The impact of the use of alternative RF frequencies on the TMCI thresholds for HL-LHC

Alternative scenarios for using different configurations of RF frequencies exist and are under study for the HL-LHC. One particular scenario considers the use of a 200 MHz fundamental system which may have advantages over the standard 400 MHz used in the LHC today. In particular, in terms of heat load generated by electron clouds, this approach appears to provide significant advantages with relaxed requirements on the necessary cooling capacity. One of the main concerns with this scenario, on the other hand, is the lowering of the transverse mode coupling instability (TMCI) which puts a hard limit on the reachable intensity. In this note we focus on the evaluation of the TMCI thresholds for the different scenarios and give some guidelines on what configurations are tolerable from a transverse stability point of view. We also briefly address the impact of an idealized transverse damper on the TMCI thresholds.