On features of the radiation from an electron moving along a helix inside a cylindrical hole in a homogeneous dielectric

TL;DR

This paper investigates the radiation emitted by an electron moving in a helix inside a dielectric cylindrical cavity, revealing conditions for enhanced radiation at specific harmonics and ratios, with implications for waveguide and cavity designs.

Contribution

It identifies conditions for radiation amplification in dielectric cavities and relates these to similar effects in waveguides, providing new insights into radiation control in such structures.

Findings

High peaks in radiation intensity at specific harmonics.

Amplification occurs at certain cavity-to-helix radius ratios.

Resonant ratios are independent of dielectric permittivity.

Abstract

The radiation from a charge moving along a helical trajectory inside a cylindrical hole in homogeneous dielectric medium is investigated. Prompted by availability of materials with large dielectric permittivity $\epsilon $ and small absorption, we discuss the features of this type of radiation for media with $\epsilon \gg 1$. It is shown that there are high peaks in the angular distribution of radiation intensity at well-defined harmonics. The conditions are specified for the cavity-to-helix radii ratio, $\rho_{1}/\rho_{0}$, under which the angle-integrated radiation intensity on some harmonics exceeds that in the empty space. Though the amplification of radiation intensity increases with increasing $\epsilon $, the corresponding "resonant" values of $\rho _{1}/\rho_{0}$ ratio are practically independent of the dielectric permittivity of surrounding medium. It is shown that an analogous amplification of radiation takes place essentially for the same values of $\rho_{1}/\rho_{0}$ also for the radiation in a cylindrical waveguide with conducting walls. An explanation of this phenomenon is given.