How does a cryogenic system cope with e-cloud induced heat load?

Since 2012, the e-clouds produced by LHC beams are inducing significant dynamic heat loads on the LHC cryogenic system. These additional heat loads are deposited on beam screens where they must be properly extracted by the cryogenic system between 4.6 K and 20 K in order to ensure a stable beam vacuum and a good thermal barrier for superconducting magnets operated at 1.9 K. First, this paper describes how the cryogenic instrumentation located in the surrounding of the beam screens allows to measure the amount of power deposited by the beam and then to estimate the e-cloud contribution. Then, as this dynamic heat load induces fast transients on the cryogenic system, the standard feedback regulation techniques cannot be used anymore due to the slow response time of the cryogenic systems. Consequently, feed-forward controls based on beam information have been successfully setup from 2015 over the 485 beam screen regulation loops to guarantee optimal transients during the beam operation where significant heat load dierences are observed all around the machine.