The cryopumping of water vapour in the continuum pressure region

Pumping speed measurements in the continuum pressure region, P>10^?3 torr, have been made for water vapour impinging on copper spheres and coils cooled to liquid nitrogen temperatures. Water vapour flow rates between 0.06 mg s^?1 and 420 mg s^?1 were used. The volumetric pumping speed was constant over the pressure range 2 × 10^?3 torr to 2 × 10^?2 torr and was, as expected, higher than that obtained in the free molecular flow region. Above 2 × 10^?2 torr the pumping speed decreased and possible reasons for this were investigated and are discussed. These included the effects of inadequate heat transfer from the liquid nitrogen refrigerant to the cryopump, a poor thermal conductivity of the cryodeposit, and an impurity, nitrogen gas, in the water vapour.     

10. Further developments with single structure vapour pumping groups

A pumping group with an additional liquid nitrogen cooled baffle or plate primarily to cryopump water vapour arising from the system is described. Reasons for using this variant are given and its performance compared with the simpler pumping group. The performance for air and other gases when charged with polyphenyl ether fluid is contrasted to those obtained with perfluoro polyether fluids with particular reference to their pumping stability for air, hydrogen and helium. Mass spectra of the residual atmosphere when using both polyphenyl ether and perfluoro polyether in both the watercooled and liquid nitrogen trapped versions are given. Comparative spectra of the watercooled version and a turbomolecular pump is also included. The choice of a fluid for specific applications is discussed taking into account its performance in the pump, chemical stability and other relevant factors. Applications in which this type of pumping group has been used successfully are discussed.     

Bombardon: an apparatus for investigating the influence of 5–20 keV ions on metal targets

An apparatus for ion bombardment in the energy range of 5–20 keV is described. The ion beam, produced by a duoplasmatron ion source, is purified by a magnetic sector field and directed into a target chamber 60 cm in diameter. The chamber is evacuated by sputter ion and titanium sublimation pumps with a total pumping speed of 20000 ls^?1 for H₂. The energy and angular distributions of particles backscattered from metal targets can be measured with an electrostatic spherical condenser which can be pivoted around the target. The whole apparatus is bakeable up to 250°C. With a 100 μA proton beam a pressure of 10^?9 torr is maintained in the target chamber. The black off pressure is a few 10^?11 torr.     

微型溅射离子泵放电模拟与抽气特性研究

为了解溅射离子泵抽气过程中内部放电与抽速的关系,考虑了N2分子的激发、电离及粒子之间的弹性碰撞等过程,利用COMSOL软件对微型溅射离子泵内部气体放电进行了数值模拟研究.得到了电子密度、温度、粒子轨迹、入射角度及入射能量的分布变化,并分析了这些因素对抽速的影响.在搭建的实验平台上对微型溅射离子泵进行了抽速测量,得到了不...     

High-speed ion pump with a multipactor cathode—The multipactor ion pump

A new type of high-speed ion pump using a multipactor cathode is proposed and the experimental results, obtained with the first trial pump, are described. The multipactor cathode has excellent characteristics as an electron source in order to obtain increased pumping speed of an ion pump, namely: (1) since it is a cold cathode made of pure metal, such as Al, it does not contaminate the vacuum condition, (2) the electron emission density is high, (3) the supply of electrons can be greatly increased in comparison with that of any other supply method, (4) the electrons can be supplied easily into a very wide area.This proposal is to make a high-speed ion pump by combining such an attractive cathode with a normal ion pump. The experimental results showed that the maximum pump current per unit pump volume reached up to 30 times that of a normal ion pump in vacuum conditions of less than 10^?4 Pa.     

