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.     

Output properties of fiber optic sensor for micro-displacement measurement at 77 K and 4.2 K

Fiber optic sensors for micro-displacement measurement are applied to displacement measurement of superconductors. Output characteristics of a fiber optic sensor were measured at 77 K and 4.2 K. The results show that the linearity between output voltage ratio and displacement is good both at 77 K and at 4.2 K, and the sensitivity at 77 K is higher than that at 4.2 K.     

Thermal conductivity of ME771 glass-epoxy laminate from millikelvin temperatures to 4 K

Permaglas ME771 is a glass-epoxy laminate which is suitable for use at cryogenic temperatures. We have measured the thermal conductivity of a sample of this material between 64 mK and 4.2 K in the direction parallel to the reinforcing fibres, enabling us to make a comparison with the better known material G-10CR. The thermal conductivity follows the form that would be expected for such a material, and is similar to that of G-10CR, which has a similar (room temperature) tensile strength. We comment on some confusion that has arisen over the difference between G-10CR, a material specifically produced for cryogenic use, and G-10, the more common equivalent.     

Microwave dielectric properties of (ABi)1/2MoO4 (A = Li,Na, K,Rb, Ag) type ceramics with ultra-low firing temperatures

A series of (ABi)_1/2MoO₄ (A = Li, Na, K, Rb, Ag) compositions were studied in regard to the sintering behavior, phase composition, microwave dielectric properties and chemical compatibility with silver and/or aluminum for electrodes. All the (ABi)_1/2MoO₄ (A = Li, Na, K, Rb, Ag) ceramics could be sintered below 700 °C with relative densities above 93%. Whereas the (KBi)_1/2MoO₄ ceramic can be sintered to a high density at around 630 °C/2 hrs with a relative permittivity ∼37, a Qf value of 4000 GHz and a temperature coefficient of resonant frequency (TCF) ∼ +117 ppm/°C. Furthermore, from the XRD analysis of co-fired ceramics, the (KBi)_1/2MoO₄ ceramic reacts with silver but not with aluminum at its densification temperature. The (ABi)_1/2MoO₄ (A = Li, Na, K, Rb, Ag) type ceramics can all be considered into the new field of ultra-low temperature co-firing dielectrics for multilayer applications.     

Synthesis of Cd1 − xMnxS nanoclusters by surfactant-assisted method: Structural, optical and magnetic properties

Cd_1 − xMn_xS nanoclusters were synthesized by surfactant-assisted chemical method for different Manganese (Mn) concentration (0.40 ≤ x ≥ 0.10) at 60 °C in argon atmosphere. Incorporation of magnetic ions (Mn) results a decrease in band gap of Cd_1 − xMn_xS nanoclusters. The room temperature ferromagnetic behaviour is demonstrated first time in Cd_0.60Mn_0.40S nanoclusters by vibrating sample magneto (VSM) measurements and the origin of magnetization has been discussed.     

Thermal conductivity of Torlon between 4.2 and 300 K

Torlon is an organic polymer (polyamide-imide) which exhibits room temperature good mechanical and thermal properties and high chemical resistance. The thermal conductivity of Torlon 4203 was measured in the range of temperature 4.2-300 K. These data complete existing measurement in the temperature range 0.1-5 K. The thermal conductivity shows a linear behavior between 30 K and 250 K and a plateau, typical of many amorphous materials, around 7 K.     

Oxygen treatment effects on properties of MgO thin films grown on single-crystalline diamond (1 0 0)

Oxygen post-treatment effects on the electronic structure and electrical properties of MgO films grown on homoepitaxial single-crystalline (1 0 0) diamond have been studied. MgO films examined were deposited at room temperature (RT) using an electron beam evaporator and were subsequently either annealed at 573-773 K for 12 h in oxygen ambient or treated by O₂ plasma for 10-40 min. RT resistivities remarkably increased after the O₂ annealing and plasma treatment, indicating that the post treatments play an essential part on the formation and positioning of bandgap states. Cathodoluminescence (CL) spectra had a broad band feature in a wavelength region from 360 to 530 nm, which were decomposed to several peaks originating mainly from the oxygen-vacancy-related F and F⁺ centers and the interstitial vacancies of MgO film. A prominent rectifying behavior of I-V property was observed for a Au/MgO/p-diamond layered structure. Based on temperature dependences of the electrical properties in a temperature region from RT to 600 K, the electrical conduction mechanism in the MgO films is discussed in relation to polaron-related conduction as well as the ionic conduction.     

