Development of Array-Type Secondary Electron Emission Monitor Toward Single-Shot Measurement of Extraction Efficiency of FEL Oscillators

To enable the single-shot measurement of extraction efficiency, a key parameter of an FEL oscillator, we developed an array-type secondary electron emission monitor capable of measuring the temporal evolution of the electron beam energy distribution in a macro-pulse at KU-FEL. The monitor consists of 24 ribbon-shaped electrodes and 2 shielding electrodes, and it is positioned after the energy analyzer magnet and just before a beam dump. The beam energy evolutions in a macro-pulse with and without FEL lasing were measured in a single shot with approximately 100 ns temporal resolution. From the results obtained, the extraction efficiency of FEL oscillators can be evaluated.