Metamaterial-based slow wave structure for travelling wave tubes

The advent of strong relativistic electron beams has led to the development of high power microwave sources. These devices generate high peaks of microwave power by transferring the kinetic energy in the electron beam to electromagnetic waves guided within a slow wave structure (SWS). Among these devices, traveling-wave tubes (TWTs) and backward wave oscillators (BWOs) are based on this principle, referred to as Cerenkov radiation. Strong interest also exists in employing the Cerenkov Maser (microwave amplification via stimulated emission of radiation) as a TWT due to its simplicity and tunability. This TWT is lined with a dielectric coating to slow down the electromagnetic waves. However, as noted by Shiffler et al. (Shiffler et al., IEEE Trans. Plasma Sci., 2010), dielectrics become vulnerable to charging and surface breakdowns. A way to avoid charging is to employ purely metallic metamaterial-based slow wave structures that emulate the behavior of a dielectric liner.