Characteristic transition of the dominant power loss from diffractive to ohmic in overmoded and periodically loaded waveguides at high frequency

TL;DR

This paper investigates the transition of dominant power loss mechanisms in overmoded, periodically loaded waveguides at high frequencies, revealing a shift from diffraction to ohmic loss that informs THz radiation transport.

Contribution

It identifies a transition point in loss mechanisms in overmoded waveguides, bridging traditional theoretical limits and aiding long-distance THz radiation transmission.

Findings

Observed a transition from diffraction to ohmic loss dominance.

Provided formal analysis of scattered fields in overmoded THz waveguides.

Revealed key tradeoffs for efficient THz radiation transport.

Abstract

The analysis of electromagnetic fields in cylindrical waveguiding structures that contain periodic ring loading, whether for applications in charged-particle accelerators or radiation transportation, has been traditionally conducted under simplifying limits, where the structure is either single-moded at the lower-frequency limit or overmoded at high-frequency limit. These limits have often allowed us to find spectral (modal) expansions for the fields under simpler analytical and computational conditions, with ohmic effects typically being the dominant power loss mechanism in the lower limit, while diffraction effects dominate the loss in the higher limit. In this Letter, we report the observation of a transition point in the character of the main loss mechanism, where ohmic loss becomes dominant in a structure typically presumed to be dominated by diffraction loss. The results follow a formal analysis for the scattered vector fields in a highly overmoded THz waveguide. The findings bridge between the traditional theoretical descriptions for the two limits and reveal key tradeoffs that inform experiments for the transportation of THz radiation over long distances.