Differential Pumping System Research Articles

In situ TEM observation of solid-gas reactions

Under a gaseous atmosphere at high temperatures, almost all the materials (metal, catalysts, etc.) change their structures and properties. For the research and development of materials, it is of vital importance to clarify mechanisms of solid-gas and liquid-gas reactions. Recently an in situ TEM system combined with an environmental holder, which has a gas injection nozzle close to a specimen-heating element, has been developed. The gas injection nozzle permits gas to flow around the specimens sitting on the heating element made of a fine W filament. The newly developed in situ TEM has a differential pumping system; therefore, the pressure in the specimen chamber is maintained in the range of higher than 1 Pa, while the pressure in the electron gun chamber can be kept in the range of 10-5 Pa. This system was applied to in situ observation of chemical reactions of metals with gases: Observation of oxidation and reduction under a gas pressure ranging from 10-5 Pa to 1 Pa at high temperatures (room temperature to ∼1473 K) were successfully carried out on pure metal and rare metal catalysts at near-atomic resolution. This in situ environmental TEM system is promising for clarifying mechanisms of many solid-gas and liquid-gas reactions that take place at high temperatures under a gas atmosphere.

Design and performance of differential pumping system of coating unit

A box type coating unit has been developed in view of dual purpose of optical and reactive coating. The system is divided in two parts namely, substrate chamber (800mm × 800 mm × 100 mm) and gun chamber (800mm × 800 mm × 100 mm). Coating material is evaporated in the substrate chamber by traverse (270°) electron beams. Reactive gas is injected in the substrate chamber by up-stream pressure controller to reach set pressures in the range of 1×10−3 mbar to 1×10−4 mbar for gas flow rate in the range of 0-30 sccm. Traverse EB guns (10 kV, 15 kW, 2 No) are mounted inside gun chamber. The gun chamber vacuum should be better than 1×10−5 mbar for the operation of EB guns. Both these chambers are connected by the apertures provided on the intermediate bifurcation plate for the passage of electron beams. Through the apertures the reactive gas leaks from the substrate chamber to the gun chamber due to differential pressure. The differential pumping system consists of individual pumping modules for the substrate chamber and the gun chamber. The paper focuses upon the design of differential pumping system in view of determination of steady state differential pressures for different flow rates of reactive gas. It has been noticed that on introduction of reactive gas in the substrate chamber, the pressures in the substrate chamber and the gun chamber oscillates before converging to steady state values. Theoretically calculated values have been compared with the experimental values as design validation.

Research for a clean and large throughput differential pumping system

The research is to design a differential pumping system not only to achieve the pressure transition with a large throughput, but also to achieve a clean system without oil vapour contamination. In the paper, the pressure in differential stages are calculated; the differential pumping system design and equipment choice are introduced; the tests of MBP, a new kind of molecular-drag pump with large throughout and clean vacuum are described and the system experiment result and analysis is presented.

Extraction of ions from solutions under atmospheric pressure as a method for mass spectrometric analysis of bioorganic compounds

The basic features of mass spectrometry, such as high sensitivity, molecular mass determination capacity, and acquisition of structural information, are not used practically to analyze non-volatile, polar, and thermally unstable compounds, in particular the majority of bioorganic substances. This is because it is impossible to evaporate these compounds without decomposition under ordinary heating. It is necessary to use non-destructive methods of evaporation and ionization of the substances in the ion source of the mass spectrometer or, alternatively, chemical protection of polar and labile groups. Existing methods of ’soft’ ionization require obligatory sample preparation procedures. This fact limits the application of these methods. Recently, certain progress has been achieved in this field of mass spectrometry applying the generation of the ions directly from solutions under atmospheric pressure. In this paper we report a method called the extraction of dissolved ions under atmospheric pressure (EDIAP). This method allows the mass spectra of non-volatile and thermolabile bioorganic compounds to be recorded with controllable fragmentation or clustering of the quasimolecular ion. Control of the mass spectrum allows unique information about the molecular mass of a substance, its structural features, and the nature of interaction between the ions and the neutral solvent molecules to be obtained. Moreover, the kinetics and mechanisms of ion-molecule reactions can be also investigated. These numerous tasks can be solved using only the ion source invented at the Institute of Analytical Instrumentation of USSR Academy of Sciences. The developed ion source is schematically shown in Fig. 1. The ion source has been installed in a MX 1320 double focusing mass spectrometer with accelerating potential of 2.5 kV. Commercially available pumps have been used in the differential pumping system. The pump speed was 5 L/s in the fore-vacuum chamber and 700 L/s in the high-vacuum chamber.

