Initial operation of a high-power frequency-doubling X-band magnicon amplifier

The magnicon is a scanning-beam microwave amplifier that is under consideration as an alternative to klystrons for powering future high-gradient electron linear accelerators. This paper reports the initial high-power operation of a frequency-doubling magnicon amplifier at 11.120 GHz. The deflection cavities operate at 5.560 GHz. The device is operating in a single-pulse mode at 650 kV and ∼225 A, using a 5.5-mm diameter beam from a plasma cathode, at a magnetic field of 6.7--8.2 kG. In order to overcome a gain saturation problem in the deflection cavities caused by plasma loading, the penultimate deflection cavity is operated very close to self-oscillation. The typical output pulselength is 100 ns full width at half maximum (FWHM), and is limited by RF breakdown of the penultimate cavity. Based on the measured far-field antenna pattern and absolute calibration of all microwave components, the measured output power is 14 MW (±3 dB), corresponding to an efficiency of ∼10%