Reduction of particle losses in HERA by generating an additional harmonic tune modulation

The combined effect of non-linear fields and a tune modulation with fast and slow frequency components results in an enhanced emittance growth and increased loss rate in hadron storage rings. In the proton storage ring of HERA, a fast harmonic tune modulation is caused by ripples in the power supplies and a slow tune modulation by the ground motion in the HERA tunnel. The recognition of the damaging effect of fast tune modulation frequencies on the particle dynamics initiated attempts to compensate for the fast frequency components in HERA. The fast tune modulation frequencies in the proton beam can be measured with a phase-locked-loop and the compensation can be established by generating an additional external tune modulation with the same frequency but with a 180° phase difference. The following work summarizes the results of recent experiments in the proton storage ring of HERA where the generation of an additional tune modulation led to a significant reduction of the proton loss rate during luminosity operation