The influence of the blocking plate diameter on the gas flux distribution in the calibration chamber

This paper is concerned with the influence of the diameter of the blocking plate on the gas flux density distribution in a typical calibration chamber. It was found that, at small values of the blocking plate diameter, the shape of the gas flux density function is similar to the sinus function, with zero deviation from the mean value of the gas flux density at mid-height of the chamber. As the blocking plate diameter increases a discontinuity appears at the edge of the “shadow zone”. Until the discontinuity occurs on the side wall, the difference between the maximum and minimum relative gas flux densities is about 3×10⁻⁴, then it grows to 3.7×10⁻³ when the relative blocking plate diameter increases to 0.83 of the chamber diameter. If we confine our attention to the region between 0.33 and 0.67 of the whole chamber height, which is reasonable in practical terms, the maximum difference decreases to 6×10⁻⁴. Even in this case, this difference is twice as great as that in the case of the chamber without or with the smallest reasonable blocking plate.     

Influence of the blocking plate located in the pumping chamber on the gas flux distributions in high vacuum primary standards

The paper presents the results of the Monte-Carlo computations of the gas flux density distribution in the chambers of typical calibration systems, as a function of two parameters: the diameter of the blocking plate, placed in the pumping chamber, and the backstream from the pump. It was found that the backstream from the pumping chamber to the calibration chamber mainly depends on the diameter of the blocking plate, and it increases significantly with the blocking plate diameter.     

Sensitivity of high vacuum standard parameters to the share of molecule specular reflections in the gas scattering

The molecular gas flow parameters were evaluated using cosine form of the scattering function of the molecules incident on the surface. This gas scattering model is commonly used for calculating the vacuum system parameters, but it is theoretically valid only if the vacuum system is in equilibrium. This also means that there is no flow in the system. We applied the Maxwell's model of gas scattering with the contribution of specular reflections to study how these reflections influence the flow parameters. In typical calibration systems with dynamic expansion of gases, a 10% contribution of the specular reflections results in the 0.18% decrease of the computed value of the gas density inside the gauge to be calibrated as compared with that when the cosine law is employed.     

Distributed Monte Carlo simulation of a dynamic expansion system

This paper presents a new approach to the implementation of the Monte Carlo (MC) method for the analysis of high vacuum metrological systems based on the principle of dynamic gas expansion. The main disadvantage of the Monte Carlo method, the very long time of computation, can be significantly reduced by using a distributed calculation schema. This paper describes the principles of the computation system and compares the computing times for some models of a chosen metrological system, performed using a network of Personal Computers.     

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.     

How to characterize gas in high vacuum?

Vacuum environments are usually characterized by the pressure and temperature of the gas. These macroscopic quantities have been adopted from classical thermodynamics. The aim of this paper is to discuss the statistical aspects of the most important phenomena that occur in high vacuum systems and to propose characterizing them using the gas number density—another macroscopic gas parameter drawn from statistical physics—since it directly influences these phenomena.     

Numerical analysis of oscillatory Couette flow of a rarefied gas on the basis of the linearized Boltzmann equation

The unsteady motion of a rarefied gas between two parallel plates, one of which is oscillating in its plane, is studied based on the linearized Boltzmann equation for a hard sphere molecular gas. The detailed numerical solution for a wide range of gas rarefaction and oscillatory frequency is presented. The transition of the solution from low to high frequencies under various degrees of gas rarefaction is discussed.     

The desorption of condensed noble gases and gas mixtures from cryogenic surfaces

In accelerators, operating at liquid-helium temperature, cold surfaces are exposed to intense synchrotron radiation and bombardment by energetic electrons and ions. Molecular desorption yield and secondary electron yield can strongly influence the performance of the accelerator. In order to predict the gas density during the operation, the knowledge of electron-induced desorption yields of condensed gases and of its variation with the gas coverage is necessary. Desorption yields under electron impact of various noble gases and gas mixtures condensed on a copper surface cooled at 4.2 K have been measured.     

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.     

Experimental verification of a Monte-Carlo simulation of the gas density in a vacuum chamber

An investigation was performed to check the results of a Monte-Carlo simulation of the gas density variations inside a vacuum chamber used for calibration purposes. The simulations revealed variations of up to 0.33% between gas densities at different calibration gauge ports. In total seven spinning rotor gauges were used to detect the differences experimentally. The mean values of the differences that could be determined with an uncertainty of 0.1% of the mean gas density only are consistent with the results of the Monte-Carlo simulation and give confidence in the simulation overall.     

The new method of traceability of a force-balanced piston gauge used as primary vacuum standard

The force-balanced piston gauge is a primary vacuum standard developed in the 1990s. The general principle of the instrument was first presented in Ooiwa A (Metrologia 30 (1994) 607). Non-rotating piston is connected to an electronic dynamometer and centered by means of transient gas flow in a double tapered gap between piston and cylinder. More details about it can be found in Delajoud, Girard(NCSL International Workshop and Symposium 2002; Vakuum Forschung Praxis 15 (2003) 24) and Tesar, Prazak(Vacuum 67 (2002) 307).Czech Metrology Institute developed its own method of the primary traceability of this instrument through the determination of its effective area. In this paper, there will be described experimental setup of this comparison as well as the experimental results from the traceability calibrations of the effective area in gauge and absolute mode using experimental method of hydrostatic comparison with the classical rotating piston balances and a digital non-rotating piston balance. It will, of course, include the uncertainty budget of this way of traceability and the final uncertainty of the pressure generation of the instrument.     

