LHC Machine Protection Against Very Fast Crab Cavity Failures

For the high-luminosity LHC upgrade program (HLLHC), the installation of crab cavities (CCs) is essential to compensate the geometric luminosity loss due to the crossing angle [1]. The baseline is a local scheme with CCs around the ATLAS and CMS experiments. In a failure case (e.g. a CC quench), the voltage and/or phase of a CC can change significantly with a fast time constant of the order of a LHC turn [2]. This can lead to large, global betatron oscillations of the beam. Against the background of machine protection, the influence of a CC failure on the beam dynamics is discussed. The results from dedicated tracking studies, including the LHC upgrade optics, are presented. Necessary countermeasures to limit the impact of CC failures to an acceptable level are proposed.