Ultrahigh Vacuum Pumping Research Articles

Optimising thermal conductivity of the epoxy using copper as filler particles for improved performance of cryosorption pumps: An experimental investigation

Fusion reactors are one of the best possible solutions to produce sustainable power. In these reactors, by-product helium needs to be continuously removed as they might react with the fuel (tritium) thereby affecting the reaction kinetics. To achieve the same, clean, vibration free and ultra-high vacuum pumps are used which are also unaffected by external electrical and magnetic fields. Considering these limitations, cryosorption pump is the most effective solution. These pumps remove helium molecules by adsorbing them on a cold adsorbent which is maintained at a low temperature by conducting heat from it to a cryopanel via an adhesive. Hence, there is a need for adhesives with high thermal conductivity (T.C.) and optimum bonding strength (B.S.). Towards this, here, we have mixed two different metallic fillers particles namely silver and copper in the epoxy adhesive in different volume fractions. The thermal conductivity and bonding strength of epoxy-silver and epoxy-copper composite adhesives are measured experimentally at the temperatures of 4 K and 7 K, and the latter is found to be the better option. Thus, epoxy-copper adhesive is selected for the development of the cryosorption pump and subsequent measurement of the helium gas pumping speed to achieve the required favourable conditions.

Lumped Ultra-High Vacuum Pumps Based on Non-Evaporable Getters

Lumped Ultra-High Vacuum Pumps Based on Non-Evaporable Getters

The lumped ultra-high vacuum pumps based on non-evaporable getters

The lumped vacuum pumps based on the non-evaporable getters (NEG) have got wide application in accelerator vacuum systems. These pumps are one of the types using for vacuum obtaining in the synchrotron source of 4th generation SFR “SKIF”. In BINP, the NEG prototypes with pumping speed of 300, 600, 900 and 1300 L/s for hydrogen were created and investigated. The pumps construction and test results are presented here.

Development of a large capacity cryopump equipped with a two-stage GM cryocooler

• A 20-inch cryopump including a two-stage GM cryocooler has been developed. • Design methodologies behind the GM cryocooler and cryopump have been addressed. • The cooling capacities of the GM cryocooler exceed 80 W and 8 W at each stage. • The pump captures N 2 with 11,000 L s −1 and endures gas impulse of 2,500 mbar L. • The pump can evacuate down to ultimate pressure of 10 -9 mbar-class. Cryopump, which involves the removal of gas by cryo-sorption, condensation and solidification onto cryo-panels, is an ideal form of ultra-high vacuum (UHV) pump due to its contamination-free operation and black hole pumping speed. The high crossover of the cryopump can provide a clean vacuum environment. Since the cryopump utilizes the cryo-pumping effects mentioned above, a cryogenic environment is a prerequisite condition. In this research paper, a 20-inch cryopump, which is driven by a two-stage Gifford-McMahon (GM) cryocooler, is developed and tested. The GM cryocooler is designed by optimizing the opening timing of the rotary valve, and the corresponding thermal losses at its each stage have been analyzed. Under the thermal loads of 80 W and 8 W at each stage of the GM cryocooler, the temperatures are measured to be 66 K and 19.5 K, respectively. The cryopump is designed with the aspect of heat transfer assessment. The model described in this paper considers two major thermal loads; radiative heat ingress and enthalpy transfer by the existence of the gas. This simple model can readily predict the thermal loads on each stage of the GM cryocooler. Since all the cryo-panels are kept below 130 K during operation, the cryopump that has been developed is therefore compatible with a UHV pump. Using nitrogen gas, the ultimate pressure, pumping speed and crossover are measured to be 9.9 × 10 -9 mbar, 11,000 L s −1 and 2,500 mbar L, respectively. Through the experiments, it is also concluded that the numerical model above can explain the thermal characteristics of the cryopump reasonably well. The cryopump will be able to respond to the market needs of the large-size display and semiconductor manufacturing processes as well as increase its energy saving and process operability. Furthermore, the reliability of the GM cryocooler can also be improved through turndown operations.

