Residual gas analysis in the TOF vacuum system

The residual gas composition in the time-of-flight (TOF) spectrometer vacuum system has been measured with a quadrupole mass spectrometer. All residual gases except hydrogen and helium are condensed and freezed on the windows of the liquid hydrogen target. As a result it increases the background during the reaction between the cooler synchrotron (COSY) beam and the target. These condensates have to be cleaned from the target windows by fast heating the target cell from 16 K up to room temperature. The partial pressure spectrums of the condensed gases on the liquid hydrogen target are also measured. The residual gas analysis shows that the majority of the condensates on the target windows are nitrogen, oxygen and water vapor. The target area has to be in a high vacuum <1×10⁻⁶ mbar in order to minimize the condensate. The target windows have to be cleaned with the fast heating cycle every 48 h.     

Industrialisation of the insulation vacuum barrier for the large hadron collider (LHC) magnet cryostats

The insulation vacuum (<10⁻⁴ Pa) of the large hadron collider magnet cryostats, thermally protecting the superconducting magnets which operate at 1.9 K in superfluid helium, is divided in to 214 m long segments separated by means of insulation vacuum barriers.The insulation vacuum barrier is a leak-tight stainless steel welded structure, composed of two concentric corrugated cylinders and one internal bellows linked together by a 6 mm thick central plate. As the vacuum barrier mechanically links the cryostat vacuum vessel operating at ambient temperature and the 1.9 K superconducting magnets, it is designed to have minimum heat conductivity. Conduction heat in-leak is intercepted at 65 K by a high-purity copper ring brazed onto the stainless steel central plate and thermally linked to a cryogenic line by a copper-aluminium soldering. The thermal performance has been experimentally validated by cryogenic testing.This paper presents the results obtained after industrialisation, manufacture and testing of prototypes and series units. Qualification of leak-tight welds in thin-sheet stainless steel (thickness 0.15-1.3 mm) has been carried out. Ultrasonic testing is performed on all brazing and soldering. Helium leak testing is performed, using dedicated tooling, to ensure a leak-tightness to a rate better than 10⁻⁹ Pa m³ s⁻¹.     

He leaks in the CERN LHC beam vacuum chambers operating at cryogenic temperatures

The 27 km long large hadron collider (LHC), currently under construction at CERN, will collide protons beam at 14 TeV in the centre of mass. In the 8 arcs, the superconducting dipoles and quadrupoles of the FODO cells operate with superfluid He at 1.9 K. In the 8 long straight sections, the cold bores of the superconducting magnets are held at 1.9 or 4.5 K. Thus, in the LHC, ∼75% of the beam tube vacuum chamber is cooled with He.In many areas of the machine, He leaks could appear in the beam tube. At cryogenic temperature, the gas condenses onto the cold bores or beam screens, and interacts with the circulating beam. He leaks creates a He front propagating along the vacuum chambers, which might cause magnet quench.We discuss the consequences of He leaks, the possible means of detections, the strategies to localise them and the methods to measure their size.     

Development of an ultra-high vacuum system for space application

The aim of this paper is to present the development of a very specific ultra-high vacuum system for the space application PHARAO. In order to reach the specified pressure (2.6×10⁻⁸ Pa) during 3 years in a self-contained system, specific solutions have been developed. A calculation of partial pressures of different chemical species (typically hydrogen, rare gases and cesium) in the different areas of the vacuum tube has been computed. Experiments have been also performed in order to verify the possibility of using different kind of materials (outgassing rates of bulk and porous titanium, silicon carbide reinforced aluminum, graphite, etc.) and pumping systems such as getters and a specially developed ion pump.     

