Development of the Electron Activity Interlock for the Input Power Couplers of TESLA-type Accelerating Cavities

The TESLA-type (teraelectronvolt superconducting linear accelerator) accelerating cavities are designed for use in high gradient linear accelerators - the operating free electron laser in Hamburg (FLASH) and the future projects X-ray free electron laser (XFEL) and international linear collider (ILC). The 1.3 GHz, 250 kW-peak RFpower is delivered through coaxial input couplers. As the environment inside of the input coupler is vacuum, at given power level a resonance vacuum discharge (multipacting) may occur. The multipacting may be destructive if the input power is not reduced or switched off immediately after ignition of discharge. Except of multipacting discharge in residual gasses or field emission could also occur. Recent input couplers have three electron pickups to detect the electron activity. The aim of this work is to get rid of these pickups and their measurement amplifiers in order to make the input coupler simpler and cheaper. The inner conductor of the coupler should play a role of electron pickup.