Quasi-Optical Mode Generator for Excitation of Very High-Order Modes up to 240 GHz

A new quasi-optical mode generator setup has been designed to excite the TE48,26 mode operating at 238 GHz. It will be the mode with the highest eigenvalue (𝝌𝟒𝟖,𝟐𝟔 = 146.80) ever measured in cold tests and therefore the successor of the TE40,23 mode operating at 204 GHz. In this paper, the design of the new coaxial cavity for the mode generator setup is presented, which is based on the cavity design of the corresponding gyrotron. Simulations using a scattering matrix code show a mode purity of 99.5 % at the output of the cavity at an operating frequency of 238.101 GHz. Recently, the main components are under manufacturing. After delivery mid-2024, first experiments will be performed.