A VUV Photoionization Aerosol Time-of-Flight Mass Spectrometer with a RF-Powered VUV Lamp for Laboratory-Based Organic Aerosol Measurements

A vacuum ultraviolet (VUV) photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) has been developed for real-time, quantitative chemical analysis of organic particles in laboratory environments. A nozzle of ∼ 0.12 mm orifice combined with an aerodynamic lens assembly and a three stage differential pumping system is used to sample particles at atmospheric pressure. The particles are vaporized on a thermal heater, and then the nascent vapor is photoionized by light generated with a RF-powered VUV lamp. A 0.41 V/cm electric field is used to drive the ions from the ionization region into the ion extraction region where a positive electric pulse repels the ions into a reflectron mass spectrometer. The mass resolution of the spectrometer is ∼ 350 and the detection limit is ∼ 400 μ m 3 . The signal intensities observed are linear with the mass concentration of aerosols. Oleic acid particles are well quantified with an uncertainty of 15% in mass concentrations ranging from 3.9 mg/m 3 to 392 mg/m 3...

Tritium migration along the cryopumping section

The transport section of the Karlsruhe Tritium Neutrino experiment (KATRIN) must provide the dramatic reduction of tritium flow and gas density from the end of a 10-m-long windowless gaseous tritium source throughout several stages of a differential pumping system. The final stage of this section, the cryogenic pumping section (CPS) based on pumping of tritium on argon frost at 4.5 K, should provide the flow ratio between inlet and outlet in the range of 107. Cryosorbed tritium may decay, emitting a few keV electrons. These electrons in their turn cause the electron-stimulated desorption of cryosorbed argon and tritium, which is redistributed along the CPS (migration process). This effect was modeled with the use of the method of angular coefficients. The main result is that the tritium migration process does not affect the CPS performance at KATRIN for a given inlet flow. Meanwhile, if the flow chosen is larger, the migration effect could be dominant.

Utilizing low-energy ion beams to study living organisms

In the present study, the survival potentials of two kinds of water-abundant living organisms, the mammalian A L cell, and the nematode Caenorhabditis elegans, were investigated in an effort to improve their tolerance of the high-vacuum conditions required for ion implantation experiments. Samples were subjected to the vacuum at a pressure of 2–5 × 10 − 2 Pa for a period of 90–150 s, and their surviving fractions were analyzed subsequently. The ion beam bioengineering facility, which makes use of a differential pumping system to minimize the sample's vacuum duration time (less than 5 min for most implantation experiments), provided the physical foundation. Analyses on the cell status during vacuum exposure indicated that decrease of temperature and desiccation are the main causes (or at least parts of them), for cell inactivation. Glycerol, one of the most popular cryo-agents, in combination with proper pre-treatment protocols, was adopted to enhance the organisms' vacuum tolerance. The survival fraction of A L cells, assayed by PI-Flow Cytometry, manifested a PI-negative (indication of living cells) fraction of 12.7 ± 3.37% at 20% (v/v) glycerol pre-treatment. C. elegans, a self-organized animal, having much larger body volume compared with the former species, displayed a better anti-vacuum potential when an adaptation to glycerol at long-term (> 1 h) and low-concentration (2%, v/v) was applied prior to being processed with high-concentration (15%, v/v) glycerol. The final vacuum survival rate of C. elegans averaged at 40.4 ± 15.35%, which was evidently superior to that of the worms without glycerol protection. Though the poor vacuum tolerance has long been a trouble for researchers who have a strong desire to study these organisms by ion beam technology, we have every confidence that any such improvement will enable new directions for research in this field.

