Orotrons with double-row periodic structure and spherocylindrical and multifocal mirrors

An experimental investigation of two modifications of orotron in (120...220) GHz frequency range is carried out. The electrodynamic system is formed by an open resonator consisted of one plane mirror on which the double-row periodic structure (DRPS) is settled down and other focusing mirror having the shape of a spherocylinder in one case or multifocal spherical mirror in the other. The longitudinal axis of spherocylinder is parallel to the axis of symmetry of DRPS. The multifocal mirror is formed by some (3 or 4) crossed spherical surfaces with the general plane of symmetry along the interaction space of the device. The comparison of output parameters of orotrons with multifocal and spherocylindrical mirrors shows that the correct choice of its geometry allows receiving the efficient increase of the interaction length and corresponding reduction of a start current value in the orotron.