Preparing for faster filling

Following the programmed technical stop last week, operators focussed on preparing the machine for faster filling, which includes multibunch injection and a faster pre-cycle phase.


The LHC1 screen shot during the first multibunch injection operation.
The LHC operational schedule incorporates a technical stop for preventive maintenance roughly every six weeks of stable operation, during which several interventions on the various machines are carried out. Last week these included the replacement of a faulty magnet in the SPS pre-accelerator, which required the subsequent re-setting of the system of particle extraction and transfer to the LHC.

At the end of last week, all the machines were handed back for operation and work could start on accommodating all the changes made into the complex systems in order for normal operation to be resumed. These ‘recovery’ operations continued through the weekend and into this week.

At the beginning of this week, operators succeeded in producing four bunches and sending them to the LHC in the same SPS cycle, thus reducing the time needed to fill the accelerator. On Tuesday, using this scheme for the first time, 25 bunches were injected in each direction (50 in total in the machine). However, this scheme has yet to be brought up to the necessary conditions for physics.

An important change that experts have implemented during the last technical stops now allows the current in the magnets to be changed at the nominal rate of 10 Amps/s (instead of 2 Amps/s). The operations team has this week applied this faster rate to the pre-cycle phase of the LHC cycle, which will allow faster turnaround of the machine between physics fills. Before the technical stop the time needed for the pre-cycle was about one and a half hours. This same operation is now about 30 minutes quicker.

On the night of Thursday 29 July,  the LHC was filled with 25 bunches per beam (16 colliding pairs per experiment). This should increase the integrated luminosity per day by a factor of 2.


by CERN Bulletin