Selection of modes in a submillimeter gyrotron with a corrugated cavity wall

Currently, there is a need for the sources of coherent radiation frequency range of 0.2-1 THz with an output power of 10-200 W. Now the most suitable sources in this area of ouput parameters are gyrotrons. The first investigations in the field of submillimeter gyrotrons were conducted in the early 70´s. In this experiments the record levels of continuous power were reached, but then these works have been temporarily halted because of the lack of applications and the emergence of more pressing tasks. Because of the complexity of creating strong static magnetic fields the majority of submillimeter low-power gyrotrons are designed using gyrofrequency harmonics. At the same time, due to increasing competition from modes at the fundamental gyrofrequency relatively low operating modes are used. Basically gyrotrons of this class are operated at accelerating voltages of 10-30 kV, currents up to 1 A and at relatively low modes. Thus, one of the problems solved for this type of gyrotrons is the selective excitation of gyrotron operating mode (usually at the second harmonics of the gyrofrequency) at the time of suppression of parasitic modes excitation at the fundamental harmonics of the gyrofrequency. Currently the main methods of selection are the creation of multimirrors resonators and stepped resonators. However these methods have some theoretical and technology disadvantages. This paper explores the principle of selection based on the use of an axisymmetric corrugated resonator with the depth of the corrugation smoothly varying along the axis.