20-50 K and 40-80 K pulse tube coolers: Two candidates for a low temperature cooling chain

Following its important cryogenics heritage for the European Space industry for both Ariane launcher and Orbital programs, Air Liquide - Advanced Technology Division (AL/DTA) is proposing different pulse tube cryocoolers all over the temperature range to answer the needs of earth observation and scientific missions.This paper presents recent performance improvement of the large heat lift 40-80 K pulse tube cooler (LPTC). Four units have been manufactured and tested. Three units are dedicated to lifetime testing in the framework of French Military Space Program (under CNES contract) and Meteosat Third Generation program (ESA contract). The batch performances are described and the product maturity is discussed in this paper.To lower the temperature range and to complete our cryogenic chain, we developed in partnership with CEA/INAC/SBT, a heat intercepted 20-50 K pulse tube cryocooler. This cooler has been developed in the framework of an ESA contract (ESA/ESTEC No 20497/0/NL/PA-20-50 K pulse tube cooler). A development phase has been performed to test and optimize different cold head architectures to reach the 300 mW@20 K specification. A no-load temperature of 12.5 K has been demonstrated on breadboard model. The outputs of the trade-off, the resulting design and the performances are described.In complement to the dilution cooler similar to the one developed for the PLANCK mission, those two pulse tube coolers are potential candidates for a very low temperature cooling chain. By optimizing the capabilities of the 20 K stage for low temperature operation (no-load in the range of 8 K) the coupling of the three independent stages becomes possible.     

The specific heat and thermal conductivity of Eccosorb CR-124 between 800 mK and 6 K

Eccosorb CR-124 is a castable iron-loaded epoxy resin with excellent absorption properties for electromagnetic waves in the GHz range. It is commonly used in low temperature instruments to absorb thermal radiation. The specific heat c(T) of Eccosorb CR-124 was measured between 800 mK and 6 K with the heat pulse method. The results were fitted to the function , with T being the temperature in Kelvin. In addition, the thermal diffusivity D(T) of Eccosorb CR-124 was determined. At a temperature of 2.3 K, a peak is observed in D(T). Consequently, the thermal conductivity λ(T) of Eccosorb CR-124 features two distinct regimes. Below 2.3 K, it fits the function . Above 2.3 K, it fits the function .     

Relationship between microstructure,hardness and corrosion resistance in 20 wt.%Cr, 27 wt.%Cr and 36 wt.%Cr high chromium cast irons

The microstructures, hardness and corrosion behavior of high chromium cast irons with 20, 27 and 36 wt.%Cr have been compared. The matrix in as-cast 20 wt.%Cr, 27 wt.%Cr and 36 wt.%Cr high chromium cast irons is pearlite, austenite and ferrite, respectively. The eutectic carbide in all cases is M₇C₃ with stoichiometry as (Cr_3.37, Fe_3.63)C₃, (Cr_4.75, Fe_2.25)C₃ and (Cr_5.55, Fe_1.45)C₃, respectively. After destabilization at 1000 °C for 4 h followed by forced air cooling, the microstructure of heat-treatable 20 wt.%Cr and 27 wt.%Cr high chromium cast irons consisted of precipitated secondary carbides within a martensite matrix, with the eutectic carbides remaining unchanged. The type of the secondary carbide is M₇C₃ in 20 wt.%Cr iron, whereas both M₂₃C₆ and M₇C₃ secondary carbides are present in the 27 wt.%Cr high chromium cast iron. The size and volume fraction of the secondary carbides in 20 wt.%Cr high chromium cast iron were higher than for 27 wt.%Cr high chromium cast iron. The hardness of heat-treated 20 wt.%Cr high chromium cast iron was higher than that of heat-treated 27 wt.%Cr high chromium cast iron. Anodic polarisation tests showed that a passive film can form faster in the 27 wt.%Cr high chromium cast iron than in the 20 wt.%Cr high chromium cast iron, and the ferritic matrix in 36 wt.%Cr high chromium cast iron was the most corrosion resistant in that it exhibited a wider passive range and lower current density than the pearlitic or austenitic/martensitic matrices in 20 wt.%Cr and 27 wt.%Cr high chromium cast irons. For both the 20 wt.%Cr and the 27 wt.%Cr high chromium cast irons, destabilization heat treatment gave a slight improvement in corrosion resistance.     

