Feedback suppression of fast vertical oscillations of the VEPP-3 SR beam
Experiments have been performed to suppress vertical oscillations of the synchrotron radiation (SR) beam of the VEPP-3 storage ring by introducing a fast feedback. These oscillations are caused both by current pulsations in the magnetic elements and by mechanical vibrations, and can not be suppressed by the existing beam stabilization system.
In experiments, the beam position sensor which was a previously developed differential detector included pin-photodiodes, an electronic section (providing filtering and double correlated sampling of signals), and an electromechanical system (automatically adjusting sensitive element to the center of SR beam).
The signal corresponding to the beam displacement from regulation position was transmitted (after processing and amplification) on a fast corrector – a pair of saddle coils imposed directly to the metal vacuum chamber of storage ring, which formed a negative feedback. A ratio calculator (for independence of feedback strength from the beam intensity) and PID-regulator (for correction of frequency characteristic) could be included in the signal processing channel.
Both the upper operating frequency and the maximal stable feedback were determined by the speed of the magnetic corrector (by delay in the penetration of the field through the metal wall of the chamber). Nevertheless, when the system was turned on the amplitude of oscillations with the frequency of power network (50 Hz) was reduced by 30 dB, and the amplitude of the powerful disturbance at frequency of 690 Hz was reduced by 25 dB.