Betatron tune measurement and control in the PETRA proton ring

The PETRA storage ring, modified for use as an injector to the HERA proton ring, requires active control of betatron tunes during the proton acceleration cycle. A tune measurement system based on a personal computer equipped with commercial data acquisition and analysis cards is used for both measurement and control of the tunes. There are significant betatron tune shifts during acceleration: at low energy from eddy currents in the aluminum vacuum chambers, and at high energies from field saturation, especially in the bending magnets. A tune measurement system with relatively fast response was built to aid in understanding and correction of these effects. The tune measurement system and the tune control system are discussed.<>