Forward-wave enhanced radiation in the terahertz electron cyclotron maser

Based on the principle of electron cyclotron maser (ECM), gyrotrons are among the most promising devices to generate powerful coherent terahertz (THz) radiation and play a vital role in numerous advanced THz applications. Unfortunately, THz ECM systems using a conventional high- Q cavity were theoretically and experimentally demonstrated to suffer from strong ohmic losses, and, accordingly, the wave output efficiency was significantly reduced. A scheme to alleviate such a challenging problem is systematically investigated in this paper. The traveling-wave operation concept is employed in a 1-THz third harmonic gyrotron oscillator, which strengthens electron-wave interaction efficiency and reduces the ohmic dissipation, simultaneously. A lossy belt is added in the interaction circuit to stably constitute the traveling-wave interaction, and a down-tapered magnetic field is employed to further amplify the forward-wave (FW) component. The results demonstrate that the proportion of ohmic losses is nearly halved, and output efficiency is nearly doubled, which is promising for further advancement of high-power continuous-wave operation of the ECM-based devices.