Development of a sub terahertz high power pulse gyrotron for collective Thomson scattering

A high power sub terahertz pulse gyrotron is under development in FIR-FU for application to collective Thomson scattering from a high density plasma in the Large Helical Device. As the first step of this development, a pulse gyrotron using an existing electron gun was constructed and tested. Oscillations with frequencies around 400 GHz was observed at the second harmonic resonance. Several modes were confirmed to be single mode oscillation with the beam voltage up to 35 kV, near the maximum rating of the electron gun. A new gyrotron is now under construction as the second step of development. This gyrotron will be operated with a newly designed electron gun with the beam voltage up to 70 kV and the beam current up to 10 A.