Design of a new UHV all-metal joint for CLIC

All-metal joints are widely used in the vacuum systems of particle accelerators. The most common ConFlat^® design consists of a flat soft copper gasket captured between two stainless steel flanges with sharp edges (knives). The gasket is plastically deformed and a high contact pressure develops around knives to obtain leak tightness. For large accelerators, a high reliability and a cost-optimized design are required. A smooth internal transition between flanges is needed for the RF waveguides of the compact linear collider (CLIC), with limited deformation of the inner part of the gasket. We present the study of a flange meeting these requirements. First the finite element analysis (FEA) of the Stanford linear accelerator center (SLAC) X-band all-metal joint, which has a similar specification, is shown. Some drawbacks, such as non-homogeneous sealing properties, are highlighted. Then, a new joint design is described. FEA results are presented and are compared with experimental measurements carried out on prototypes.     

Comparison of new PEEK seals with traditional helicoflex for ultra high vacuum applications

The use of engineering resins has increased dramatically in the last years and now the mechanical and chemical properties of the most recent products render these new materials excellent candidates for ultra high vacuum (UHV) applications. In particular, a relatively inexpensive polymer like PEEK^® can become competitive when vacuum seals have to be manufactured. In this paper, a systematic series of tests is described, aimed at comparing the properties of PEEK^® and traditional Helicoflex seals. Two different designs for the new PEEK^® seals were tested. Their performances were compared not only in cases of metal but also of glass plain surfaces. A complete temperature scan was carried out for both applications (metal and glass surfaces) up to 200°C. At room temperature the vacuum properties of PEEK^® seals are comparable to those of the more traditional Helicoflex gaskets. At higher temperatures the only significant drawback of the proposed PEEK^® prototypes is a significant He permeation. On the other hand, gaschromatographic-mass spectrometer analysis confirms that the outgassing of this material is compatible with UHV requirements. In the temperature range investigated, one of the tested solutions gives very positive results; given the lower cost and much easier handling of this prototype with respect to Helicoflex technology, the proposed design can be considered with great attention as a possible future replacement.     

Aufbau und Eigenschaften verschiedener ölfreier Vakuumpumpen für den Grob- und Feinvakuumbereich

The development of high vacuum pumps and systems during the last 35 years can be characterized by a trend of gradual elimination of liquids exposed to vacuum environment. The need for high purity vacuum process equipment precipitated the development of new pumping techniques: iongettering pumps, turbomolecular pumps and cryopumps. During the last 5 years, a number of dry coarse-vacuum pumps have been developed. Some are entirely oilfree, some still use lubricants at the seals separating the driving mechanism from the vacuum side. This review contains general design and performance characteristics of four classes of equipment: hermetically sealed pumps using bellows to isolate the driving mechanism, a variety of multistaged positive displacement blowers, pumping trains based on turbo-drag pumps, and multistaged reciprocal piston pumps. It is entirely practical to achieve pressure of 10⁵ to 10⁶ while discharging to atmosphere. Despite a complete absence of conventional lubrication in some of these pumps, periods exceeding 10000 hours without maintenance are obtained, providing a viable technology for clean vacuum systems.     

Prüfung von Flanschverbindungen in GFK-Rohrleitungen NW 200 durch Kurz- und Langzeitbeanspruchung – Teil I: Dichtverhalten

Testing of flanged joints in GRP pipelines of 200 mm nominal diameter by means of short-term and long-term stressing. Part I: Sealing behaviour . The first part of this report deals with the sealing behaviour of joints with fixed and loose flanges in GRP pipelines of 200 mm nominal diameter. Tests were made with seven different flanges from three manufacturers and four different types of sealing rings. At room temperature the spring rate of the GRP flanges amounted to between 8% and 18% of that of welded steel flanges and at a temperature of 80°C within the pipe it was 5% to 16% of that of the steel flanges. Of the sealing rings tested a bulged soft rubber ring with steel reinforcement was found to have the flattest resilience characteristic and required the least bolt force to produce a tight joint under operational conditions. Its relaxation rate was low after low bolt force had been applied and increased rapidly when the initial bolt force was increased to higher values. Because of their lower spring rates, the GRP flanges sealed with this ring required 2.5 to 3.5 times as much initial bolt force as welded steel flanges. In an 1100-hour creep test at 80°C internal temperature and 10 bar internal pressure, a joint consisting of loose steel flanges and GRP shoulders exhibited considerably less loss of initial force than a fixed GRP flanged joint. Because losses of initial force increase at a disproportionately high rate as the force is raised, high initial force would not seem to increase remarkably the reliability of the seal in the long term. Since rigid flanges require less initial force than less rigid ones, high spring rate appears desirable. Apparently it could best be achieved by loose steel flanges with GRP shoulders. The results of the strength tests will be presented in the second part of this report.     

