Pacey, T.H. Dunning, D.J. Saveliev, Y.M. Xia, G.X. JACoW Geneva, Switzerland 978-3-95450-182-3 10.18429/JACoW-IPAC2017-WEPVA021 English 3302-3304 WEPVA021 Contribution to a conference proceedings 2017 2017-05 http://dx.doi.org/10.18429/JACoW-IPAC2017-WEPVA021 http://jacow.org/ipac2017/papers/wepva021.pdf Dielectric lined waveguides have drawn interest due to their application as high gradient accelerating structures, in both externally driven and wakefield schemes. We present simulation studies of sub-picosecond electron bunches interacting with dielectric structures in the self-wake regime. The parameter space for a tunable, sub-millimeter aperture, terahertz frequency structure is investigated. The potential application as a longitudinal phase space dechirper is demonstrated, with specific application to CLARA at Daresbury Laboratory. The impact of transverse effects is considered and minimised. The resulting FEL output is simulated.