  Among the most promising terahertz (THz) radiation devices, gyrotrons can
generate powerful THz-wave radiation in an open resonant structure.
Unfortunately, such an oscillation using high-Q axial mode has been
theoretically and experimentally demonstrated to suffer from strong ohmic
losses. In this paper, a solution to such a challenging problem is to include a
narrow belt of lossy section in the interaction circuit to stably constitute
the traveling wave interaction (high-order-axial-mode, HOAM), and employ a
down-tapered magnetic field to amplify the forward-wave component. A scheme
based on the traveling-wave interaction concept is proposed to strengthen
electron beam-wave interaction efficiency and simultaneously reduce the ohmic
loss in a 1-THz third harmonic gyrotron, which is promising for further
advancement of high-power continuous-wave operation.
