Improvement of a beam position monitor for Δr feedback on RF system

When the beam intensity of the 12 GeV proton synchrotron is increased, oscillations occur in the radial direction of the beam, and the beam loss increases at the phase transition. The beam loss at the transition point was due to the ΔR feedback system oi RF acceleration. The ordinary electrostatic pickup¹⁾ used for RF feedback system was replaced with a new large size pickup²⁾. Improvements were made in the following respects: 1. large size to obtain high signal to noise ratio, 2. no side walls to eliminate the noise due to beam hitting, 3. smooth ground for the shield electrode, 4. minimization of the distance between the electrode and vacuum feedthrough and the insertion of an oscillation damping resistor between them, 5. calibration wires were installed between the sensing electrode and the shield electrode. Electrode signals were processed by an average type rectifier and normalizer. The position signal was fed to an RF system through an analogue isolator. This paper deals with the modifications in the beam position feedback of the RF system.