| Paper | Title | Page |
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| MOPOR022 | Beam Dynamics Observations of the 2015 High Intensity Scrubbing Runs at the Cern Sps | 648 |
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| Beam quality degradation caused by e-cloud effects has been identified as one of the main performance limitations for high intensity LHC beams with 25 ns bunch spacing in the SPS. In view of the beam parameters targeted with the LHC injectors upgrade (LIU) project, about two weeks of SPS machine time in 2015 were devoted to dedicated scrubbing runs with high intensity LHC 25 ns and dedicated 'doublet' beams in order to study the achievable reduction of e-cloud effects and quantify the consequent beam performance improvements. This paper describes the main observations concerning the coherent instabilities and beam dynamics limitations encountered as well as a detailed characterisation of the performance reach with the highest beam intensity presently available from the pre-injectors. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR022 | |
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| MOPOR026 | Measurement of the Energy Distribution Function of Electrons Generated by Radio-frequency Induced Multipacting in a Beam Pipe | 664 |
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| The development of Electron Multipacting (EM) in high intensity particle accelerators depends, amongst others, on the Secondary Electron Yield (SEY) of surfaces facing the beam. In-situ studies of electron clouds in particle accelerators must cope with operation schedule and other technical constrains. To overcome these difficulties, CERN implemented a Multipactor test bench, where EM is generated by Radio-Frequency (RF), using the beam pipes as a coaxial resonators. This tool was already successfully used to assess the effectiveness of low SEY carbon coatings on dipoles of the SPS at CERN and to study the conditioning dynamics of beam pipes. In this paper we present the development of an in-house built Retarding Field Energy Analyser (RFEA) to measure the Electrons Energy Distribution Function (EEDF) in the Multipactor test bench. The design of the electrodes was based on simulations in order to optimize sensitivity and energy resolution. The setup was tested with an electron gun at different energies before insertion in the Multipactor test bench. The evolution of the EEDF is measured at different RF powers. Feasibility to perform measurements in the machine is discussed. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR026 | |
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| TUPMW016 | Effect of the LHC Beam Screen Baffle on the Electron Cloud Buildup | 1454 |
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Funding: Research supported by the High Luminosity LHC project Electron Cloud (EC) has been identified as one of the major intensity-limiting factors in the CERN Large Hadron Collider (LHC). Due to the EC, an additional heat load is deposited on the perforated LHC beam screen, for which only a small cooling capacity is available. In order to preserve the superconducting state of the magnets, pumping slots shields were added on the outer side of the beam screens. In the framework of the design of the beam screens of the new HL-LHC triplets, the impact of these shields on the multipacting process was studied with macroparticle simulations. For this purpose multiple new features had to be introduced in the PyECLOUD code. This contribution will describe the implemented simulation model and summarize the outcome of this study. |
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| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMW016 | |
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| TUPMW017 | Electron Cloud Observations during LHC Operation with 25 ns Beams | 1458 |
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| While during the Run 1 (2010-2012) of the Large Hadron Collider (LHC) most of the integrated luminosity was produced with 50 ns bunch spacing, for the Run 2 start-up (2015) it was decided to move to the nominal bunch spacing of 25 ns. As expected, with this beam configuration strong electron cloud effects were observed in the machine, which had to be mitigated with dedicated 'scrubbing' periods at injection energy. This enabled to start the operation with 25 ns beams at 6.5 TeV, but e-cloud effects continued to pose challenges while gradually increasing the number of circulating bunch trains. This contribution will review the encountered limitations and the mitigation measures that where put in place and will discuss possible strategies for further performance gain. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMW017 | |
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