Measurement of Terahertz Smith-Purcell Radiation on an Absolute Scale for Bunch-Length Diagnostics

Summary form only given. Coherent terahertz Smith-Purcell radiation, typically formed by a relativistic bunch moving above a periodic grating, is characterized by a broad spectrum of frequencies which depend on the observation angle. It can be used as a bunch length diagnostic technique by measuring, on a relative scale, the radiated power versus the observation angle and determining the cut-off frequency. For short bunches in the order of 100 microns this method requires broadband detectors at terahertz frequencies in addition to mechanical means for scanning at the different observation angles. An exact calculation of the radiated power on an absolute scale could be used as a simple method for bunch length diagnostics having the features of a real-time measurement at a single observation angle at the millimeter-wave regime. An exact model of Smith-Purcell radiation from a charged particle moving above a finite-length grating will be presented following an update on the experimental status.