An 805 MHz high-power klystron

Summary form only given. Northrop Grumman has designed, built and tested an 805 MHz, 2.75 MW peak power klystron in support of the Spallation Neutron Source currently under construction in Oak Ridge, Tennessee. The klystron was tested at a pulse length of 1.67 msec and a repetition rate of 60 Hz (10% duty) producing an average power of 275 kW. The electron beam was produced by a mod-anode controlled electron gun. The amplifier section consisted of a total of 6 cavities, including one cavity operating at the second harmonic. Each of the cavities, with the exception of the output cavity, incorporated tuners, allowing their resonant frequencies to be optimized. The nominal power transfer curve of the klystron is shown in the figure below. The efficiency at saturation was 55%. One of the requirements of this tube was to operate into a 1.5:1 mismatch in the output waveguide. The drive curve of the klystron, with the mismatch in the output waveguide, is also shown in the figure. In this case the efficiency was 64% at saturation. This efficiency could be realized in a future klystron by adjusting the impedance of the output cavity, if the waveguide mismatch requirement were lessened. The phase characteristic of the klystron was measured from small signal up to saturation of the klystron. The second through fifth harmonics were measured as well. Design and performance data will be presented.