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Challenges and Progress in p-Pb Intensity Ramp Attempts at LHC

This document summarizes the issues encountered during the p-Pb intensity limit experiments conducted on November 26, 2012. The experiments aimed to ramp Pb bunches alongside multiple proton bunches but faced significant challenges, including vacuum leaks, interlock BPM failures, and high transverse emittances. These problems resulted in beam dumps and prevented successful injection of p-Pb beams. The document details attempts to troubleshoot the BPM issues, adjust injector settings, and achieve desired bunch intensities in the LHC system.

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Challenges and Progress in p-Pb Intensity Ramp Attempts at LHC

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  1. p-Pb Intensity Limit M. Schaumann For the p-Pb team: R. Alemany, P. Baudrenghien, E. Calvo-Giraldo, S. Hancock, J.M. Jowett, M. Lamont, D. Manglunki, S. Redaelli, R. Versteegen, J. Wenninger, … and others

  2. MD on p-Pb intensity limit, 26/11/2012 Third attempt to ramp a few Pb bunches with many proton bunches • Prevented twice in September, first by Wire scanner vacuum leak and then problems with IR6 interlock BPMs that continually dumped the low intensity proton beam • Tried to get past the BPM problems on 26/11/2012 with lower and higher intensities but problem seemed to persist for low p intensity and several difficulties getting higher intensity p beam from injectors

  3. Charges vs Bunch num 1.4 1010 1.3 1010 Max bunch charges  > 1.3 1010 may induce reflections in IR6 interlock BPMs 1.2 1010 1 1010 8 109 200/225 ns injection in LHC. The third train injection dumped the beam IR6interlocked BPMs MD Starts  setting up the LHC for B1: Pb– B2: p No problems to inject Pb in B1 (RF and timing OK) Beam dumped  spurious BLM trigger in IP5 Setting up the 200/225 ns beams at the injectors First 24 p+ bunches in LHC dumped because BLM IR7 losses  wrong ADT settings First p+ bunch in LHC p+ Pb Reyes Alemany

  4. Since we suspected that the intensity related problem of the interlocked BPMs was the origin of the dump, we decided to try to go beyond 5 1010 p+/bunch, where reflections should not appear. The rest of the MD was spent trying to set up the beam in the injectors. No further LHC injection took place. Several issues found at the injectors: Huge transverse emittaces > 10 μm rad (normalized)  on the 29thof Nov wrong settings were found on the PS extraction bump. Once corrected, the emittaces became ~ normal ( H = 2 μm rad, V = 1 μm rad) Not possible to extract 5 10^10 p+/bunchfrom PS due to a BPM wrong gain  solved the same night Notpossible to extractthe beam from SPS to LHC due to wrong SPS cycle settings  solvedthe same night Due to the length of the 200/225 ns proton cycle, more than 20 seconds, the SPS BPMs cannot read the orbit and give an extraction interlock towards LHC. Remaining issues in LHC: The behavior of the interlocked BPMs in IR6 for low intensity proton bunches. Reyes Alemany

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