Papers

AVS1996 Session VT-MoM: Accelerators and Gas-Beam Interactions in Accelerators

Monday, October 14, 1996 8:20 AM in Room 104A/B

Monday Morning

Start	Invited?	Item
8:20 AM		VT-MoM-1 A Very Low Cost and High Reliability Flangeless Bellowless Aluminum Alloy Vacuum Beam Pipe in a High Energy Accelerator H. Ishimaru (KEK National Laboratory for High Energy Physics, Japan) In traditional high energy accelerator technology, the vacuum beam pipes are connected by flanges and bellows. This type of connection is a primary concern for potential leaks decreasing the reliability of the system. This paper describes a flangeless and bellowsless extruded aluminum alloy beam pipe joined by automatic welding greatly simplifing the system. The system will substantially reduce the number of components and labor cost, thus, increasing the reliability of the accelerator. The accelerator beam pipe design is based on a 99.99% high purity aluminum for providing a uniformed high frequency wall current. The 99.99% high purity aluminum is co-extuded with an high strength 7N01-T5 aluminum alloy with extrudability, weldability properties. The 7N01-T5 aluminum alloy has high resistively to eddy current to avoid deformation of the beam pipe during quench of the superconducting magnet. Unit tensile stress against beam pipe with supported and fixed to magnet at room temperature is proportional to thermal expansion coefficient, modulus of elasticity, and temperature difference. To realize small inner compression stress, a chemical process removing water adsorption is used with dichloropropane at 70C mild bakout instead of ordinary high temperature bakeout procedure. A finite element analysis against inner compression stress was made for the long beam pipe with fixing of both ends. Thermal cycle test was made for 8.5 m long aluminum alloy beam pipe without problem. The flangeless and bellowsless accelerator satisfy with very low cost, high reliability and minimum high frequency impedance.
8:40 AM		VT-MoM-2 The Surface Analysis and ESD Test on Ozone Gas Treated Aluminum Alloy Y. Maeda (National Laboratory for High Energy Physics, Japan); T. Momose (Miyagi National College of Technology, Japan); K. Asano, Y. Suetsugu, S. Kato, K. Kanazawa, H. Ishimaru (National Laboratory for High Energy Physics, Japan) In electron storage rings, the beam lifetime is limited by collision of electron beam with residual gas molecules such as CO, CO2 and CH4 desorbed from beam duct surface. The main cause of the gas desorption from the beam duct surfaces is photon stimulated gas desorption (PSD) by synchrotron irradiation. The authors have been concentrated on reducing PSD of aluminum beam duct surface. The original oxide layers of a beam duct manufactured by the normal extrusion are contaminated with a mixture of carbon and hydrocarbon. Three of the authors reported that PSD from aluminum surfaces whose original oxide layers were removed by argon ion etching was three orders of magnitude lower than that of the aluminum surfaces with original oxide layers. To remove carbon and hydrocarbon in oxide layers and to make the layers clean, we applied ozone gas treatment. Sample pieces were cut from an aluminum beam duct. The sample was exposed to oxygen gas containing ozone at a concentration of 250 ppm at pressures of 1 atm for 72 hours with flowing rate of 1 l/min. After the treatment, the sample surfaces were checked by Auger electron spectroscopy (AES). Electron stimulated gas desorption (ESD) was applied to the sample surfaces with and without the ozone gas treatment. The electron beam energy was 400 eV and emission current 20 mA. The ozone treated surfaces showed no carbon within AES detection limit of 3 atw%. The treated surfaces showed that desorption coefficient of 2E-4 2x10-4 for CO and 1E-4 1x10-4 for CO2 was about one half of that without the treatment at the beam dose of 1022 electrons/m2. PSD of aluminum beam ducts will be measured by exposing to synchrotron radiation.
9:00 AM		VT-MoM-3 Operational Experience of Novel Vacuum Chambers Incorporating Massive Titanium-Sublimation Pumping in the CESR Interaction Region R. Kersevan, N. Mistry, Y. Li (Cornell University) New vacuum chambers have recently been installed in the interaction region of the Cornell Electron-Positron Storage Ring CESR in order to improve the pumping and reduce the operating pressure of the collider in the vicinity of the CLEO detector as the beam currents are increased by a large factor. Lost-particles generated by the beams interacting with the residual gas are a major source of background in CLEO and could lead to radiation damage of sensitive components such as the new Silicon Vertex Detector installed around a two-centimeter radius beryllium beampipe. This paper shows how Titanium- Sublimation Pumps (TiSPs) are used as an inexpensive and efficient way to attain pressures in the low nanoTorr range in the face of large outgassing induced by intense synchrotron radiation. Laboratory measurements of pumping speed in these chambers using calibrated leaks are compared against performance in the ring. A history of the dynamic pressure rise in the ring (Torr/mA) since the most recent start-up of CESR will also be shown. (*) Work supported in part by the National Science Foundation
9:20 AM		VT-MoM-4 Installation of a 14mm Vacuum Chamber for an Undulator in the 1.3 GeV Storage Ring at SRRC G. Hsiung, J. Shyy, K. Hsu (Synchrotron Radiation Research Center, Taiwan); S. Hsu, K. Hsiao (Synchrotron Radiation Research Center,Taiwan); J. Chen (Synchrotron Radiation Research Center and National Tsing-Hua University, Taiwan) An aluminum alloys vacuum chamber, 4m in length, for an undulator was installed in the 1.3 GeV electron storage ring of the Synchrotron Radiation Research Center (SRRC) in this spring. The inner cross section of this vacuum chamber is in elliptical shape of 10mm in height and 80mm in width. A beam life time of 7 hours at 200 mA beam current was quickly achieved after beam-self cleaning on the new chamber walls. The impact of this new vacuum chamber, before and after the installation, to the storage ring was compared . The injection rate was reduced. The stronger beam loss during the injection was measured. The effects of small vertical aperture and the effective pumping to the electron beam life time were studied. The planning in upgrading the storage ring vacuum system is also descripted.
