Tuesday 7/7 & Night 8/7 06:53 Beam lost due to RF problem, understood  08:30 Access –VIP, Experiments, QPS, EPC, ABT, RF, BI, …. 15:15 Access over, expert working on CMS MAD (access system) 16:15 Firebrigade going in for evacuation alarm, false alarm 18:30 Start pre-cycle 19:45 No beam from the SPS, dipole problem 20:45 Start injection: injection OK, no steering required 22:20 Stable Beams fill no. 3974, –Some problems finding CMS collisions 05:36 Beams dumped, earth fault on RB.A78 –Slow Power Abort, expect to be down at about 10:00 –Then access for inspection …. 08/07//2015LHC Morning meeting – WH & JU1

RF Investigations The abort gap population was indeed caused by debunching. The problem seems caused by the Synchro loop that locks the VCXO (crystal oscillator) to the reference (ramping in sync. with magnetic field). The problem appeared on MONDAY 6/7 around 6 AM and has been present since. The sensitivity comes from the dielectric constant of PCB (parasitic capacitances) that changes with temp/humidity. Thanks to the new AC plant, temperature is regulated within +- 1 degree. But humidity has risen from 35% (7 degrees dew point) end June to 70% on Tuesday morning (17 degree dew point). The drift of VCO centre frequency has likely been caused by this change in humidity. It had happened in Summer 2010 already. Re-adjusted and monitoring put in place, CV contacted «If you report on the incident, make it clear that it is not an instability. Only instrumental. » 08/07//2015LHC Morning meeting – WH & JU2 Philippe Baudrenghien

RF synchroloop going unstable also without beam 08/07//2015LHC Morning meeting – WH & JU3

Small UFOs are back Five above 10 %: –14 % dump level 9L6 –10 % dump level 30R8 –24 % dump level 23R2 – …. 08/07//2015LHC Morning meeting – WH & JU4

The Plan 08/07//2015LHC Morning meeting – WH & JU5 ? ? Postpone if not back before noon