Applications of the 1000-turns Orbit Measurement System at LEP

The software of the LEP beam orbit measurement system [1] allows the acquisition of the beam position for over 1000 consecutive turns. The acquisition can be synchronized to a deflection by a kicker in order to observe coherent betatron oscillations. In this paper we describe the use of this technique to study the dependence of head-tail damping on beam parameters and the tune dependence on the oscillation amplitude for various LEP optics [2]. Coherent oscillations can be represented in phase space to observe the effect of resonances and other non-linear behavior [4, 5]. Coherent oscillations can also be excited using a sinusoidal deflection in order to maintain the oscillation amplitude [6]. Thus, precise measurements of the phase advance are obtained by harmonic analysis of the signal at each pick-up. This technique has been used to measure the beam energy dependence of the phase advance due to chromaticity [7] and the bunch current dependence of the phase advance due to impedance [8]. Finally, we describe a method to obtain the betatron function from the measured phase advance and report about its accuracy and applications at LEP [9, 10].