9:40 AM		VT-MoM-5 Calculated Physical Adsorption Isotherms of Neon and Radon on a Heterogeneous Surface J. Hobson (National Vacuum Technologies, Inc, Canada) The physical adsorption isotherms on a heterogeneous surface of neon (Ne) have received limited attention, and those of radon (Rn) virtually none. The other inert gasses helium, argon, krypton, and xenon have been explored extensively, both theoretically and experimentally. The purpose of the present paper is to calculate the physical adsorption isotherms of Ne and Rn on a heterogeneous surface over wide ranges of temperature, pressure, and coverage. The model used is the same as that used recently for hydrogen (1), wherein the isotherm was carried to the vapor pressure at the higher pressures, and to Henry's Law at the lowest pressures, with the intermediate range being described by the Dubinin Raduskevic (DR) equation (2). All that is required for this model is a knowledge of the vapor pressures of the adsorbates as a function of temperature, and the DR constant B. By comparison with the measured values of B for the other inert gases, values of (1/sqrtB) of 440 cals/mole for Ne and 2685 cals/mole for Rn were obtained. Using these values, calculations were carried out for Ne at temperatures of 7, 10, 15, 20, 27.2 (normal boiling point), 300 and 500K. In all, the pressure range extended from 10/sup-15/ to 10/sup7/ torr (about 10/sup-17/ to 10/sup9/ Pascals), and the relative coverage range from 10/sup-15/ to 10/sup3/ monolayers. Where relevant experimental data are available they are compared with the results. (1) J.P.Hobson, JVST A, 13(3) 549 (1995). (2)MM.Dubinin and L.V. Radushkevich, Prod. Acad. Sci. USSR 55, 331 (1947).
10:00 AM		VT-MoM-6 Fabrication and Performance of the APS Accelerator Vacuum Systems J. Noonan, J. Gagliano, G. Goeppner, R. Rosenberg, D. Walters, C. Liu (Argonne National Laboratory) The Advanced Photon Source (APS) is a high-intensity x-ray synchrotron radiation facility that is moving out of construction into operations. The storage ring vacuum system must operate at pressures 10 /super -9/ torr or better with 100 mA beam of 7 GeV positron stored. In order to achieve this UHV operation, the storage ring is one of the largest vacuum systems that uses aluminum chambers AND aluminum ConFlat flanges. Special fabrication processes were required. In addition bake-out procedures were developed to maintain vacuum integrity at the aluminum/stainless steel flange assembly. The knowledge gained in fabricating and assembling the aluminum vacuum system will be described. The APS accelerator vacuum systems are now operational. The operational pressures will be compared with calculated gas loads developed using finite element analysis of the system conductance.
