Measurement of local impedance by an orbit bump method

A new method of local transverse coupling impedance measurement has been developed to estimate the impedance distribution along a storage ring. The method is based on measurement of the closed orbit deviation caused by the wake field generated at the impedance location by the off-axis beam. This method provides better accuracy than the known method based on betatron phase advance measurement, because the beam position monitors operate in narrow-band (orbit) mode, but not in wide-band (turn-by-turn) mode used for phase advance measurement. The physical principles and limitations of the method are described using both analytical formulae and computer simulation.