LHC Report: spring cleaning over, bunches of luminosity

Scrubbing was completed on Wednesday 13 April. The run had seen over 1000 bunches per beam successfully circulating at 450 GeV. Measurements showed that electron cloud activity in the cold regions had been suppressed. A decrease of vacuum activity in the warm regions demonstrated that the cleaning had also achieved the required results there. As discussed in the last Bulletin, the scrubbing was performed with high intensity bunches with 50 nanosecond spacing. Given the potential luminosity performance with this spacing (more bunches, higher bunch intensity from the injectors) and in the light of the results of the scrubbing run, the decision was taken to continue the 2011 physics run with this bunch spacing.


A few issues with 50 nanosecond spacing had to be resolved when standard operations for luminosity production resumed. Once things had been tidied up, stable beams were provided for the experiments, firstly with 228 bunches per beam and then with 336 bunches per beam. The 336 bunch fill that went into physics mode early on Sunday morning (17 April) produced a new record luminosity of 3.7 x 1032 cm-2s-1 and an integrated luminosity of 10 inverse picobarns in 9 hours. The LHC has now delivered over 62 inverse picobarns in 2011, easily passing the total of 49 inverse picobarns for the whole of last year

For 50 nanosecond injection into the LHC, the SPS takes batches of 36 bunches from the PS. It can stack 1, 2, 3, or 4 batches before sending the beam to the LHC. Up to now the SPS has been sending down 2 times 36 bunches. 72 bunch injection already represents a considerable amount of beam power, and the injection process needs to be carefully tuned and monitored. The importance of constant vigilance was underlined on Monday when an injection kicker misfire dumped half of an incoming 72 bunch batch on the downstream protection devices, leading to quenches in about a dozen superconducting magnets. After careful system checks normal LHC operation was resumed.


by CERN Bulletin