Comparison of high resolution “balanced” and “direct conversion” measurement of SwissFEL resonant kicker amplitude

High stability resonant kicker magnet system is being developed as part of Swiss X-ray Free Electron Laser (SwissFEL) project at Paul Scherrer Institute. A prototype kicker has been built and tested in order to prove the required high pulse-to-pulse stability of the system. Amplitude stability better than 4 ppm rms has been measured using the developed “balanced” method based amplitude measurement system. This method is capable of high resolution measurement (even cycle by cycle), but it has by nature reduced dynamic range (+/- 200 ppm). To get a full range measurement a complementary system is being developed (“direct conversion”). Fast 16-bit ADCs and signal processing are used to measure the kicker's amplitude and phase during the RF pulse with resolution below the ADC quantization noise. The results from the two methods are compared and discussed.