Emittance-Conserving Transverse Excitation using the "AC-Dipole" Principle.

The so-called "AC-Dipole" principle allows the excitation of transverse oscillations to large (several sigma) excursions without emittance blow-up. The idea was originally proposed and tested at BNL for resonance crossing with polarised beams, using an orbit corrector dipole with an excitation frequency close to the betatron tune, hence "AC-Dipole". This method of beam excitation has several potential applications in the LHC, such as phase advance and beta measurements, dynamic aperture studies and the investigation of resonant driving terms. The technique was recently tested in the CERN SPS using the transverse damper as an "AC-Dipole" providing the fixed frequency excitation. Results from this experiment are presented, along with a brief explanation of the underlying principle.