Development of copper beam ducts with antechambers for advanced high-current particle storage rings

There has been continuous progress at the High Energy Accelerator Research Organization (KEK) in R&D on vacuum beam ducts adaptable to future high-current particle storage rings. Here we proposed copper beam ducts with antechambers to deal with the severe issues attributed to the high beam currents. The proposed antechamber scheme can withstand intense synchrotron radiation (SR), provide a beam duct with low beam impedance, and effectively reduce the electron cloud effect (ECE) in positron/proton rings. Several trial models were manufactured by a pressing or cold-drawn method, and assembled with electron beam welding. Special vacuum components, such as connection flanges, distributed pumps, and gate valves, were customized for the beam ducts. TiN coating on the inner surface of the beam duct was also investigated as a mitigating measure for the ECE. Trial models of the copper beam ducts were installed into the KEK B-factory (KEKB), and their performances were evaluated using real positron and electron beams.     

Mass spectrometric studies of material evolution from magnetic liquid seals

Evolution of ferrofluid contained in two vacuum rotary feedthroughs is studied for the first time by a time-of-flight mass spectrometer in order to provide information on the background material these seals introduce into a high-vacuum system. The seals used diester and poly(phenyl ether) based ferrofluids. The rate of evolution of the diester was found to be of the order of 3 × 10^?10 g s^?1 that of the poly(phenyl ether) was below the detection limit of the mass spectrometer, i.e., 10^?10 g s^?1. The oxygen and water evolution rates, which are generally of prime interest in vacuum application, were found to be 10^?9 g s^?1 for both seals at 3000 rpm. The feedthroughs were successfully employed in precision abrasion mass spectrometric experiments.     

Application of magnetofluid seals for high-speed rotating cryostats

A practical application of the magnetofluid seals in a rotating cryostat is described. These seals ensure both the sealing of the cold shaft going through several series-connected chambers operating under various pressures (up to 10^?3 Pa), and the coolant evacuation out of the test section. The peculiarities of their operation at high rotational velocities (ω = 10–40 ms^?1) low temperatures and high vacuum are shown.     

Vakuum‐Lineardurchführungen mit Magnetflüssigkeitsdichtungen

Vacuum linear feedthroughs with magnetic fluid seal A magnetic fluid sealed feedthrough is a device that transmits linear motion into a vacuum chamber with minimal frictional resistances and minimal contamination level.They are widely employed in high and ultra‐high vacuum equipment among others in semiconductor fabrication industry and robotics applications. The operating conditions of magnetic fluid seals during reciprocating motion are so different from those with rotating motion that the use of their conventional structures for reciprocating motion seals yield no good results. Analysis of sealing mechanism of magnetic fluid seal in reciprocating motion shows that the operation of these seals is affected by the carry‐over and the magnetic fluid deformation in the sealing gap, which depends on the velocity of reciprocating motion. The reduction of magnetic fluid quantity in the sealing gap,caused by the reciprocating motion of the shaft is reason of the seal failure. In the paper a short characteristic of magnetic fluid sealing technology , principle of sealing, behaviour of the ferrofluid and seal failure mechanism in the linear motion of the shaft are given. Moreover some new structure designs of vacuum linear feedthroughs with magnetic fluid seals, which have practical application value are presented.     

