AVS2001 Session VST2-ThP: Vacuum Issues in Accelerators Poster Session
Thursday, November 1, 2001 5:30 PM in Room 134/135
Thursday Afternoon
Time Period ThP Sessions | Topic VST Sessions | Time Periods | Topics | AVS2001 Schedule
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VST2-ThP-1 Vacuum System Design for the 3GeV-proton Synchrotoron of JAERI-KEK Joint Project
M. Kinsho (Japan Atomic Energy Research Institute) The 3 GeV synchrotron accelerator for JAERI-KEK joint project is aimed to supply a high-intensity proton beam to both the 50 GeV synchrotron ring and the neutron production target. For this purpose, the 3 GeV synchrotron, having a circumference of 313.5 m, is designed to accelerate a high-power beam of 1MW, by setting 25 Hz as a repetition rate and 8.3 x 1013 as a proton number for each acceleration. A rapid-cycling magnetic field is necessary to operate a synchrotron with such a high repetition rate. Since an eddy-current effect in a metal duct would produce an unacceptable perturbation of the magnetic field and unnecessarily large ohmic losses, an alumina ceramic is a candidate material for vacuum ducts in the dipole and quadrupole magnets. The required beam apertures, being a circular cross-section, are 187 and 247 mm in diameter for the vacuum ducts to be installed in the dipole and quadrupole magnets, respectively. The duct lengths for each magnet are 3.5 and 1 m. Since such a long duct is difficult to make with accuracy in the radial dimension, when sintered at once, it can only be manufactured by jointing duct segments of about 0.5 m long. The mechanical strength and deterioration under high level of radiation were examined for various kinds of alumina ceramic and for the joint. Almost all the ceramics to be tested have a sufficiently high flexural strength of 300 MPa, or more, before irradiating a 2.5 GeV-electron beam, and they did not show any significant deterioration in the flexural strength as far as an absorption dose is up to 1000 MGy. |
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VST2-ThP-2 The Greatest Ultra-high Vacuum System of Cryopump in China
C.Y. Zhang, J.M. Chen (Beijing Institute of Satellite Environment Engineering, P.R. China) A large ultra-high vacuum facility of cryopump has been developed in China. The vacuum chamber in this facility consists of three parts, that is: the main chamber, 12m diameter and 22m height; the auxiliary chamber 7.5m diameter and 15m length; the special test chamber, 5m diameter and 15m length. The volume of the main and auxiliary chamber is 3200m3. The chambers are made up of the stainless steel. It is the greatest ultra-high vacuum facility in China. The roughing vacuum systems consist of 4 sets of the JZJLH-5000 roots vacuum pump system and a cold trap, which is 2m diameter and used as to prevent back streaming of pump oil. The roots vacuum pump system includes a ZJ-5000 main roots pump, a ZJB-1200 roots pump, a ZJL-600 circulatory gas cooled roots pump and a H150 rotary plunger vacuum pump. The degree of vacuum in the chamber can reach 0.7 Pa after 5h roughing time. The ultra-high pump systems in the main and auxiliary embrace the 8 sets of cryopump, which are installed on the outside of the chamber, an internal Helium cryopump (cryo panel), which is set in the chamber, and three sets of turbo molecular pump, which are used as auxiliary ultra-high pump system and the main pump for the vacuum leak system. The cryopump has a 5x104l/S volume of flow rate, the internal Helium cryopump 2x106l/S and the turbo molecular pump 2200 l/s. The vacuum measure system consists of the tens gauge heads and vacuum gauges, which include the nude gauge, Bayard-Alpert gauge, total pressure range of vacuum gauge. It can attain the measure range of pressure from 105 Pa to 10-6 Pa. |
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VST2-ThP-5 Development of TiN Coating for the SNS Ring Vacuum Chambers*
P. He, H.C. Hseuh, R. Todd (Brookhaven National Laboratory) The inner surface of the ring vacuum chambers of the US Spallation Neutron Source (SNS) will be coated with ~ 100 nm of titanium nitride (TiN). This will minimize the secondary electron yield from the chamber wall, and thus avoid the so-called e-p instability caused by electron multipacting as observed in positron storage rings and a few high-intensity proton storage rings. An R&D program has been carried out to develop coating parameters that give proper stoichiometry and suitable thickness for the vacuum chambers. DC sputtering and DC-magnetron sputtering were conducted in chambers of relevant material and geometry to SNS ring vacuum systems. Auger Electron Spectroscopy and Rutherford Back Scattering were used to analyze the coating for thickness, stoichiometry and impurity. Excellent results were obtained with magnetron sputtering. This paper will present the development of the coating process, the surface analysis results and the coating of the 4-m long production chambers. |
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VST2-ThP-6 DAΦNE Vacuum Performance and Conditioning
A. Clozza (Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati, Italy) A 510 MeV high luminosity Φ-factory is operating at INFN Frascati National Laboratory, Italy. The accelerator complex consists of a full energy Linac, a small damping ring and two electron-positron high current storage rings. The behaviour of the vacuum under operation, the dynamic pressure and the beam conditioning versus beam dose will be presented. A desorption efficiency below 1x10-6 molec./phot. has been reached in some sections of the vacuum chamber, while a value in the range of some times 10-5 molec./phot. has been reached in other sections. Possible reasons that could explain these differences will be also presented. |
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VST2-ThP-7 Presentation of the ESRF Vacuum System from an Operational Point of View
D. Schmied (European Synchrotron Radiation Facility, France) Since several years the European Synchrotron Radiation Facility [ESRF] serves 40 beamlines with a stable photon beam during 5600 h per year and a reliability of 97%. The vacuum system, as one of the subsystems, appears to pay an crucial role in the operation of such a facility. A review is given about the main difficulties experienced and the actions taken to overcome them. Aspects of instrumentation, interlocks, machine vacuum parts and control will be discussed. |