PTB所建激光干涉振动一次绝对校准标准简析

按照ISO/16063-11：1999《激光干涉绝对法振动校准》所述,激光干涉振动一次绝对校准方法主要有条纹计数法、最小点法与正弦逼近法三种,其复现频率范围为1Hz～10kHz.而德国联邦物理技术研究院（PTB）现已建立和保存的低频、中频、高频振动激光干涉一次绝对校准标准的复现频率范围则达0.1Hz～20kHz.此外,PTB还实现了旋转运动物理量值--角加速度的复现;其复现频率范围也达到0.3Hz～1kHz.作为曾在PTB1.22实验室进行过研究工作的访问学者,作者旨在通过对PTB所建激光干涉振动一次绝对校准标准的     

Working standard of the unit of gas flow in a vacuum VÉT 49-2-2006

The working standard for the unit of gas flow in a vacuum VéT 49-2-2006 is described. The composition of the standard and metrological characteristics are provided. A local verification scheme is given for the measurement provisions of gas flow in a vacuum. __________ Translated From Izmeritel’naya Tekhnika, No. 3. pp. 45–48, March, 2007.     

Vacuum stability and residual gas density estimation for the vacuum chamber upgrade of the ATLAS interaction region of the Large Hadron Collider

The CERN Large Hadron Collider (LHC) has 54 km of ultra-high vacuum (UHV) beam chambers out of which about 90% are at cryogenic temperature (1.9 K) and the rest at room temperature. During operation, the residual gas density in the beam pipes is dominated by beam induced effect such ion, electron and photon-stimulated gas desorption. Therefore, the computation of gas density profile is of great importance to confirm the vacuum stability, and to estimate the beam lifetime. Moreover, the gas density profiles are essential to determine the machine induced background in the experimental areas, and to define the pressure profile in the cryogenic sectors where there is no vacuum instrumentation available.In this paper, the vacuum stability is studied for a newly proposed upgrade of the vacuum chamber at the ATLAS interaction point, using the vacuum stability code called VASCO. The residual gas density profile along the ATLAS vacuum chambers and the effects of photon and electron flux hitting the vacuum chamber walls are presented and analysed.     

The state primary standard for the unit of refractive index

The structure, working principle, and basic metrological characteristics are given for the State primary standard for a unit of refractive index GÉT 138-2003.Translated from Izmeritelnaya Tekhnika, No. 11, pp. 3–6, November, 2004.     

Study of the distribution of solids in a counterflow baffled gas-suspension chamber by the beta-ray method

The distribution of solids over the height and cross section of a counterflow baffled gas-suspension chamber has been investigated by the beta-ray method. The particles are decelerated by introducing spiral mesh baffles.     

The state primary standard for the unit of mean laser power

An upgraded state primary standard is considered for the unit of mean laser radiation power. The technical characteristics and working principle are given. __________ Translated from Izmeritel’naya Tekhnika, No. 7, pp. 3–6, July, 2007.     

The spatial distribution of flux waveform across the limbs in a three-phase transformer core

A scale model of three-phase three-limbed transformer cores, in which the magnetic path length varied significantly within the width of the limbs, was instrumented to observe the flux distribution in the laminations. Across the width of the center limb the local field was found to decrease monotonically with distance from the window and was minimum at the middle of the limb. In the outside limbs the local field was maximum near the window and gradually decreased across the width. The harmonic components varied in a similar fashion, although those in the center limb were 65 percent higher than those in the outside limbs. The experimental results confirmed that the magnetic material locally traverses a characteristic hysteresis loop.     

The influence of a hot cathode vacuum gauge on the residual gas composition

The residual atmosphere of an UHV chamber is known to be influenced by the hot cathode gauge (HCG) via processes on the hot cathode and by ionisation. In the presence of such a gauge, some gases are pumped while several residuals are generated, depending on the condition of the chamber's inner surface, gauge parameters and gases that are released spontaneously or introduced on purpose.We analysed the influence of the HCG in three different cases of gas accumulation lasting typically for 1 h: (1) in the leak tight vessel, where the background outgassing from the walls was the only inflow Q_backg=1.6×10⁻⁸ mbar l H₂ s⁻¹, (2) during the constant nitrogen inflow in the vessel and (3) during the constant deuterium inflow. Both inflow values were in the order of 1×10⁻⁶ mbar l s⁻¹. The absolute total pressure in the 13 l system was monitored by a capacitance manometer. After the accumulation, the composition of the accumulated gases was analysed by a quadrupole mass spectrometer (QMS), calibrated with the gases of interest. Regarding the operation of the HCG, an obvious difference is noted both in the pressure rise curves and QMS spectra. The generation of carbon-contained residuals by the HCG was evident, but the most unexpected was its pumping action: nitrogen content decreased from 99% (HCG off) to 62% (HCG on) and deuterium content decreased from 65% (HCG off) to only 2% (HCG on).     

Synthesis of the nanocrystalline CoFe2O4 ferrite thin films by a novel sol-gel method using glucose as an additional agent

Polycrystalline and nanometer-sized CoFe₂O₄ ferrite thin films are successfully synthesized using glucose as an addition agent. The thermal gravimetric/differential thermal analyzer, X-ray diffractometer, electron diffraction, scanning electron microscope, atomic force microscope and vibrating sample magnetometer are used to characterize the effects of the calcination temperature on the crystalline structure, morphology and magnetic properties of the Co-ferrite thin films. CoFe₂O₄ ferrite thin films have a single phase inverse spinel structure and are crystallized at and above 300 °C which is much lower than the required temperature in the traditional ceramic method (about 500-600 °C). Co-ferrite thin films annealed at relative low temperature of 400 °C show very small particle size with average of 32 nm and excellent magnetic properties for information storage applications.