Vibration characterization and mitigation at the Gemini-South telescope

We describe the methods used to mitigate the vibrations encountered in some of the instruments of the Gemini South telescope. We found a persistent vibration at 55Hz with others occurring occasionally at 14 and 100Hz. Two types of AO controllers -Kalman and H∞- were implemented in the MCAO Tip-Tilt loop. First results show clear improvements in vibration rejection and overall performance for these advanced controllers over the classical integrator. It is shown that the reduction in the standard deviation of residual slopes is highly dependent on turbulence, wind speed and vibration conditions, ranging in slopes RMS- from an almost negligible reduction for high speed wind to a factor of 5 for a combination of low wind and strong vibrations.