Nonevaporable getter-MEMS for generating UHV conditions in small volumina

The industrial use of quantum sensors requires further miniaturization of the experimental peripherals, i.e., the high vacuum chamber, laser technology, and control electronics. A central part of the high vacuum chamber is the maintenance of vacuum conditions. For this purpose, a prototype of a compact, i.e., miniaturized, ultrahigh vacuum pump in the form of a nonevaporable getter (NEG) pump at a wafer level (MEMS), is developed within the scope of this work. With regard to the basic conditions of the functionality of the NEG, a miniaturized heating plate with temperature sensors is analytically and numerically developed, constructed, and characterized in an ultrahigh vacuum test stand. This is followed by the integration of the NEG into the existing system, which, in connection with the characterization of material-specific parameters, enables a first correlation of heat input and pumping power. Thus, performance data of the getter-MEMS under high-vacuum confinement confirm its usability for quantum sensors. In addition, optimization potentials are shown with regard to all partial aspects of the MEMS.

A simple vacuum suitcase for enabling plasma facing component characterization in fusion devices.

We have demonstrated a vacuum suitcase to transport samples in vacuo to a surface analysis station for characterization of tokamak plasma facing components (PFCs). This technique enables surface analysis at powerful, dedicated stations that are not encumbered by design constraints imposed on them by a tokamak. The vacuum suitcase is an alternative solution to characterizing PFCs using diagnostics that are designed and built around a tokamak. The vacuum suitcase, called the Sample Exposure Probe (SEP), features mobile ultra-high vacuum pumping. Active pumping under high vacuum enables sample transfer between the Lithium Tokamak eXperiment-β (LTX-β) and a high resolution X-ray Photoelectron Spectroscopy (XPS) system that is situated close by. A thermocouple inserted in the back of the sample head measures heat flux from the plasma during exposure, and together with a button heater, allows the sample to match the LTX-β PFCs in high temperature operations. As vacuum conditions are better during transfer and analysis than in the tokamak, less contamination is introduced to the samples. XPS scans on a dedicated analysis station enable peak identification due to higher resolution and signal to noise ratio. A similar probe could be implemented for other fusion devices. The SEP is the first vacuum suitcase implementation for fusion applications that incorporates active pumping.

Growing semiconductor structures for high-performance solar cells in open space

Practical space activities of the country in near-Earth space and in deep space have been developing for more than fifty years. During this time, many new scientific and technical problems were solved, the latest technologies were developed and mastered. This article describes the prerequisites for conducting an experiment on growing semiconductor structures for highly efficient solar cells in the conditions of orbital flight of an international space station. The advantages of carrying out the process in a deep vacuum formed as a result of the manifestation of the molecular screen effect are shown to obtain new thin-film materials with unique properties. A ground-based simulator of a space module and a working molecular screen prototype are described. The features of the preliminary design of a universal automated installation of molecular beam epitaxy in space are discussed. The rationale for the economic efficiency of space technology based on the absence of the need for expensive ultrahigh vacuum pumping facilities, cryogenic equipment and vacuum volumes containing a large amount of stainless steel is given. The experience of three orbital flights of the American Shuttle spacecraft is analyzed, confirming the economic feasibility of projects related to the production of semiconductor heterostructures in space flight conditions.

Ultrahigh Vacuum Technologies Developed for a Large Aluminum Accelerator Vacuum System

A large particle accelerator requires an ultrahigh vacuum (UHV) system of average pressure under <TEX>$1{\times}10^{-7}$</TEX> Pa for mitigating the impact of beam scattering from the residual gas molecules. The surface inside the beam ducts should be controlled with an extremely low thermal outgassing rate under <TEX>$1{\times}10^{-9}Pa{\cdot}m^3/(s{\cdot}m^2)$</TEX> for the sake of the insufficient pumping speed. To fulfil the requirements, the aluminum alloys were adopted as the materials of the beam ducts for large accelerator that thanks to the good features of higher thermal conductivity, non-radioactivity, non-magnetism, precise machining capability, et al. To put the aluminum into the large accelerator vacuum systems, several key technologies have been developed will be introduced. The concepts contain the precise computer numerical control (CNC) machining process for the large aluminum ducts and parts in pure alcohol and in an oil-free environment, surface cleaning with ozonized water, stringent welding process control manually or automatically to form a large sector of aluminum ducts, ex-situ baking process to reach UHV and sealed for transportation and installation, UHV pumping with the sputtering ion pumps and the non-evaporable getters (NEG), et al. The developed UHV technologies have been applied to the 3 GeV Taiwan Photon Source (TPS) and revealed good results as the expectation. The problems of leakage encountered during the assembling were most associated with the vacuum baking which result in the consequent trouble shootings and more times of baking. Then the installation of the well-sealed UHV systems is recommended.

