPT signal as a function of the temperature of the Rb cell and estimated it to be approximately 1.3 ×10−9/K. The frequency of a 10 MHz crystal oscillator has been stabilized to the CPT spectrum between the two ground states in 87Rb. The relative frequency stability is approximately 2.3×10−12 for an average time of 68 s.

Pulsed photoacoustic system calibration for highly excited molecules

Abstract: The proposal of a simple method for pulsed photoacoustic system calibration is presented. Analysis of the photoacoustic signal shape is performed with different types of absorbing molecules (SF6 and C2H4) and the same buffer gas (Ar). Different total pressures (ptotal) of such gas mixtures and different laser fluences are used to obtain experimental results and compare them with theory. Results from such a comparison are used directly for the calculation of a calibration curve. A single experimental point calibration procedure for the case of highly vibrationally excited absorbing SF6 molecules is confirmed.

Deposition systems and susceptor assemblies for depositing a film on a substrate

Abstract: Parasitic deposits are controlled in a deposition system for depositing a film on a substrate, the deposition system of the type defining a reaction chamber for receiving the substrate and including a process gas in the reaction chamber and an interior surface contiguous with the reaction chamber. Such control is provided by flowing a buffer gas between the interior surface and at least a portion of the process gas to form a gas barrier layer such that the gas barrier layer inhibits contact between the interior surface and components of the process gas. A deposition system for depositing a film on a substrate using a process gas includes a reaction chamber adapted to receive the substrate and the process gas. The system further includes an interior surface contiguous with the reaction chamber. A buffer gas supply system is adapted to supply a flow of a buffer gas between the interior surface and at least a portion of the process gas such that the flow of the buffer gas forms a gas barrier layer to inhibit contact between the interior surface and components of the process gas when the process gas is disposed in the reaction chamber.

Constant volume combustor having a rotating wave rotor

Abstract: A constant volume combustor device includes, in one form, a detonative combustion. The apparatus includes inlet and outlet ports that interface with a plurality of fluid flow passageways on a rotor. A buffer gas is routed through some of the inlet and outlet ports and into and out of the plurality of fluid flow passageways. One of the inlet ports is a buffer gas inlet port that when placed in registry with a fluid flow passageway allows the flow of buffer gas into the respective passageway. Fuel is delivered into the buffer gas proximate the buffer gas inlet port so that only a portion of the buffer gas inlet port receives any fuel. In one form the wave rotor of the constant volume combustor is supported by magnetic bearings.

Buffer gas loading and evaporative cooling in the multi-partial-wave regime

Abstract: This thesis describes the study of collisions in the multi-partial-wave regime relevant to the buffer gas cooling and trapping of atoms. A quantitative model is formulated to describe the dynamics of evaporative cooling and is used to infer elastic and inelastic collision rate constants of gel = 2.15(+2.5,−1.2) × 10−10 cm/s and gin = 1.36(+1.2,−0.7) × 10−12 cm/s between two chromium atoms in the temperature range of 0.02-1 K and explains a long standing discrepancy between theory and experiment. Magnetic trapping is then extended to atomic manganese where up to 2×1012 Mn atoms are trapped in all six hyperfine states, allowing for the exploration of the role of the hyperfine interaction in spin-exchange collisions. In addition, we simultaneously trap a Mn-Cr mixture and measure an inter-species inelastic rate constant of gMn,Cr = 1.5 (±0.2)×10−13 cm/s. Demonstrating that buffer gas loading is a viable alternative to laser cooling, we have magnetically trapped and evaporatively cooled metastable helium in large numbers. 10 He* atoms are trapped at an initial temperature of 400 mK and evaporatively cooled into the ultracold regime, resulting in a cloud of 2± 0.5× 10 atoms at 1.4± 0.2 mK and an increase in phase space density of 5 orders of magnitude. Efficient evaporation indicates low collisional loss for He* in both the ultracold and multi-partial-wave regime, in agreement with theory.

Magnetic trapping of buffer-gas-cooled chromium atoms and prospects for the extension to paramagnetic molecules

Abstract: We report the successful buffer-gas cooling and magnetic trapping of chromium atoms with densities exceeding 1012 atoms per cm3 at a temperature of 350 mK for the trapped sample. The possibilities of extending the method to buffer-gas cool and magnetically trap molecules are discussed. To minimize the most important loss mechanism in magnetic trapping, molecules with a small spin–spin interaction and a large rotational constant are preferred. Both the CrH (6Σ+ ground state) and MnH (7Σ+) radicals appear to be suitable systems for future experiments.

Controlling diffusion of He-3 by buffer gases: A structural contrast agent in lung MRI

Abstract: Purpose: To study the influence of admixing inert buffer gases to laser-polarized 3 He in terms of resulting diffusion coefficients and the consequences for image contrast and resolution. Materials and Methods: The diffusion coefficient of 3 He was altered by admixing buffer gases of various molecular weights ( 4 He, N2, and SF6). The influence of the pulse sequence and the diffusion coefficient on the appearance of MRI of (laserpolarized) gases was analyzed by comparison of basic theoretical concepts with demonstrative experiments. Results: Excellent agreement between theoretical description and observed signal in simple gradient echoes was observed. A maximum signal gain can be predicted and was experimentally validated. Images acquired under such conditions revealed improved resolution. The nature and concentration of the admixed gas defines a structural threshold for the observed apparent diffusion coefficient (ADC) as demonstrated with diffusion-weighted MRI on a pig’s lung flooded with suitable gas mixtures. Conclusion: A novel procedure is proposed to control the diffusion coefficient of gases in MRI by admixture of inert buffer gases. Their molecular mass and concentration enter as additional parameters into the equations that describe structural contrast. This allows for setting a structural threshold up to which structures contribute to the image. For MRI of the lung this enables images of very small structural elements (alveoli) only, or in the other extreme, all airways can be displayed with minimal signal loss due to diffusion.

