Development of a 200 MHz, Multiple Beam Klystron

75756-A compact, RF power source is needed to support proton drift tube linacs at Fermi National Laboratory. The source must produce 5 MW pulsed RF power at 201.25 MHz for 500 microseconds at 15 Hz rate. Also, the source must operate linearly 15% below saturation. An efficiency of about 50 percent and a gain of 50 dB are required, with a desirable tube lifetime exceeding 30,000 hours. This project will develop a multiple beam klystron (MBK) that uses approximately six beamlets in a multicavity circuit. The number of beamlets chosen will provide a significant reduction in the beam voltage and klystron length over what would be possible with a single beam device. The reduced beam voltage will also facilitate high efficiency while still achieving the required gain and bandwidth. The resulting decrease in cathode emission current density will provide a lifetime predicted to exceed 150,000 hours. In Phase I, advanced three-dimensional computational tools will be employed to design a 200 MHz MBK, consistent with the Fermilab requirement. The design will include six electron beams, a magnetic circuit (including one or more solenoids and field shaping iron), an efficient compact, interaction circuit with discrete single gap cavities, RF input couplers, a 9-inch coaxial hard line output with vacuum window, and a spent beam collector. Commercial Applications and Other Benefits as described by the awardee: The reduced operating voltage provided by multiple beams, coupled with the reduced size and cost of power supplies and support equipment, should make the multiple beam klystron an ideal candidate for linac applications. Demonstration of multiple beam technology for the Fermilab program should lead to additional applications for multiple beam sources.