Delivering high-purity vacuum ultraviolet photons at the Brazilian toroidal grating monochromator (TGM) beamline

Vacuum ultraviolet beamlines based on grating monochromators share the problem of high-order harmonics contamination. In the low-photon energy range up to 25 eV, this problem may be overcome by letting the light beam pass through a high-pressure gas region. Here the photons with energies higher than the gas ionization threshold are absorbed and dumped. We have recently proposed and demonstrated a simple and inexpensive type of mixed gas metallic film filter. We present here the design and results of a complete gas-phase harmonics filter based on a very efficient and affordable differential pumping system which currently works at a bending magnet beamline at LNLS. Besides the efficient depletion of high-order harmonics, a noble gas harmonic filter has additional advantages. It can also provide a precise photon energy calibration, as well as a means for determining the resolving power. The use of such a gas filter is very important for photochemistry and molecular dynamics where even a very small portion of high-energy photons can mask the fragments generated by the first order photons.

New system for secondary electron detection in variable‐pressure scanning electron microscopy

A novel secondary electron detection system combining a two-stage detector head and a differential pumping system is presented. The detector head consisted of a scintillation Everhart-Thornley detector and a microsphere plate, separating it from the lower vacuum in the intermediate chamber (below 0.1 mbar). The system was arranged asymmetrically, which should contribute to a lower gas leakage through the plate and a longer life span of the plate. The system offered all the advantages of the scintillator detector in a wide range of gas pressures, from high vacuum to those of the order of 10 mbar, typical of high-pressure scanning electron microscopy.

A chamber for studying planetary environments and its applications to astrobiology

We have built a versatile environmental simulation chamber capable of reproducing atmospheric compositions and surface temperatures for most of the planetary objects. It has been especially developed to make feasible in situ irradiation and characterization of the sample under study. The total pressure in the chamber can range from 5 to 5 × 10−9 mbar. The required atmospheric composition is regulated via a residual gas analyser with ca ppm precision. Temperatures can be set from 4 K to 325 K. The sample under study can be irradiated with ion and electron sources, a deuterium ultraviolet (UV) lamp and a noble-gas discharge UV lamp. One of the main technological challenges of this device is to provide the user the possibility of performing ion and electron irradiation at a total pressure of 0.5 mbar. This is attained by means of an efficient differential pumping system. The in situ analysis techniques implemented are UV spectroscopy and infrared spectroscopy (IR). This machine is especially suitable for following the chemical changes induced in a particular sample by irradiation in a controlled environment. Therefore, it can be used in different disciplines such as planetary geology, astrobiology, environmental chemistry, materials science and for instrumentation testing.

The lava lake-induced volcanic plume at Nyiragongo Volcano (DRC): Environmental effects on crop and population

Stable isotopes, such as C, N, O and S, are successfully used as classical environmental tracers. During the last few years, heavy stable isotopes are getting more and more attention as tracers and proxies in biogeochemical and environmental studies. Multicollector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) has enabled scientists to obtain high precise isotopic analyses of heavy elements such as C1, Ca, Fe, Cu, Zn, Hg and Pb. These isotopic systems can be used as important tracers in studying metal contaminants, biomedical processes and pollution of aquatic environments. MC-ICPMS is a powerful technique for the isotopic analysis of most elements, with the exception of light elements such as H, C, N and O and noble gases. The advantage of the ICP source is that it can ionize all elements with very high sensitivity. Various inlet systems can be used to introduce samples into the mass spectrometer, for instance gas chromatography (GC), liquid chromatography (LC), laser ablation, or conventional liquid nebulization. The aerosol is transported by an Ar and/or He gas flow into the ICP source where it is effectively ionized and introduced into the mass analyzer through a differential pumping system. The variable multicollector detector array allows the user to adjust the detector positions along the focal plane of the mass spectrometer so that all isotopes of interest can be measured simultaneously. Molecular interferences as carbides, nitrides, oxides, argides or doubly-charged species can show up in the mass spectrum and interfere with the elemental isotope peaks. High mass resolution is needed to effectively discriminate against these interferences. The ion optics of the Finnigan NEPTUNE is specially designed to meet this requirement and expand the power of isotope ratio measurements even to elements where previously isobaric interferences were the limit. The presentation will discuss the applications of S, C1, Fe and Hg isotopes to study various processes linked to geochemistry and health using the Finnigan NEPTUNE.

