700 MHz HOM-IOT: design and first test results

IOTs (inductive output tubes) are relatively novel vacuum electron devices that have established their position as reliable and highly efficient UHF amplifiers, predominantly in the television transmitter service. In this application, they reach output power levels equivalent to about 50 kW CW. Scientific applications, like proton accelerators, require UHF amplifiers with considerably higher output power capability. Super power klystrons are available for this service; however, IOTs offer some advantages over klystrons in terms of efficiency: higher basic efficiency; power regulation possible at full output power (no saturation); inconsequential drop of efficiency at reduced output power. Higher order mode IOTs (IOM-IOTs) possess the added advantage of lower operational voltage and smaller size. Based on these expectations, a development of a 700 MHz HOM-IOT, sponsored by the Los Alamos National Laboratory, has been carried out by CPI. The development attention was paid to the suppression of both unwanted modes and stray radiation from the space between electron gun and body. Focusing the electron beam was another issue that required high modeling effort.