A procedure for obtaining transverse wall impedance and working line from transfer function measurements

In order to measure the variation of betatron tune versus momentum, the 'working line', the effect of the wall impedance must be eliminated. The method is based on a comparison between the longitudinal particle distribution calculated from the transfer function of a slow and a fast wave, and the measured longitudinal distribution. The difference between the two is due to the transverse wall impedance. A matching routine yields the correct longitudinal and betatron distributions, the working line and the stability diagram. However, the data have to be treated prior to this operation to eliminate a number of parasitic effects in order to ensure a sufficient precision. The results of the method are presented.