High-power twin-beam gyrotrons operating at the second gyrofrequency harmonic

The results of two experiments with a gyrotron operating at the second gyrofrequency harmonic, using two active electron beams, are reported. The internal (additional) beam is coupled weakly to the field by a spurious mode. The currents of the two beams can be controlled independently. The output characteristics of the gyrotons are plotted for various beam currents. The additional beam substantially enhances the operating mode stability and makes an appreciable contribution to the output power. The maximum output power was 0.87 MW at 25% efficiency, beam currents of 57 A and 13 A, and voltage 60 kV. The highest efficiency was 40%. The results suggest that electron-optical systems with two active beams, regardless of some complications of gun design, are promising for short-wave gyrotrons to operate at the fundamental cyclotron resonance. The specific power dissipation in the collector is observed to decrease (in comparison with a single-beam analog).