Understanding Ion Pump Emissions : Classification, Source Identification and Elimination of Emissions from Ion Pumps

Ion pumps continue to be a staple in ultra-high vacuum (UHV) applications. Since their adoption as a primary UHV pump in the 1960's, it has been known that a variety of particles can emanate from within the ion pump and cause undesirable effects on current measurements and optics components. Historically the solution has been baffling and shielding which results in longer conductance paths to the ion pump. Those solutions can work, but require a larger pump and more vacuum plumbing to compensate for conductance losses. The first step was to fully understand the nature of the particles and their charges. Once those were characterized options for emissions reduction were evaluated. It was determined that an efficient design of shielding near the source of the particle generation site was the most cost effective solution. With a slight modification to the chamber of a small ion pump, internal shielding was developed that reduced the emissions by a factor of up to 1000 times.

Understanding Ion Pump Emissions

Ion pumps continue to be a staple in ultra-high vacuum (UHV) applications. Since their adoption as a primary UHV pump in the 1960's, it has been known that a variety of particles can emanate from within the ion pump and cause undesirable effects on current measurements and optics components. Historically the solution has been baffling and shielding which results in longer conductance paths to the ion pump. Those solutions can work, but require a larger pump and more vacuum plumbing to compensate for conductance losses. The first step was to fully understand the nature of the particles and their charges. Once those were characterized options for emissions reduction were evaluated. It was determined that an efficient design of shielding near the source of the particle generation site was the most cost effective solution. With a slight modification to the chamber of a small ion pump, internal shielding was developed that reduced the emissions by a factor of up to 1000 times. Ionenpumpen Emissionen Seit der standmäßigem Gebrauch von Ionenpumpen in UHV Apparaturen in den 1960er Jahren ist bekannt, dass Partikelemission aus der Pumpe unerwünschte Auswirkungen auf Strommessgeräte und optische Komponenten haben können. Zur Lösung der Problematik kommen Abschirmsysteme und Baffles zum Einsatz, die jedoch die Strömungswiderstände auf dem Weg zur Pumpe erhöhen. Oftmals sind dann größere Pumpen zum Ausgleich der Leitwertverluste erforderlich. Zur Entwicklung eines alternativen Lösungsansatzes wurden zunächst alle von der Pumpe freigesetzten Teilchenarten und ihre Ladungen untersucht. Verschiedene Möglichkeiten zur Unterdrückung des Teilchenflusses in Richtung Vakuumkammer wurden erarbeitet. Die kostengünstigste Methode ist eine Abschirmung des Teilchenflusses in räumlicher Nähe zum Ort der Partikelfreisetzung. Mit geringfügigen Veränderungen am Kammersystem einer kleinen Ionenpumpe konnte eine interne Abschirmung entwickelt werden und die Partikelemission bis zu einem Faktor von 1000 reduziert werden.

Study of Hydrogen Pumping through Condensed Argon in Cryogenic pump

In ultra high vacuum (UHV) range, hydrogen is a dominant residual gas in vacuum chamber. Hydrogen, being light gas, pumping of hydrogen in this vacuum range is limited with widely used UHV pumps, viz. turbo molecular pump and cryogenic pump. Pre condensed argon layers in cryogenic pump create porous structure on the surface of the pump, which traps hydrogen gas at a temperature less than 20° K. Additional argon gas injection in the cryogenic pump, at lowest temperature, generates multiple layers of condensed argon as a porous frost with 10 to 100 A° diameters pores, which increase the pumping capacity of hydrogen gas. This pumping mechanism of hydrogen is more effective, to pump more hydrogen gas in UHV range applicable in accelerator, space simulation etc. and where hydrogen is used as fuel gas like tokamak. For this experiment, the cryogenic pump with a closed loop refrigerator using helium gas is used to produce the minimum cryogenic temperature as ~ 14° K. In this paper, effect of cryosorption of hydrogen is presented with different levels of argon gas and hydrogen gas in cryogenic pump chamber.