A comparative study of the properties of thermally evaporated CuIn2n + 1S3n + 2 (n = 0, 1, 2 and 3) thin films

CuInS₂, CuIn₃S₅, CuIn₅S₈ and CuIn₇S₁₁ compounds were synthesized by the horizontal Bridgman method using high-purity copper, indium and sulphur elements. Crushed powders of these ingots were used as raw materials for the vacuum thermal evaporation. So, CuIn_2n + 1S_3n + 2 (n = 0, 1, 2, and 3) thin films were deposited by single source vacuum thermal evaporation onto glass substrates heated at 150 °C. The structural, compositional, morphological, electrical and optical properties of the deposited films were studied using X-ray diffraction (XRD), energy dispersive X-ray, atomic force microscopy and optical measurement techniques. XRD results revealed that all the films are polycrystalline. However, CuInS₂ and CuIn₃S₅ films had a chalcopyrite structure with preferred orientation along 112 while CuIn₅S₈ and CuIn₇S₁₁ films exhibit a spinel structure with preferred orientation along 311. The absorption coefficients of the all CuIn_2n + 1S_3n + 2 films are in the range of 10⁻⁴ and 10⁻⁵ cm⁻¹. The direct optical band gaps of CuIn_2n + 1S_3n + 2 layers are found to be 1.56, 1.78, 1.75 and 1.30 eV for n = 0, 1, 2, and 3, respectively. CuIn₃S₅ and CuIn₅S₈ films are p type with electrical resistivities of 4 and 12 Ω cm whereas CuInS₂ and CuIn₇S₁₁ are highly compensated with resistivities of 1470 and 1176 Ω cm, respectively.     

Influence of NH4Cl on the < 1 0 0> directed growth and properties of ADP crystal

Good quality, pure and ammonium chloride added < 1 0 0> directed ADP single crystals with different sizes were grown by Sankaranarayanan-Ramasamy method with the vision to improve the properties of the crystal. The grown crystals have cylindrical morphology and the crystals were subjected to UV-Vis., DTA, microhardness, laser damage threshold, dielectric, piezoelectric and SHG studies. The addition of ammonium chloride improves the quality and yields crystals with transparency more than 80% in minimum duration of growth. Higher laser damage threshold and mechanical stability were observed in ammonium chloride added ADP crystals. Low dielectric loss shows that the grown crystal contains minimum defects. Good piezoelectric behaviour was observed for the grown crystals. The SHG efficiency of the crystals was obtained using Nd-YAG laser, which is approximately 3 times that of pure ADP and shows the suitability of the ingot for nonlinear optical applications.     

The behavior of Co atoms on Si (111)-7 × 7 surfaces at low temperatures

The behavior of Co atoms on Si (111)-7 × 7 surfaces at low temperatures was studied by using a variable-temperature scanning tunneling microscopy (VT-STM). Co atoms deposited on Si (111)-7 × 7 surfaces are randomly adsorbed at 100 K. Co atoms start to react with adatoms of Si (111)-7 × 7 surfaces at temperatures between 126 K and 130 K. The reaction transfers the bright dots of Co atoms to dark dots under the STM observation of negative bias. Analysis of the reaction occurrence sites and comparing with the results of room temperature deposition shows that the Co atoms tend to diffuse and react with the adatoms of Si (111)-7 × 7 surfaces at the center sites of unfaulted half unit cell (UHUC) at higher temperatures.     

Superelastic behavior of aged and thermomechanical treated NiTi alloy at Af + 10 °C

The phase transformation in NiTi shape memory alloys is very sensitive to aging and thermomechanical treatment (cold work and annealing). In this research, a Ni-rich alloy has been cold-rolled and then subjected to various annealing treatments and also aging treatments at different temperatures and times. To investigate the superelastic behavior, mechanical testing was carried out at A_f + 10 °C to eliminate the effect of testing temperature on the superelasticity parameters including loading/unloading plateau and mechanical hysteresis. The effect of dislocations and precipitates resulted from thermomechanical and aging treatments on the transformation behavior was studied by Differential Scanning Calorimetry (DSC) and three point bending (TPB) tests. The results showed that these treatments are effective on the thermal and mechanical-induced phase transformation characteristics. Transformation temperatures increase and loading/unloading plateau and thermal and mechanical hystereses decrease by increasing aging and annealing time. Increasing of aging and annealing temperatures results in decreasing of loading/unloading plateau and thermal and mechanical hysteresis.     

Synthesis, structure refinement at 296 K and physico-chemical characterizations of KMnHP3O10

Potassium manganese(III) monohydrogentriphosphate KMnHP₃O₁₀ was synthesized by flux method and characterized by single-crystal X-ray diffraction, crystallizes in the monoclinic system with centric space group C2/c. The parameters of the unit cell are a = 12.104(1), b = 8.287(1). c = 9.150(1) Å, β = 110.97(1)° and Z = 4. The structure was solved at 296 K using 893 independent reflections and refined until R(F) = 0.022; wR(F²) = 0.045. The atomic arrangement of the title compound consists of MnO₆ octahedra linked by hydrogentriphosphate anions to form a three-dimensional framework containing tunnels parallel to the c-axis where the K⁺ cations are inserted. The structure of KMnHP₃O₁₀ contains a single Mn site which is surrounded by typical Jahn-Teller [2 + 2 + 2] distorted octahedron. The title material has been also characterized by different physico-chemical techniques: powder X-ray diffraction, IR, NMR and CI spectroscopies and DTA-TGA-DSC thermal analysis.     

