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| MOPOR009 | The HL-LHC Impedance Model and Aspects of Beam Stability | 606 |
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Funding: Research supported by the High Luminosity LHC project The LHC upgrade to the HLLHC foresees new challenging operational scenarios from the beam dynamics point of view. In order to ensure good machine operation and performance, the machine impedance, among other possible sources of instabilities like beam-beam and electron cloud, needs to be carefully quantified profiting also from the current LHC operation. In this work we present the HLLHC impedance model mainly focusing on the contribution of low-impedance collimators and crab cavities: the first reduces the broad-band impedance baseline thanks to the higher jaw material conductivity, the second increases the machine luminosity at the price of increasing the coupled bunch stabilizing octupole current threshold. Other elements like the injection protection absorber (TDI) will be also discussed. |
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| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR009 | |
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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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| 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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| WEPOY044 | Review of CPU and GPU Faddeeva Implementations | 3090 |
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Funding: CERN, Doctoral Studentship EPFL, Doctorate The Faddeeva error function is frequently used when computing electric fields generated by two-dimensional Gaussian charge distributions. Numeric evaluation of the Faddeeva function is particularly challenging since there is no single expansion that converges rapidly over the whole complex domain. Various algorithms exist, even in the recent literature there have been new proposals. The many different implementations in computer codes offer different trade-offs between speed and accuracy. We present an extensive benchmark of selected algorithms and implementations for accuracy, speed and memory footprint, both for CPU and GPU architectures. |
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| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOY044 | |
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