Experimental studies of RF breakdowns in the coupler of the TTF RF gun

During the TTF-FEL Phase I, the RF gun of the TESLA Test Facility (TTF) has been operated with long RF pulses (up to 0.9 ms) and high RF peak power (up to 3 MW). RF breakdowns have been observed and localized in the RF input coupler. In this report we will present statistics of RF breakdowns for different RF pulse length, peak power and repetition rates from 0.1 Hz to 2 Hz. We will also discuss the origin of these breakdowns.