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.     

A transparent vacuum window for high-intensity pulsed beams

The HiRadMat (High-Radiation to Materials) facility [1] will allow testing of accelerator components, in particular those of the Large Hadron Collider (LHC) at CERN, under the impact of high-intensity pulsed beams. To reach this intensity range, the beam will be focused on a focal point where the target to be tested is located. A 60 mm aperture vacuum window will separate the vacuum of the beam line which is kept under high vacuum 10⁻⁸ mbar, from the test area which is at atmospheric pressure. This window has to resist collapse due to beam passage. The high-intensity of the beam means that typical materials used for standard vacuum windows (such as stainless steel, aluminium and titanium alloy) cannot endure the energy deposition induced by the beam passage. Therefore, a vacuum window has been designed to maintain the differential pressure whilst resisting collapse due to the beam impact on the window. In this paper, we will present calculations of the energy transfer from beam to window, the design of the window and associated mechanical calculations.     

13 years’ operational experience of SPring-8 vacuum system

The first electron beam was stored in SPring-8 storage ring in March 1997. An overview of the 13 years’ operational experience concerning the vacuum system of the SPring-8 storage ring is presented. The evolution of the vacuum system and their performance are summarized. Moreover, the main vacuum failures and their impact on accelerator operation are described in detail. We analyze the relationship between the difference types of vacuum failure and downtime of user experiment.     

Storage ring vacuum system pressure modelling at Diamond

Two complementary vacuum system simulation programs, “MCTPVac” and “Pressure Profile”, have been developed and tested at Diamond and used to model sections of the Diamond storage ring. The MCTPVac program implements the Monte Carlo Test Particle (MCTP) method in 3 dimensions. The Pressure Profile program uses a 1-dimensional method based on a steady-state diffusion equation. The validity of the MCTPVac program is confirmed by comparison with previously-published results and formulae for simple geometries. The pressure predictions made by the two methods for the Diamond storage ring injection straight are then compared with each other and to actual observed pressures.     

Improvement of beam lifetime and vacuum system of the PF-AR

Successive improvements have been performed on the vacuum system for the Photon Factory Advanced Ring (PF-AR) at the High Energy Accelerator Research Organization (KEK). The main purpose is to prolong electron beam lifetime for stable operation as an intense pulsed X-ray source. In the past three years, a total of 61 sputter ion pumps (SIPs) were additionally installed, and the increased effective pumping speed amounts to 13% of total. Comparison between calculated and observed beam lifetimes indicates that the lifetime is restricted mainly by the residual gas scatterings and that improvement of the vacuum will realize still longer lifetime. Sudden beam lifetime drops caused by dust trappings have been investigated for many years. The frequency of the lifetime drops has decreased as operation time elapsed after a large-scale reconstruction. Effect of distributed ion pumps (DIPs) on the lifetime drops has also been investigated experimentally.     

上海光源储存环真空系统

上海光源储存环真空系统已于2007年底建成并开始运行.这个真空系统采用了双室结构的薄壁不锈钢真空室,其尺寸公差都小于1mm,真空室安装位置公差都小于2mm;分散的吸收器有序排列在抽气室内,把同步辐射光准直并引入光束线,同时吸收废弃的同步辐射光,把热量转移到真空室外;波纹管内的高频屏蔽机构为单指型,避免了指间接触力和磨擦;(SIP+NEG)复合泵、SIP和TSP共用,采用合理的激活NEG泵和升华钛丝的工艺程序,提供了强大的抽速和容量.真空预调试时各段真空室内的极限真空都达到5×10 -9Pa.全环真空室安装并连通后,大部分真空室不烘烤,只烘烤全环真空泵的情况下,极限真空达到2×10 -8Pa.储存环运行在束流剂量260Ah、能量3.5GeV、流强220mA时,动态压强为0.8×10 -7Pa,束流寿命21h,达到了真空系统的设计指标1.33×10 -7Pa.     

超导扭摆磁铁光束线前端真空系统

6T单周期超导扭摆磁铁是合肥同步辐射光源的一个插入件，用于将可用光范围扩展到X射线波段。由该磁铁引出的光束线的前端已调试完毕，其中静态真空达2．46×10－8Pa。主要介绍了该前端超高真空系统的计算设计及调试。     

Conceptual design of the vacuum system of the Spanish synchrotron light source (ALBA) storage ring

ALBA will be a third generation synchrotron light facility to be built near Barcelona (Spain). The design phase of ALBA is almost completed and the first components are ready to be ordered. Commissioning of the storage ring is foreseen to start at the end of 2008. The circumference of the storage ring of ALBA is 268.8 m and it will be divided into 16 vacuum sections by ultra high vacuum (UHV) gate valves. The vacuum chamber will be made of stainless steel with vertical aperture of 28 mm and 72 mm width. The vacuum chamber will be connected to an antechamber with a slot of 10 mm height. The antechamber will have the crotch absorbers which will absorb the unwanted synchrotron radiation. The pumping will be by sputter ion pumps (SIP), NEG pumps and titanium sublimation pumps (TSP), with an overall pumping speed from SIP of 57,400 l/s. This will maintain an average dynamic pressure of around 1 × 10⁻⁹ mbar to achieve a beam lifetime >15 h at the designed current.     