Hyperfine interactions in graphene and related carbon nanostructures

Hyperfine interactions, magnetic interactions between the spins of electrons and nuclei, in graphene and related carbon nanostructures are studied. By using a combination of accurate first principles calculations on graphene fragments and statistical analysis, I show that both isotropic and dipolar hyperfine interactions in sp2 carbon nanostructures can be accurately described in terms of the local electron spin distribution and atomic structure. A complete set of parameters describing the hyperfine interactions of 13C and other nuclear spins at substitution impurities and edge terminations is determined. These results permit the design of graphene-based nanostructures allowing for longer electron spin coherence times which are required by spintronics and quantum information processing applications. Practical recipes for minimizing hyperfine interactions in carbon nanostructures are given.     

Finite Element Analysis of Sealing Performance of Rubber D-Ring Seal in High-Pressure Hydrogen Storage Vessel

Sealing structures of high-pressure hydrogen storage vessel are always considered as one of the significant components. This paper aims to study the sealing performance of the combined sealing structure composed of a rubber D-ring and a wedge-ring used in high-pressure hydrogen storage vessel by elucidating the swelling mechanisms due to dissolved hydrogen. Comparisons of the sealing performance between the D-ring and the O-ring are made in terms of the effects of some important factors including the wedge-ring, hydrogen pressure and swelling. Three aspects of conclusions are obtained by FEA: (1) The wedge-ring with a wedge angle 45° is the most suitable, compared with the angles 30° and 60°, irrespective of the shape of rubber rings. (2) The peak contact stress for the D-ring seal is larger than that for the O-ring seal under hydrogen pressure range 0–100 MPa. (3) The O-ring seal could be replaced well by the D-ring seal, whereas the design height of the seal groove should be larger for the D-ring seal than for the O-ring seal due to swelling effect, in order to prevent the D-ring seal from extrusion through the upper side of the seal groove.     

Cold leak tests of LHC beam screens

In order to guide the high energy proton beams inside its two 27 km long vacuum rings, the Large Hadron Collider (LHC) at CERN, Geneva, makes use of superconducting technology to create the required magnetic fields. More than 4000 beam screens, cooled at 7-20 K, are inserted inside the 1.9 K beam vacuum tubes to intercept beam-induced heat loads and to provide dynamic vacuum stability. As extremely high helium leak tightness is required, all beam screens have been leak tested under cold conditions in a dedicated test stand prior to their installation. After describing the beam screen design and its functions, this report focuses on the cold leak test sequence and discusses the results.     

Fire Sprinkler Heads, Design, and Failure

Sprinkler heads are a mature product that can fail to function via a variety of different mechanisms. Mechanical damage and corrosion can occur year round. Additionally, there can be seasonal failures due to creep of fusible alloys in summer. Serious problems also have occurred due to sticking of sliding O-ring seals. These problems have lead to product recalls, and subsequent revisions in design standards.     

Wire-free constructions in suction hoses

Rubber Suction/Delivery hoses can be made without the use of the traditional steel helix; using instead a sandwich of rubber between two layers of synthetic macrofilament yarn, arranged circumferentially in the hose body. This construction resists vacuum and pressure, recovers rapidly after crushing, may be cut to length as required and fitted with re-usable flanges. These advantages make for great facility of hose supply and economy in the handling of abrasive solids and slurries.     

Ein Neues Schnellverbindungs-System

A fast coupling system for high vacuum is described. The coupling is based on a link-chain system with conical connectors and conical throwover flanges. A table, based on the Pneurop-Norm, presents the data for flanges and chains in the range from 50 to 500 mm nominal bore-dimensions. All parts are fully compatible to the Pneurop-Norm. A calculation of the chain forces and a large number of test results are given. The final part of the article shows a remote operated coupling and a fast bellow joined. The system is successfully used in the 160 m vacuum-beam line of the Swiss Institute for Nuclear Research.     

The pressure profile in a long outgassing vacuum tube

As a simple extension of the long tube formula, an analysis is given whereby the pressure profile may be determined along a uniformly outgassing pipe pumped at both ends. The theoretical analysis is extended to include nonuniform outgassing situations such as occur in particle storage rings. These findings are used to determine the optimum vacuum system configuration for various vacuum system parameters, while affording minimum vacuum system cost. Calculations were checked experimentally using a stainless steel tubing with a 5.7 cm inside diameter, and a length of ～50 m.     

