High power oscillation test of 300 GHz band gyrotron for practical use in collective Thomson scattering diagnostics in LHD

A high power 300 GHz band pulse gyrotron has been developed based on the design concept for stable and single mode oscillation verified with a prototype gyrotron. The oscillation frequency is 303.3 GHz and the power target is 300 kW. Oscillation test has been carried out and a maximum single mode oscillation power higher than 320 kW was attained. No competing mode was observed during the turn on and turn off phases of the oscillation pulse. The frequency spectrum is very narrow and stable during the pulse width. The radiation beam has a Gaussian like pattern. The test results have proved that this gyrotron can be practically used in the collective Thomson scattering (CTS) diagnostics in the Large Helical Device (LHD).