Experimental and theoretical investigation of broadband high-power windows for millimeter waves

Transmission windows guaranteeing a reliable vacuum air seal for extraction of high power millimeter waves from a vacuum tube oscillator (for example a gyrotron) and for coupling of the wave into an applicator vessel (for example a nuclear fusion reactor) are addressed. The windows used so far usually consist of plane disks of low loss dielectric material mounted perpendicularly to the direction of wave propagation. Since only waves in a narrow frequency range can penetrate this type of window this is only useful for monofrequent systems. For frequency variable systems, using for example step tunable gyrotrons, cyclotron autoresonance masers, or free electron masers as a source, special windows are required, that can transmit a relatively large frequency range (greater than or equal to +/- 5 ). Different broadband window types are developed and further investigated. The main point of the work is the realization of the required frequency dependences. For the construction of the different test windows materials are used that are suitable for transmission of high power waves.