Performance enhancement of frequency-doubling gyroklystron amplifier by magnetic field tapering

A uniform magnetic field across the device is often used to analyze gyroklystron. In this paper, a tapered magnetic field is applied across the two-cavity 35 GHz frequency-doubling gyroklystron to improve its performance. Device performance is compared between tapered and uniform magnetic field cases using particle-in-cell code “CST.” The result confirms that the tapered magnetic field significantly improves the device performance parameters such as output power, efficiency, gain, and bandwidth compared to uniform magnetic field conditions. With a 1.6-kW driver power, 306 kW RF output power along with 22.8 dB gain is achieved for a tapered magnetic field case, while 227 kW RF output power along with 21.5 dB gain is achieved for a uniform magnetic field case. When the magnetic field is uniform, the efficiency and bandwidth of a gyroklystron are approximately 21.6% and 100 MHz, respectively; however, for the tapered magnetic field, it can rise to 29.1% and 120 MHz, respectively. Device efficiency results suggest that a tapered magnetic field improves energy transfer from the electron beam to the RF field. A parametric study for both magnetic field cases examines the effect of magnetic field strength, beam current, beam voltage, and pitch factor on the device. This detailed research recommends optimizing frequency-doubling gyroklystron performance with tapered magnetic fields.