Results of a high-power klystron dip test in the KEK linac

A dip test, which is a measurement of klystron heater activity, was recently adopted as a standard method to determine the klystron heater power in the KEKB electron-positron linac. Before we adopted a dip measurement, it took about half a day to measure the emission as a function of the heater wattage for one klystron. Two years ago, we began to use the dip test as a quick way to measure the emission characteristics from the klystron cathode; it took only 10 to 15 minutes. After achieving successful results, we made dedicated measuring systems and measured the dips of the cathode emission of 60 operating klystrons in the KEKB electron-positron linac. These data are important to estimate the klystron cathode life, and are used to select candidate klystrons for replacement in the summer shut down period.