High efficient quasi-optical mode converter for coaxial ITER gyrotron

A 2 MW, 170 GHz, TE_34,19 mode coaxial-cavity gyrotron is under development for ITER at Forschungszentrum Karlsruhe (FZK), Germany. A prototype of the quasi-optical (q.o.) mode converter has been designed and tested for this gyrotron to transform the cavity mode into a fundamental Gaussian distribution. High power measurements show that the fundamental Gaussian mode content of the RF wave beam is about 85% at the output window. A new method has been used to improve the performance of the q.o. mode converter. The simulation results reveal that the fundamental Gaussian mode content can be enhanced to 97.7% at the output window plane.