Development of a sub terahertz high power pulse gyrotron

A high power sub terahertz pulse gyrotron with a frequency around 400 GHz and the output power of tens of kW is under development in FIR-FU. Use of this gyrotron as a power source of collective Thomson scattering from a high density fusion plasma will reduce the plasma dispersion effect and the background ECE. As the first step of this development, a 200 GHz, TE₀₃ mode pulse gyrotron operating at the fundamental resonance was constructed. The design of this gyrotron was optimized for an existing electron gun. The oscillation test was carried out and many modes other than the TE₀₃ mode were observed. There was an indication of second harmonic oscillation with a frequency of about 400 GHz. In the second step, an electron gun working at the beam voltage of 70 kV will be used to realize the target gyrotron.