High frequency characteristics of a magnetically insulated transmission line oscillator oscillating in HEM11 mode

Abstract

Coaxial disk-loaded waveguide has been widely used in magnetically insulated transmission line oscillators (MILO). Although TM00 mode is assumed to be its main mode, the asymmetric mode might be excited by slight asymmetry of the structure, asymmetric emission of the beam, or both. So the research on asymmetric mode in coaxial disk-loaded waveguide is necessary. The general eigen equation with both symmetric and asymmetric modes in coaxial disk-loaded slow-wave structures is theoretically analyzed. Then, a HEM11 mode working MILO is designed and a tentative experiment is carried out to test its performance. Employing an electron beam of about 480 kV and 39 kA, HEM11 mode working MILO generates a high power microwave output of about 1.2 GW with 40 ns pulse duration at 1.98GHz. The power conversion efficiency is about 6.5% and the generated microwave mode is TE11 in the coaxial output region.

Magnetically insulated transmission line oscillator oscillated in a modified HEM11mode

“…Imaging an axial periodicity of this cavity, we can derive the eigenfunction in a quite familiar way as that in Refs. [11] and [12], and the dispersion curves are illustrated in Fig. 2(a), as well as the dispersion curves of a corresponding 1-D SWS shown in Fig.…”

“…To develop a more compact system, a MILO which oscillates at HEM 11 mode would be helpful; and a model of this particular MILO has been presented in Refs. [11] and [12]. In this new type of MILO, a TE 11 mode microwave could be generated directly in the coaxial output region so that a mode converter is not required.…”

“…So the uniformity of the electrostatic field must be ensured in designing an HEM 11 mode working MILO, such as the model used in Refs. [11] and [12]. But the selection of HEM 11 mode by tuning cavity depth of each resonant cavity in the 1-D SWS has only been proved in simulation without electrons.…”

“…According to Ref. [11], HEM 11 mode is a TMlike mode in the slow wave structure (SWS) region that could interact with the electrons in a similar way as well as a TM 00 mode wave. The only difference between these two modes is that HEM 11 mode has a nonzero azimuthal wave number.…”

HEM11mode magnetically insulated transmission line oscillator: Simulation and experiment

“…Because of the unfavourable electric field intensity pattern of this mode, a mode converter is usually inserted between the tube and the radiated antenna. [9,10] However, a mode converter is never 100% efficient and the introduction of the mode converter increases the length, weight, and complexity of the HPM system.…”