Monte Carlo simulation of gas flow through the KATRIN DPS2-F differential pumping system

The Karlsruhe Tritium Neutrino experiment (KATRIN) is a large vacuum system and aims to measure the electron neutrino mass from the β decay of tritium with unprecedented sensitivity. To achieve this purpose, the tritium gas flow has to be significantly reduced along the beamline by means of a modular differential pumping system. This paper studies systematically the vacuum performance of one of the differential pumping systems (known as DPS2-F) based on turbomolecular pumps. The flow reduction rates in the complete system are described by a matrix equation as a function of the capture factor of the turbomolecular pumps employed. The results show that a total reduction factor greater than 10 5 can be attained, which is one of the prerequisites to achieve XHV conditions in the spectrometers used in the downstream end of the experiment.

Development of ultrahigh vacuum floating‐type low‐energy ion gun with differential pumping facilities for high‐resolution depth profiling

AbstractAn ultrahigh vacuum floating‐type low‐energy ion gun (UHV‐FLIG) with a differential pumping system was developed. The developed UHV‐FLIG ensured high ion current densities of ∼45 and ∼20 µA cm−2 for Ar+ ions of 300 and 100 eV, respectively, under the UHV condition of the analysis chamber below ∼4 × 10−6 Pa. The application of the developed UHV‐FLIG to Auger electron spectroscopy (AES) sputter depth profiling of a GaAs/AlAs superlattice material revealed that the ultimate high depth resolution of ∼1.0 nm was achieved by sputter etching using 100 eV Ar+ ions. The present results confirmed that lowering the primary energy of Ar+ ions to 100 eV is still significantly effective for achieving higher depth resolution in sputter depth profiling. Copyright © 2005 John Wiley & Sons, Ltd.

Transport beam line for ultraslow monoenergetic antiprotons

A beam line for the transportation of slow antiprotons from a multiring electrode trap to an experimental chamber is described. The beam line is equipped with a three-stage differential pumping system in order to maintain a pressure lower than 1×10−12 Torr in the trap region while simultaneously having a pressure of around 1×10−6 Torr in the chamber. Tests have shown that 105 positive ions per trapping cycle were successfully extracted at 250 eV from the trap positioned in a superconducting solenoid. The ions were then further transported through three small apertures to the target area located 3.5 m downstream of the trap. Results from the first delivery of a 250 eV antiproton beam are described.

Ion beam charging of silicon nanoparticles in helium background gas: Design of the ion beam aerosol charger

An ion beam aerosol charger that ionizes aerosol nanoparticles of less than 10 nm diameter using an ion beam was designed for use in the electrostatic manipulation of gas-suspended nanoparticles. Pulsed laser ablation of a solid target in a high purity helium gas under pressure of 2–10 Torr (266–1330 Pa) was employed to fabricate nanometer-sized silicon particles. The ion beam, which was generated by cold cathode Penning ionization of He atoms, was accelerated with an energy of 0–5 keV, penetrated a skimmer located within the differential pumping system, and then entered the aerosol ionization chamber. The silicon nanoparticles were both positively and negatively charged by the direct impact of the ion beam or the secondary electrons generated from the surrounding He gas. The change in the concentration of ions and charged aerosols was measured by ion probes. It was found that the concentration of charged particles was drastically increased to 2–50 times that at baseline.

