Abstract: Second harmonic operation is of special significance due to its low magnetic field interaction.For a single cavity,of W band TE02 mode second harmonic gyrotron oscillator,the operating parameters,start current,mode completion and interaction between electron beam and wave can be determined.Employing a PIC code,the gyrotron oscillator is simulated.The results show that this oscillator can generate 67.5kW output power at 101GHz with over 18% efficiency,good stability is predicted in the case of 60kV,6A electr...