A new cleaning facility for particle-free UHV-components

A new cleaning facility has been installed at Deutsches Elektronen-Synchrotron DESY in Hamburg to prepare UHV components hydrocarbon and particle free. Both requirements are important for accelerators using superconducting accelerating structures with high gradients as well as for optical components like mirrors used for the transport of intense photon beams in synchrotron radiation beamlines.The goal of this facility is to combine standard cleaning techniques with latest clean room technology in a manageable way. Thus the new cleaning facility is installed in a clean room which fulfils class 10,000 and in its central part class 100 specifications.¹ The cleaning process following the standard UHV cleaning steps consists of a fine degreasing of the components in an ultrasonic bath. For rinsing ultra pure water² is used. Finally the components are dried using up to 110°C hot filtered air (according to clean room class 100 requirements). Comparable cleaning results for small components are achieved using a dishwasher, which is loaded from outside the clean room. Vacuum chambers of up to 4.8 m length can be treated.A small preassembly area equipped with an oil free pumping station for leak detection and residual gas analysis completes the facility.     

Performance of a cryogenic vacuum system (COLDEX) with an LHC type beam

The cold bore experiment installed in the super proton synchrotron has been used to study the performance of a vacuum system operating at cryogenic temperatures in the presence of a large hadron collider (LHC) type proton beam. The ∼2 m long cryostat, which can be cooled below 3 K, is fitted with an actively cooled beam screen which can be temperature controlled between 5 and 100 K. Molecular desorption and deposited heat load measurements, with or without gas pre-condensation, have been performed. Implications to the LHC design and operation will be discussed.     

Design of the vacuum system for Diamond, the UK third generation light source

The Diamond synchrotron, which is due to come into operation with beam for users in 2007, is being constructed at the Rutherford Appleton Laboratory, Oxford. The design status of the vacuum system of the storage ring as at 31st December 2002 will be reported.Diamond is based on a 24 cell 3 GeV electron storage ring of 561.6 m circumference. As is the case for most such machines, the operational pressure has been specified as 10⁻⁹ mbar to give a beam lifetime >10 h at the design current of 300 mA. The storage ring vacuum system will use conventional technology and most of the vacuum vessels will be constructed of stainless steel. With the exception of the insertion device (ID) vacuum chambers, the ring has not been designed to be baked in situ, but all components will be vacuum baked as sub assemblies before installation. The vacuum system is designed to achieve the required pressure after 100 A h of beam conditioning using the pumping scheme, which will be described.Twenty-one ID straights are available for ID, of which seven will be installed at the start of operations. Three types of vacuum vessel will be used in these straights, a stainless-steel make-up pipe, a NEG coated narrow-gap vacuum chamber for conventional IDs and a wider vacuum chamber to house in vacua IDs. The ID straights have an isolation valve installed at each end, and in situ baking can be used in these restricted locations, for example to activate the NEG coatings.The vacuum system for the beam line front ends has been designed to provide good vacuum isolation between the storage ring and the experimental beam lines, whether or not an interposing window is fitted.Pumping schemes, pressure measurement and calculated pressure profiles will be described.     

Molecular pumping properties of the LHC arc beam pipe and effective secondary electron emission from Cu surface with artificial roughness

A simplified 2D method of angular coefficients is applied to calculations of the molecular pumping properties of complex vacuum systems. An optimization of geometry for the cold LHC beam vacuum chamber with electron shields is performed.An additional interesting application of the angular coefficients method is the estimation of the effective secondary electron emission from surface with artificial roughness. This method allows to take into account re-reflection of electrons using experimental data of the secondary electron energy distributions and surface reflectivity. The suppression efficiency of the secondary electron emission from Cu as a function of roughness parameter is presented. This result is a good input for designing future accelerators and storage rings with potential electron-cloud problems.     

Vacuum performance of a beam screen with charcoal for the LHC long straight sections

The vacuum chamber inside the cryogenic magnets in the LHC Long Straight Sections will have a beam screen at a temperature between 5 and 20 K to protect the cold bore against the synchrotron radiation, electron and ion exposure. The desorbed molecules of H₂ will leave the inner part of the beam screen through the pumping slots on the beam screen and eventually condense on the cryosorber, which is mounted on the shadowed (outer) part of the beam screen for magnets operating at 4.5 K. The design of the experimental set-up, the results of the adsorption capacity measurements for charcoal, the pumping speed and the capture factor of the beam screen with charcoal for a proposed LHC vacuum chamber configuration are described in this paper.     

