The possibility of using single-stepped cavities to replace the common tapered cavities was studied using particle-in-cell simulations in an A6 magnetron with diffraction output (MDO). The replacing of the tapered cavities by the single-stepped cavities in a 12-cavity MDO increases the interaction space where the charged particles interact with the induced RF waves. The electronic efficiency of the 12-cavity MDO with single-stepped cavities driven by the transparent cathode [2] of GW output power level can be as high as 73% for α = 18.2°, 74% for α = 17.5°, and 72% for α = 12.5° at β = 32°, where α is the angle between the outer wall and z-axis, and β is the angle between the inner wall and z-axis. The depth of single-stepped cavities is changed when α is changed, which results in different frequency range of magnetron operating modes. When a 400-kV voltage pulse of 10-ns duration is applied to a transparent cathode or a solid cathode, the output power can be as high as 1 GW. Without loss of generality, for α = 12.5° at β = 32°, the peak efficiency around 70% of 12-cavity MDO with single-stepped cavities design occurs at the voltage (V ~ 400 ± 50 kV). The results presented in this paper provide references for relativistic magnetron mode selection or mode switching experiments when choosing the input parameters (magnetic field and accelerating voltage) allowing the magnetron to operate in the desired operation mode.

The design of an agile 5° irregular ring metamaterial for a 24-cavity relativistic magnetron with diffraction output (MDO) using single-stepped cavities for frequency switching is presented. By inserting six pieces of 5° irregular ring metamaterials in place of the traditional 5° vanes of a slow wave structure, the operating frequency can be tuned. When U = 400 kV high voltage is applied, with an applied magnetic field B = 0.36 T, the operating mode can be switched from the TE41 mode with a frequency of 2.585 GHz to the TE31 mode with a frequency of 2.282 GHz. The 24-cavity anode block is an electromagnetic medium which can support the operating mode working under its cutoff frequency, and the insertion of the irregular ring metamaterials alters its dispersion relation. The results suggest a new technique to achieve frequency agility by changing the dispersion relation of the electromagnetic system using a metamaterial unit cell. This work seeks to design a compact high power microwave source for a narrowband directed microwave wave beam that is suitable for frequency agility.

We present the design of an A6 relativistic magnetron with diffraction output (MDO) which looks like a crab and we named it the “crab-like” A6 MDO. This article shows that the crab-like A6 MDO driven by a transparent cathode can radiate the TE₁₁ mode with an output power of about 1 GW when an optimized applied voltage of $U=440$ kV and magnetic field of $B=0.43\hspace{0.17em}$ T are used. Its electronic efficiency, as obtained using UNIPIC particle-in-cell (PIC) simulations, can be as high as 44% in S-band. The UNIPIC PIC code used in simulations also demonstrates that the crab-like A6 MDO can radiate both two electron spokes in the TE₂₁ mode with an operating frequency of 2.1 GHz and four electron spokes in the TE₂₁ mode with an operating frequency of 2.5 GHz when different magnetic field amplitudes are used for an applied voltage of $U=400\hspace{0.17em}$ kV. This result suggests that this configuration is favorable for mode switching. This work seeks to design a compact high power microwave source for a narrowband directed microwave wave beam that is suitable for mode switching investigations.

We present an S-band high-power microwave (HPM) oscillator based on crossed-elliptical metamaterial (MTM) rings in a circular waveguide and powered by a high-power electron beam. Particle-in-cell (PIC) simulations demonstrate that when an output horn antenna of radius of 200 mm is used, an output power of 443 MW of a backward wave TE ₄₁ mode below its cutoff frequency at 2.80 GHz can be generated using a pulsed electron beam with a voltage of 990 kV and a current of 1.736 kA in a 1.8-T solenoidal magnetic field, corresponding to an electronic efficiency up to 26%. Meanwhile, another degenerate frequency of 2.80 GHz of a forward wave in the TM ₀₁ mode with an output power of 9 MW is also observed. When an output horn antenna of radius 150 mm is used, this crossed-elliptical MTM oscillator operates mainly in a forward TM ₀₁ mode at 2.80 GHz with an output power of 325 MW at an electronic efficiency of 19%, and at the same time, a backward wave TE ₄₁ mode below its cutoff frequency of 2.80 GHz with an output power of 8 MW can be observed. Simulations indicate that this slow-wave structure (SWS) consisting of a periodically crossed-elliptical MTM loaded circular waveguide can support degenerate mode operation. This result suggests that this configuration is favorable for mode switching and this work seeks to design a compact HPM source.

We present computer simulations of a “crablike” 12 resonator cavity relativistic magnetron with diffraction output (MDO) designed by doubling the number of cavities from our earlier 6 resonator cavity crablike MDO. This work aims to design a compact high-power narrowband microwave source with frequency switching capabilities. UNIPIC particle-in-cell computer simulations show that the crablike 12-cavity MDO with a transparent cathode radiates the TE₁₁ mode with output power 1 GW and electronic efficiency as high as 41% when powered using a 400 kV voltage pulse and 0.41 T magnetic field. Computer simulations also demonstrate that the crablike 12-cavity MDO can radiate different modes, such as the TE₂₁ mode, the TE₃₁ mode, the TE₄₁ mode, and the TE₅₁ mode. The TE₂₁ mode, in particular, can be radiated at three different frequencies, as low as 2.12 GHz, a median operating frequency of 2.4 GHz, and a higher operating frequency of 2.91 GHz, when different magnetic fields are used.

We present the design of an agile slow wave structure for a “crab-like” A12 relativistic magnetron with diffraction output using single-stepped cavities. By regrouping the interaction region as three sets of four cavities, the TE₃₁ operating mode is generated at 2.60 GHz with 1.0 GW output power for an applied voltage of U = 350 kV and a magnetic field of B = 0.34 T. By regrouping the interaction region as four sets of three cavities, the TE₄₁ operating mode is generated at 2.82 GHz with 1.0 GW output power for an applied voltage of U = 355 kV and a magnetic field of B = 0.36 T. Furthermore, by regrouping the interaction region as six sets of two cavities, the TE₃₁ mode and the TE₂₁ mode are generated. When an applied voltage of U = 350 kV and a magnetic field of B = 0.33 T are used, its output power can be as high as 1.0 GW for the TE₃₁ mode operating at 2.5 GHz. In addition, when an applied voltage of U = 350 kV and a magnetic field of B = 0.42 T are used, its output power can be as high as 1.0 GW with operating mode TE₂₁ at 2.62 GHz. It was found that the rearrangement of the slow wave structure can control the operating mode and, at the same time, lower the operating condition of the beam/wave interaction compared to the traditional 12-cavity relativistic magnetron. The result suggests that this configuration is favorable for mode switching through mechanical rearrangement of the slow wave structure. This work seeks to design a compact high power microwave source for a narrowband directed microwave beam that is suitable for mode switching investigations.