EVALUATION AND MODELING OF LONGITUDINAL STORAGE RING IMPEDANCE USING CURRENT DEPENDENT BUNCH LENGTHENING AND BUNCH DEFORMING EFFECTS

DELTA is a 1.5 GeV synchrotron radiation facility. The storage ring has been designed especially for low longitudinal impedance to allow also for high electron densities in the case of few bunch operation besides the standard multibunch operation mode. Bunch length and longitudinal bunch profile depend on bunch charge as well as on the longitudinal impedance as major factor of influence. Measurement of turbulent bunch lengthening and potential well distortion effects on optical basis using a streak camera turned out to be an excellent tool to evaluate the longitudinal impedance. The paper presents experimental data concerning bunch lengths and longitudinal profiles for various beam energies, intensities and RF-settings as well as theoretical aspects (impedance modeling of the storage ring). The analysis using the Keil-Schnell-Boussard criterion confirms the theoretical value of the impedance. The paper also presents results concerning the influence of two small gap insertion devices and a 3rd harmonic cavity.