Investigation of tunable gyrotron on a cone-shaped waveguide

The results of calculations of a nonlinear model of a tunable frequency gyrotron on a cone-shaped waveguide and the main wave TE01 are presented. It is shown that the adjustment range can reach 2.8 %. To extend this band, it is necessary to lengthen the cone-shaped part of the waveguide without changing the angle of increase in the radius of the waveguide.

The wave efficiency of a waveguide expanding along the axis is 21 % at a working frequency of 10 GHz. To achieve these parameters, it is necessary to divide the gyrotron electromagnet into two parts – the main electromagnet and auxiliary one, which has a limited length and can move along the waveguide. The second magnet can be made in the form of a set of individual electromagnets of limited length the set of electromagnets must fill the entire length of the cone-shaped waveguide. The fulfillment of this condition will allow to move the resonant magnetostatic field along the waveguide by switching the current in the coils of this set of electromagnets, which will exclude the mechanical movement of the auxiliary electromagnet. At a frequency of 200 GHz, the wave efficiency is reduced to 15 %, while the ohmic losses in the walls of the waveguide are 3 % of the power of the electron beam.

The dependence of the gyrotron efficiency on the initial angular spread of electron velocities was investigated. It was concluded that the initial angular spread of the electron velocities has very little effect on the efficiency of the tunable gyrotron.

The wave efficiency of a waveguide narrowing in length can reach 29 % at a frequency of 200 GHz, ohmic losses in the walls of a copper waveguide amount to 4 % of the power of the electron beam. Calculations have shown that a lamp backward wave gyrotron with a waveguide narrowing along the axis is more efficient than the version of the gyrotron traveling wave tube. However, in both cases, the synchronous value of the magnetostatic field must be displaced along the axis, depending on the required operating frequency, otherwise there occurs either a rearrangement of the electron beam or a return of the energy to the high-frequency field by the electron beam.

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