Surface Photocatalysis-TPD Spectrometer for Photochemical Kinetics

A surface photocatalysis-TPD apparatus devoted to studying kinetics and mechanism of photocatalytic processes with various signal crystal surfaces has been constructed. Extremely high vacuum (∼0.2 nPa) in the ionization region is obtained by using multiple ultrahigh vacuum pumps. Compared with similar instruments built previously by others, the H2, CH4 background in the ionization region can be reduced by about two orders of magnitude, and other residual gases in the ionization region can be reduced by about an order of magnitude. Therefore, the signal-to-noise ratio for the temperature programmed desorption (TPD) and time of flight (TOF) spectra is substantially enhanced, making experimental studies of photocatalytic processes on surfaces much easier. In this work, we describe the new apparatus in detail and present some preliminary studies on the photo-induced oxygen vacancy defects on TiO2(110) at 266 nm by using the TPD and TOF methods. Preliminary results suggest that the apparatus is a powerful tool for studying kinetics and mechanism of photochemical processes.

NSLS-II Project and Its Vacuum System Design

National Synchrotron Light Source II (NSLS-II) is a 3-GeV, 792-meter circumference, 3rd generation synchrotron radiation facility being constructed at Brookhaven National Laboratory. It will replace the existing NSLS, a three-decade old, 2nd-generation light source. To deliver photon beams with <1 nm spatial resolution and 0.1 meV energy resolution for the users, NSLS-II will have extremely high brightness, flux and stability; and ultra low emittance of ≤1 nm-rad. The design of the storage ring and the vacuum systems will be presented, with emphasis on beam vacuum chamber design, fabrication, ultrahigh vacuum pumping arrangement, photon beam tracking, absorber positioning and pressure profiles.

A new fully automated gas flowmeter at the PTBfor flow rates between 10-13 mol/s and 10-6 mol/s

For applications in vacuum metrology, gas flowmeters have to deliver pure gas flows with well-knownmolar flow rates of low (< 10-6 mol/s) and very low values. Accurate flowmeters are used to generate pressures in continuous expansion systems, to measure leak rates, and to measure pumping speeds of ultrahigh-vacuum pumps. At the Physikalisch-Technische Bundesanstalt (PTB) a new, fully automated, all-metal flowmeter was commissioned for use with a continuous expansion system in the pressure range 10-10 Pa to 3 × 10-2 Pa. It delivers gas flows with molar flow rates between 4 × 10-13 mol/s and 10-6 mol/s (throughputs 10-6 Pa l/s to 3 Pa l/s at 23 °C) withrelative standard uncertainties ranging from 1.45% at 4 × 10-13 mol/s down to 0.14% at 10-6 mol/s.

Research into Vacuum and Dynamic Characteristics of Cryopanels for Fusion Reactor Ultra-High Vacuum Pumps

ABSTRACTThe present article is devoted to investigation of cryogenic pumping assembly developed at Russian Federal Nuclear Center (VNIIEF). The main scheme of facility is given, where KH-50M pump is a principle unit. The research concerns the pumping speed for the cryopanel cooled to ∼5K, dependent on gas load. The coolant consumption for the selected model of pump is determined.

New low background crossed molecular beam apparatus: Low background detection of H2

A low background and almost hydrocarbon free (∼1×10−14 Torr) molecular beam apparatus with an improved universal detector, based on electron bombardment ionization, has been constructed for crossed molecular beam research. Extremely high vacuum (∼1×10−12 Torr) for the detector’s ionization region is achieved using multiple ultrahigh vacuum pumps. In addition to a home-made liquid nitrogen cryopump and a turbomolecular pump, a two stage cryogenic He cold head (∼10 K) is used to pump the detector’s ionization region. Using this arrangement, the H2 background in the detector can be reduced by about two orders of magnitude in comparison with previously built similar instruments. Therefore, the signal-to-noise for detecting H2 product detection sensitivity is substantially enhanced, making experimental studies of H2 elimination channels in photodissociation processes much easier. Backgrounds at m/e=28 (CO+), 16 (CH4+,O+), 15 (CH3+), 14 (CH2+), and 13 (CH+) in the ionization detection region are also significantly reduced. In this article, we will describe the new apparatus in detail and present some preliminary results of the unimolecular decomposition studies of CH3OH at 157 nm excitation to demonstrate the capabilities of low background detection H2 using this new instrument.