Breaking the pumping speed barrier in mass spectrometry: discontinuous atmospheric pressure interface

The performance of mass spectrometers with limited pumping capacity is shown to be improved through use of a discontinuous atmospheric pressure interface (DAPI). A proof-of-concept DAPI interface was designed and characterized using a miniature rectilinear ion trap mass spectrometer. The interface consists of a simple capillary directly connecting the atmospheric pressure ion source to the vacuum mass analyzer region; it has no ion optical elements and no differential pumping stages. Gases carrying ionized analytes were pulsed into the mass analyzer for short periods at high flow rates rather than being continuously introduced at lower flow rates; this procedure maximized ion transfer. The use of DAPI provides a simple solution to the problem of coupling an atmospheric pressure ionization source to a miniature instrument with limited pumping capacity. Data were recorded using various atmospheric pressure ionization sources, including electrospray ionization (ESI), nano-ESI, atmospheric pressure chemical ionization (APCI), and desorption electrospray ionization (DESI) sources. The interface was opened briefly for ion introduction during each scan. With the use of the 18 W pumping system of the Mini 10, limits of detection in the low part-per-billion levels were achieved and unit resolution mass spectra were recorded.     

Ion beam reactively sputtered silicon nitride coatings

An ion beam source was used to deposit silicon nitride films by reactive sputtering a silicon target with an Ar+N₂ beam. The nitrogen fraction in the sputtering gas was 0.05 to 0.80 at a total pressure of 6 to 20×10^?5 torr. The ion beam current was 50 mA at 500 V. A rate of deposition of about 2 nm min^?1 (0.12 μm h^?1) was found, and the spectra indicated that Si₃N₄ was obtained for a fraction of nitrogen higher than 0.50. However, the AES spectra also indicated that the sputtered silicon nitride films were contaminated with oxygen and carbon and contained significant amounts of iron, nickel, and chromium, most probably sputtered from the holder of the substrate and target.     

A new generation of getter‐coated sputter ion pumps for XHV applications

A new concept of sputtered ion getter pump is presented. The body of this pump is internally coated by a getter thin film constituted by a layer of TiZrV together with a protective covering of palladium, according to a technology that CERN (European Center for Nuclear Research) licensed us. TiZrV is a well‐known alloy able to pump getterable gases such as hydrogen, oxygen, nitrogen, carbon monoxide and dioxide. With the exception of H², the sorption of these gases is not reversible and it causes a progressive contamination of the bulk of the material. With the addition of the palladium overlayer, the pumping action is limited to hydrogen and carbon monoxide, but the lifetime of the film is strongly enhanced, thanks to the possibility of an unlimited number of thermal activations, which restore the initial performances of the film. An innovative sputter ion pump design, optimized for both pumping speed in ultra high vacuum and getter film sputtering, will be introduced. Moreover, pumping speed measurements and ultimate pressure data, obtained after a relatively short bake‐out at temperature lower than standard procedures, will be reported.     

Instrumentation and vacuum aspects of chemical ionization mass spectrometry

Instrumental modifications involved in conversion of a mass spectrometer for chemical ionization are discussed. These modifications include a gas-tight ion source for operation at 1 torr, a differential pumping system, a gauge for source pressure monitoring, an inlet system for the reagent gas, increase of the electron energy up to 500 eV and modifications in the electron current regulator. Some of the applications and advantages of the technique are briefly reviewed.     

Electron backscattered diffraction analyses combined with environmental scanning electron microscopy: potential applications for non-conducting,uncoated mineralogical samples

Abstract

Operational techniques have been developed which combine electron backscattered diffraction (EBSD) analysis with orientation contrast and secondary electron imaging in environmental scanning electron microscopy (ESEM). This is specifically directed towards the analysis of uncoated, non-conducting materials such as ceramics and mineral surfaces, where surface charge effects have a severe detrimental effect on EBSD microstructural analysis. Initial experimentation to establish optimum chamber conditions was based on single Ge crystals, using both H₂O vapour and N₂ imaging gases. Reliable EBSPs with correct crystallographic solutions were collected up to pressures of ～4 torr (1 torr ≈1.33 mbar) under H₂O vapour conditions and ～2 torr in N₂, well above the minimal values for gaseous secondary electron detector imaging and surface charge neutralisation. Using these initial pressure and gas type guidelines, polycrystalline structures (with grain mosaics of 50–100 µm) in etched steel were analysed by automated, long duration crystal orientation mapping (COM). Optimum chamber conditions were established at ～1 torr pressure in H₂O vapour environments. At higher gas pressures, increased electron scattering generated more unsolved EBSPs, requiring advanced filtering to reduce map noise. For tests with non-conductors, a suite of single crystal and polycrystalline minerals (garnet, calcite, and olivine) were analysed. Optimum EBSPs were obtained under H₂O vapour conditions at pressures of 0.6–1.8 torr, and beam conditions were sufficiently stable for the collection of manual COMs. This new method of combining EBSD and ESEM will greatly improve the potential for microstructural analysis of sensitive, non-conducting ceramic surfaces.     