Materials and processing of vacuum components for the high-intensity proton beam accelerator, J-PARC

The Japan Proton Accelerator Research Complex (J-PARC) project of the proton beam accelerator, involving a 400-MeV linac, a 3-GeV rapid-cycling synchrotron and a 50-GeV synchrotron, started in 2002. Materials used as vacuum components, such as electroformed copper, titanium, stainless steel and alumina ceramics, were examined from the point of view outgassing and electrical breakdown. The mechanical characteristics of a hydro-formed titanium bellows and a quick-disconnect flange system were also investigated.     

A thin gold coated hydrogen heat pipe-cryogenic target for external experiments at COSY

A gravity assisted Gold coated heat pipe (GCHP) with 5-mm diameter has been developed and tested to cool a liquid hydrogen target for external beam experiments at COSY. The need for a narrow target diameter leads us to study the effect of reducing the heat pipe diameter to 5 mm instead of 7 mm, to study the effect of coating the external surface of the heat pipe by a shiny gold layer (to decrease the radiation heat load), and to study the effect of using the heat pipe without using 20 layers of‘ super-insulation around it (aluminized Mylar foil) to keep the target diameter as small as possible. The developed gold coated heat pipe was tested with 20 layers of super-insulation (WI) and without super-insulation (WOI). The operating characteristics for both conditions were compared to show the advantages and disadvantages.     

FRP Dewar for measurements in high pulsed magnetic fields

We describe a liquid helium glass-fibre reinforced plastic (G-FRP) Dewar which we designed, fabricated and tested for excitation spectrum measurements in high pulsed magnetic fields of up to 50 T. The sensitivity of high-resolution magnetic measurements carried out at low temperatures in such high fields is limited inevitably by magnetic and electric properties of the structural Dewar materials involved. Magnetic properties of various G-FRP Dewar-purpose materials are explored with a χ-meter furnished with a RF SQUID magnetometer. The Dewar materials and multilayer insulation effects contributing to the magnetic response signal are analyzed. It has also been discovered that field noise caused by the magnetization of the Dewar materials can be suppressed substantially by using special glass-epoxy technologies. The liquid helium evaporation rate is 3.8 l/day while the hold time is 27 h, the influencing factors are discussed.     

Cooling Capabilities of Adiabatic Demagnetization Refrigerators

The development of adiabatic demagnetization refrigerators (ADR) over the last decade has resulted in significant improvements in performance and ease of use, including continuous operation, relatively high cooling power (30–35 μW at 100 mK), and cryogen-free operation. ADR systems are small, efficient, and require no auxiliary pumps or gas-handling systems. Consequently they are compact, convenient, low-cost options for ground-based research and instrument development. This paper presents an assessment of state-of-the-art ADRs in terms of temperature and cooling power capabilities, with emphasis on their applicability to quantum fluids and solids research.     

Vacuum-system design for the large-scale cryogenic gravitational wave telescope

The large-scale cryogenic gravitational wave telescope (LCGT) requires ultra-high vacuum tubes which the laser beams pass through. Two 3-km vacuum tubes are kept in ∼10⁻⁷ Pa of vacuum pressure so as to reduce scattering-effects due to residual gas molecules. The stainless-steel material with electro-chemical buffing is the most available for use as long tubes of 1 m in diameter. To reduce noises due to scattered light from the surface of tubes, a lot of baffles are inserted into the tubes.     

