After a flying start, with the first stable beams at the new energy of 4 TeV on 5 April, the LHC successfully operated with 1380 bunches per beam – the maximum planned for 2012 – on 18 April. In the days that followed, the machine reached a record peak luminosity of about 5.6 × 1033 cm–2 s–1, with a bunch intensity of 1.4 × 1011 protons per bunch and a new highest stored energy of 120 MJ per beam.
As it entered a two-day machine-develop-ment period on 21–22 April, almost 1 fb–1 of data had been delivered to the experiments, a feat that took until June in 2011. The machine development focused on topics relevant for the 2012 physics-beam operation and was followed by a five-day technical stop, the first of the year.
The restart from 27 April onwards was slowed down by several technical faults that led to low machine availability and the ramp back up in intensity took longer than initially planned. LHC operation was further hampered by higher than usual beam losses in the ramp and squeeze. These required time to investigate the causes and to implement mitigation measures.
On 10 May the machine began running again with 1380 bunches and a couple of days later saw one of the year’s best fills, lasting for 13 hours and delivering an integrated luminosity of 120 pb–1 to ATLAS and CMS. By 15 May, after careful optimization of the beams in the injectors, the luminosity was back up to pre-technical-stop levels. The aim now is for steady running accompanied by a gentle increase in bunch intensity in order to deliver a sizeable amount of data in time for the summer conferences.