Design and investigation of gas cluster ion accelerator

A gas cluster ion accelerator with energies up to 20 keV is described. Parameters of the main components of the equipment were determined. It was demonstrated that a pulse regime of the accelerator can be realized with a relatively low (500 l/sec) pumping speed of the cluster ion source. Conditions for stable cluster beam generation were found. In pulse mode ion clusters appear in the accelerated beam in the first stages of ion beam evolution. A model describing the behavior of the ion beam in the pulse regime is suggested. To analyze the beam mass composition two systems were constructed: a magnetic mass-separation system and a time-of-flight system. Cluster ions Ar_n⁺ with number of atoms/charge n ≥ 500 were detected in the beam by using deflection in a homogeneous magnetic field. Clusters up to 3000 atoms/charge were detected by using time-of-flight measurements.     

Pumping performance analysis on turbomolecular pump

The pumping speed, conductance, and throughput of turbomolecular pump are investigated by both experiment and numerical simulation. The mass flow rates varying from 0.2 to 19.2 sccm (standard cubic centimeter per minute) for various inlet pressures are conducted in experiment. The experimental and analytic pumping speeds versus the inlet pressures of turbomolecular pump for N₂ were revealed. The pumping speeds obtained from experimental and simulation analysis are consistent at inlet pressures ranged from 5 × 10⁻² to 8 × 10⁻² Pa. When the inlet pressure is below 10³ Pa, the conductance decreases because the flow enters the transition flow region. Finally, the influence of inlet pressure on the throughput is also reported.     

Ion beam nitriding of titanium and titanium alloy

Titanium and Ti8A/1Mo1V alloy have been nitrided with an ion beam source of nitrogen or agon and nitrogen, at a total pressure of 2?10×10^?4 torr. The treated surface has been characterized by surface profilometry, X-ray diffractometry, Auger Electron Spectroscopy (AES), and microhardness measurements. It was found that tetragonal Ti₂N phase forms in pure titanium and Ti8A/2Mo1V alloy with traces of AIN in the alloy. Two opposite processes were found to compete during the ion beam nitriding: (a) formation of nitrides in the surface layers; (b) sputtering of the nitrided layers by the ion beam. The highest surface hardness, of about 500 kg mm^?2 in titanium and 800 kg mm^?2 in Ti8A/1Mo1V, was obtained by nitriding with an ion beam of pure nitrogen at 4.2×10^?4 torr, at beam voltage of 1000 V.     

Analysis and modelling of water based bubble pump at atmospheric pressure

Bubble pump (BP), an essential component in coffee percolators, is used to drive solar water heating systems and single pressure absorption refrigerators. However, its mass flow rate cannot be readily predicted. Heat input, tube diameter and submergence ratio affect its mass flow rate. BP has the same working concept as air-lift pump, but its flow is complicated due to the condensation of vapour bubbles. Neither curve fitting models, nor air-lift pump models, can predict the mass flow rate with high fidelity. A new model based on the pumping characteristics of BP is presented and verified by a water based setup at atmospheric pressure. Results show that the average errors for the BP with tube diameter of 6–12 mm, and for the BP with submergence ratio of 0.5–0.8 are 13% and 11%, respectively. The BP performance increases when the tube diameter decreases or the submergence ratio increases.     

