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The cold bore experiment (COLDEX), that can be cooled below 3 K, has been fitted with a ~ 2 m long actively cooled beam screen equipped with cryosorber to simulate the LHC Long Straight Section (LSS) beam screens. Effects of both synchrotron radiation at grazing incidence with 194 eV critical energy and gas injections have been studied. Results as a function of temperature, gas species and gas coverage are presented. Possible implications to LHC LSS design and operation are discussed.

The bake-out and activation of the TiZrV NEG coatings of the 6 km Long Straight Sections (LSS) of the Large Hadron Collider (LHC) is in its final step. After the bakeout and the NEG activation, the average ultimate pressure, over more than one hundred vacuum sectors, is below 10^-10 Pa. Therefore, the nominal requirement for the four experimental insertions is fulfilled. The nominal performances are also ensured for all the insertions housing the collimator systems, the RF cavities and the beam dumping systems. The main difficulties encountered during the bake-out and the activation of the NEG coated chambers is presented and discussed. In particular, the acceptance test and the limiting factors of the reached ultimate pressures are addressed. Furthermore, the influence on the ultimate pressures of the beam components (collimators, beam instrumentation, etc.) is discussed. Finally, preliminary results obtained from a NEG vacuum pilot sector installed in the laboratory and dedicated to the evaluation of the NEG performance is presented

The cold bore experiment (COLDEX) installed in a beam line of the electron-positron accumulator (EPA) at CERN, has been used to study the effect of synchrotron radiation onto the LHC dipole beam screen. The ~ 2 m long cryostat, that can be cooled below 3 K, is fitted with an actively cooled beam screen. A 'sawtooth' copper co-laminated type beam screen has been submitted to grazing synchrotron radiation with 194 eV critical energy. Experiments studying the effect of photon dose, gas condensation onto beam screen or cold bore and temperature oscillations is presented. Implications to LHC operation is discussed.

After the 2011 run, actions were put in place during the 2011/2012 winter stop to limit beam induced radio frequency (RF) heating of LHC components. However, some components could not be changed during this short stop and continued to represent a limitation throughout 2012. In addition, the stored beam intensity increased in 2012 and the temperature of certain components became critical. In this contribution, the beam induced heating limitations for 2012 and the expected beam induced heating limitations for the restart after the Long Shutdown 1 (LS1) will be compiled. The expected consequences of running with 25 ns or 50 ns bunch spacing will be detailed, as well as the consequences of running with shorter bunch length. Finally, actions on hardware or beam parameters to monitor and mitigate the impact of beam induced heating to LHC operation after LS1 will be discussed.

Secondary electron emission of surfaces exposed to oscillating electromagnetic field is at the origin of the multipacting effect that could severely perturb the operation of particle accelerators. This contribution tries to illustrate by measurement results, the origin of the secondary electron emission as well as the main reasons for the discrepancies between technical materials and pure metals. The variation of the secondary electron yield with the incident electron energy will be discussed for various types of technical surfaces. The influence of a gas condensation on these surfaces will also be addressed in the context of the LHC accelerator. Various treatments aiming at a permanent reduction of the secondary electron yield will be presented. A special attention will be paid to the decrease of the secondary electron yield under electron or photon impact and to its possible beneficial consequences for the processing of devices prone to multipacting.

The vacuum inside the LHC pipes has a key role in correct operation of the accelerator. The interaction of the beam with residual gas in the pipes can lead to the loss of the beam itself and damage accelerator components. Nevertheless, beam-gas interactions can be exploited to indirectly measure the gas pressure inside the beam pipe, detecting the secondaries produced. The showers generated are detected by Beam Loss Monitors, whose signals depend on the gas pressure. This technique would also allow to punctually measure the gas pressure in sections of the accelerator where vacuum gauges are not frequent, such as the arcs. The problem has been addressed by means of FLUKA simulations and the results have been benchmarked with direct measurements performed in the LHC in 2011.

Machine studies have been performed at the end of the 2010 proton run to study the machine performance with bunch trains with 50 and 75 ns spacings in preparation for the proton run in 2011. The results of the observations and measurements will be summarized and compared with existing models. Possible running scenarios for 2011 will be outlined.

