Compensation of Beam Induced Effects in LHC Cryogenic Systems

This paper presents the different control strategies deployed in the LHC cryogenic system in order to compensate the beam induced effects in real-time. LHC beam is inducing important heat loads along the 27 km of beam screens due to synchrotron radiations, image current and electron clouds. These dynamic heat loads disturb significantly the cryogenic plants and automatic compensations are mandatory to operate the LHC at full energy. The LHC beam screens must be maintained in an acceptable temperature range around 20 K to ensure a good beam vacuum, especially during beam injections and energy ramping where the dynamic responses of cryogenic systems cannot be managed with conventional feedback control techniques. Consequently, several control strategies such as feed-forward compensation have been developed and deployed successfully on the machine during 2015 where the beam induced heat loads are forecast in real-time to anticipate their future effects on cryogenic systems. All these developments have been first entirely modeled and simulated dynamically to be validated, allowing then a smooth deployment during the LHC operation.