Compensation for field shaking due to magnet vibration

Recently, a global feedback scheme for beam stabilization has been broadly discussed for the third generation light source. Since the low frequency disturbance of the orbit mainly comes from the quadrupole magnet vibration of a certain dominant mode, a feedforward effect is developed to cancel field vibration without beam position monitor feedback. We applied a seismic accelerometer to detect magnet vibration driving the compensation current into the trim coil of the quadrupole. Better than 99% cancellation of field vibration due to 10 μm magnet vibration was observed in the laboratory. This method is superior to the feedback system in many aspects, such as locality, simplicity and economy