10:40 AM		VT-MoM-8 Study of Distributed Ion-pumps in CESR Y. Li, N. Mistry, R. Kersevan (Cornell University) It is desirable to lower the anode voltage of the distributed ion-pumps (DIPs) in CESR in order to suppress a beam instability caused by the 'leakage' electric field from the DIPs and to extend the lifetime of the pumps and their power supplies. The DIP pumping speed is measured as a function of anode voltage with and without stored beam. It is found that the DIP pumping speed remains relatively unchanged with anode voltage changing from the 'normal' operation value of 7.4 kV to as low as 1.8 kV, when there is stored beam in CESR. A simple model is used to explain the operation of DIPs under the influence of stored beams. (*) Work supported in part by the National Science Foundation
11:00 AM		VT-MoM-9 Tests of an Environmentally Safe UHV Cleaning Process for BNL Accelerators and Storage Rings C. Foerster, C. Lanni, R. Lee (Brookhaven National Laboratory); G. Mitchell, W. Quade (Dow Chemical Advanced Cleaning Systems) A large measure of the successful operation of the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory (BNL) for over a decade can be attributed to the cleaning of its UHV components during and after construction. A new UHV cleaning process, which had to be environmentally and personnel safe, was needed to replace the harsh, unfriendly process which was still in use. Dow Advanced Cleaning Systems was contracted to develop a replacement process without the use of harsh chemicals and which must clean vacuum surfaces as well as the existing process. Acceptance of the replacement process was primarily based on Photon Stimulated Desorption (PSD) measurements of beam tube samples run on NSLS beam line U10B. One meter long beam tube samples were fabricated from aluminum, 304 stainless steel and oxygen free copper. Initially, coupon samples were cleaned and passed preliminary testing for the proposed process. Next, beam tube samples of each material were cleaned, and the PSD measured on beam line U10B using white light with a critical energy of 487ev. Prior to cleaning, the samples were contaminated with a mixture of cutting oils, lubricants, vacuum oils and vacuum grease. The contaminated samples were then baked. Samples of each material were also cleaned with the existing process after the same preparation. Beam tube samples were exposed to between 10\super 22\ and 10\super 23\ photons per meter for a PSD measurement. Desorption yields for H\sub 2\, CO, CO\sub 2\, CH\sub 4\ and H\sub 2\O are reported for both the existing cleaning and for the replacement cleaning process. Preliminary data, residual gas scans, and PSD results are given and discussed. The new process is also compared with new cleaning methods developed in other laboratories. Work performed under the auspices of the U.S. Department of Energy, under contract DE-AC02-76CH00016 and W-31-109-ENG-38.
11:20 AM		VT-MoM-10 Fine Structure Dependent Hydrogen Permeation in Titanium Nitride Films for Extremely High Vacuum Application S. Tsukahara, Y. Ikeda, K. Saito (ULVAC Japan, Ltd.) To lower the outgassing rate of stainless steel SS it can be coated by a titanium nitride TiN film that works as a barrier to the desorption/permeation of the hydrogen included in the bulk SS into the vacuum space.\super 1\ The resultant TiN film coated material TiN/SS with the outgassing rate as low as 10\super -12\ Pa-m-s\super -1\ range at the ultimate pressure is useful for extremely high vacuum apparatus application. We examined the following experimental steps to find a way how to improve further the outgassing rate of the practical chamber. 1. Various TiN films were prepared on electrolytically polished stainless steel SUS304L plates by the hollow cathode discharge HCD ion plating method using several different apparatus controlling various conditions. The sample is note as TiN/SUS304L. 2. Hydrogen permeation of TiN/SUS304L and SUS304L plate samples was measured at 500, 400, and 300oC. The hydrogen permeation constant K\sub TiN\ of the 0.6 - 2.0 \mu\m thick TiN films at 500oC varied between 6x10\super-10\and 4x10\super -12\ Pa\super 1/2\-m\super 2\-s\super -1\, whereas that of stainless steel K\sub SUS\ was 1.6x10\super -8\ Pa\super1/2\-m\super2\ -s\super -1\ at 500oC . 3. Cross-sectional transmission electronmicrographs up to lattice images of TiN/SUS304L samples were observed at various magnifications and the total and fine structures from the SS substrate to the TiN film were inspected. The crystalline quality and grain size from 50 nm to 300 nm of TiN films varied depending on the deposition parameters. 4. From the TiN fine structure dependence of K\sub TiN\ we speculate that the large parts of the measured hydrogen permeation of TiN film is caused by crystalline grain boundary parts. The experimental result that a TiN film with less grain boundaries and less defects shows less hydrogen permeation and thus lower outgassing rate is simple and reasonable. The important factors to grow a TiN film with less defects by the HCD ion plating method are the application of bias voltage to the substrate, the nitrogen pressure at the process, the temperature of the substrate and the film, the titanium intermediate layer between the substrate and the TiN film, and the deposition rate. \super 1\ K.Saito, S.Inayoshi, Y.Ikeda, Y.Yang, and S.Tsukahara, J.Vac.Sci.Technol. A13, 556 (1995).
11:40 AM		VT-MoM-11 Synchrotron Radiation Induced Desorptions on Aluminum Surfaces J. Chen (Synchrotron Radiation Research Center and National Tsing-Hua University, P.R. China); G. Hsiung (Synchrotron Radiation Research Center); C. Chang (Synchrotron Radiation Research Center and National Tsing-Hua University, P.R. China); J. Shyy, T. Lin (Synchrotron Radiation Research Center) The photon-induced desorption (PID) on aluminum surfaces were studied by irradiating the aluminum samples in an experimental station and the aluminum chambers in the 1.3 GeV electron storage ring of the Synchrotron Radiation Research Center. The effects on the PID due to the changing parameters of the storage ring and due to the glow discharge cleaning (GDC) treatment on the samples were investigated. Water vapor behavior was mainly concerned in the storage ring vacuum chamber desorptions. A different behavior was observed between the desorptions of the GDC treated and untreated surfaces.