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Lessons of SPS Scraping with LHC Beams

Lessons of SPS Scraping with LHC Beams. V. Kain, K . Cornelis , L . Drosdal , M. Meddahi , A. Mereghetti , O. Mete, E. Veyrunes. SPS Scraping – Experience from LHC Run I. Systematically large non-Gaussian tails in particle distribution for LHC beams  High beam losses at injection LHC

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Lessons of SPS Scraping with LHC Beams

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  1. Lessons of SPS Scraping with LHC Beams V. Kain, K. Cornelis, L. Drosdal, M. Meddahi, A. Mereghetti, O. Mete, E. Veyrunes

  2. SPS Scraping – Experience from LHC Run I • Systematically large non-Gaussian tails in particle distribution for LHC beams • High beam losses at injection LHC • High beam losses during squeeze in the LHC with tight collimators • Transverse beam scraping in the SPS for LHC beams became essential. Example of collimator scan in the LHC at 450 GeV With and without scraping in the SPS L. Drosdal, B. Salvachua, G. Valentino SPS Collimation Review

  3. SPS Scraper in SPS LSS1 • Horizontal and vertical graphite fingers that can be moved into the beam ~10 mm • The scraping occurs at the end of the ramp to get rid of the off-momentum scattered particles. BCT during a 50 ns LHC cycle in the SPS: about 3 % of the intensity is scraped. SPS Collimation Review

  4. SPS scraping towards the end of the ramp • The scraping process starts at energy 409 GeV and lasts for about 250 ms. SPS Collimation Review

  5. How is the scraper setting chosen? • The scrapers scrape at about ~2.5 – 2.9 s • The settings are chosen such to remove the tails but not to impact on the core of beam Results of scraper setting versus emittance after scraping and losses in the LHC transfer lines % of dump threshold in the LHC for 144 bunch injection SPS Collimation Review

  6. Issues with sps scraping SPS Collimation Review

  7. Beam Loss around the SPS Ring • Losses recorded during MD of scraping whole beam in the SPS • Numbers need to be scaled to operational scenario • Scattered particles are lost all around machine • Peak loss obviously in point 1 Need to increase several BLM thresholds for the whole cycle to be able to deal with scraping losses. Sun glasses? Is under study. A. Mereghetti SPS Collimation Review

  8. Evolution of Scraper Setting and Scraped Intensity • Settings of scrapers in H and V change • Partly due to reduce scraped intensity: mainly in V • was reduced through the autumn from 3 % to about 2 % • In H scraper setting is following the change of the SPS orbit SPS Collimation Review

  9. Change of H Scraper Setting and Beam Position Horizontal setting evolution Horizontal beam position at scraper fitted from surrounding BPMs Position can change by ~ 1mm in one week issue with dp/p SPS Collimation Review

  10. Consequences and Origin of Orbit Movement • Scraper needs setting up/ verification before EACH LHC filling • …and the LHC beam is only scraped at one moment in the cycle not throughout the whole energy range • Origin of orbit movement not identified yet • Possibly only an issue for cycles with LHC optics and not fixed target beams • Tune close to integer • Possibly generated by LHC extraction equipment in LSS6 • Would LSS2 extraction equipment do the same thing? SPS Collimation Review

  11. Limit on maximum Number of Scraper Cycles • Current SPS scraper is moved by a stepping motor in and out of beam every LHC cycle • It is only used for LHC cycles during LHC filling • Theoretical limit of number cycles: ~400’000 • Number of cycles by end of February 2013: 187’000 • If it has to be used on a more regular basis and the number of cycles before system fatigue becomes limit: magnetic bump instead of mechanical system • Concept is available • More complicated (machine protection), more space required in the machine • Could bring more absorption SPS Collimation Review

  12. Conclusion • The SPS scrapers are systematically used to prepare the LHC beams • The system has proven to be operationally reliable and robust for the current mode of operation: • Only high intensity LHC beams • Only one energy • Only for LHC filling • The big inconvenience for scraping/collimation in the SPS: • Lack of sufficient orbit stability • To make the systems do their job, they need continuous tuning SPS Collimation Review

  13. EXTRA slides SPS Collimation Review

  14. SPS Scraper is robust • A robustness test was carried out at the end of LHC run I • Scraping the whole beam: 288 bunches • The spare system was used • Result: the scraper survived. Detailed investigation still to come. Signs of discoloration. Indication of state change? SPS Collimation Review

  15. Losses on the transfer line collimators SPS Collimation Review

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