Molecular cryosorption properties of porous copper, anodised aluminium and charcoal at temperatures between 10 and 20 K

New types of anodised aluminium, porous copper and charcoal-based materials are being developed as cryosorbing materials and have been studied in collaboration with a number of research institutes. The major aim was to find a suitable cryosorber with a working temperature in the range between 5 and 20 K that could be used in the LHC vacuum chamber inside the superconducting magnets at a temperature of 4.5 K and higher. The design of the experimental set-up, the results of cryosorption capacity measurements for porous copper, anodised aluminium and charcoal-based materials are described in this paper.     

Vacuum performance of a carbon fibre cryosorber for the LHC LSS beam screen

A new carbon fibre material was developed at the Institute of Solid State Chemistry and Mechanochemistry at the Siberian Branch of the Russian Academy of Science (SB RAS) to meet the requirements of a cryosorber for the large hadron collider (LHC) vacuum chamber. The material must have a large sorbing capacity, a certain pumping speed, a working temperature range between 5 and 20 K, a low activation temperature (below room temperature), a certain size in order to fit into the limited space available and it should be easy to mount. The vacuum parameters of the LHC vacuum chamber prototype with a carbon fibre cryosorber mounted onto the beam screen were studied in the beam screen temperature range from 14 to 25 K at the Budker Institute of Nuclear Physics SB RAS. This carbon fibre material has shown sufficient sorption capacity for hydrogen at operational temperatures of the beam screen in the LHC long straight sections. It is also very important that this material does not crumble and makes a convenient fixation onto the beam screen in comparison to the widely used granulated charcoal. The problem of fluff and ways of reducing the quantity of fluff in the beam channel were studied. The results of these studies show that the carbon fibre material is a possible cryosorber-candidate for use in the LHC and other long vacuum system at cryogenic temperatures. The experimental set-up and results of measurements of the H₂ cryosorption capacity of this carbon fibre material are presented in this paper.     

Investigation of Inner Vacuum Sucking method for degassing of molten aluminum

Hydrogen is a harmful gas element that is appreciably soluble in aluminum and its alloys. Removal of hydrogen from molten aluminum has been one of the most important tasks in aluminum melt processing. In this paper, a patented degassing process, which is based on principle of vacuum metallurgy, is proposed. A porous head that connects a vacuum system is immersed in the molten aluminum. The vacuum is created within the porous head and the dissolved hydrogen will diffuse unidirectionally towards the porous head according to Sievert's law. In this way, the hydrogen in the molten aluminum can be removed. The Fick's diffusion equation is used to explain hydrogen transfer in the molten aluminum. RPT experiments are carried out to evaluate the effectiveness of the new degassing process. The experiments indicate that the hydrogen content can be dramatically reduced by use of this process.     

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.     

电真空器件残气质谱分析和贮存寿命的快速测试研究

电真空器件内的残气压强是制管和管子工作过程中管内吸气剂材料吸气后形成的平衡压强,器件击破后质谱分析室本底气体会被吸气剂吸收。因质谱分析室放出的本底气体量一般远小于吸气剂在器件内原吸收的气体量,故器件内的残气压强的新平衡值增量可以忽略,分析室本底不会影响正确的分析结果;大气漏入管内后只表现出该管内惰性气体氩的积累;据此,我们提出了充氩法贮存寿命的快速测试方法。只有吸气剂失效或吸气饱和后管内残气质谱图才反映出漏入的大气成份或分析室本底气体干扰的特征。     

灭弧室用磁控真空计的研究

介绍了同轴场式脉冲磁控真空计的测量原理以及设计中的有关问题。给出了某些真空灭孤室的压强－离子电流曲线。测量结果表明，该磁控计的压强－离子电流曲线为幂指数函数，磁控放电的离子电流与磁场强度无关，但磁场强度必须足以产生稳定的磁控放电。压强－离子电流曲线与灭弧室电极几何构造和触头的状况有关。     

空间行波管排气过程中残余气体的质谱分析

电真空器件内残余气体直接影响其阴极的发射能力与寿命。本文利用高灵敏度四极质谱仪监测了空间行波管在整个排气过程中的残余气体,对各阶段气体成分及含量进行了分析。结果表明:烘烤前,水为主要气体,占80%。前期擦拭用无水乙醇易污染真空系统;升温过程中氢迅速增多,当烘烤温度达到220℃时,H₂成为系统中主要气体;整个烘排过程H₂的分压小于10^-3Pa,其余气体分压均小于10^-4Pa;烘烤结束后,H₂分压为2.4×10^-8Pa,占74%。H₂O分压为6×10^-9Pa,占20%;离子泵与吸气剂泵组可有效抽除残余气体,且对H₂的抽速高于对其他气体抽速;另外,质谱仪自身会放出H₂、H₂O、CH₄、CO₂等气体,在真空系统压力达到10^-9Pa范围时,质谱仪自身放气已不可忽略。     

Performance of the vacuum system for the PETRA III damping wiggler section

A record low horizontal emittance of 1 nm-rad was successfully obtained in PETRA III third generation synchrotron light source. A key system that allowed reaching such value includes 20 permanent magnet damping wigglers installed in two long straight sections. The wigglers radiate almost 1 MW at maximum current of hard X-ray radiation which issues a challenge for the design of SR absorbers and vacuum system components for the damping wiggler section. The paper describes in detail the design consideration, manufacturing and experimental performance of absorbers and vacuum system. The first experimental results of PETRA III damping wiggler section operation are presented.     

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.     

