Second harmonic TE15,2 550 GHz gyrotron experiment at NRL

Near-THz gyrotrons are of interest for applications such as re mote sensing, materials processing, and dynamic nuclear pola rization enhanced nuclear magnetic resonance applications 1 . At the Naval Research Laboratory, we are developing a second harmonic gyrotron designed to operate at 550 GHz. 2 An interaction cavity based on the TE15,2 mode with an effective length of about 1 cm and a Q of 7400 has been designed and is in the process of being assembled within the gyrotron tube with the output coupler. To avoid complications arising from strict alignment requirements, a simple Vlasov-type output coupler with a single quasi- parabolic reflecting mirror has also been designed using newly derived design equations. The converter has been verified by numerical simulations to generate an output beam with approximately 97% fundamental Gaussian content, though approximately 25% of the gyrotron power is lost within the converter. Simulations show that this lost power is mostly due to diffraction and mode conversion at the launcher cut 3 . Design calculations and simulations for the cavity and output coupler will be presented in addition to preliminary experimental results.