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| TUPCH171 |
Calculation, Measurement and Analysis of Vacuum Pressure Data and Related Bremsstrahlung Levels on Straight Sections of the ESRF
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1417 |
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- R. Kersevan, P. Berkvens, P. Colomp
ESRF, Grenoble
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One of the major personal safety issues of modern synchrotron radiation (SR) light sources is the minimization of the exposure of beamline staff and users to high-energy bremsstrahlung (BS) radiation generated in the straight sections of the storage ring and entering the optics hutches of the beamlines. This is particularly important when insertion device (ID) narrow-gap chambers are installed, nowadays characterized by very low specific conductances. At the ESRF, this has led to the implementation of systematic measurements of BS levels and vacuum conditioning curves, in conjunction with the installation of non-evaporable getter (NEG)-coated ID chambers. A dedicated beamline is used to do on-axis measurements of the BS intensity during the initial conditioning period of newly installed NEG-coated ID chambers. This paper will show results of measurements and calculations performed throughout the years, and comment on the suitability from the radiation safety point of view of the installation of NEG-coated chambers in large numbers around the ring.
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| TUPCH172 |
Status Report on the Performance of NEG-coated Chambers at the ESRF
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1420 |
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- R. Kersevan, M. Hahn, i. Parat
ESRF, Grenoble
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At the ESRF, the use of NEG-coated narrow gap chambers for insertion device (ID) straight sections has become the standard choice for in-air IDs. A total of 25 chambers have been installed at different times in the ring, with 19 being installed as of Jan 2006, for a total length of 82 m. The vacuum performance has been excellent for all but one of them. It has been found that the now standard "10mm" design, i.e. a 5 m-long, 57x8 mm2 ellipse, is compatible with the multi-bunch operation at 200 mA. Runs at higher currents, performed in preparation of current upgrades, have gone smoothly. During 2005, a 3.5 m-long prototype of a chamber suited for installation in the achromat part of the lattice has been installed in the ring. It was characterized by a much smaller cross-section (30x20 mm2, HxV) as compared to a standard chamber (74x33 mm2, HxV), and by the absence of three lumped pumps, replaced by the NEG-coating. The data taken during a full run have been extremely encouraging, to the point of considering the adoption of a similar design for a future upgrade of the storage ring lattice and vacuum system. A status report will be given, alongside with a discussion of future plans.
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| TUPCH173 |
Understanding of Ion Induced Desorption Using the ERDA Technique
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1423 |
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- M. Bender, H. Kollmus
GSI, Darmstadt
- W.A. Assmann
LMU, München
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In heavy ion synchrotrons like SIS18 at GSI high energetic ions can impact on the beam pipe and release gas molecules. This so called "ion induced desorption" deteriorates the accelerator vacuum and as a consequence the beam life time and luminosity. To minimize the pressure increase it is necessary to understand the physics of ion induced desorption. The elastic recoil ion detection analysis (ERDA) can give a time resolved element specific depth profile of a probe under ion bombardment. A UHV-ERDA setup has been installed at GSI to investigate correlations between desorption and material properties as well as its dose dependant evolution. Recent experiments have shown the influence of the surface state of a sample such as the oxide layer on steel as well as the importance of a high-purity bulk such as in silicon and OFHC copper. We will present the results of gold coated copper in comparison to stainless steel as applicable materials for accelerators.
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| TUPCH174 |
Vacuum Issues and Challenges of SIS18 Upgrade at GSI
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1426 |
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- H. Kollmus, M.C. Bellachioma, M. Bender, A. Kraemer, J. Kurdal, H.R. Sprenger
GSI, Darmstadt
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For the present experiment programm and for the planned FAIR facility the heavy ion synchroton SIS18 at GSI has to reach the space charge limit for highly and intermediate charged heavy ions. For the booster mode of SIS18 the number of 1x1012 ions per second in 4 Hz operation mode is specified. To achive this requirement a dynamic vacuum in the 10-12 mbar region has to be garanteed. The poster will present the status of recent R & D work concerning the SIS18 vacuum upgrade, with a focus on the new GSI NEG coating facility and on ion-induced desorption measurements using advanced ion beam analysis.
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| TUPCH175 |
The Vacuum System of FAIR Accelerator Facility
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1429 |
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- A. Kraemer, M.C. Bellachioma, H. Kollmus, H.R. Sprenger, St. Wilfert
GSI, Darmstadt
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The FAIR accelerator complex consists of two superconducting synchrotrons (SIS100 and SIS300) with a circumference of 1083.6m each, a high energy beam transport system (HEBT) with a total length of about 2.5km and four storage rings (CR, RESR, HESR and NESR). Their length varies between 200m and 550m. For each of the subsystems, different vacuum requirements have to be fulfilled. The vacuum system of SIS100 and SIS300 consists of cryogenic and bakeable room temperature sections, where a pressure in the lower 10-12 mbar range is needed. For HEBT, also a combination of cryogenic and room temperature sections, a vacuum pressure of 10-9 mbar is sufficient. The storage rings will be operated in a pressure range from 10-9 mbar to 10-12 mbar. In the poster a detailed layout of the vacuum systems and technical solutions will be presented.