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VST2-ThP-8 A White Irradiation Test facility at Elettra (WhITE)
F. Mazzolini, J. Miertusova, F. Pradal (Sincrotrone Trieste S.C.p.A., Italy) Photon Stimulated Desorption (PSD) provides the primary gas load in Electron Accelerators and Storage Rings. Dedicated experimental setups have been installed in various Synchrotron Radiation Facilities in order to understand the vacuum behavior of different materials with respect to non monochromatized Synchrotron Light irradiation. This has been performed by measuring the variation of the desorption yield due to the accumulated dose. The need to investigate the feasibility of a White Irradiation Test setup at Elettra (WhITE), the Italian Synchrotron Radiation Facility, has been suggested by several reasons: the evaluation of vacuum performance of new materials to be used at Elettra, such as the Non Evaporable Getter coatings; the preconditioning of new vacuum components before their final installation; the evaluation of the efficiency of different cleaning pretreatments on vacuum components; the assessment of any interaction between the photon flux and the vacuum instrumentation. The use of an already installed "standard" Bending Magnet Front-End (BMFE) has been verified. It involves a remarkable saving in time and money and the BMFE can be easily recovered to standard operations (hosting a regular beamline), by just removing the irradiation arrangement. The installation of WhITE on a currently unused BMFE Left Branch Light Port has been considered. Only a minor modification on the Front-End itself is required: the insertion of a collimator in order to avoid low energy photons striking the conductance aperture. It can also be used to reduce the divergence of the photon beam hitting the sample. In this article we present the layout, current status and first results of WhITE. |
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VST2-ThP-9 Measurements of Photon Stimulated Desorption from a Copper Beam Chamber after Complete Removal of Surface Oxide1
C.L. Foerster, C. Lanni (Brookhaven National Laboratory) Photon Stimulated Desorption(PSD) was measured from a copper beam chamber after completely removing the vacuum surface oxide in order to reduce the PSD. Measurements of PSD and reflected specular photons were performed on NSLS beamline U9a at Brookhaven National Laboratory. PSD causes a pressure rise in accelerator and storage ring vacuum which limits their performance. For this experiment, a KEKB factory beam chamber from a previous experiment was chemically etched and chemically cleaned prior to installation on beamline U9a. Previous PSD measurements have shown that this chemical treatment removes any memory of prior exposure or conditioning. After installation, the copper chamber and end stop were vacuum baked to 250 °C for more than a week to completely remove vacuum surface oxides. The chamber was exposed to more than 1x1023 photons direct from the source having a critical energy of 595 eV and striking at an incident angle of 100 mrad. The major PSD yields for hydrogen, carbon monoxide, carbon dioxide, methane, and water are reported as a function of accumulated photon flux and preparation. The PSD yields for the copper chamber, after oxide removal, were found to be greatly reduced when compared to previous measurments at this laboratory and by those reported from other laboratories. |
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VST2-ThP-10 Photon Stimulated Desorption from the Aluminum Surface with Water Vapor Exposure
J.-R. Chen (Synchrotron Radiation Research Center and National Tsing-Hua University, Taiwan); K.Y. Yang, J.Y. Yang (National Tsing-Hua University, Taiwan); G.-Y. Hsiung (Sychrotron Radiation Research Center, Taiwan) The photon stimulated desorptions (PSD) from aluminum surfaces were studied. The aluminum samples, after the treatment of water vapor exposure, were irradiated by the synchrotron light with a critical photon energy of 2 keV. It was observed that the signal of H2O gas was exponentially reduced during the synchrotron light irradiation. As the surface getting "dry", the phenomenon changed. In order to study the H2O-PSD behavior, experiments were carried out with different conditions, such as different target bias, sample temperature, photon flux and photon dose. The experimental system, results and discussions are described in this paper. |
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VST2-ThP-11 Study of Outgassing and Photon Stimulated Ion Desorption of Copper with Synchrotron Radiation
Y.J. Hsu, C.-C. Lee, S.-H. Chang, G.-Y. Hsiung, J.-R. Chen (Synchrotron Radiation Research Center, Taiwan) The surface characterizations of oxygen free copper by utilizing photoemission spectra (PES), thermal desorption spectra (TDS), photon stimulated ion desorption (PSID), and target current measurement with various surface treatments have been studied. In contrast to aluminum alloy, the XPS data showed the adsorbates on copper surface were apparently reduced after the surface annealing. In the PSID, copper showed the similar main ion desorption species as that of aluminum alloy while surface irradiated with synchrotron white light. However, the desorption yield of copper was much smaller than that of aluminum alloy. The desorptiom yield as a function of photon energy from 10 ~200 eV indicated ion desorption of copper were mainly excited by the generation of photoelectrons. |
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VST2-ThP-12 Study the Photoelectron Yield for Al and Cu Materials
G.-Y. Hsiung (Synchrotron Radiation Research Center, Taiwan); C.Y. Yang (National Tsing-Hua University, Taiwan); C.-C. Lee, Y.J. Hsu, J.-R. Chen (Synchrotron Radiation Research Center, Taiwan) The photoelectron yield (PEY) from the Al and Cu materials is measured at the 19B beam line in SRRC. The surface of the test samples is treated by different methods, including the chemical cleaning, glow discharge cleaning, exposing water vapors, etc., prior to the photon irradiation. The alternate surface analysis by XPS, SIMS, TDS, etc. is applied to the samples for comparison of the various surface conditions relating to the PEY. The PEY for the unbaked samples is also compared. The results will be discussed. |