First Lasing From a High-Power Cylindrical Grating Smith–Purcell Device

Over the past year, a collaborative effort between Advanced Energy Systems and Commissariat à l'Energie Atomique/Centre d'Etudes Scientifiques et Techniques d'Aquitaine has achieved the first lasing of a cylindrical Smith-Purcell free-electron laser (CSPFEL). These proof-of-principle experiments employed an 80-keV 45-A 200-ns full-width at half-maximum thin annular electron beam propagating just above a cylindrical grating. The interaction of the beam with the evanescent grating mode resulted in strong beam bunching and generation of high-power millimeter-wave radiation. First lasing of the CSPFEL was achieved with a grating period of 2 cm (5-GHz fundamental). Further experiments were performed with a 6-mm period grating (15-GHz fundamental) yielding 10 kW at the second harmonic, 30 GHz. This paper discusses only the second experiment. Comparison of the experimental results with particle-in-cell (PIC) simulations shows good agreement. An experiment at 100 GHz is in progress. The basic properties of Smith-Purcell radiation and the evanescent grating mode will be presented first. Then the experimental configuration and results will be discussed. The next section will cover the PIC simulations and comparison with the experiment. The final section will summarize the results and discuss the future directions for this research. The long-term goal is the development of compact terahertz devices with sufficient power to address applications that are impractical or impossible with the existing sources