Measurements of Terahertz Radiation Generated using a Metallic, Corrugated Pipe

TL;DR

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

Contribution

First experimental measurement of THz radiation from a corrugated metallic pipe, including spectral analysis and comparison with theoretical calculations.

Findings

Measured central frequency and bandwidth of THz radiation

Observed wakefield effects on the beam

Compared spectral power with diffraction background

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, but with short rise time, 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. For the THz pulse we obtain and compare with calculations: the central frequency, the bandwidth, and the spectral power---compared to a diffraction radiation background signal.