High-Efficiency Klystron Tests at the CERN Xbox3 Facility

Klystrons are a type of radio-frequency amplifier widely used in high-energy physics. In recent years, efforts have been made to improve klystron efficiency to reduce power consumption. This report details the adjustments made at the CERN Xbox3 X-band test stand to facilitate the testing of high-efficiency klystrons. We present measurements of the output power, gain, and spectral composition for an E37117 klystron developed in collaboration with Canon Electron Tubes and Devices under the high-efficiency klystron programme at CERN. This prototype is designed to produce a peak output power of 8 MW, however our results show that the klystron significantly underperforms, producing only around 5 MW. Although it may not fully resolve the discrepancy, for future measurements we have installed a new load to dissipate the klystron output power that has a better impedance match with the line. As well as improving the reflected power and vacuum levels in the line, this may have an effect on the klystron output power. Finally, we discuss the challenges involved in implementing calorimetric measurements to provide an independent measurement of the average output power of the klystron.