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LHC Weekend Updates: Beam Stability Achieved Amid Technical Challenges

Over the weekend, Thomas Bohl of SPS.RF resolved issues with beam stability at LHC. The Longitudinal damper module was fixed, optimizing conditions for fill 2623. Despite challenges like skewed losses in squeeze, the team managed to achieve stable beams for extended durations. However, technical glitches persisted, leading to power permit disruptions and a spike warning during collisions. The eventful weekend also saw beam losses, cryogenics supervision issues, and chromaticity trims adjustments. Despite this, the team maintained a commendable peak luminosity and worked through challenges to sustain beam quality. Stay tuned for more updates on LHC operations.

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LHC Weekend Updates: Beam Stability Achieved Amid Technical Challenges

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  1. Saturday • Early morning reprise: • Thomas Bohl (SPS RF) solved the bunch length problem. The Longitudinal damper module was saturated. Now it's perfect. • Spikey losses in squeeze – more or less as normal– warnings to 48% • Long running sum losses going into collisions – TCLA, MQWs… • Tweaked tunes up for next fill • Also rolled back chromaticity trims to before TS LHC status

  2. Saturday • Saturday 09:00 to 22:00 fill 2621 • 13h 17m of stable beams • 119.4 pb-1 in Atlas • 124.6 pb-1 in CMS • Peak luminosity • 4.23e33 in Atlas • 4.23e33 in CMS • 1.23e11 ppb ~2.4 micron from luminosity LHC status

  3. Losses in the squeeze #2621 Spikey LHC status

  4. Losses going into collisions Primary collimator – skew – B2 LHC status

  5. Losses going into collisions Primary collimator – skew – B1 LHC status

  6. Sat – Sun – fill 2621 LHC status

  7. 2621 – luminosity lifetime LHC status

  8. Early Sunday morning • 23:00 little delay with SPS bunch length and coupling adjustment • 00:15 filling – slightly higher bunch current – 1.36e11 ppb • Heavy-ish cleaning at the end of the ramp • Assumed to be high chromaticity cleaning of tails • 01:15 cryogenics supervision lost for S12 • Resulting in a clean squeeze – one spike warning • But beams lost going into collision • lost 60A Power Permit in S12at instant of dump • dump triggered by beam losses on RS10 of MQWA.E5R7 – loss already developing before PP went off • [PP won’t dump beam but will wait for BPF = false… tbc] • 02:25 60A Power Permit ok again for S12 after reboot of cryogenics crate "cs-ccr-q18ds3" • 03:00 injecting again LHC status

  9. Nearly into collisions LHC status

  10. Orbit? LHC status

  11. Sunday morning • 03:50 start ramp • Squeeze • again a loss-spike at ~2.1m (~47%)and 1.5 m • no BLM warning level during collision BP • 04:25 Stable beam #2623 • 1.23e11 ppb, 4.13e33 cm-2s-1. • Emittance from lumi: ~2.5 micron • 8:15 cold compressor off in point 2 – cooling water problem – cryo working feverishly to recover situation… maintaining stable beams in the meantime LHC status

  12. Pile-up through the ages • Clear drop in brightness after TS • Not good for performance • Also associated with the tails… Scans LHC status

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