Bunch length measurement using beam spectrum (CESR storage ring)

A procedure for extracting the bunch length from the beam-induced voltage spectrum is applied at CESR, for various bunch currents, to indicate whether the turbulent lengthening threshold is exceeded by short, high-current bunches. The approach is to monitor the signal spectrum from one of the detector buttons up to 8 GHz. The measuring system is calibrated by reference to a low-current bunch (1 mA), which is assumed to have a Gaussian profile with the theoretically predicted length. In this experiment, a single bunch was used with a natural length of 15 mm. No bunch lengthening was detected up to a current of 20 mA.<<ETX>>