COMMISSIONING OF MULTIBUNCH FEEDBACK SYSTEMS AT THE FAST RAMPING STRETCHER RING ELSA

At the Electron Stretcher Facility ELSA [1] of Bonn University, an external beam of either unpolarized or polarized electrons is supplied to hadron physics experiments. The ELSA stretcher ring operates in the energy range of 1.2 GeV to 3.5 GeV and achieves a duty cycle of up to 80 % using a fast energy ramp of 4 GeV/s. Under these conditions, an increase of the internal beam current from an actual value of 20 mA up to 200 mA is planned. Such an upgrade is mainly limited by the excitation of multibunch instabilities. As one active counteraction, we have installed state-of-the-art bunch-by-bunch feedback syst ems for the longitudinal, as well as for both transverse planes. The detailed setup with all main components and first results of the commissioning of the longitudinal system are presented.