A beam-position monitor system at the VEPP-4M electron−positron collider

The VEPP-4M storage ring has been designed for experiments with colliding electron−positron beams, a synchrotron radiation beam, and extracted γ-ray beams at energies of 1−5 GeV. A correct equilibrium beam orbit must be kept in the storage ring to maintain the required experimental conditions. A beam position monitor system is used for this purpose. It includes 54 beam position monitors, monitor signal-processing modules, and synch signals distributors. In 2013–2016, new signal processing modules with a high time resolution were developed and installed at the VEPP-4M storage ring. These have two main advantages over the old modules. First, the new modules allow separate position measurements of electron and positron bunches at an interval between the bunch signals as long as 18 ns. Second, they are able to perform fullfledged turn-by-turn beam position measurements, which is very important for adjustment of the storagering parameters. Turn-by-turn beam position measurements can be performed during injection of a new beam, beam kicking, beam loss, or at an arbitrary instant of time. The structures and main features of the new modules are described, the measurement accuracy is analyzed, and some results of their operation at the storage ring are presented.