Impact and Mitigation of Electron Cloud Effects in the Operation of the Large Hadron Collider

In 2015 and in 2016 the Large Hadron Collider has been routinely operated with 25 ns bunch spacing. With this beam configuration electron clouds develop in a large fraction of the beam chambers, in spite of a very large electron dose accumulated on the surfaces. This posed several challenges to different aspects of the beam operation. In particular, the machine settings had to be optimized in order to mitigate coherent and incoherent effects of the electron cloud on the beam dynamics while a specifically designed feed-forward control had to be implemented and optimized in order to dynamically adapt the regulations of the cryogenic system to the strong heat load deposited by the electron cloud on the beam screens of the cryogenic magnets. At the same time, the data collected from the different accelerator subsystems (heat loads, vacuum pressures, evolution of the bunch by bunch beam parameters) allowed to significantly improve our models and understanding on these phenomena