上海光源BL11B前端区真空系统设计

同步辐射光束线前端区真空系统的作用是将光束线站各设备的不同工作真空环境平稳过渡到储存环的超高真空状态,且可以在必要时通过真空联锁保护储存环真空不受破坏。本文从真空材料和获得、测量设备选择,系统气载分析,系统布局和压强分布计算,真空联锁保护,系统调试等几个方面介绍了硬X通用谱学光束线（BL11B）前端区真空系统的设计和调试方法。对该前端区无束流条件下的静态压强和经束流清洗后的动态压强分布进行了分析、模拟计算,并完成了真空系统的在线调试。调试结果显示,与储存环接口泵站处静态等效氮压强为1.5×10^-8 Pa,动态等效氮压强为9×10^-8 Pa,均满足甚至优于设计指标。证明此设计和调试方法在工程实施中是可靠的。     

岛津PEC-A_2样品表面处理装置真空系统故障维修

PEC—A_2样品表面处理装置是岛津公司为EPM-810Q电子探针样品表面进行喷金处理装置,其主要包括抽真空系统和喷金电流控制系统,抽真空系统由机械泵和油扩散组成,真空度可达到6.7×10~3Pa torr。     

SSRF电子储存环铝合金超高真空室研制

上海光源3.5GeV电子储存环超高真空室采用铝合金材料,经数控加工后焊接而成,其结构复杂,精度要求高.在预制研究中成功地完成了一段6 m长典型真空室的设计、制造与调试.该真空室的平面度达到0.23 mm,横向偏移量1.4mm,内表面单位面积出气率4.1×10-10 Pa·m/s.在研制中暴露出结构设计和加工工艺等方面的多种问题,并找到了妥善解决的方法,为工程批量生产准备了条件.     

Status of the cyclotron vacuum system at TRIUMF

The world's largest cyclotron was built at TRIUMF in 1972 and commissioned to full energy in 1974 [Harwood VJ, Yandon JC. TRIUMF Design Note, TRI-69-7, 1969 [1], Blakely RG, Moore RW, Harwood VJ. TRIUMF Design Note, TRI-69-9, 1969 [2]]. The cyclotron accelerates negatively charged hydrogen ions up to 500 MeV, and protons are produced by inserting a stripping foil in the beam which removes two electrons from each negatively charged hydrogen ion and allows the remaining bare protons to be channeled out of the accelerator. By making these protons strike different kinds of targets, intense beams of neutrons, pions and muons can also be created, thus making possible many different experiments. The volume of the cyclotron vacuum tank is about 100 m³ and operates at 2×10⁻⁸ Torr pressure during beam production. Most of the vacuum is achieved by cryopumping with a B-20 cryogenerator and six cryopumps. The B-20 is a Stirling cycle refrigerator, which supplies helium gas at 16 and 70 K to the cryopanels in the tank. The tank is also equipped with two turbo pumps. The vacuum system went through a few modifications during more than 30 years of operation. This paper presents the status of the cyclotron vacuum system and discusses the latest upgrades.     

Development of SPring-8 vacuum system

SPring-8 storage ring has been available for user operation with low emittance and extreme stability for over 10 years. However there occurred some problems in the components of the storage ring due to high-brightness synchrotron radiation (SR) and low-emittance operation. On the vacuum system of the storage ring, an accurate pressure could not be measured near the photon absorber due to scattered high-energy SR to the gauge head. High-energy SR activated dissolved oxygen in cooling water, and the activated dissolved oxygen corroded the inside of the photon absorbers in SR irradiation part. Air leakage occurred at an injection chamber due to impact by a small-size electron beam produced by low-emittance operation.We investigated the cause of the aforementioned difficulties with the vacuum system and prescribed the treatments described in this paper. In addition, we are making continual efforts at further system upgrades such as developing an RF shield that suppresses temperature increase in the shield in possible high-current operation.     

Validity of the Space-Time Enlargement Law for vacuum breakdown

This paper investigates, theoretically and experimentally, the applicability of the Space-Time Enlargement Law to vacuum-insulated systems. A discussion on how characteristics of possible vacuum breakdown mechanisms determine the distribution function of the breakdown voltage random variable is presented. By superimposing effects of electrode surface enlargement and inter-electrode gap enlargement, expressions for the mean value and standard deviation of the breakdown voltage random variable are obtained. In the case of time extensions, the assumption of complete independence of consecutive discharge processes is discussed. Experimental testing of the Enlargement Law was performed on Rogowski type two-electrode systems, with different electrode surface areas, inter-electrode gaps and vacuum pressures. Measurements were conducted using industrial ac voltage, dc voltage with 50 V/s rate of rise, standard atmospheric pulse voltage (1,2/50 μs), and commutational pulse voltage (250/2500 μs). The final conclusion, based on the comparison of theoretical considerations and the experimental results, is that the Space-Time Enlargement Law can be applied in the design phase during the development of vacuum devices, with certain limitations, regardless of the type of the applied voltage.     