Acceleration characteristics of spherical and nonspherical pellets by the LHD impurity pellet injector

An impurity pellet injector with three differential pumping systems has been developed to study the particle/impurity transport in combination with bremsstrahlung profile measurement in the Large Helical Device (LHD) plasma. For this purpose three different shaped pellets are tested; sphere, hemisphere, and cylinder. The characteristics of the pellets accelerated by pressurized helium gas were studied as a function of shape and mass of the pellets and He gas pressure. The velocity of the pellets was measured at two different positions using a He–Ne laser, two optical fibers, two lenses, and a slit with two narrow apertures. The delay time until the pellet begins to accelerate, and the effect of opening time of the vacuum valves for differential pumping on the amount of He gas leakage were also investigated. The difference in the velocities among the three different shaped pellets is discussed with the simple analytical model.

A differentially pumped electrostatic lens system for photoemission studies in the millibar range

A high pressure photoemission system is described that combines differential pumping with an electrostatic lens system. This approach allows optimized differential pumping without loss of signal, thereby increasing the high-pressure performance by at least 2 orders of magnitude compared to passive differential pumping systems. A general analysis of aperture-based high-pressure photoemission is presented, followed by a description of the prototype system which has operated at pressures up to 7 mbar on a synchrotron beamline. Using this approach, photoemission experiments should be possible up to 100 mbar. Example data are presented for dielectric samples in gas atmospheres, for a copper catalyst under reaction conditions, and for liquid water in equilibrium with its vapor.

Development of a Field Emission VP-SEM and Some Initial Applications

The use of variable pressure SEMs (VP-SEMs) is increasing in various fields of science and industry, allowing microscopy in a variable pressure environment of 1 ∼ 270 Pa utilizing backscattered electrons for imaging. The VP-SEM allows microscopy of insulated samples without the need for sample preparation. Charging artifacts can be minimized as well. When the VP-SEM is operated with a cooling stage, which allows cooling of samples at −20° and above, vaporization of water from samples is reduced. This permits microscopy of wet samples at close to the natural state for extended periods of time.Poor S/N ratio and deterioration of resolution, both of which are due to collisions among residual gas molecules and primary/backscattered electrons, have limited the performance of VP-SEMs. For resolving these limitations, we have completed the development of a new field emission VP-SEM which operates with a stable Schottky field emission source, a new environmental secondary electron detector (ESED), and a multi-stage differential pumping system. Fig. 1 shows a sectional view of the column with the differential pumping system. This design allows stable gun vacuum conditions with variable specimen chamber pressure 10 through 3,000 Pa, permitting a pressure difference from the gun by 1011 Pa without problems.

A differential pumping system for the gas filter of the high flux beamline at SRRC

A gas filter system is designed for the high flux beam line at SRRC to reduce the intensity of the high order contamination to <10 −4. To reach a pressure of <1×10 −8 Torr at the front end and the end station, a differential pumping system is adopted. The differential pumping system contains special vacuum chambers and turbo molecular pumps along the photon beam path. The specially designed vacuum chamber has a larger inner cross section varied from 118 mm×22 mm to 109 mm×42 mm. In order to reduce the extra ordinary large conductance, while keeping the high photon flux, the inner cross section of the chamber is divided into 22 channels which are separated by a 0.3 mm thin wall in between channels. The prototype chambers have been fabricated and tested. The testing results show that the designed goal was achieved. However, the gas pressure in viscous flow was higher than expected. A new chamber is designed for better results. The results of several designs and tests are described and discussed in this paper.

Estimation of minimum power consumption and pumps cost for the differential pumping system

The air-to-air vacuum sealing device is composed of evacuated multi stages and the differential pumping system to maintain the pressure of the deposition chamber at 5×10 −2 Pa. The differential pumping system is adopted to evacuate the deposition chamber with minimum power consumption and pumps cost through the estimation of air flow rate and pressure. The air flow rate of each stage ( Q) and pressure ( P) is calculated accurately in region of viscos flow, viscos slip flow, transient flow, molecular flow based on the experimental results.