BNL, Upton, Long Island, New York, USA
We have developed and tested a technique, which significantly improves the accuracy of the orbit bump method of local impedance measurement. This technique is based on in-phase sine-wave (AC) excitation of four fast correctors adjacent to the vacuum chamber section, impedance of which is measured. The narrow-band sine-wave signals provide better signal-to-noise ratio. Use of fast correctors to the beam excitation eliminates the systematic error caused by hysteresis. The systematic error caused by orbit drift is also suppressed because the measured signal is not affected by the orbit motion outside the excitation frequency range. The measurement technique is described and the result of experimental testing carried out at NSLS-II is presented.
