Experimental investigation of wake fields excited by a rough surface

An experiment has been carried out at the TESLA Test Facility (TTF) linac to investigate the wake fields generated by picosecond electron bunches in narrow beam pipes with artificially roughened inner surface. Two methods were employed: (a) the energy structure imposed on the bunches by the wake fields was analysed with a magnetic spectrometer, and (b) the generated THz radiation was directly recorded in an interferometer equipped with Golay cell detectors. Both methods indicate the presence of strong wake field effects as expected from simulations in which the rough surface is modelled by a dielectric layer.