High-efficiency operation of the relativistic X-band gyrotron with strong output reflections

Abstract

Summary form only given. High-efficiency operation of the relativistic X-band gyrotron with 50% reflections in the output waveguide is presented. For the electron beam energy of 230 keV and the injection current of 12 A the maximum efficiency exceeding 50% was achieved in the steady-state regime with output power of about 1.5 MW. As the injection current growth up to 32 A the output power increased up to 2.8 MW with efficiency more than 30%. At a current of 55 A, the regime changed to a periodic self-modulation with a period of about 15 ns with average output power and efficiency up to 1.9 MW and 15% correspondingly. This values was two times greater than were reported in for 80% reflector. At the same time the maximal modulation depth reduced from 100 to 35%. The further possibilities of increasing output power in the steady-state regime in the gyrotron with end reflections was demonstrated by using 2.5-D version of the PIC-code KARAT. For the 280 kV, 60 A electron beam in the gyrotron with resonator of reduced length output power could achieved 7 MW with efficiency >40%. To achieve chaotic self-modulation regime in the experiment the distance between output reflector and gyrotron resonator opening was increased from 9 to 54 cm. It should be noted, that under general theoretical consideration the increasing of the delayed time (in the given case the distance between resonator and reflector) decreases the bifurcation parameters for the periodic and chaotic self-modulation regimes. The output power increased up to 2.8 MW with 15% efficiency for periodic self-modulation regimes in this configuration. As injection current growth the period doubling route form the periodic to chaotic self-modulation regimes was observed. The maximum output power of 2.5 MW with 17% efficiency was obtained in the chaotic oscillation regime.