Reflection protection of BEPC II linear accelerator klystron

In the RF system of the accelerator, when the reflected power back to the klystron in the current RF pulse exceeds certain threshold, the system should send out an alarm signal before the next RF pulse arrives, and then cut off the trigger signal. By this way, the klystron ceramic window can be protected by reducing the damage caused by the high-power RF reflection; the online lifetime of the klystron can be prolonged. Three cost-effective and easy-to-implement solutions have been introduced: the mask alarm scheme by using the PicoScope virtual oscilloscope, the chip-made reflective protection plug-in based on the RF detection and alarm output functions, and the upgrade of the original RF power meter. The '3+1' reflection protection response time test method was innovatively proposed, it was used to thoroughly test the above three schemes. Finally, better results were obtained by using the latter two schemes. After comprehensive consideration, the upgraded RF power meter was used in the final implementation plan. At present, the upgraded RF power meter has been operating online stably and reliably for more than one year. (authors)