Upgrade of the Computer-Controlled Test System for the Excitation of Very High-Order Modes in Waveguides

Fusion gyrotrons are operating in highly oversized cavities to achieve a RF output power in the range of several MW [1]. Before installation into the gyrotron the proper verification of the utilized oversized waveguide components, e.g. the quasi-optical mode converter, is mandatorily required to prevent failures. The quasi-optical mode converter consists of the launcher and mirrors. The verification can be performed using a quasi-optical mode generator [2], which is used in a low-power test setup. The verification procedure is done in two steps. In a first step, the required gyrotron mode is excited in a specially for this purpose designed cavity [3], which is the most challenging and time consuming part of the measurement. The excited mode can be used in the second step to verify the quasi-optical system. The current mode generator setup at KIT is already presented in [4]. It is equipped with high-precision linear drivers for a computer-controlled adjustment. In the present work, this mode generator is upgraded in hardware and software. For the hardware modification, a goniometer is installed, where nowadays a fully computer-controlled adjustment using all degrees of freedom is possible. ... mehrUsing this upgrade the counter-rotating amount of the generated mode can be reduced to 0.2 %. In addition, the control code has been modified towards the next higher level of intelligent automation by calculating the operating frequency.
The results of the upgraded test system are presented using a 140 GHz TE28,10-mode generator. The operating TE28,10-mode is the chosen one for the 1.5 MW upgrade [5] of the 1 MW, 140 GHz, TE28,8-mode gyrotron operating at the stellarator W7-X [6], which is currently under development.
Possible exchange: Testing of components of the quasi-optical mode converter is mandatory prior to installation into the gyrotron. Thus, this field is important for any gyrotron developer. The exchange of ideas to develop precise mode generators would be very fruitful.