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| TUPCH177 |
Measurement of the Sorption Characteristics of NEG Coated Pipes: The Transmission Factor Method
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1432 |
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- A. Bonucci, A. Conte, P. Manini, S. Raimondi
SAES Getters S.p.A., Lainate
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ZrTiV Non Evaporable Getter (NEG) coatings of vacuum chambers have found application in the particle accelerators to lower the gas pressure, during the operative conditions. For that, the characterization of the actual pumping speed of the NEG coating is a key issue. It is carried out by means of the dynamic sorption method according to ASTM F798-82 standard, conducted "offline" on a sample (coupon), suitably positioned inside the chamber to be coated and recovered after the process. To evaluate in-situ the sorption characteristics of getter coated chambers, a different measurement technique (Trasmission Factor Method) is here described. It is based on the measurement of pressures ratio at the inlet and the outlet of a coated pipe, under a flow of test gas. A calibration curve permits to evaluate sticking probability of the coated surface from the pressure ratio. The use of reference samples to calibrate the method is quite difficult. A better approach is a modellistic one, finding the dependency of pressure ratio on the average sticking probability, the pipe length and the section geometry and dimensions. Preliminary experimental results will be shown.
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| TUPCH178 |
Deposition of Non Evaporable Getter (NEG) Films on Vacuum Chambers for High Energy Machines and Synchrotron Radiation Sources
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1435 |
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- P. Manini, A. Bonucci, A. Conte, S. Raimondi
SAES Getters S.p.A., Lainate
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Non Evaporable Getter (NEG) films, sputter deposited onto the internal surfaces of vacuum chambers reduce thermal out-gassing and provide conductance-free distributed pumping ability, allowing the achievement of very low pressure inside narrow and conductance limited chambers, like Insertion Devices. NEG films do show additional interesting features, like low secondary electron yield and low gas de-sorption rates under ions, electrons and photons bombardment. They seem therefore ideal to reduce electron multi-pacting and dynamic gas de-sorption induced beam instabilities in high energy machines. This paper presents SAES getters experience in the NEG coating of chambers of different geometries and sizes for a variety of projects related to high energy machines and synchrotron radiation facilities. Examples of applications, as well as most common issues related to chambers preparation, film deposition, characterization and quality control, are given. Areas where further work is still necessary to fully take advantage of NEG film properties will be also discussed.
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| TUPCH179 |
R&D on Copper Beam Ducts with Antechambers and Related Vacuum Components
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1438 |
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- Y. Suetsugu, H. Hisamatsu, K.-I. Kanazawa, K. Shibata, M. Shimamoto, M. Shirai
KEK, Ibaraki
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A beam duct with antechambers is able to reduce the effect of photoelectrons and, as a result, to suppress the electron cloud effect of positron or proton beam. It will be adopted for a future high current positron/proton rings and also a damping ring of a linear collider. Copper beam ducts with one or two antechambers were manufactured for test and the feasibility was studied. The test chambers were then installed into the KEK B-factory positron ring and the performance was investigated with a beam current up to 2000 mA. The temperature, the pressure and the electron density in the beam channel were measured during the beam operation. The photoelectron, for example, was found to be well suppressed as expected compared to that of a simple circular beam duct. The related vacuum components, such as a connection flange, a bellows chamber and a gate valve with the same cross section to the beam duct, were also developed and tested together with the beam duct.
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| TUPCH182 |
Radiation Monitors as a Vacuum Diagnostic in the Room Temperature Parts of the LHC Straight Sections
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1441 |
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- V. Talanov
IHEP Protvino, Protvino, Moscow Region
- V. Baglin, T. Wijnands
CERN, Geneva
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In the absence of collisions, inelastic interactions between protons and residual gas molecules are the main source of radiation in the room temperature parts of the LHC long straight sections. In this case the variations in the radiation levels will reflect the dynamics of the residual pressure distribution. Based on the background simulations for the long straight section of the LHC IP5 and on the current understanding of the residual pressure dynamics, we evaluate the possibility to use the radiation monitors for the purpose of the vacuum diagnostic, and we present the first estimates of the predicted monitor counts for different scenarios of the machine operation.
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| TUPCH183 |
H2 Equilibrium Pressure in a NEG-coated Vacuum Chamber as a Function of Temperature and H2 Concentration
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1444 |
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Non Evaporable Getter (NEG) coating is used in the LHC room- temperature sections to ensure a low residual gas pressure for its properties of distributed pumping, low outgassing and desorption under particle bombardment; and to limit or cure electron cloud build-up due to its low secondary electron emission. In certain regions of the LHC, and in particular close to the beam collimators, the temperature of the vacuum chamber is expected to rise due to energy deposition from particle losses. Gas molecules are pumped by the NEG via dissociation on the surface, sorption at the superficial sites and diffusion into the NEG bulk. In the case of hydrogen, the sorption is thermally reversible, causing the residual pressure to increase with NEG temperature and amount of H2 pumped. Measurements were carried out on a stainless steel chamber coated with TiZrV NEG as a function of the H2 concentration and the chamber temperature, to estimate the residual gas pressure in the collimator regions for various LHC operation scenarios, corresponding to different particle loss rates and times between NEG regenerations. The results are presented in this paper and discussed.
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