Achieving ultra high vacua: pumps and pumping systems

During the several decades of ultra high vacuum history many changes have occurred both in technology and users' needs, and even the meaning of ‘ultra high vacuum’ has somehow evolved. The focus has moved from achieving the lowest pressure, when the only gas load is wall outgassing (static vacuum), to obtaining low contamination and high purity with a flow of process gas (dynamic vacuum). The dream of a universal pump seems now less realistic, as the use of the different vacuum pumping techniques is more clearly defined for each application. This is valid also for the ion getter pumps, the traditional ultra high vacuum pump, which in most cases is used in combination with other pumps in the design of systems. Many attempts have been made in the past to improve the performance of the ion getter pumps at higher pressure, with limited success. Relatively little attention has been paid to the performance improvement at lower pressure. Some of the factors which cause pumping speed to decay at low pressure are analysed, and a possible configuration is proposed. Experimental results are then illustrated.

Apparatus for the measurement of the optical constants and thermal radiative properties of pure liquid metals from 0.4 to 10 μm

Measurements of the optical constants and thermal radiative properties of high-temperature solid tungsten and molten aluminum have been made using a new instrument that includes two independent optical systems and surface control and analysis capability. The two optical systems, one for measuring the complex index of refraction by ellipsometry, the other for measuring the normal spectral emissivity by direct comparison to an integral blackbody cavity, operate over the wavelength range 0.4–10 μm with sample temperatures between 940 and 1630 K. The surface science capabilities of the instrument permit the preparation of high-purity samples of known composition in situ. The apparatus includes two 5-keV argon-ion sputter guns, an ultrahigh vacuum pumping system, and an Auger spectrometer. The two sputter guns allow surface cleaning to occur while optical measurements are being made, or while Auger spectroscopy is determining the surface composition of solid or liquid samples. The ellipsometric optical system uses a novel radiation source (a carbon composite element), refractive optics (calcium fluoride), interference filters for spectral selection, and both calcite and wire grid polarizers to cover the extended wavelength range. The system for measuring the normal spectral emissivity uses reflective optics and an integral blackbody cavity that is located in the wall of the crucible holding the liquid sample. The use of two measurement techniques gives independent determinations of the normal spectral emissivity and thus allows reliable estimation of experimental errors.

Argon isotope analysis by a newly developed mass spectrometric system for K-Ar dating.

A new mass spectrometer and the associated analytical systems, called HIRU, was designed and constructed for the argon isotope analysis of minerals from young volcanic rocks as well as metamorphics and granitoids. HIRU is composed of a sample holder, an extraction oven, purification lines, standard gas lines, a mass spectrometer, and an ultra high vacuum pumping system. All the parts, except for the sample holder, were made of stainless steel and connected with ICF flanges using Cu gaskets or ultra high vacuum metal valves. The mass spectrometer is a 15cm sector type with an oblique incidence-single focusing system using an electron bombard ion source and three collectors which contain 8 (for 36Ar), 6 (38Ar) and 4 (40Ar) stage secondary electron multipliers respectively.Argon isotope analysis by HIRU is summarized and the precision and reliability of the new mass spectrometric system are discussed in this paper. A series of analysis for argon isotopes, such as taking a set of spectrum, the calculation of isotopic ratios, argon content, and ages is carried out with a computer-controlled system. HIRU has mde it possible to date geological materials with high sensitivity (eg. tens mg of mica of Cretaceous age), high precision (ca. 1% of error for argon content), reliability (possible for rocks older than 0.1 Ma), and convenience (eg. 5–6 samples can be dated per day).

MBE Growth of Mercury Cadmium Telluride: Issues and Practical Solutions

ABSTRACTThe growth of thin films of mercury-based materials by molecular beam epitaxy (MBE) presents significant experimental problems which must be overcome in order to successfully grow infrared detector materials such as mercury cadmium telluride (MCT). Many of the problems associated with the use of Hg in MBE arise from its high room temperature vapor pressure (2 mTorr) and its low sticking coefficient. The MBE system must be designed for Hg usage by considering such things as the ultra high vacuum pumping system, the Hg source, Hg containment, and Hg removal. In addition, Hg is a toxic heavy metal and must be handled appropriately. Other problems involved with the growth of MCT are associated with the design of the MBE furnaces which are used to evaporate cadmium telluride and tellurium.