Beam-coupling impedance measurements and simulations of a movable collimator in BRing at HIAF

The dynamic vacuum effect is the primary constraint on the beam intensity in high intensity heavy ion synchrotrons. The dynamic vacuum effect induced by the charge exchange beam loss will seriously limit the ion intensity and beam lifetime in the Booter ring (BRing) of the HIAF. The collimator is a critical and indispensable component to mitigate the dynamic vacuum effect for high intensity heavy ion circular accelerators. A dedicated collimation system has been designed for BRing to decrease the ion-induced gas desorption to suppress the dynamic vacuum effect. Nevertheless, this intercepting structure may introduce a longitudinal and transverse beam-coupling impedance in the BRing. In this article, comprehensive studies were undertaken to characterize the beam-coupling impedance of the movable collimator. Furthermore, we describe systematically the results from the single- and two-wire bench transmission measurements and the numerical simulations. A satisfactory agreement was obtained between the numerical simulations and wire transmission bench measurements. The 24 movable collimators have been fully processed and are entering the on-line installation stage in the Booster Ring.