Simulation of smith- purcell terahertz radiation: the dartmouth and mit experiments

Summary form only given. The generation of Smith-Purcell (S-P) radiation at terahertz frequencies is under investigation at Dartmouth College (using a low energy continuous electron beam) and at Massachusetts Institute of Technology, with a high-energy short-pulse beam repeated at 17.1 GHz. We have performed simulations of these experiments with the two dimensional particle-in-cell code MAGIC. In the calculation, we use the actual experimental parameters but we suppose that the continuous, thin (but infinitely wide), mono-energetic electron beam is guided by a strong axial magnetic field for the Dartmouth experiment, no field for that of MIT. For the Dartmouth simulation we observe superradiant S-P emission at the expected angle. We find excellent agreement with the theory proposed by H.L. Andrews and co-workers. In particular, we study the S-P gain as a function of the beam current: it is shown to exhibit a cube-root behavior. The existence of a start current is also demonstrated. In the simulation of the MIT experiment, the prebunched highly relativistic beam generates many harmonics of the fundament al 17.1 GHz frequency. We compare and contrast our results with those obtained with a ground-plane replacing the grating in order to isolate the S-P signal