Development of 300 GHz Band Gyrotron for Collective Thomson Scattering Diagnostics in the Large Helical Device

A 300 GHz pulse gyrotron has been developed for use in collective Thomson scattering (CTS) diagnostics in the Large Helical Device (LHD). Single-mode oscillation power of more than 320 kW was produced. The radiation beam has a Gaussian pattern. The frequency spectrum is very narrow and stable across the pulse width. No competing mode was observed in the oscillation pulse, including during the turn-on and turn-off phases.