Studies of the photoelectron yield and photon reflectivity at grazing incidence (11 mrad) from candidate LHC vacuum chamber materials have been made on a dedicated beam line on the Electron Positron A ccumulator (EPA) ring at CERN. These measurements provide realistic input toward a better understanding of the electron cloud phenomena expected in the LHC. The measurements were made using synchrotro n radiation with critical photon energies of 194 eV and 45 eV; the latter corresponding to that of the LHC at the design energy of 7 TeV. The test materials are mainly copper, either, i) coated by co- lamination or by electroplating onto stainless steel, or ii) bulk copper prepared by special machining. The key parameters explored were the effect of surface roughness on the reflectivity and the pho toelectron yield at grazing photon incidence, and the effect of magnetic field direction on the yields measured at normal photon incidence. The implications of the results on the electron cloud phenom ena, and thus the LHC vacuum chamber design, is discussed.

We discuss the predicted electron cloud build up in the arcs and the long straight sections of the LHC, and its possible consequences on heat load, beam stability, long-term emittance preservation, and vacuum. Our predictions are based on computer simulations and analytical estimates, parts of which have been benchmarked against experimental observations at the SPS.

The secondary electron emission of surfaces exposed to the impact of energetic electrons contributes significantly to the electron cloud build-up. For the prediction of the consequences of this effect the measurements of the secondary electron yield carried out at CERN are an important source of information. New experimental results concerning the total secondary electron yield for very low primary electron energy (between 5 eV and 50 eV) will be also given in the case of as received copper. Furthermore the energy distribution of the re-emitted electrons is drastically influenced by the primary electron energy. The ratio of the number of reflected electrons to the total number of re-emitted electrons has been measured and its variation with the primary electron energy will be shown. As a consequence of these new experimental data, a numerical approximation to express the secondary electron yield as a function of the primary electron energy will be given for the low incident electron energy region (E < 50 eV). It has been shown that the decrease of the secondary electron yield due to the electron bombardment could reduce sufficiently the consequences electron cloud effect. To understand further the origin of this decrease, the results of experiments showing the variation of the electron induced desorption yield with the incident electron dose will be compared to the concomitant reduction of the secondary electron yield.

The electron cloud is of major concern for most of the storage rings operating with large bunch currents and low bunch spacing. The Large Hadron Collider (LHC) operated at cryogenic temperature will have to face the electron cloud when running with proton beams. For this reason, the first experimental studies related to the electron cloud in a LHC type cryogenic vacuum system have been launched in 2002 after the closure of the Electron Positron Accumulator (EPA) synchrotron radiation experimental program. The cold bore experiment (COLDEX) has been installed in the CERN Super Proton Synchrotron (SPS) where electron clouds could be produced with proton beams. The detailed results of the investigations, which include measurements of the dynamic heat deposition, dynamic total pressure rise and residual gas composition as a function of beam operation dose will be presented. The beam conditioning efficiency is studied as a function of temperature. The results of dedicated experiments with pre-condensed gas layers onto the beam screen are shown. The preliminary results with 75 ns bunch spacing are presented. The experimental results obtained as a function of beam operation dose are compared to the outputs of the ECLOUD simulation code. Finally, the implications to the LHC design and operation are discussed.

The HiLumi-LHC machine upgrade has officially started as an approved LHC project (see dedicated presentations at this conference on the subject). One important feature of the upgrade is the installation of very high-gradient triplet magnets for focusing the beams at the collision points of the two high-luminosity detectors ATLAS and CMS. Other important topics are new superconducting D1 and D2 magnets, installation of crab cavities and new tertiary collimators, and re-shuffling of the dispersion suppression area. Based on the current magnetic lattice set-up and beam orbits, a detailed study of the emission of synchrotron radiation (SR) and related photon-induced desorption (PID) has been carried out. A significant amount of SR photons are generated by the two off-axis beams in the common vacuum chamber of the triplet area, about 57 m in length. Ray-tracing Montecarlo codes Synrad+ and Molflow+ have been employed in this study. The related PID pressure profiles are shown, together with simulations using the code VASCO for the analysis of beam losses and background in the detectors, including electron cloud effects.

During the incident of sector 3-4, the two beam vacuum sectors of 2.8 km each and four insulation vacuum sectors i.e. 750 m were vented to atmospheric pressure. Besides the mechanical damages of the nested bellows and plug-in-modules due to the mouvement of the cold masses under the helium pressure, soot and debris of superinsulation were spread inside the beam and insulation vacua. The presentation will cover the extend of the damage from Q6R3 till Q6L4. The strategy deployed to repair, to clean and to qualify the damaged vacuum systems will be discussed. Scheduling and compatibilty with beam operation issues will be also adressed.