Improvement in efficiency of pulse klystron for electronic linac

The original klystron consisted of four cavities placed at the same intervals. To improve this klystron, a fifth cavity (resonant cavity) was added, resulting in an increase in efficiency up to 49 percent. Another five-cavity klystron with a gain of 56 dB and efficiency of 54 percent was developed. In order to further improve this, modification was made to permit control of detuning characteristics of the third and forth cavity, and the arrangement of cavities were changed. In this report, a study is also made to determine the relations of the efficiency and cavity distance ratio of a pulse klystron for electronic linac. Results show: 1) The microwave output efficiency is greatly affected by the distance between cavity resonators, 2) The efficiency is greatly affected by the focusing coil current in a klystron, 3) A greater reduction in energy consumption can be achieved with higher-output klystrons, regardless of whether it is pulse type or continuous type (this denies the insistence by some researchers that an increase in efficiency of a pulse klystron will not make great contributions to reduction in energy consumption), and 4) It is very difficult to increase the efficiency to above 50 percent. (Nogami, K.)