The Intensity Mionitor Device for PETRA

The PETRA intensity monitor is a transformer with an iron tape core mounted on a piece of ceramic beam chamber. The inside of the ceramic chamber is coated entirely with a < .2 ¿m stainless steel film which on one hand is thick enough to present a continous metal chamber boundary to the high frequency components of the electromagnetic bunch fields (this coating is necessary to avoid excessive power losses due to higher order mode excitation). On the other hand the coating must be thin enough to measure currents up to 8 individual bunches of different intensities by picking up the lower frequency components of the injected or circulating beam. Design and performance are discussed.