Bunch-by-bunch Feedback and Diagnostics at Bessy Ii

At the light source BESSY II new digital bunch-bybunch feedback systems [1] have been put into operation in January 2013, replacing the existing analog as well as the obsolete digital systems. From the first days of operation the new system successfully suppresses transverse and longitudinal beam instabilities in wide range of machine parameters. The system offers also many new diagnostics opportunities. In this contribution first operational experience, the developed data analysis techniques and experimental data will be presented. INTRODUCTION BESSY II is a 3 generation light source, with a beam energy of 1.7 GeV. Typical beam parameters are listed in Tab. 1. In the past year the facility has seen an number of improvements in order to react to steadily increasing user requirements concerning beam quality and beam stability. Since September 2012 it is operated in top-up mode, using the full-energy injector synchrotron to continuously replace lost electrons during user operation [2]. In addition a faster orbit feedback has been commissioned successfully reducing beam orbit disturbances up to 10 Hz [3]. In January 2013 new digital bunch-by-bunch feedback (BBFB) systems [1] have been put into operation, replacing the existing analog as well as the obsolete digital controllers, while reusing established amplifiers and transverse and longitudinal kickers [4, 5, 6]. From the first days of operation the new system successfully suppresses transverse and longitudinal beam instabilities in wide range of machine parameters. The system offers also many new diagnostics opportunities, these include the analysis of instability modes, measurement of the feedback loop gain, and determination of the transfer function. In addition the analysis of the input data stream allows a passive determination of machine properties like betatron and synchrotron frequencies as well as the longitudinal phases for every bunch. Table 1: BESSY II Beam Parameters Parameter Value Energy 1.70 GeV Total beam current I 300 mA Circumference 2πR 240 m RF Frequency fRF 499.6 MHz Harmonic number h 400 Synchrotron frequency fs 4.4 kHz Horizontal betatron frequency fx 1060 kHz Vertical betatron frequency fy 928 kHz The integration of external triggers permits the analysis of post-mortem data and the characterization of beam-loss events, as well as monitoring of the injection process.