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A 2 MW, CW, 170 GHz coaxial cavity gyrotron for electron cyclotron heating and current drive in the International Thermonuclear Experimental Reactor (ITER) is under development in cooperation between European Research institutions. The design of critical components, especially the electron gun, cavity and quasi-optical (q.o.) RF-output system has been studied on a short pulse coaxial gyrotron (pre-prototype) at the Forschungszentrum Karlsruhe (FZK). Recent results of the experimental investigations will be presented and discussed.

A 2MW, 170GHz, 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.