Performance of the SRS vacuum system

At the Daresbury Laboratory of the Science and Engineering Research Council is the SRS, the world's first dedicated high energy synchrotron radiation source. The SRS has been described elsewhere¹⁻³ and is essentially a 2 GeV electron storage ring of about 30 m diameter and designed for an ultimate beam current of 1 A. It is over seven years since commissioning of the SRS started, during which time nine out of a possible twelve beam lines have been built and scheduled experiments have been running for over six years. This paper will describe the general performance of the vacuum system and the specific experience gained on the performance of various types of vacuum pumps and gauges.     

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.     

BEPCII储存环真空系统性能

本文描述了BEPCII储存环真空系统的结构、特点以及运行状况.储存环真空系统于2006年3月开始安装,仅用8个月时间完成储存环正、负电子环约480米长的真空设备安装、检漏和烘烤,并且每个区段的真空优于6.0×10-8 Pa.2006年11月18日电子束在储存环成功储存,标志着储存环真空系统能够正常运行.随着积分流强的增加,由同步辐射光引起的气体解吸量逐渐减小,动态真空变好.当积分流强达到100A·hr时,单位流强引起的压强上升小于1×10-10 Pa/mA.真空系统运行稳定,在8个多月的运行中,没有发生真空设备故障.     

等离子体显示板真空紫外荧光测试系统

设计等离子体显示板(PDP)真空紫外荧光测试系统来测评PDP荧光粉的特性。系统通过巧妙设计测试腔,模拟PDP放电单元,为激发PDP荧光粉发光提供所需要的较强真空紫外线,使系统能够分析出荧光粉的光谱功率分布、发光亮度、带宽、发射谱线主峰波长、色品坐标、颜色纯度和主波长等各种光学特性。实验结果数据表明,该系统的可重复性好、精度高,为研制高质量的等离子体显示板提供了依据。     

Status and performance of MGC-20 cyclotron vacuum system

A variable energy compact cyclotron has been installed at the Nuclear Research Centre NRC, Atomic Energy Authority AEA, Egypt. It is equipped to accelerate protons, deuterons, α-particles and ³He. The vacuum system has to provide high vacuum within the 10⁻⁶ mbar range in order to accelerate particles and to have stable beam. The total vacuum volume includes the acceleration chamber and the ion beam transport line is ≈3 m³. The pump-down time of the system to the steady high vacuum is measured. Results on the performance of the forevacuum and the high-vacuum pumps will be presented. The characteristics of the vacuum system components are evaluated.     

Cryogenic system of the MAX-Wiggler

A novel insertion device for electron storage rings called the MAX-Wiggler has been constructed and commissioned at MAX-lab. The MAX-Wiggler is a cold bore superconducting wiggler magnet with 47 3.5 T poles and a period length of 61 mm aimed for the production of X-rays at the 1.5 GeV electron storage ring MAX-II at MAX-lab. This note describes the cryogenic system of the MAX-Wiggler, theoretical predictions of the heat loads to the cryostat, and measured heat loads at operation. The cryostat is a helium cooled bath type cryostat. The design criterion for the cryostat was to have a liquid He boil-off less than 3 l/h, which corresponds to a heat load of 2.1 W. The theoretical calculations predicted a heat load of 0.87 W to the liquid He bath. Of the 0.87 W predicted heat load, 0.17 W was predicted to be induced by the stored beam in MAX-II, 0.12 W from synchrotron radiation and 0.05 W from image currents. The measured heat load to the liquid He bath is larger than predicted from the theoretical calculations and at nominal working conditions it is 1.7 W. The measured contribution to the total heat load from the stored beam of 200 mA in MAX-II is 0.86 W, 0.59 W from image currents and 0.26 W from synchrotron radiation. The measured contribution from the image current is 0.59 W, about 10 times larger than expected from the theoretical calculations, which is assumed to depend on that the Cu plating of the inner surfaces of the cold bore has a lower electrical conductivity than foreseen. The higher than expected heat load from synchrotron radiation is assumed to come from a positioning error of the upstream absorber for synchrotron radiation. There is no observable increase of the heat load with the wiggler at full field. Even though the heat loads are higher than expected, the design criterion of obtaining a cryostat with a liquid He boil-off inferior to 3 l/h with 200 mA of stored current in MAX-II has been met.