Theoretical and Simulation Study of 'Comb' Electron beam and THz generation

TL;DR

This paper presents a theoretical and simulation analysis of a 'comb' electron beam in a compact THz source, demonstrating how microbunching enhances super-radiant emission and detailing the beam generation and radiation characteristics.

Contribution

It introduces a detailed simulation framework for a comb electron beam-based THz source, including beam transport and radiation emission analysis, which is novel for this type of FEL system.

Findings

Super-radiant THz emission is enhanced by beam modulation.

The developed C++ code accurately predicts radiation pulse energy.

Feasibility of generating and transporting comb beams is demonstrated.

Abstract

A compact accelerator based super-radiant THz source is under development at Inter University Accelerator Centre (IUAC), New Delhi. The facility is based on the principle of pre-bunched Free Electron Laser (FEL) which will produce THz radiation in the range of ~0.18 to 3 THz from a modulated electron beam. A photocathode electron gun will generate a short train of microbunches (a "comb" beam) driven by a fiber laser system capable of producing multi micro-pulse laser beam with variable separation ( "comb" laser pulse). Upon acceleration, the electron beam will be injected in to a compact undulator magnet tuned to the same frequency as the separation of the electron micro-bunches. The paper discusses the process of enhancement of super-radiant emission of radiation due to modulation in the comb beam and the conditions required to achieve maximum enhancement of the radiation power. The feasibility study of generating a comb beam at the photocathode and its transport through the beamline while preserving its temporal structure has been reported. To evaluate the characteristics of the radiation emitted from the comb beam, a C++ based particle tracker and Lienard-Wiechert field solver has been developed. The conceptual understanding of the emission of radiation from comb beam is shown to conform with the numerical results. The code has been used to calculate the radiation pulse energy emitted into the central cone of undulator for various comb beam configurations.