Experimental Observation of Energy Modulation in Electron Beams Passing through Terahertz Dielectric Wakefield Structures

Abstract

We report the observation of a strong wakefield induced energy modulation in an energy-chirped electron bunch passing through a dielectric-lined waveguide. This modulation can be effectively converted into a spatial modulation forming microbunches with a periodicity of 0.5-1 ps and, hence, capable of driving coherent terahertz radiation. The experimental results agree well with theoretical predictions.

Transverse operator method for wakefields in a rectangular dielectric loaded accelerating structure

“…(15) and (22) are independent. Each equation corresponds to a specific type of propagating wave, (15) to longitudinal section magnetic (LSM) modes, (22) to longitudinal section electric (LSE) modes.…”

“…Rectangular structures can be used for measurements on new dielectric materials effective in sustaining high acceleration rates and tolerant of pulsed heating of the structure [4]. Planar structures are also being studied (along with cylindrical geometries) for generating terahertz radiation in the frequency range 0.5-1.0 THz [4] and for energy spread reduction (''silencer'') systems for FEL linacs [22].…”

Terahertz radiation source based on self-wake beam bunching

“…If originally all particles in the beam had identical energy (Figure 2, right, red curve), after passing through the wakefield structure an energy modulation appears along the beam length (Figure 2, right, blue curve). This effect was demonstrated recently by observing this energy modulation on a spectrometer [13]. It is important for the experiment that the original beam possessed a linear energy chirp: this allowed for separation of the energy modulation in the spectrometer.…”

“…It is important for the experiment that the original beam possessed a linear energy chirp: this allowed for separation of the energy modulation in the spectrometer. The energy modulation can also be produced by self-wakefields for various other current profiles [13]. The wakefield structure used for energy modulation can be externally powered; in this case the radiation source based on this approach operates as an amplifier.…”

“…We propose to use the beam's self-wake action along with compression in a chicane to introduce THz content into the beam. This approach is based on our recent successful experiments at the ATF facility of Brookhaven National Laboratory [13,14]. FIGURE 2.…”