Coherent Cherenkov-cyclotron radiation excited by an electron beam in a two-spiral metamaterial waveguide

M Liu,C Liu,M I Fuks,E Schamiloglu,S C Yurt,A Elfrgani

doi:10.1063/1.5049380

Abstract

We present the analysis of a microwave generator that uses two-spiral metamaterial (MTM) plates in a below cutoff WR340 waveguide that interacts with a high-power electron beam, motivated by recent results obtained by researchers at MIT. Particle-in-cell simulations using the MAGIC code demonstrated that power levels of 12 MW are achieved in a backward wave mode at a frequency of 2.47 GHz from an anomalous Doppler instability using a 1 μs pulsed electron beam of energy 400 keV, current 82 A in a 415 G magnetic field. In addition, a backward wave with 9 MW output power is achieved at a frequency of 2.54 GHz attributed to a Cherenkov instability using a 1 μs pulsed electron beam of energy 400 keV, current 82 A in a 1200 G magnetic field. MAGIC simulations demonstrate that the beam-wave interaction electronic efficiency can be as high as 27.4%. Nonlinear simulations indicate that beam interception leads to secondary electron emission from surfaces, which makes the anomalous Doppler instability and Cherenkov instability more complicated by a shift in frequency. This work seeks to clarify some discrepancy between particle-in-cell simulations and experiments at MIT over a range of guide magnetic field.

Highlights

Many researchers have been studying MTM-based high power microwave sources.[1,2,3,4,5,6,7,8,9] An MTM structure is an artificial material with novel electromagnetic properties and is often implemented as a periodic structure with period much smaller than the operating wavelength.[10,11] An electron beam interacting with an MTM structure generates Cherenkov radiation in the backward direction, which is usually called reversed Cherenkov radiation or backward Cherenkov radiation
Some use periodic split ring resonators (SRRs) placed inside a circular waveguide[4,12,13] while others use complementary SRR (CSRR) MTM plates inserted in a rectangular waveguide,[6,7,14,15,16] and both types of MTM-loaded waveguides can support quasi-TE or TM modes at a frequency below the cutoff frequency of the empty metallic waveguide
Our particle-in-cell (PIC) simulations using MAGIC17 show that when beam interception takes place, initiating secondary electron emission (SEE), the operating mode may switch from an antisymmetric mode to a symmetric mode and vice versa, with output power reduction

Summary

Introduction

Many researchers have been studying MTM-based high power microwave sources.[1,2,3,4,5,6,7,8,9] An MTM structure is an artificial material with novel electromagnetic properties and is often implemented as a periodic structure with period much smaller than the operating wavelength.[10,11] An electron beam interacting with an MTM structure generates Cherenkov radiation in the backward direction, which is usually called reversed Cherenkov radiation or backward Cherenkov radiation.

Results

Conclusion