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LHC report: towards a bright HL-LHC

Another very successful five-day machine development block took place last week


Studies relating to both the LHC and its luminosity upgrade, the HL-LHC, were carried out. Work has been done on a special setting of the focusing magnets in the LHC, which are required to keep the beams in the machine aperture and to focus them to very small sizes at the heart of the experiments. This configuration of the LHC optics (called Achromatic Telescopic Squeeze) is baseline for the HL-LHC and is being considered for operational use in 2017.

Detailed aperture measurements and collimator tests were performed. The results of these tests indicate that the LHC team can continue the annual reduction in beam size at the LHC high-luminosity interaction points in 2017 by bringing the collimators even closer to the beam core.

The battle with electron cloud is not over and it is currently unclear whether the LHC arcs will ever become electron-cloud free. In the quest to find a solution, the LHC was half-filled with the usual 25-ns beams and half-filled with a new bunch pattern consisting of eight bunches followed by four empty buckets. This configuration decreases the heat load to the cryogenics system from the electron cloud by about a factor of two. This approach could be an alternative for operating the high-intensity HL-LHC beams in the event of a persistent electron cloud.

Single bunches with HL-LHC-like brightness have been brought to 6.5 TeV and put in collision for a sufficient amount of time for the first time. The LHC beams are being made extremely stable using new techniques, and this is an important result as we look to the very high bunch population demanded by the HL-LHC.

The baseline operational mode of the radio frequency cavities in the HL-LHC, known as Full Detuning, leaves some freedom to play with the bunches: the bunches are now located within the constraints of the RF system in a configuration that minimises the required RF power. This new way of running the radio frequency cavities has just been demonstrated for the first time at 6.5 TeV.

Finally, several studies took place with a view to optimising and further improving the beam instrumentation to measure beam sizes and other beam characteristics with high precision. All these studies will hopefully result in more collisions and more luminosity for the LHC experiments in the short- and long-term future.

The LHC exited the MD session into the year’s final two weeks or so of proton physics, while the teams are already sneaking in some preparation for the upcoming proton-lead run.