An alternative method to measure amplitude dependence of the closest tune approach

In the linear regime, a minimum closest approach of the fractional horizontal and vertical tunes exists, due to linear coupling between the transverse planes. Simulation-, theoretical-, and beam-based studies of the LHC in Run 1 and 2 however, also demonstrated the existance of an amplitude dependence of the closest tune approach. This Ampiltude DEpendent Closest-Tune-Approach (ADECTA “Add-Ek-Ta”) is a topic of interest due to its potential to generate large distortions of the tune footprint in the vaccintity of the Qx − Qy = n resonance, which may then impact Landau damping. The measurement technique utilized in previous beam-based studies features a number of significant limitations however, most particularly that it is impractical to apply at top-energy in the LHC. This note presents the result of tests of an alternative measurement technique which can overcome limitations of the previous method.