As RHIC beam intensity increases beyond original scope, pressure rises have been observed in some regions. The luminosity limiting pressure rises are associated with electron multi-pacting, electron ...stimulated desorption and beam induced desorption. Non-Evaporable Getter (NEG) coated beamtubes have been proven effective to suppress pressure rise in synchrotron radiation facilities. Standard beamtubes have been NEG coated by a vendor and added to many RHIC UHV regions. BNL is developing a cylindrical magnetron sputtering system to NEG coat special beryllium beamtubes installed in RHIC experimental regions. It features a hollow, liquid cooled cathode producing power density of 500W/m and deposition rate of 5000 Angstrom/hr on 7.5cm OD beamtube. The cathode, a titanium tube partially covered with zirconium and vanadium ribbons, is oriented for horizontal coating of 4m long chambers. Ribbons and magnets are arranged to provide uniform sputtering distribution and deposited NEG composition. Vacuum performance of NEG coated tubes was measured. Coating was analyzed with energy dispersion spectroscopy, auger electron spectroscopy and scanning electron microscopy. System design, development, and analysis results are presented.
The inner surfaces of the 248 m Spallation Neutron Source (SNS) accumulator ring vacuum chambers are coated with ∼ 100nm of titanium nitride (TiN) to reduce the secondary electron yield (SEY) of the ...chamber walls. There are approximately 135 chambers and kicker modules, some up to 5m in length and 36cm in diameter, coated with TiN. The coating is deposited by means of reactive DC magnetron sputtering using a cylindrical cathode with internal permanent magnets. This cathode configuration generates a deposition rate sufficient to meet the required production schedule and produces stoichiometric films with good adhesion, low SEY and acceptable outgassing. Moreover, the cathode magnet configuration allows for simple changes in length and has been adapted to coat the wide variety of chambers and components contained within the arcs, injection, extraction, collimation and RF straight sections. Chamber types and quantities as well as the cathode configurations are presented herein. The unique coating requirements of the injection kicker ceramic chambers and the extraction kicker ferrite surface will be emphasized. A brief summary of the salient coating properties is given including the interdependence of SEY as a function of surface roughness and its effect on outgassing.
With increasing ion beam intensity during recent RHIC operations, rapid pressure rises of several decades were observed at most warm sections and at a few cold sections. The pressure rises are ...associated with electron multi-pacting, electron stimulated desorption and beam ion induced desorption; and have been one of the major intensity and luminosity limiting factors for RHIC. Improvement of the warm sections has been carried out in the last few years. Extensive in-situ bakes, additional UHV pumping and anti-grazing ridges have been implemented. Several hundred meters of NEG coated beam pipes have been installed and activated. Vacuum monitoring and logging were enhanced. Preventive measures, such as pumping before cool down to reduce monolayer condensates, were also taken to suppress the pressure rises in the cold sections. The effectiveness of these measures in reducing the pressure rises during machine studies and during physics runs are discussed and summarized.
The Spallation Neutron Source (SNS) ring is designed to accumulate high intensity protons. Ultrahigh vacuum of 10-9 Torr is required in the accumulator ring to minimize beam-residual gas ionization. ...To reduce the secondary electron yield (SEY) and the associated electron cloud instability, the ring vacuum chambers are coated with titanium nitride (TiN). This paper describes the design, fabrication, assembly and vacuum processing of the ring and beam transport line vacuum chambers as well as the associated instrumentation
We present the conceptual design of the NSLS-II injection system 1, 2. The injection system consists of a low-energy linac, booster and transport lines. We review two different injection system ...configurations; a booster located in the storage ring tunnel and a booster housed in a separate building. We briefly discuss main parameters and layout of the injection system components.
Beam loss along the Spallation Neutron Source's accumulator ring is mainly located at the collimator region and injection region. This paper discusses the electron cloud build-up, control and ...collection at these two regions simulated with the three-dimension program CLOUDLAND.
In the SNS accumulator ring, ceramic vacuum chambers are used for the 8 injection kickers to avoid shielding of a fast-changing kicker field and to minimize eddy current heating. The inner surface of ...the ceramic chambers was coated with Cu to reduce the beam coupling impedance and provide passage for beam image current, and a TiN over layer to reduce secondary electron yield. The ferrite surfaces of the 14 extraction kicker modules were also coated with TiN. Customized masks were used to produce longitudinal coating strips of 1 cm x 5 cm with ∼ 1 mm separation among the strips. The coating methods, the physical and electromagnetic properties of the coatings and the effect to the beam and to the electron cloud build-up are summarized.
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