Miniature Kinematic Mirror Mount for UHV Service

A miniature kinematic mount allows adjustment of mirror pointing inside ultrahigh vacuum (UHV) by rotating finely threaded screws outside of vacuum. The mount assembly is less than 0.620 in. in diameter, so it fits through the standard tubing used with miniature conflat flanges. The mount is a point-iine-plane device with a sapphire ball at the point position, so that no lubrication is required in vacuum.     

Investigation of the resistance welding of multilayers aluminum-coated polymer complexes used as envelopes of vacuum insulation panels

Vacuum Insulation Panels (VIPs) are thermal insulators consisting of a core material enveloped by a high barrier film or envelope required to maintain the vacuum.Multilayered aluminum-coated polymer complex are the common barrier envelopes of VIPs used as high performance thermal insulation in building applications. The multilayer complex is sealed to maintain the vacuum for a long period of time. From a mechanical and barrier properties standpoint, sealed edges represent the weak point of the envelope assembly. This paper investigates the influence of sealing parameters on the properties of the weld. T-peel and tensile tests in combination with Optic Microscopy observations were used to characterize the heat seals. A minimum seal initiation temperature of 115 °C was identified for the studied complex. Peel strength increased sharply to reaching a maximum value at (140 °C–5 s), which considered as optimum temperature–time couple. Above and beyond these values, a gradual decrease was observed and microscopic images indicate the appearance of roll generated by the expelled polymer mass from the center to the edges of the weld which strongly impacts the morphology of the welded area.     

Modelling of cohesion and adhesion damage of seal based on dynamic shear rheometer testing

Most current seal designs are based on the volumetric properties of materials and voids. In order to improve seal design, the possibility of introducing mechanistic principles into seal design was investigated. Introducing mechanistic concepts into seal design means that principles such as elasticity and viscoelasticity could be used in terms of stress-strain to explain phenomena such as damage in the seal structure. Two main failure parameters of seals – cohesion failure (fatigue cracking due to ageing of binder and loss of elasticity) and adhesion failure or stripping (occurring between stone to bitumen or bitumen to base) – are investigated using the complex modulus (G ^*) which is one of the viscoelastic parameters of bituminous materials. This paper therefore investigates the testing procedure of cohesion fatigue damage (CFD) and Adhesion Fatigue Damage (AFD) of bituminous seal material using the Dynamic Shear Rheometer (DSR). The CFD and AFD modelling are based on the stiffness reduction principle of materials under the action of cyclic stress. Based on the Lifetime Optimisation Tool (LOT) research programme from Delft University of Technology, a DSR testing procedure and approach was adopted for seals. The tests were performed on 70/100 penetration grade bitumen columns (for CFD) and on stone columns constituted with dolorite glued together with 70/100 penetration grade bitumen (for AFD). It was observed that the model for CFD depends more on stress, while the model for AFD appears to depend more on temperature. This observation agrees with the fact that adhesion damage is more sensitive to temperature change, whereas cohesion damage is more prone to be influenced by applied fatigue stress. The CFD and AFD models provide an indication of non-linear development of the accumulated fatigue damage of seal. This is represented by the modelling of the change of G ^*, as suggested in this investigation.     

Vakuumkomponenten für UHV und XHV aus Aluminium

Vacuum components of aluminum for UHV and XHV — weldability and outgassing behavior It has been shown that present‐day aluminum alloys possess sufficient stability to produce aluminum CF flanges for multiple tightening cycles. In order to preserve the mechanical strength it is vitally important that the critical limiting temperature of the materials is not exceeded both during the production process and later in the application. Reproducible welding parameters guarantee vacuum tight welding seams with neat root formation. It could be verified experimentally that critical temperatures in the knife edge area will not be exceeded in case of design according to material properties and special welding parameters. Comparative measurements of identically designed vacuum chambers of stainless steel and aluminum proved that UVH conditions can be achieved much faster and with less energy input (lower bakeout temperature) with aluminum than with stainless steel.     

Slippery seals combat friction

Stiction is a major cause of lost power and energy in systems with moving parts such as electric motors. In this article Blue Diamond, discusses the benefits of treating O-ring and rotary shaft seals with its SSHT non-stick process, which can dramatically reduce friction losses.