Preparation and microstructure characterization of novel La2 − xSr2 − xNb2O10 − x oxides

The aim of the present work is to report the study of samples with the La_2 − xSr_2 − xNb₂O_10 − x stoichiometry obtained under different synthesis conditions. The materials were characterized and studied by means of Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), X-ray diffraction analysis (XRD), and AC Susceptibility. A preliminary identification of the main peaks appearing in the diffraction patterns is shown for the synthesized phases. The La_2 − xSr_2 − xNb₂O_10 − x compound undergoes a structural change as a function sintering temperature, with three kinds of the stabilized structure, one is from 1173 < T ≤ 1373 K, another from 1423 < T ≤ 1573 K and the last one from 1623 < T ≤ 1723 K.     

Influence of dislocations on the Kapitza conductance of copper at temperatures between 1 and 2 K

An experiment is described in which the dependence of the Kapitza conductance of copper to He II on the dislocation density near the interface is investigated in the temperature range of 1–2 K. A dependence is found, which has not been reported before, giving support to the dislocation -based theoretical models. The Kapitza conductance for a low-dislocation-density sample is shown to be an order of magnitude below the usual values, and within the range of validity of these theories.Supported by the Science Research Council.     

Synthesis, low-temperature sintering and the dielectric properties of the ZnO-(1 − x)TiO2-xSnO2 (x = 0.04-0.2)

ZnO-(1 − x)TiO₂-xSnO₂ (x = 0.04-0.2) ceramics were prepared by conventional mixed-oxide method combined with a chemical processing. Fine particle powders were prepared by chemical processing to activate the formation of compound and to improve the sinterability. One wt.% of V₂O₅ and B₂O₃ with the mole ratios of 3:1 were used to lower the sintering temperature of ceramics. The effect of Sn content on phase structure and dielectric properties were investigated. The results show that the substituting Sn for Ti accelerates the hexagonal phase transition to cubic phase, and an inverse spinel structure Zn₂(Ti_1−xSn_x)O₄ solid solution forms. The best dielectric properties obtained at x = 0.12. The ZnO-0.88TiO₂-0.12SnO₂ ceramics sintered at 900 °C exhibit a good dielectric property: ?_r = 29 and tan δ = 9.86 × 10⁻⁵. Due to their good dielectric properties, low firing characteristics, ZnO-(1 − x)TiO₂-xSnO₂ (x = 0.04-0.2) can serve as the promising microwave dielectric capacitor.     

Enhanced magnetic behavior of Al substituted LaFeO3 (La(1 − x)AlxFeO3, x = 0.10 and 0.30)

La_(1 − x)Al_xFeO₃ (x = 0, 0.1, 0.3) has been prepared by solid state reaction method. The formation of pure crystallographic phase of LaFeO₃ and the substitution of Al³⁺ in all the doped samples have been confirmed by Rietveld analysis. The magnetic measurements viz., magnetization curves, hysteresis loops etc. in the temperature range 300-5 K showed that magnetization of the doped samples has been appreciably enhanced compared to that of the pristine LaFeO₃. The maximum enhancement factor of ~ 19 for saturation magnetization measured at room temperature has been found in La_0.7Al_0.3FeO₃.     

Thermal relaxation of residual stresses in shot peened surface layer of (TiB + TiC)/Ti-6Al-4V composite at elevated temperatures

As an effective and important surface treatment method, shot peening can introduce high residual compressive stress and microstructure variation at near surface deformation layers. In this work, residual stresses relaxation behaviors of the shot peened layer of (TiB + TiC)/Ti-6Al-4V composite were investigated during thermal exposure, and the microstrain was calculated according to the integral breadth after isothermal annealing. The microstrain decreased fast and reached the minimum at 500 °C, which resulted from the thermal recovery and dynamic recrystallization. At elevated temperatures, the residual compressive stresses were relaxed in the whole deformation layers, which were caused by the thermally activated gliding of dislocations. The processes of relaxation can be described using a Zener-Wert-Avrami function and the activation energy of the residual stresses relaxation was higher than that of titanium self diffusion, which was ascribed to the hindrance effects of reinforcements as sink sources of dislocations during annealing.