Thermal conduction measurement of miniature coaxial cables between 0.3 and 4.5 K for the wiring of superconducting detectors

Thermal conduction of thin coaxial cables made of 70-30 CuNi and stainless steel 304 with a PTFE insulator was measured in a temperature range between 0.3 and 4.5 K. Thermal conductivity of the 70-30 CuNi and PTFE was measured independently and their contribution to the thermal conduction of the coaxial cables was investigated. The thermal conductivity of the 70-30 CuNi differed from the literature by 25% at 0.36 K and 40% at 4.2 K, and the alloy exhibited a weak temperature dependence, which indicated the effects of mechanical treatment. It has been confirmed that the thermal conduction of the coaxial cables are low enough to keep a cold stage of ³He cryostats at a temperature below 0.3 K, even when one hundred cables are installed between 0.3 and 3 K for the read-out of superconducting tunnel junction arrays. The cables were installed in a cryogen-free ³He cryostat, and the operation below 0.3 K was successful.     

Application of diamond-like Carbon (DLC) coatings for gravitational wave detectors

A laser interferometer gravitational wave detector requires an ultra high vacuum in the tubes in which the laser beams pass. To avoid noise due to scattered light from the surface of tubes, the surface should be treated with “black” coating without increasing the outgassing rate. We found that diamond-like Carbon (DLC) coatings are suitable for this aim. An outgassing rate of at was achieved for DLC coatings on SUS304 without baking. This rate was better than the surface of SUS316 with baking. The reflectivity of the DLC surface was 5% at minimum for a laser beam of Nd:YAG () which is used as a light source for the gravitational wave detector.     

Experimental study of the behaviour of leather under vacuum conditions

A characterization of the device-pumping behaviour of our vacuum reactor for plasma treatment of materials at low pressure is presented. The analysis of the pumpdown curves measured both in the viscous and in the molecular regimes was made to study the outgassing flowrates of several leather materials. Estimates of the relevant flowrates in different pressure ranges and measurements of the flow composition have been obtained. Such data can be interpreted in the framework of simplified desorption models and could be used in order to design the pumping system needed for vacuum treatment of such materials. We have also measured other related quantities such as the moisture uptake and the weight loss.     

Thickness Dependence of Critical Current of Superfluid 3He Film

We have measured the critical current J _c , which is defined as the onset of dissipative flow, for a thickness range from 0.3 to 4 μm using inter-digitated capacitors. In the thickness dependence of J _c , two distinct dissipation regimes were observed. The crossover occurred at a thickness of ∼1 μm.     

Cryogenic Design of the Setup for MARE-1 in Milan

A large worldwide collaboration is growing around the project of Micro-calorimeter Arrays for a Rhenium Experiment (MARE) for a direct calorimetric measurement of the neutrino mass. To validate the use of cryogenic detectors by checking the presence of unexpected systematic errors, two first experiments are planned using the available techniques composed of arrays of 300 detectors to measure 10¹⁰ events in a reasonable time of 3 years (step MARE-1) to reach a sensitivity on the neutrino mass of ∼2 eV/c². Our experiment in Milan is based on compensated doped silicon implanted thermistor arrays made in NASA/GSFC and on AgReO₄ crystals. We present here the design of the cryogenic system that integrates all the requirements for such experiment (electronics for high impedances, low parasitic capacitances, low micro-phonic noise).     

Recycled carbon fibre for high performance energy absorption

This paper compares the mechanical properties of virgin and recycled woven carbon fibre prepreg and goes on to assess the potential for recycled carbon fibre reinforced plastic (rCFRP) to be used in high performance energy absorption structures. Three sets of material were examined: fresh containing virgin fibres and resin, aged which was an out of life but otherwise identical roll and recycled which contained recycled fibre and new resin. The compressive strength and modulus of rCFRP were approximately 94% of the values for fresh material. This correlated directly with the results from impact testing where rCFRP conical impact structures were found to have a specific energy absorption of 32.7 kJ/kg versus 34.8 kJ/kg for fresh material. The tensile and flexural strength of rCFRP were 65% of the value for fresh material. Tensile and flexural moduli of rCFRP were within 90% of fresh material and ILSS of rCFRP was 75% that of fresh.