Electron cloud buildup is a major limitation for high-energy particle accelerators such as the CERN Super Proton Synchrotron (SPS). Amorphous carbon thin films with low initial secondary electron ...yield (SEY≅1.0 ) have been applied as a mitigation material in the SPS vacuum chambers. This paper summarizes the experimental setups for electron cloud monitoring, coating procedures, and recent measurements performed with amorphous carbon coated vacuum chambers in the SPS. The electron cloud measured by dedicated monitors is completely suppressed for LHC-type beams. Even after more than one year’s exposure in the SPS with the machine in operation, the coating does not show any increase in the secondary electron yield. The study of coated vacuum chambers for the SPS dipole magnets is in progress; the correlation between electron cloud reduction and pressure rises is not yet fully understood. Some prototypes have already been installed in the accelerator and plans for the implementation of an optimized coating technique are under development.
During Run 1 of the LHC, one of the injection kicker magnets caused occasional operational delays due to beam induced heating with high bunch intensity and short bunch lengths. In addition, there ...were also sporadic issues with vacuum activity and electrical flashover of the injection kickers. An extensive program of studies was launched and significant upgrades were carried out during Long Shutdown 1 (LS 1). These upgrades included a new design of beam screen to reduce both beam coupling impedance of the kicker magnet and the electric field associated with the screen conductors, hence decreasing the probability of electrical breakdown in this region. This paper presents operational experience of the injection kicker magnets during the first years of Run 2 of the LHC, including a discussion of faults and kicker magnet issues that limited LHC operation. In addition, in light of these issues, plans for further upgrades are briefly discussed.
Carbon thin films for electron cloud mitigation and anti-multipacting applications have been prepared by dc magnetron sputtering in both neon and argon discharge gases and by plasma enhanced chemical ...vapour deposition (PECVD) using acetylene. The thin films have been characterized using Secondary Electron Yield (SEY) measurements, Scanning Electron Microscopy (SEM), Nuclear Reaction Analysis (NRA) and X-ray Photoemission Spectroscopy (XPS). For more than 100 carbon thin films prepared by sputtering the average maximum SEY is 0.98 ± 0.07 after air transfer. The density of the films is lower than the density of Highly Oriented Pyrolytic Graphite (HOPG), a fact which partially explains their lower SEY. XPS shows that magnetron sputtered samples exhibit mainly sp2 type bonds. The intensity on the high binding energy side of C1s is found to be related to the value of the SEY. In addition the initial surface concentration of oxygen has no influence on the resulting SEY, when it is below 16%. The thin films produced by PECVD have a much higher maximum SEY of 1.49 ± 0.07.
Storage conditions in air, namely wrapping in aluminium foil, preserves the low SEY by more than one year. Such coatings have already been applied successfully in accelerators and multipacting test benches.
•Carbon coatings by dc magnetron sputtering with secondary electron yield of 1.•The secondary electron yield of 1 is preserved for more than one year in air.•The secondary electron yield and density are lower than for HOPG.•The amount of H2 during coating influences the secondary electron yield.
During the past decade, intense experimental studies on the heavy-ion induced molecular desorption were performed in several particle accelerator laboratories worldwide in order to understand and ...overcome large dynamic pressure rises caused by lost beam ions. Different target materials and various coatings were studied for desorption and mitigation techniques were applied to heavy-ion accelerators. For the upgrade of the CERN injector complex, a coating of the Super Proton Synchrotron (SPS) vacuum system with a thin film of amorphous carbon is under study to mitigate the electron cloud effect observed during SPS operation with the nominal proton beam for the Large Hadron Collider (LHC). Since the SPS is also part of the heavy-ion injector chain for LHC, dynamic vacuum studies of amorphous carbon films are important to determine their ion induced desorption yields. At the CERN Heavy Ion Accelerator (LINAC 3), carbon-coated accelerator-type stainless steel vacuum chambers were tested for desorption using 4.2MeV/u Pb54+ ions. We describe the experimental setup and method, present the results for unbaked and baked films, and summarize surface characterizations such as secondary electron yield measurements, x-ray photoemission spectroscopy, and scanning electron microscopy studies. Finally, we present a high-energy scaling of lead-ion induced desorption yields from the MeV/u to GeV/u range.
We discuss the possibility of creating novel research tools by producing and storing highly relativistic beams of highly ionised atoms in the CERN accelerator complex, and by exciting their atomic ...degrees of freedom with lasers to produce high-energy photon beams. Intensity of such photon beams would be by several orders of magnitude higher than offered by the presently operating light sources, in the particularly interesting gamma-ray energy domain of 0.1-400 MeV. In this energy range, the high-intensity photon beams can be used to produce secondary beams of polarised electrons, polarised positrons, polarised muons, neutrinos, neutrons and radioactive ions. New research opportunities in a wide domain of fundamental and applied physics can be opened by the Gamma Factory scientific programme based on the above primary and secondary beams.
The Electron Multipacting (EM) phenomenon is a limiting factor for the achievement of high luminosity in accelerators for positively charged particles and for the performance of RF devices. At CERN, ...the Super Proton Synchrotron (SPS) must be upgraded in order to feed the Large Hadron Collider (LHC) with 25 ns bunch spaced beams. At such small bunch spacing, EM may limit the performance of the SPS and consequently that of the LHC. To mitigate this phenomenon CERN is developing a carbon thin film coating with low Secondary Electron Yield (SEY) to coat the internal walls of the SPS dipoles beam pipes. This paper presents the progresses in the coating technology, the performance of the carbon coatings and the strategy for a large scale production.
To rectify the problems of electron clouds observed in RHIC and unacceptable ohmic heating for superconducting magnets that can limit future machine upgrades, we started developing a robotic plasma ...deposition technique for \(in-situ\) coating of the RHIC 316LN stainless steel cold bore tubes based on staged magnetrons mounted on a mobile mole for deposition of Cu followed by amorphous carbon (a-C) coating. The Cu coating reduces wall resistivity, while a-C has low SEY that suppresses electron cloud formation. Recent RF resistivity computations indicate that 10 {\mu}m of Cu coating thickness is needed. But, Cu coatings thicker than 2 {\mu}m can have grain structures that might have lower SEY like gold black. A 15-cm Cu cathode magnetron was designed and fabricated, after which, 30 cm long samples of RHIC cold bore tubes were coated with various OFHC copper thicknesses; room temperature RF resistivity measured. Rectangular stainless steel and SS discs were Cu coated. SEY of rectangular samples were measured at room; and, SEY of a disc sample was measured at cryogenic temperatures.
LHC Upgrades in preparation of Run 3 Arduini, G.; Baglin, V.; Bartosik, H. ...
Journal of instrumentation,
05/2024, Letnik:
19, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Abstract The Large Hadron Collider (LHC) Long Shutdown 2 (2019–2021), following LHC Run 2, was primarily dedicated to the upgrade of the LHC Injectors but it included also a significant amount of ...activities aimed at consolidation of the LHC machine components, removal of known limitations and initial upgrades in view of the High-Luminosity LHC (HL-LHC) to favour the intensity ramp-up during Run 3 (2022–2025). An overview of the major modifications to the accelerator and its systems is followed by a summary of the results of the superconducting magnet training campaign to increase the LHC operation energy beyond the maximum value of 6.5 TeV reached during Run 2. The LHC configuration and the scenarios for proton and ion operation for Run 3 are presented considering the expected performance of the upgraded LHC Injectors and the proton beam intensity limitations resulting from the heat load on the cryogenic system due to beam-induced electron cloud and impedance.
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