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The LHC successfully returned to operation in April 2015 after almost 2 years of Long Shutdown 1 (LS1) for various upgrade and consolidation programs. During Run 2 (2015 - 2018) the LHC operated for more than 3600 fills and it has reached a total integrated luminosity of more than 150 fb-1. This paper summarizes the dynamic vacuum observations in different locations along the LHC during the dedicated fills as well as during the physics runs with different beam parameters. The beam-induced dynamic pressure rise in presence of synchrotron radiation and electron multipacting have been investigated and are presented here. A clear beam conditioning effect has been observed in Run 2., CERN Yellow Reports: Conference Proceedings, Vol. 7 (2020): ECLOUD’18 : Proceedings of the Joint INFN-CERN-ARIES Workshop on Electron-Cloud Effects, 3–7 June 2018, La Biodola, Isola d’Elba, Italy

The presented document if the Letter of Intent for the Gamma Factory Proof-of-Principle Experiment.

This contribution discusses the possibility of broadening the present CERN research programme making use of a novel concept of light source. The proposed, Partially Stripped Ion beam driven, light source is the backbone of the Gamma Factory (GF) initiative. It could be realized at CERN by using the infrastructure of the already existing accelerators. It could push the intensity limits of the presently operating light-sources by up to 7 orders of magnitude, reaching fluxes of 10¹⁷ photons/s in the interesting gamma-ray energy domain between 1 MeV and 400 MeV. The GF light-source cannot be replaced, in this energy domain, by a FEL source as long as the multi TeV electron beams are not available. Its intensity is beyond the reach of the Inverse Compton Scattering sources. The unprecedented-intensity, energy-tuned gamma beams, together with the gamma-beams-driven secondary beams of polarized leptons, neutrinos, neutrons and radioactive ions are the basic research tools of the proposed Gamma Factory. A broad spectrum of new opportunities, in a vast domain of uncharted fundamental and applied physics territories, could be opened by the Gamma Factory research programme., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The LHC Injectors Upgrade project (LIU) has been initiated to improve the performances of the existing injector complex at CERN to match the future requirements of the HL-LHC (High Luminosity LHC). In this framework, the Proton Synchrotron (PS) will undergo fundamental changes for many of its main systems: the injection energy will be increased to reduce space-charge effects, the transverse damper will be improved to cope with transverse instabilities, and the RF systems will be upgraded to accelerate higher beam intensity and brightness. These hardware improvements are triggered by a series of studies meant to identify the most critical performance bottlenecks, like space charge, impedances, longitudinal and transverse instabilities, as well as electron-cloud. Additionally, alternative production schemes for the LHC-type beams have been proposed and implemented to circumvent some of the present limitations. A summary of the most recent advances of the studies, as well as the proposed hardware improvements is given.

The build up of an Electron Cloud (EC) has been observed at the CERN Proton Synchrotron (PS) during the last stages of the LHC high intensity beam preparation, especially after the bunch shortening before extraction. Two dedicated EC experiments, both equipped with two button pick-ups, a pressure gauge, a clearing electrode and a small dipole magnet, are available in two straight sections of the machine. A measurement campaign has been carried out, in order to scan the EC build-up of LHC-type beams with different bunch spacing, bunch intensity and bunch length. Such information, combined with the results from build up simulations, is of relevance for the characterization in terms of Secondary Emission Yield (SEY) of the chamber inner surface. The interest is twofold: this will enable us to predict the EC build up distribution in the PS for higher intensity beams in the frame of the upgrade program, and it will provide validation of the EC simulation models and codes.

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 4.2 MeV/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.

Electron cloud build-up is a major limitation for the operation of the SPS with LHC beam above nominal intensity. These beams are envisaged in the frame of the LHC luminosity upgrade and will be available from the new injectors LPSPL and PS2. A series of studies have been conducted in order to identify possible means to suppress electron multipacting by coating the existing SPS vacuum chambers with thin films of amorphous carbon. After a description of the experimental apparatus installed in the SPS, the results of the tests performed with beam in 2008 will be presented.

Amorphous carbon (a-C) coatings can reliably be produced with a maximum secondary electron yield (SEY) close to 1 at room temperature. Measurements at low temperature (LHe) are in progress. Analysis by X-ray Photoemission Spectroscopy (XPS) shows a correlation between the lineshape of C1s spectrum in XPS and the maximum SEY of the investigated samples. The initial level of oxygen on the surface of the various samples does not seem to be related to the initial maximum SEY value. However, the increase of the SEY with air exposure time on each individual sample is related to the amount of oxygen containing adsorbates. Storage in different environments has been investigated (static vacuum, aluminium foil, dry nitrogen and desiccators), and shows significant differences in the “aging” behaviour. Aging is very moderate when storing samples wrapped in aluminium foil in air. Samples which have undergone aging due to inappropriate storage can be recovered nearly to the initial value of their SEY by surface treatments such as conditioning by electron beam, annealing under vacuum and ion bombardment. However, an enhanced sensitivity to air exposure is observed for most of these curing methods.

Cracow Epiphany Conference on Advances in Heavy Ion Physics, Krakow, Poland, 8 Jan 2019 - 11 Jan 2019; Acta physica Polonica / B Particle physics and field theory, nuclear physics, theory of relativity B 50(6), 1191 - 1203 (2019). doi:10.5506/APhysPolB.50.1191, Published by Inst. of Physics, Jagellonian Univ., Cracow

Amorphous carbon (a-C) coatings have been tested in electron cloud monitors (ECM) in the Super Proton Synchrotron (SPS) and have shown for LHC type beams a reduction of the electron cloud current by a factor 104 compared to stainless steel (StSt). This performance has been maintained for more than 3 years under SPS operation conditions. Secondary electron yield (SEY) laboratory data confirm that after more than 1 year of SPS operation, the coating maintains a SEY below 1.0. The compatibility of coexisting StSt and a-C surfaces has been studied in an ECM having coated and uncoated areas. The results show no degradation of the properties of the a-C areas. The performance of diamond like carbon (DLC) coating has also been studied. DLC shows a less effective reduction of the EC current than a-C, but conditioning is faster than for StSt. Three a-C coated dipoles were inserted in the SPS. However, even with no EC detected, the dynamic pressure rise is similar to the one observed in the StSt reference dipoles. Measurement in a new ECM equipped with clearing electrodes to verify the relation between pressure signals and intensity of the EC, as well as an improvement of the diagnostics in the dipoles are in progress.