On the measurement and interpretation of coupling impedance data in the frequency and time domain

In order to prevent beam instabilities due to the coupling impedance of vacuum tanks containing septum magnets, electrostatic inflectors, etc., in a proton synchrotron the author makes routine measurements with portable instruments before installation. A center conductor of 1 cm diameter placed in the standard vacuum pipe forms a 125 Omega coaxial line. If a nonstandard vacuum tank is inserted one observes reflection and transmission coefficients. To save the laborious impedance transformations in the frequency domain the reflected and transmitted waveforms are photographed in the time domain. Their interpretation in terms of frequency dependent impedances is discussed.