Abstract
In this paper, a W-band multi-beam extended interaction klystron operating in the coaxial high order mode (HOM) is proposed. The HOM coaxial cavity with large transverse dimensions is suitable for accommodating multiple electron beams, promising to achieve high output power in the millimeter-wave frequency band. However, the operating method also brings lower characteristic impedance and a higher risk of mode competition. Based on the angular boundary condition of the coaxial HOM electric field, we propose a coaxial multi-gap cavity with a ridge structure to solve these problems. The TM51-2π mode is selected as the operating mode, of which the characteristic impedance can overwhelm that of the competing mode. The corresponding five-beam gun with a total current of 7 A (5 × 1.4 A) at a voltage of 25 kV is focused by a 0.65 T permanent magnet system. To demonstrate the capability of the device, the 3D particle-in-cell simulation predicts an output power of up to 30 kW at 94.4 GHz. The gain and electric efficiency are 54.8 dB and 17.2%, respectively.
Highlights
In recent years, with the rapid development of large-scale experimental devices and microwave electronic systems, higher requirements have been put forward for the performance of millimeter-wave power devices.1,2 As a linear device, the extended interaction klystron (EIK) exhibits characteristics such as high interaction efficiency and high gain-bandwidth product, which is promising for obtaining high output power in the millimeter-wave frequency band.3–6 Its interaction circuit consisting of several multigap cavities has high unit length gain and short interaction structure, which is beneficial for increasing the electron beam transmission rate
A W-band multi-beam extended interaction klystron operating in the coaxial high order mode (HOM) is proposed
The TM51-2π mode is selected as the operating mode, of which the characteristic impedance can overwhelm that of the competing mode
Summary
With the rapid development of large-scale experimental devices and microwave electronic systems, higher requirements have been put forward for the performance of millimeter-wave power devices. As a linear device, the extended interaction klystron (EIK) exhibits characteristics such as high interaction efficiency and high gain-bandwidth product, which is promising for obtaining high output power in the millimeter-wave frequency band. Its interaction circuit consisting of several multigap cavities has high unit length gain and short interaction structure, which is beneficial for increasing the electron beam transmission rate. A W-band planar multi-beam EIK was proposed in Ref. 8, and the simulation predicted that the device could obtain 11.28 kW output power with 14.84% electric efficiency. Based on the angular boundary condition of the coaxial TMmn mode, we propose a design methodology for a more stable and efficient structure. It can provide the following advantages: (1) Through the angular matching of the coupling cavity and the gap cavity, the HOM electric field can be more concentrated on the position of the beam tunnel, leading to the increase in R/Q. This paper is organized as follows: The design methodology of the HOM coaxial cavity is presented in Sec. II, including the physical model and the mode analysis.
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