Beam Capture Efficiency in the Presence of Resonance Islands

In the framework of the new continuous transfer and extraction scheme of the CERN PS, a series of measurements has been done to explore the phase space and the topology of the resonance islands. This paper proposes a method to extract the beam capture efficiency as a function of the measured centre-of-charge position. The underlying relation is derived from first principles and illustrated with an explicit example and numerical test. Possible influences on the measurement, like filamentation processes inside the islands, are discussed and evaluated. The exact knowledge of the theoretical island position in phase space is very important for the determination of the capture efficiency. A new procedure making use of iterative elimination is introduced, to determine position as well as acceptance of an island by simulation, without bias from background generated by un-captured particles.