Efficient pumping scheme for neodymium-doped materials by direct excitation of the upper lasing level

An efficient pumping scheme that involves direct excitation of the upper lasing level of the Nd(3+) ion is demonstrated experimentally. The results obtained for direct upper laser level pumping of Nd:YAG R2 (869 nm) and Nd:YVO(4) (880 nm) were compared with traditional ~808-nm pump band excitation. A tunable cw Ti:sapphire laser was used as the pump source. In Nd:YAG, the oscillator slope efficiency increased by 10% and the threshold decreased by 11%. In Nd:YVO(4), the slope efficiency increased by 5% and the threshold decreased by 11%. These results agree with theory. The increase in optical efficiency indicates that laser material thermal loading can be substantially reduced.     

Downward two-phase flow applications for a non-conventional heat pump

A non-conventional heat pump working by a difference in density between two branches of a hydraulic vertical loop has been described. This system called thermogravimetric heat pump, TGHP, operates with a non-conventional regenerative thermodynamic cycle which remarkably improves COP values. The lower density in the ‘downward branch’ is obtained by a liquid–vapour two-phase flow. Performances and main geometrical characteristic trends, such as plant height Z and two-phase column diameter D_T–PD have been drawn, varying the minimum cycle temperature between 15 and 25 °C and the user temperature, T_max, in the range 60–70 °C. The carrier fluid is demineralized water; according to the peculiar working fluid—PP 50, HFC 134a and HFC 338cca—different solutions can be obtained, such as for 10–12 storey buildings or for skyscrapers. Yet, the results obtained with HFC 338cca must be accepted with some cautions while waiting for a better characterisation of such fluid. Chemical compatibility, thermal stability, environmental impact have been also taken into account in the choice of the operating couple, carrier fluid—working fluid. While the thermodynamic conversion process is non-conventional, the TGHP can be assembled by standardised technology. The compressor of a conventional plant is here replaced by a feeding pump and COP values obtained through a regenerative TGHP are globally larger than those of a common heat pump.     

Optimized annular triode ion pump for experimental areas in the LHC

The large hadron collider will be the world next generation accelerator to be operational in 2007 at CERN. The UHV requirements force the installation of ion pumps in the experimental areas of ATLAS. Due to the unacceptable particle background that standards ion pumps may generate, a reduction in the amount of material constitutive of the pump body is required. Hence, a stainless steel 0.8 mm thick body annular triode ion pump has been designed. A pumping speed of ∼20 l/s at 10⁻⁹ mbar is provided by 15 pumping elements. Finite elements analysis and destructive tests have been performed in its design. Final vacuum tests results are shown.     

Effect of optical pumping on alkali-atom Doppler-limited spectra

Using a three-level model and semiclassical density matrix formalism, we show that optical pumping influences both line positions and amplitudes in Doppler-broadened alkali-atom D₁ and D₂ spectra for intensities much lower than the two-level atom saturation intensity. The influence on the D₂ spectrum is particularly interesting due to the presence of closed hyperfine transitions unaffected by optical pumping. This effect is of importance for example when lasers are frequency stabilized using linear absorption or when the alkali-atom vapour pressure is determined using absorption measurements.     

Design and performance characteristics of sorption pumps

This paper describes the design and performance characteristics of two types of refrigerated Molecular Sieve Sorption pump that produces and maintains a pressure of the order of 10⁻³ torr in volume of 10–50 l. in case of evacuation of air from atmospheric pressure. The main feature of this method of pumping is its freedom from pumping fluids. Some of its applications along with its limitations are discussed. Applications to multistage sorption pumping and the use of sorption pumps in combination with mechanical dry pump are illustrated.     

Experimental Study of Oil‐Free Claw Vacuum Pump Characteristics

Experimental study of pumping characteristics of a pilot model of a claw single‐stage vacuum pump with identical rotors was carried out. The curves of pumping speed vs. pressure at different rotary speed and the ultimate pressure at different rotors speed were determined on a test unit. Indicator pressure diagrams in working chambers of claw vacuum pump were obtained with the help of special sensors. Thus, an experimental data bank concerning the pumping characteristics of claw vacuum pump was created. It may be used for estimation of mathematical model adequacy and further development of the pump design.