Estimation of residuals for the homogenized solution: The case of the beam with random Young's modulus

In this paper the estimation of residuals for the homogenized solution in elastic problem is taken into account. The case of the beam with Young's modulus randomly varying along the axis is considered. The analysis is performed by means of numerical simulation which is validated by comparison with particular solutions reported in the literature. The convergence to the homogenized solution and the behavior of the residuals are studied in terms of the parameter ɛ, which represents the ratio between the microscopic and the macroscopic scale. After validation with the literature results, the procedure is used to analyze the influence on the convergence of the correlation law of Young's modulus with log-normal distribution. Moreover the particular case of the two-phase beam is considered. The effect of different boundary conditions is also investigated.     

Design and performance of a non-destructive beam-profile monitor utilizing charge-division method at HIMAC

A non-destructive beam-profile monitor employing micro-channel plates and a resistive anode that can be applied to a detector has been developed. The monitor works by a method of charge division to determine the spatial position for an event of residual gas ions on a detector. Two monitor units for measuring the transverse horizontal and vertical density distributions of a circulating beam were installed in the HIMAC synchrotron. The monitor has been used for an electron-cooling experiment with a spatial resolution of less than ±0.38 mm, as well as for studies of beam dynamics under routine operation in the synchrotron. The design and reliability of the monitor as well as some results of the performance are described.     

真空断路器弧后鞘层发展过程仿真分析

以真空断路器弧后鞘层发展过程为对象,采用等离子体流体力学模型,求解电子、离子密度和平均电子能量的漂移扩散方程和耦合电场的泊松方程,引入粒子间碰撞反应,仿真分析其弧后介质恢复变化和鞘层发展阶段电子和离子的空间分布、密度分布以及间隙电势分布。采用对比分析法,研究不同初始条件对鞘层发展的影响,结果表明:在保持其余参数不变的条件下,暂态恢复电压(TRV)斜率和间隙轴向长度均与鞘层发展速度呈正相关,初始等离子体密度和弧后金属蒸气压强均与鞘层发展速度呈负相关。     

光束线真空保护联锁与控制系统研制

介绍了光束线前端区装置的组成及光束线真空保护联锁与控制要点。根据光束线真空保护联锁与控制的要求，本实验室研制了真空传感器、快速关闭阀及快阀控制器等真空保护联锁与控制系统所需的关键部件，进一步提高了光束线真空保护联锁与控制系统的反应速度和可靠性。     

SSRF电子储存环真空室材料电子激发解吸的实验研究

用电子激发方法对SSRF储存环初步选定的真空室材料的动态出气特性进行了实验研究 ,得到了主要解吸气体成分的电子激发解吸系数与电子入射累积剂量的关系 ,对真空室材料经不同表面处理后的电子激发解吸特性进行了比较 ,初步确定了该真空室的表面处理工艺 ,为SSRF储存环超高真空系统的建立提供了一定的实验依据     

基于等效合成波方法的双真空管空气折射率测量仪

在高精度测量中必须实时补偿空气折射率的影响。文中提出了等效合成波的概念,利用长度不等的两个真空管构成两个虚拟波长并推导出等效合成波测量公式,并由此建立了一种新型的双真空管空气折射率测量仪。该仪器具有结构紧凑、能实现实时测量的优点。系统测量分辨率为1×10-8,与Edlen公式方法进行的比对实验结果表明,其测量精度优于1×10-7,并具有很好的稳定性和抗干扰能力。     

10 kV真空断路器弹簧操动机构合闸传动优化设计

真空断路器弹簧操动机构中四杆机构杆件结构与合闸弹簧参数对动触头合闸速度和位移特性具有直接影响,包括冲程弹跳与机构磨损量等。以10kV断路器用弹簧操动机构为对象,采用SolidWorks软件建立运动系统三维模型;引入动力学仿真软件ADAMS对三维模型进行运动特性分析。在保证分闸储能位分闸弹簧压缩量不变的条件下,以连架杆与连杆尺寸、合闸弹簧预紧拉力为优化变量,以动触头最高瞬时速度最低和相对杆长之和最小为目标,采用DOE参数化分析方法对机构进行多参数多目标优化设计,以调控机构输出特性。     

Measurement of the gas-flow reduction factor of the KATRIN DPS2-F differential pumping section

The gas-flow reduction factor of the second forward Differential Pumping Section (DPS2-F) for the KATRIN experiment was determined using a dedicated vacuum-measurement setup and by detailed molecular-flow simulation of the DPS2-F beam tube and of the measurement apparatus. In the measurement, non-radioactive test gases deuterium, helium, neon, argon and krypton were used, the input gas flow was provided by a commercial mass-flow controller, and the output flow was measured using a residual gas analyzer, in order to distinguish it from the outgassing background. The measured reduction factor with the empty beam tube at room temperature for gases with mass 4 is 1.8(4) × 10⁴, which is in excellent agreement with the simulated value of 1.6 × 10⁴. The simulated reduction factor for tritium, based on the interpolated value for the capture factor at the turbo-molecular pump inlet flange is 2.5 × 10⁴. The difference with respect to the design value of 1 × 10⁵ is due to the modifications in the beam tube geometry since the initial design, and can be partly recovered by reduction of the effective beam tube diameter.     

Experimental investigation of local bending effects in the vicinity of a junction between a straight sandwich beam and a curved sandwich beam

The junction between a curved and a straight sandwich beam is investigated experimentally using electronic speckle pattern interferometry. This technique facilitates a whole field measurement of the displacements through the thickness of the sandwich beam. The experimental results are compared with results obtained using a high order sandwich theory model. The results generally show good agreement within the accuracy of the measurements, thus indicating that the gross response of the model is predicted accurately by the high order sandwich theory, while the localised bending effects in the vicinity of curvature change in sandwich panels have not been verified experimentally.