Measurements of Terahertz Generation in a Metallic, Corrugated Beam Pipe

TL;DR

This paper reports on measurements of terahertz radiation generated by an ultra-relativistic beam passing through a corrugated metallic pipe, demonstrating spectral properties and wakefield effects at Brookhaven's ATF.

Contribution

First experimental measurement of THz generation in a metallic corrugated pipe with detailed spectral analysis and wakefield characterization.

Findings

Successful measurement of THz radiation spectrum

Observation of wakefield effects on the beam

Validation of the corrugated pipe as a THz source

Abstract

A method for producing narrow-band THz radiation proposes passing an ultra-relativistic beam through a metallic pipe with small periodic corrugations. We present results of a measurement of such an arrangement at Brookhaven's Accelerator Test Facility (ATF). Our pipe was copper and was 5 cm long; the aperture was cylindrically symmetric, with a 1 mm (radius) bore and a corrugation depth (peak-to-peak) of 60 um. In the experiment we measured both the effect on the beam of the structure wakefield and the spectral properties of the radiation excited by the beam. We began by injecting a relatively long beam compared to the wavelength of the radiation to excite the structure, and then used a downstream spectrometer to infer the radiation wavelength. This was followed by injecting a shorter bunch, and then using an interferometer (also downstream of the corrugated pipe) to measure the spectrum of the induced THz radiation.