Phase and Frequency Locked Magnetrons for SRF Sources

Typically, high power sources for accelerator applications are many megawatt microwave tubes that may be combined together to form ultra high-power localized power stations. The RF power is then distributed to multiple strings of cavities through high power waveguide systems, which are expensive to produce and to operate, because of reduced efficiency and lower reliability. Magnetrons are the lowest cost microwave source in $/kW with the highest efficiency, typically greater than 85%, but the frequency and phase stability of magnetrons has been a problem when used as power sources for accelerators. Novel variable frequency cavity techniques have been developed which will be utilized to phase and frequency lock magnetrons, allowing their use for either individual cavities, or cavity strings. Economies of scale will further reduce magnetron costs, in addition to removing the capital, efficiency, and reliability costs of combining and/or distributing power. Ferrite and YIG (Yttrium Iron Garnet) rods were inserted into the individual cells of a cold test fixture built to model an S-band California Tube Lab magnetron strapped p-mode structure. An external magnetic field, orthogonal to the magnetic RF field of the magnetron varied the permeability of the ferrite and YIG materials, and the results recorded. A feed-back loop was designed to control the magnetic field which will control the phase and frequency difference between a reference signal, and the output of the magnetron. A complete magnetron will be built and tested in Phase II with appropriately located ferrites or garnets. The magnetron will have a permanent magnet focusing system and individual solenoids designed to control the magnetron modes of operation. Suppressing the competing modes will increase the phase purity of the p-mode. Commercial Applications and other Benefits: Phase and Frequency locked magnetrons have wide uses in the commercial, military, and scientific markets, because they represent the most cost effective source of microwave energy.