Electron cloud observation in the LHC (original) (raw)
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Analysis of the Electron Cloud Observations with 25 ns Bunch Spacing at the LHC
2014
Electron Cloud (EC) effects have been identified as a major performance limitation for the Large Hadron Collider (LHC) when operating with the nominal bunch spacing of 25 ns. During the LHC Run 1 (2010 - 2013) the luminosity production mainly used beams with 50 ns spacing, while 25 ns beams were only employed for short periods in 2011 and 2012 for test purposes. On these occasions, observables such as pressure rise, heat load in the cold sections as well as clear signatures on bunch-by-bunch emittance blow up, particle loss and energy loss indicated the presence of an EC in a large portion of the LHC. The analysis of the recorded data, together with EC build up simulations, has led to a significant improvement of our understanding of the EC effect in the different components of the LHC. Studies were carried out both at injection energy (450 GeV) and at top energy (4 TeV) aiming at determining the energy dependence of the EC formation and its impact on the quality of the proton beam.
First electron-cloud studies at the Large Hadron Collider
Physical Review Special Topics - Accelerators and Beams, 2013
bunch spacing, important electron-cloud effects, like pressure rise, cryogenic heat load, beam instabilities, or emittance growth, were observed. Methods have been developed to infer different key beam-pipe surface parameters by benchmarking simulations and pressure rise as well as heat-load observations. These methods allow us to monitor the scrubbing process, i.e., the reduction of the secondary emission yield as a function of time, in order to decide on the most appropriate strategies for machine operation. To better understand the influence of electron clouds on the beam dynamics, simulations have been carried out to examine both the coherent and the incoherent effects on the beam. In this paper we present the methodology and first results for the scrubbing monitoring process at the LHC. We also review simulated instability thresholds and tune footprints for beams of different emittance, interacting with an electron cloud in field-free or dipole regions.
Beam–induced electron cloud in the LHC and possible
1998
Synchrotron radiation from proton bunches in the LHC cre-ates photoelectrons at the beam screen wall. These pho-toelectrons are accelerated towards the positively charged proton bunch and drift across the beam pipe between suc-cessive bunches. When they hit the opposite wall, they gen-erate secondary electrons which can in turn be accelerated by the next bunch if they are slow enough to survive. We summarize the results of an intensive research program set up at CERN and discuss recent multipacting tests as well as the importance of several key parameters, such as pho-ton reflectivity, photoelectron and secondary electron yield. Then, based on analytic estimates and simulation results, we discuss possible solutions to avoid the fast build-up of an electron cloud with potential implications for beam sta-bility and heat load on the cryogenic system. 1
Present understanding of electron cloud effects in the large hadron collider
Proceedings of the 2003 Bipolar/BiCMOS Circuits and Technology Meeting (IEEE Cat. No.03CH37440), 2003
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.
LHC and SPS Electron Cloud Studies
AIP Conference Proceedings, 2005
The additional heat load onto the LHC beam screens of the cold magnets in the bending sections (~21 km) is still considered as one of the main possible limitations of the LHC performances. Since more than three years, the characteristics of the electron cloud are being studied in the SPS at ambient (RT) and cryogenic temperatures in both dipole and field free conditions. The results obtained in the SPS in 2003 showed a vacuum cleaning (or vacuum scrubbing) on both ambient and cryogenic surfaces. On the contrary, the heat load and the electron intensity (current collected at the detector) under both dipole and field free conditions at 4.5 or 30 K had shown only a limited decrease after 12 A.h of beam i.e. beam conditioning. Water contamination coming from the unbaked upstream and downstream parts of the SPS (non-baked machine) was suspected to be responsible for this behavior. The upgrade of the existing detectors as well as the design and results obtained with the new strip detector installed in a quadrupole are presented. Preliminary results on the electron cloud build up in the quadrupole will also be presented and compared to the predictions of the simulations. The effects of the gases physisorbed at cryogenic temperature in the SPS and in the laboratory are shown and the applicability to the LHC will be discussed.
Electron Cloud Effects in the CERN SPS and LHC
Proceedings of …, 2000
Electron cloud effects have been recently observed in the CERN SPS in the presence of LHC type proton beams with 25 ns bunch spacing. Above a threshold intensity of about 4 × 1012 protons in 81 consecutive bunches, correspond-ing to half of the nominal 'batch' intensity to be ...
A Simulation Study of the Electron Cloud in the Experimental Regions of the LHC
The LHC experimental regions (ATLAS, ALICE, CMS and LHCb) are characterised by having a variable geometry, non-uniform magnetic field, and the presence of two beams that will collide at the Interaction Point (IP). A detailed study of electron multipacting in the experimental chambers is needed to establish the pressure increase due to electron stimulated desorption, especially critical in the experimental regions. Furthermore, knowledge of the predicted electron cloud density all along the experimental regions will allow for an estimation of its possible effects on the beam stability.
Beam-Induced Electron Cloud in the LHC and Possible Remedies
1998
Synchrotron radiation from proton bunches in the LHC creates photoelectrons at the beam screen wall. These photoelectrons are accelerated towards the positively charged proton bunch and drift across t he beam pipe between successive bunches.When they hit the opposite wall, they generate secondary electrons which can in turn be accelerated by the next bunch if they are slow enough to
Physical Review Special Topics - Accelerators and Beams, 2001
Photoemission and secondary emission are known to give rise to a quasistationary electron cloud inside the beam pipe through a beam-induced multipacting process. We investigate the electron-cloud build up and related effects via computer simulation. In our model, macroparticles representing photoelectrons are emitted synchronously with the passing proton or positron bunch and are subsequently accelerated in the field of the beam. As they hit the beam pipe, new macroelectrons are generated, whose charges are determined by the energy of the incoming particles and by the secondary emission yield of the beam pipe. A quasistationary state of the electron cloud is eventually reached due to space charge. The equilibrium density is used as an input parameter for a second program that analyzes the electron-cloud driven single-bunch instability. The electron cloud simulation also allows the evaluation of the heat load on the cold Large Hadron Collider beam screen, which must stay within the available cooling capacity, and the electron charge deposited on or emitted from the electrodes of the beam-position monitors.