Design and operational results of a 'one-turn-delay feedback' for beam loading compensation of the CERN PS ferrite cavities

Abstract

II. PRINCIPLE OF ONE-TURN-DELAY FEEDBACKThe periodic transient beam loading in the CERN PS ferrite cavities was diagnosed in 1989 to be the source of performance limitations for the antiproton production beam [l]. A project was then launched to lower the transient beam induced voltage by a factor of four, with a "one-turn-delay feedback" system reducing the equivalent cavity impedance on the first 3 revolution frequency side-bands around the cavity tune frequency. The design is able to cope with a wide frequency range due to particle acceleration (15 % velocity variation) and choice of harmonic number (h= 10 to 20). Loop gain is above 0 dB in the vicinity of revolution frequency harmonics over an instantaneous bandwidth of 3 to 4 times the 3 dB bandwidth of the original RF system. Fast digital electronics is applied extensively, resulting in a very reliable and compact implementation. The various functions are described, closed loop performance of a cavity is shown and measurements with beam are presented.

Measurement of transverse beam emittance of split beams for the CERN Proton Synchrotron Multi-Turn Extraction

“…The transverse profiles can be measured by means of wire scanners (elements with a name beginning with WS). A transverse feedback system (TFB) [32,33] provides excitation when the resonance is crossed to increase the probability of a particle being trapped in stable islands [16,34]. Kicker dipoles (KFA) are used to create fast deformation of the closed orbit and to extract the beam using the magnetic extraction septum (SMH16).…”