The study of the sheet-beam extended interaction oscillator, a compact, low voltage (~12kV) high power
terahertz radition source is presented in this paper. In this structure, the sheet beam interacts with the electromagnetic mode
of TM<sub>31</sub>, 2π mode, and the generated electromagnetic wave is coupled and enhanced in the rectangle cavities. The sheet
beam, high mode operation and rectangular cavity are helpful to enhance the beam-wave interaction, increase the
frequency and the coupling strength, respectively. A 0.1THz cavity is designed, with cathode voltage of 12KV, beam
current of 0.6A, and the guiding magnetic field strength of o.5T, simulation results show that the electromagnetic wave is
generated with the frequency of 0.1THz and the peak power of 1kW at the output window.