Bench Measurements of the Energy Loss of a Stored Beam to Vacuum Components

Since 1975 measurements of higher order mode losses have been carried out at DESY. The method in use had been proposed by J. Rees and M. Sands): Short current pulses (2 ?? = 100 psec) on a thin coaxial wire simulate a relativistic particle bunch. Changes in the bunch shape allow the determination of energy losses due to higher mode excitation. Measurements on simple cavity structures agree well with calculations. Results for a large variety of vacuum structures in the PETRA storage ring are given including structures, the losses of which can no longer be easily calculated. For these structures the results of the measurements described here are the only source of information for improvements.