A study of sub-terahertz and terahertz gyrotron oscillators

Abstract

We present a theoretical study on some of the key physics issues associated with over-moded, sub-terahertz, and terahertz (THz) gyrotron oscillators. Simulations of a large number of fundamental and second cyclotron harmonic modes yield a broad database for physics observations as well as a test of relevant scaling laws. Linear properties over a broad magnetic field range exhibit a number of interesting trends. Nonlinearly, despite the possibility of multimode excitation, each mode is found to exist as a dominant single mode in a narrow magnetic field range, and a significant fraction of these modes are due to second cyclotron harmonic interactions. The wall resistivity, while a relatively minor concern for sub-terahertz gyrotrons, is shown to play a radically different role in the THz regime. It affords a linear advantage to the harmonic modes while also significantly degrading their output efficiencies. These results are interpreted in terms of the nature of harmonic mode competition and the scaling laws for the cavity quality factors.