Electron-cloud Build-up Simulations in the Proposed PS2: Status Report (original) (raw)

ELECTRON CLOUD STUDIES FOR THE UPGRADE OF THE CERN PS

The observation of a significant dynamic pressure rise as well as measurements with dedicated detectors indicate that an electron cloud develops in the CERN PS during the last stages of the RF manipulations for the production of LHC type beams, especially with 25 ns bunch spacing. Although presently these beams are not degraded by the interaction with the electron cloud, which develops only during few milliseconds before extraction, the question if this effect could degrade the future high intensity and high brightness beams foreseen by the LHC Injectors Upgrade project is still open. Therefore several studies are being carried out employing both simulations and measurements with the electron cloud detectors in the machine. The aim is to develop a reliable electron cloud model of the PS vacuum chambers in order to identify possible future limitations and find suitable countermeasures.

Comparison between electron cloud build-up measurements and simulations at the CERN PS

2012

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

Electron-Cloud Build-Up: Theory and Data

Lawrence Berkeley National Laboratory, 2011

We present a broad-brush survey of the phenomenology, history and importance of the electron-cloud effect (ECE). We briefly discuss the simulation techniques used to quantify the electron-cloud (EC) dynamics. Finally, we present in more detail an effective theory to describe the EC density build-up in terms of a few effective parameters. For further details, the reader is encouraged to refer to the proceedings of many prior workshops, either dedicated to EC or with significant EC contents, including the entire "ECLOUD" series [1-22]. In addition, the proceedings of the various flavors of Particle Accelerator Conferences [23] contain a large number of EC-related publications. The ICFA Beam Dynamics Newsletter series [24] contains one dedicated issue, and several occasional articles, on EC. An extensive reference database is the LHC website on EC [25]. THE BASIC OVERALL PICTURE The qualitative picture of the development of an electron cloud for a bunched beam is as follows: 1. Upon being injected into an empty chamber, a beam generates electrons by one or more mechanisms, usually referred to as "primary," or "seed," electrons. 2. These primary electrons get rattled around the chamber from the passage of successive bunches. 3. As these electrons hit the chamber surface they yield secondary electrons, which are, in turn, added to the existing electron population.

Electron cloud effects in the CERN PS

PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268), 2001

The beam-induced electron cloud build-up is one of the major concerns for the SPS and the design of the future LHC. Recently, this effect has been observed also in the PS with the nominal LHC-type beam, consisting of a batch of 72 bunches of 1.110 11 p/b spaced by 25 ns. The electron cloud induces baseline distortion in electrostatic pickup signals that is observed, both in the last turns of the PS when the full bunch length is reduced to less than 4 ns, and in the transfer line between the PS and the SPS rings. Experimental observations are presented and compared to simulation results and predictions from theory. Furthermore, possible cures, such as variation of the bunch spacing, inserting gaps in the bunch train and applying weak solenoidal fields, are also discussed.

E-Cloud Effects on Singe-Bunch Dynamics in the Proposed PS2

One of the options considered for future upgrades of the LHC injector complex entails the replacement of the PS with the PS2, a longer circumference and higher energy synchrotron. Electron cloud effects represent an important potential limitation to the achievement of the upgrade goals. We report the results of numerical studies aiming at estimating the e-cloud density thresholds for the occurrence of single bunch instabilities.

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.

Electron-cloud simulation results for the SPS and recent results for the LHC

Lawrence Berkeley National Laboratory, 2002

We present an update of computer simulation results for some features of the electron cloud at the Large Hadron Collider (LHC) and recent simulation results for the Super Proton Synchrotron (SPS). We focus on the sensitivity of the power deposition on the LHC beam screen to the emitted electron spectrum, which we study by means of a refined secondary electron (SE) emission model recently included in our simulation code.

Dependence of e-cloud on the longitudinal bunch profile: studies in the PS & extension to the HL-LHC

Recent studies have shown that the prospects for significantly increasing bunch intensities in the LHC for the luminosity upgrade (HL-LHC) may be severely limited by the available cryogenic cooling capacity and the electron-cloud (EC) driven beam instability. However, it is planned that during the HL-LHC era the bunch intensities in the LHC will go up by nearly a factor of two compared to the LHC-design values. This motivates the exploration of additional EC mitigation techniques that can be adopted in addition to those already in place. Preliminary simulations indicated that long flat bunches can be beneficial over Gaussian bunches to reduce the EC build up. Rigorous studies using realistic bunch profiles have never been done. Therefore, we have undertaken an in-depth investigation in the CERN 26 GeV PS to see if we can validate the previous findings and, in particular, if flattening the bunch can mitigate the EC. Here we present the results from dedicated EC measurements in the PS...

Electron-Cloud Build-Up Simulations and Experiments at CERN

Power

We benchmark the predictions of electron-cloud buildup simulations against measurements at the CERN SPS. Specifically we compare the electron flux at the wall, electron-energy spectra, heat loads and the spatial distribution of the electrons for two different bunch ...

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 ...