Fine-tuning of ceramic-based chemical sensors via novel microstructural modification: Part II: Low level CO sensing by molybdenum oxide, MoO3

Abstract: Employing a buffer gas mixture of CO and CO2, the equilibrium oxygen partial pressure was varied across the Mo/MoO3 proximity line by varying the ratio of concentration of the two gases, as described in an earlier communication. This led to the reduction of MoO3 in one case and oxidation of the reduced phase (Mo or MoO2) in the other with a concomitant variation in the microstructural features of the resulting species. The formation and growth of the new oxide surface under conditions of oxygen potential modulation has been found to impart enhanced sensing characteristics to the MoO3-based chemical sensors for low levels of carbon monoxide (14–100 ppm CO) in the ambient. © 2006 Elsevier B.V. All rights reserved.

Laser Synthesis of Oxide Nanopowders

Abstract: Oxide nanopowders Y2O3, ZrO2, YSZ (Y2O3-stabilized ZrO2), Ce0.8Gd0.2O2 and Y2O3- Al2O3 compounds were prepared with the help of laser evaporation and subsequent vapor condensation in the flow of buffer gas. An efficient technology and setup to produce high purity weakly agglomerated nanopowders are demonstrated. The output rate, alteration of elemental composition, size distribution and crystalline structure of the nanopowders depending on parameters of laser radiation and buffer gas flow are reported.

Apparatus for manufacturing semiconductor single crystal

Abstract: This apparatus for manufacturing a semiconductor single crystal includes: a crucible; a heater; a crucible driving unit; a chamber for housing the crucible and the heater; and a hydrogen mixed gas supplying device for supplying into the chamber a hydrogen mixed gas including an inert gas in admixture with a hydrogen-containing gas that contains hydrogen atoms, wherein the hydrogen mixed gas supplying device includes: a hydrogen-containing gas supply unit; an inert gas supply unit; a hydrogen-containing gas flow rate controller; an inert gas flow rate controller; and a buffer tank for mixing together the hydrogen-containing gas and the inert gas so as to form a hydrogen mixed gas and for holding the hydrogen mixed gas.

Rate constant of the reaction of NO3 with CH2I2 measured with use of cavity ring-down spectroscopy

Abstract: We have applied cavity ring-down spectroscopy to a kinetic study of the reaction of NO3 with CH2I2 in 25–100 Torr of N2 diluent at 298 K. The rate constant of reaction of NO3 + CH2I2 is determined to be (4.0 ± 1.2) × 10−13 cm3 molecule−1 s−1 in 100 Torr of N2 diluent at 298 K. The rate constant increases with increasing pressure of buffer gas below 100 Torr. The reaction of CH2I2 with NO3 has the potential importance at nighttime in the atmosphere.

Radiation source for the generation of short-wavelength radiation

Abstract: In a radiation source for the generation of short-wavelength radiation, it is the object of the invention to effectively increase the protection of the collimator optics by a buffer gas without substantially reducing the radiation transmission. A vacuum chamber which encloses a radiation-emitting plasma and is outfitted with at least one feed line and one outlet line for a buffer gas in order to ensure protection against debris for at least one optical element which directs the radiation to a radiation outlet opening in the vacuum chamber has chamber areas with particle deceleration of varying magnitude by the buffer gas. The particle deceleration is greater at least in a first chamber area in which the optical element is arranged than in any other chamber area.

Diagnostics of water-containing gas mixtures using thermal laser-induced gratings

Abstract: Laser-induced gratings (LIGs) experiments, employing vibrational-overtone excitation of H 2 O molecules through rovibrational transitions of the (2 1 1) ← (0 0 0) band around 820 nm to produce gratings, have been performed in humid ambient air, in a room-temperature cell with neat water vapor or that diluted in buffer gas at pressures of 0.02–4 bar, and in the vicinity of premixed atmospheric pressure CH 4 -air flame, with the aim to investigate the feasibilities of the techniques for accomplishing gas diagnostics or tracing H 2 O at various temperatures and pressures. In highly vibrationally-excited H 2 O rapid multi-stage collisional thermalization processes occur, and as a result both strong oscillatory (due to standing acoustic waves) and stationary (due to stationary density modulations) contributions to LIGs have been observed in gas mixtures. Temporal profiles of LIG signals recorded at various conditions of gas mixtures employed have been analysed in frame of a model of a two- or three-stage R – T , V – V ′, and V – T collisional relaxation of H 2 O and buffer gas molecules. The informative parameters, like adiabatic sound velocity, gas temperature, H 2 O mole fraction have been derived. The results of the analysis are presented, demonstrating possibilities and challenges of the technique in application to gas diagnostics.