The second harmonic heating system for the NORTH tokamak

A substantial contribution in the understanding of fusion plasmas can be achieved by conducting experiments in simplified plasma devices. One of those devices is NORTH, located in Denmark. Part of the research activity on NORTH is focused on non-linear interaction of microwaves with toroidally magnetized plasmas. An additional microwave heating system was recently installed in the device. The source can deliver 800 W of 5.8 GHz microwaves, which are coupled into the plasma by a custom-made 3D printed horn antenna. The antenna design was validated by numerical modelling and experimental measurements. Here we discuss this validation, and describe the system and its commissioning. Additionally, we present a newly developed diagnostic to monitor the plasma response in the frequency range up to 6 GHz, based on a fast 12.5 GS/s digitizer. By exploiting this system, we have characterized the new source. Furthermore, we have preliminary investigated the interaction of the 5.8 GHz microwave with the plasma, and we present first observations of wave coupling in NORTH.