High purity mode operation of a gyrotron

Summary form only given, as follows. High frequency gyrotrons are characterized by their capacity to deliver high powers and their frequency step-tunability due to the alternation of the operating mode. Very often the gyrotron output needs to be converted into a Gaussian-like beam because the gyrotron generates radiation with TE/sub mn/ mode structure. High output mode purity is necessary for an effective conversion. In order to improve mode purity, a nonlinear cavity which was designed using a scattering matrix code and exquisitely fabricated is installed in the Gyrotron FU VA.